Address some staticcheck issues (#823)

* address some staticcheck issues

* address some staticcheck issues

* address some staticcheck issues

* address some staticcheck issues

Makefile

@@ -59,11 +59,6 @@ bench-input:
 regression-test:
 	go test -v regression_test.go
 
-# ----------------------------------------------------------------
-# Experimental executables:
-scan:
-	go build github.com/johnkerl/miller/cmd/scan
-
 # ----------------------------------------------------------------
 # Formatting
 # go fmt ./... finds experimental C files which we want to ignore.
@@ -121,4 +116,4 @@ release_tarball: build check
 
 # ================================================================
 # Go does its own dependency management, outside of make.
-.PHONY: build mlr scan check unit_test regression_test bench fmt staticcheck dev docs
+.PHONY: build mlr check unit_test regression_test bench fmt staticcheck dev docs

internal/pkg/auxents/auxents.go

@@ -62,14 +62,6 @@ func Dispatch(args []string) {
 	// Else, return control to main for the rest of Miller.
 }
 
-// auxListUsage shows the available auxents.
-func auxListUsage(verbName string, o *os.File, exitCode int) {
-	fmt.Fprintf(o, "Usage: mlr %s [options]\n", verbName)
-	fmt.Fprintf(o, "Options:\n")
-	fmt.Fprintf(o, "-h or --help: print this message\n")
-	os.Exit(exitCode)
-}
-
 // auxListMain is the handler for 'mlr aux-list'.
 func auxListMain(args []string) int {
 	ShowAuxEntries(os.Stdout)

internal/pkg/auxents/regtest/invoker.go

@@ -24,7 +24,6 @@ func RunMillerCommand(
 	stdout string,
 	stderr string,
 	exitCode int,
-	executionError error, // failure to even start the process
 ) {
 	argsString = strings.TrimRight(argsString, "\n")
 	argsString = strings.TrimRight(argsString, "\r")
@@ -59,7 +58,7 @@ func RunMillerCommand(
 		}
 	}
 
-	return stdout, stderr, exitCode, nil
+	return stdout, stderr, exitCode
 }
 
 // RunDiffCommandOnStrings runs either diff or fc (not-Windows / Windows

internal/pkg/auxents/regtest/regtester.go

@@ -57,7 +57,6 @@ package regtest
 
 import (
 	"container/list"
-	"errors"
 	"fmt"
 	"io/ioutil"
 	"os"
@@ -422,14 +421,6 @@ func (regtester *RegTester) executeSingleCmdFile(
 	expectFailFileName := caseDir + slash + ShouldFailName
 	postCompareFileName := caseDir + slash + PostCompareName
 
-	cmd, err = regtester.loadFile(cmdFilePath, caseDir)
-	if err != nil {
-		if verbosityLevel >= 2 {
-			fmt.Printf("%s: %v\n", cmdFilePath, err)
-		}
-		return false
-	}
-
 	if verbosityLevel >= 2 {
 		fmt.Println("Command:")
 		fmt.Println(cmd)
@@ -502,7 +493,7 @@ func (regtester *RegTester) executeSingleCmdFile(
 
 	// ****************************************************************
 	// HERE IS WHERE WE RUN THE MILLER COMMAND LINE FOR THE TEST CASE
-	actualStdout, actualStderr, actualExitCode, err := RunMillerCommand(regtester.exeName, cmd)
+	actualStdout, actualStderr, actualExitCode := RunMillerCommand(regtester.exeName, cmd)
 	// ****************************************************************
 
 	// Unset any case-specific environment variables after running the case.
@@ -859,11 +850,9 @@ func (regtester *RegTester) loadEnvFile(
 		}
 		fields := strings.SplitN(line, "=", 2)
 		if len(fields) != 2 {
-			return nil, errors.New(
-				fmt.Sprintf(
-					"mlr: could not parse line \"%s\" from file \"%s\".\n",
-					line, filename,
-				),
+			return nil, fmt.Errorf(
+				"mlr: could not parse line \"%s\" from file \"%s\".\n",
+				line, filename,
 			)
 		}
 		keyValuePairs.Put(fields[0], fields[1])
@@ -898,11 +887,9 @@ func (regtester *RegTester) loadStringPairFile(
 		}
 		fields := strings.SplitN(line, " ", 2) // TODO: split on multi-space
 		if len(fields) != 2 {
-			return nil, errors.New(
-				fmt.Sprintf(
-					"mlr: could not parse line \"%s\" from file \"%s\".\n",
-					line, filename,
-				),
+			return nil, fmt.Errorf(
+				"mlr: could not parse line \"%s\" from file \"%s\".\n",
+				line, filename,
 			)
 		}
 		pair := stringPair{first: fields[0], second: fields[1]}

internal/pkg/dsl/ast_build.go

@@ -6,7 +6,6 @@
 package dsl
 
 import (
-	"errors"
 	"fmt"
 
 	"github.com/johnkerl/miller/internal/pkg/lib"
@@ -255,12 +254,7 @@ func (node *ASTNode) CheckArity(
 	arity int,
 ) error {
 	if len(node.Children) != arity {
-		return errors.New(
-			fmt.Sprintf(
-				"AST node arity %d, expected %d",
-				len(node.Children), arity,
-			),
-		)
+		return fmt.Errorf("expected AST node arity %d, got %d", arity, len(node.Children))
 	} else {
 		return nil
 	}

internal/pkg/dsl/cst/block-exit.go

@@ -6,7 +6,7 @@
 package cst
 
 import (
-	"errors"
+	"fmt"
 
 	"github.com/johnkerl/miller/internal/pkg/dsl"
 	"github.com/johnkerl/miller/internal/pkg/lib"
@@ -70,7 +70,7 @@ func (root *RootNode) BuildReturnNode(astNode *dsl.ASTNode) (*ReturnNode, error)
 	} else {
 		lib.InternalCodingErrorIf(true)
 	}
-	return nil, errors.New("Internal coding error: Statement should not be reached.")
+	return nil, fmt.Errorf("internal coding error: statement should not be reached.")
 }
 
 func (node *ReturnNode) Execute(state *runtime.State) (*BlockExitPayload, error) {

internal/pkg/dsl/cst/builtin_functions.go

@@ -5,7 +5,6 @@
 package cst
 
 import (
-	"errors"
 	"fmt"
 
 	"github.com/johnkerl/miller/internal/pkg/bifs"
@@ -53,9 +52,9 @@ func (root *RootNode) BuildBuiltinFunctionCallsiteNode(
 		} else if builtinFunctionInfo.variadicFuncWithState != nil {
 			return root.BuildVariadicFunctionWithStateCallsiteNode(astNode, builtinFunctionInfo)
 		} else {
-			return nil, errors.New(
-				"CST BuildFunctionCallsiteNode: builtin function not implemented yet: " +
-					functionName,
+			return nil, fmt.Errorf(
+				"at CST BuildFunctionCallsiteNode: builtin function not implemented yet: %s",
+				functionName,
 			)
 		}
 	}
@@ -79,11 +78,9 @@ func (root *RootNode) BuildMultipleArityFunctionCallsiteNode(
 		return root.BuildTernaryFunctionCallsiteNode(astNode, builtinFunctionInfo)
 	}
 
-	return nil, errors.New(
-		fmt.Sprintf(
-			"CST BuildMultipleArityFunctionCallsiteNode: function name not found: " +
-				builtinFunctionInfo.name,
-		),
+	return nil, fmt.Errorf(
+		"at CST BuildMultipleArityFunctionCallsiteNode: function name not found: " +
+			builtinFunctionInfo.name,
 	)
 }
 
@@ -99,14 +96,12 @@ func (root *RootNode) BuildZaryFunctionCallsiteNode(
 	callsiteArity := len(astNode.Children)
 	expectedArity := 0
 	if callsiteArity != expectedArity {
-		return nil, errors.New(
-			fmt.Sprintf(
-				"mlr: function %s invoked with %d argument%s; expected %d",
-				builtinFunctionInfo.name,
-				callsiteArity,
-				lib.Plural(callsiteArity),
-				expectedArity,
-			),
+		return nil, fmt.Errorf(
+			"mlr: function %s invoked with %d argument%s; expected %d",
+			builtinFunctionInfo.name,
+			callsiteArity,
+			lib.Plural(callsiteArity),
+			expectedArity,
 		)
 	}
 
@@ -134,14 +129,12 @@ func (root *RootNode) BuildUnaryFunctionCallsiteNode(
 	callsiteArity := len(astNode.Children)
 	expectedArity := 1
 	if callsiteArity != expectedArity {
-		return nil, errors.New(
-			fmt.Sprintf(
-				"mlr: function %s invoked with %d argument%s; expected %d",
-				builtinFunctionInfo.name,
-				callsiteArity,
-				lib.Plural(callsiteArity),
-				expectedArity,
-			),
+		return nil, fmt.Errorf(
+			"mlr: function %s invoked with %d argument%s; expected %d",
+			builtinFunctionInfo.name,
+			callsiteArity,
+			lib.Plural(callsiteArity),
+			expectedArity,
 		)
 	}
 
@@ -175,14 +168,12 @@ func (root *RootNode) BuildUnaryFunctionWithContextCallsiteNode(
 	callsiteArity := len(astNode.Children)
 	expectedArity := 1
 	if callsiteArity != expectedArity {
-		return nil, errors.New(
-			fmt.Sprintf(
-				"mlr: function %s invoked with %d argument%s; expected %d",
-				builtinFunctionInfo.name,
-				callsiteArity,
-				lib.Plural(callsiteArity),
-				expectedArity,
-			),
+		return nil, fmt.Errorf(
+			"mlr: function %s invoked with %d argument%s; expected %d",
+			builtinFunctionInfo.name,
+			callsiteArity,
+			lib.Plural(callsiteArity),
+			expectedArity,
 		)
 	}
 
@@ -217,14 +208,12 @@ func (root *RootNode) BuildBinaryFunctionCallsiteNode(
 	callsiteArity := len(astNode.Children)
 	expectedArity := 2
 	if callsiteArity != expectedArity {
-		return nil, errors.New(
-			fmt.Sprintf(
-				"mlr: function %s invoked with %d argument%s; expected %d",
-				builtinFunctionInfo.name,
-				callsiteArity,
-				lib.Plural(callsiteArity),
-				expectedArity,
-			),
+		return nil, fmt.Errorf(
+			"mlr: function %s invoked with %d argument%s; expected %d",
+			builtinFunctionInfo.name,
+			callsiteArity,
+			lib.Plural(callsiteArity),
+			expectedArity,
 		)
 	}
 
@@ -293,14 +282,12 @@ func (root *RootNode) BuildBinaryFunctionWithStateCallsiteNode(
 	callsiteArity := len(astNode.Children)
 	expectedArity := 2
 	if callsiteArity != expectedArity {
-		return nil, errors.New(
-			fmt.Sprintf(
-				"mlr: function %s invoked with %d argument%s; expected %d",
-				builtinFunctionInfo.name,
-				callsiteArity,
-				lib.Plural(callsiteArity),
-				expectedArity,
-			),
+		return nil, fmt.Errorf(
+			"mlr: function %s invoked with %d argument%s; expected %d",
+			builtinFunctionInfo.name,
+			callsiteArity,
+			lib.Plural(callsiteArity),
+			expectedArity,
 		)
 	}
 
@@ -345,14 +332,12 @@ func (root *RootNode) BuildTernaryFunctionWithStateCallsiteNode(
 	callsiteArity := len(astNode.Children)
 	expectedArity := 3
 	if callsiteArity != expectedArity {
-		return nil, errors.New(
-			fmt.Sprintf(
-				"mlr: function %s invoked with %d argument%s; expected %d",
-				builtinFunctionInfo.name,
-				callsiteArity,
-				lib.Plural(callsiteArity),
-				expectedArity,
-			),
+		return nil, fmt.Errorf(
+			"mlr: function %s invoked with %d argument%s; expected %d",
+			builtinFunctionInfo.name,
+			callsiteArity,
+			lib.Plural(callsiteArity),
+			expectedArity,
 		)
 	}
 
@@ -433,14 +418,12 @@ func (root *RootNode) BuildRegexCaptureBinaryFunctionCallsiteNode(
 	callsiteArity := len(astNode.Children)
 	expectedArity := 2
 	if callsiteArity != expectedArity {
-		return nil, errors.New(
-			fmt.Sprintf(
-				"mlr: function %s invoked with %d argument%s; expected %d",
-				builtinFunctionInfo.name,
-				callsiteArity,
-				lib.Plural(callsiteArity),
-				expectedArity,
-			),
+		return nil, fmt.Errorf(
+			"mlr: function %s invoked with %d argument%s; expected %d",
+			builtinFunctionInfo.name,
+			callsiteArity,
+			lib.Plural(callsiteArity),
+			expectedArity,
 		)
 	}
 
@@ -487,14 +470,12 @@ func (root *RootNode) BuildDotCallsiteNode(
 	callsiteArity := len(astNode.Children)
 	expectedArity := 2
 	if callsiteArity != expectedArity {
-		return nil, errors.New(
-			fmt.Sprintf(
-				"mlr: function %s invoked with %d argument%s; expected %d",
-				".",
-				callsiteArity,
-				lib.Plural(callsiteArity),
-				expectedArity,
-			),
+		return nil, fmt.Errorf(
+			"mlr: function %s invoked with %d argument%s; expected %d",
+			".",
+			callsiteArity,
+			lib.Plural(callsiteArity),
+			expectedArity,
 		)
 	}
 
@@ -551,14 +532,12 @@ func (root *RootNode) BuildTernaryFunctionCallsiteNode(
 	callsiteArity := len(astNode.Children)
 	expectedArity := 3
 	if callsiteArity != expectedArity {
-		return nil, errors.New(
-			fmt.Sprintf(
-				"mlr: function %s invoked with %d argument%s; expected %d",
-				builtinFunctionInfo.name,
-				callsiteArity,
-				lib.Plural(callsiteArity),
-				expectedArity,
-			),
+		return nil, fmt.Errorf(
+			"mlr: function %s invoked with %d argument%s; expected %d",
+			builtinFunctionInfo.name,
+			callsiteArity,
+			lib.Plural(callsiteArity),
+			expectedArity,
 		)
 	}
 
@@ -618,25 +597,21 @@ func (root *RootNode) BuildVariadicFunctionCallsiteNode(
 	callsiteArity := len(astNode.Children)
 
 	if callsiteArity < builtinFunctionInfo.minimumVariadicArity {
-		return nil, errors.New(
-			fmt.Sprintf(
-				"mlr: function %s takes minimum argument count %d; got %d.\n",
-				builtinFunctionInfo.name,
-				builtinFunctionInfo.minimumVariadicArity,
-				callsiteArity,
-			),
+		return nil, fmt.Errorf(
+			"mlr: function %s takes minimum argument count %d; got %d.\n",
+			builtinFunctionInfo.name,
+			builtinFunctionInfo.minimumVariadicArity,
+			callsiteArity,
 		)
 	}
 
 	if builtinFunctionInfo.maximumVariadicArity != 0 {
 		if callsiteArity > builtinFunctionInfo.maximumVariadicArity {
-			return nil, errors.New(
-				fmt.Sprintf(
-					"mlr: function %s takes maximum argument count %d; got %d.\n",
-					builtinFunctionInfo.name,
-					builtinFunctionInfo.maximumVariadicArity,
-					callsiteArity,
-				),
+			return nil, fmt.Errorf(
+				"mlr: function %s takes maximum argument count %d; got %d.\n",
+				builtinFunctionInfo.name,
+				builtinFunctionInfo.maximumVariadicArity,
+				callsiteArity,
 			)
 		}
 	}
@@ -680,25 +655,21 @@ func (root *RootNode) BuildVariadicFunctionWithStateCallsiteNode(
 	callsiteArity := len(astNode.Children)
 
 	if callsiteArity < builtinFunctionInfo.minimumVariadicArity {
-		return nil, errors.New(
-			fmt.Sprintf(
-				"mlr: function %s takes minimum argument count %d; got %d.\n",
-				builtinFunctionInfo.name,
-				builtinFunctionInfo.minimumVariadicArity,
-				callsiteArity,
-			),
+		return nil, fmt.Errorf(
+			"mlr: function %s takes minimum argument count %d; got %d.\n",
+			builtinFunctionInfo.name,
+			builtinFunctionInfo.minimumVariadicArity,
+			callsiteArity,
 		)
 	}
 
 	if builtinFunctionInfo.maximumVariadicArity != 0 {
 		if callsiteArity > builtinFunctionInfo.maximumVariadicArity {
-			return nil, errors.New(
-				fmt.Sprintf(
-					"mlr: function %s takes maximum argument count %d; got %d.\n",
-					builtinFunctionInfo.name,
-					builtinFunctionInfo.maximumVariadicArity,
-					callsiteArity,
-				),
+			return nil, fmt.Errorf(
+				"mlr: function %s takes maximum argument count %d; got %d.\n",
+				builtinFunctionInfo.name,
+				builtinFunctionInfo.maximumVariadicArity,
+				callsiteArity,
 			)
 		}
 	}

internal/pkg/dsl/cst/cond.go

@@ -6,7 +6,7 @@
 package cst
 
 import (
-	"errors"
+	"fmt"
 
 	"github.com/johnkerl/miller/internal/pkg/dsl"
 	"github.com/johnkerl/miller/internal/pkg/lib"
@@ -57,7 +57,7 @@ func (node *CondBlockNode) Execute(
 		boolValue = false
 	} else if !isBool {
 		// TODO: line-number/token info for the DSL expression.
-		return nil, errors.New("mlr: conditional expression did not evaluate to boolean.")
+		return nil, fmt.Errorf("mlr: conditional expression did not evaluate to boolean.")
 	}
 
 	if boolValue == true {

internal/pkg/dsl/cst/dump.go

@@ -17,7 +17,6 @@ package cst
 
 import (
 	"bytes"
-	"errors"
 	"fmt"
 	"os"
 	"strings"
@@ -138,12 +137,7 @@ func (root *RootNode) buildDumpxStatementNode(
 			} else if redirectorNode.Type == dsl.NodeTypeRedirectPipe {
 				retval.outputHandlerManager = output.NewPipeWriteHandlerManager(root.recordWriterOptions)
 			} else {
-				return nil, errors.New(
-					fmt.Sprintf(
-						"%s: unhandled redirector node type %s.",
-						"mlr", string(redirectorNode.Type),
-					),
-				)
+				return nil, fmt.Errorf("mlr: unhandled redirector node type %s.", string(redirectorNode.Type))
 			}
 		}
 	}
@@ -216,11 +210,9 @@ func (node *DumpStatementNode) dumpToFileOrPipe(
 ) error {
 	redirectorTarget := node.redirectorTargetEvaluable.Evaluate(state)
 	if !redirectorTarget.IsString() {
-		return errors.New(
-			fmt.Sprintf(
-				"%s: output redirection yielded %s, not string.",
-				"mlr", redirectorTarget.GetTypeName(),
-			),
+		return fmt.Errorf(
+			"mlr: output redirection yielded %s, not string.",
+			redirectorTarget.GetTypeName(),
 		)
 	}
 	outputFileName := redirectorTarget.String()

internal/pkg/dsl/cst/emit_emitp.go

@@ -39,7 +39,6 @@
 package cst
 
 import (
-	"errors"
 	"fmt"
 
 	"github.com/johnkerl/miller/internal/pkg/cli"
@@ -171,11 +170,9 @@ func (root *RootNode) buildEmitXStatementNode(
 			retval.topLevelEvaluableMap = evaluable
 
 		} else {
-			return nil, errors.New(
-				fmt.Sprintf(
-					"mlr: unlashe-demit node types must be local variables, field names, oosvars, or maps; got %s.",
-					childNode.Type,
-				),
+			return nil, fmt.Errorf(
+				"mlr: unlashed-emit node types must be local variables, field names, oosvars, or maps; got %s.",
+				childNode.Type,
 			)
 		}
 
@@ -183,11 +180,9 @@ func (root *RootNode) buildEmitXStatementNode(
 		retval.isLashed = true
 		for _, childNode := range emittablesNode.Children {
 			if !EMITX_NAMED_NODE_TYPES[childNode.Type] {
-				return nil, errors.New(
-					fmt.Sprintf(
-						"mlr: lashed-emit node types must be local variables, field names, or oosvars; got %s.",
-						childNode.Type,
-					),
+				return nil, fmt.Errorf(
+					"mlr: lashed-emit node types must be local variables, field names, or oosvars; got %s.",
+					childNode.Type,
 				)
 			}
 		}
@@ -276,12 +271,7 @@ func (root *RootNode) buildEmitXStatementNode(
 			} else if redirectorNode.Type == dsl.NodeTypeRedirectPipe {
 				retval.outputHandlerManager = output.NewPipeWriteHandlerManager(root.recordWriterOptions)
 			} else {
-				return nil, errors.New(
-					fmt.Sprintf(
-						"%s: unhandled redirector node type %s.",
-						"mlr", string(redirectorNode.Type),
-					),
-				)
+				return nil, fmt.Errorf("mlr: unhandled redirector node type %s.", string(redirectorNode.Type))
 			}
 		}
 	}
@@ -999,12 +989,7 @@ func (node *EmitXStatementNode) emitRecordToFileOrPipe(
 ) error {
 	redirectorTarget := node.redirectorTargetEvaluable.Evaluate(state)
 	if !redirectorTarget.IsString() {
-		return errors.New(
-			fmt.Sprintf(
-				"%s: output redirection yielded %s, not string.",
-				"mlr", redirectorTarget.GetTypeName(),
-			),
-		)
+		return fmt.Errorf("mlr: output redirection yielded %s, not string.", redirectorTarget.GetTypeName())
 	}
 	outputFileName := redirectorTarget.String()
 

internal/pkg/dsl/cst/emitf.go

@@ -6,7 +6,6 @@
 package cst
 
 import (
-	"errors"
 	"fmt"
 
 	"github.com/johnkerl/miller/internal/pkg/dsl"
@@ -120,12 +119,7 @@ func (root *RootNode) BuildEmitFStatementNode(astNode *dsl.ASTNode) (IExecutable
 			} else if redirectorNode.Type == dsl.NodeTypeRedirectPipe {
 				retval.outputHandlerManager = output.NewPipeWriteHandlerManager(root.recordWriterOptions)
 			} else {
-				return nil, errors.New(
-					fmt.Sprintf(
-						"%s: unhandled redirector node type %s.",
-						"mlr", string(redirectorNode.Type),
-					),
-				)
+				return nil, fmt.Errorf("mlr: unhandled redirector node type %s.", string(redirectorNode.Type))
 			}
 		}
 	}
@@ -169,12 +163,7 @@ func getNameFromNamedNode(astNode *dsl.ASTNode, description string) (string, err
 	} else if astNode.Type == dsl.NodeTypeDirectFieldValue {
 		return string(astNode.Token.Lit), nil
 	}
-	return "", errors.New(
-		fmt.Sprintf(
-			"%s: can't get name of node type \"%s\" for %s.",
-			"mlr", string(astNode.Type), description,
-		),
-	)
+	return "", fmt.Errorf("mlr: can't get name of node type \"%s\" for %s.", string(astNode.Type), description)
 }
 
 // ----------------------------------------------------------------
@@ -198,12 +187,7 @@ func (node *EmitFStatementNode) emitfToFileOrPipe(
 ) error {
 	redirectorTarget := node.redirectorTargetEvaluable.Evaluate(state)
 	if !redirectorTarget.IsString() {
-		return errors.New(
-			fmt.Sprintf(
-				"%s: output redirection yielded %s, not string.",
-				"mlr", redirectorTarget.GetTypeName(),
-			),
-		)
+		return fmt.Errorf("mlr: output redirection yielded %s, not string.", redirectorTarget.GetTypeName())
 	}
 	outputFileName := redirectorTarget.String()
 

internal/pkg/dsl/cst/evaluable.go

@@ -7,7 +7,6 @@
 package cst
 
 import (
-	"errors"
 	"fmt"
 	"os"
 
@@ -80,8 +79,8 @@ func (root *RootNode) BuildEvaluableNode(astNode *dsl.ASTNode) (IEvaluable, erro
 		return root.BuildUnnamedUDFNode(astNode)
 	}
 
-	return nil, errors.New(
-		"CST BuildEvaluableNode: unhandled AST node type " + string(astNode.Type),
+	return nil, fmt.Errorf(
+		"at CST BuildEvaluableNode: unhandled AST node type %s", string(astNode.Type),
 	)
 }
 

internal/pkg/dsl/cst/for.go

@@ -5,7 +5,7 @@
 package cst
 
 import (
-	"errors"
+	"fmt"
 
 	"github.com/johnkerl/miller/internal/pkg/dsl"
 	"github.com/johnkerl/miller/internal/pkg/lib"
@@ -195,11 +195,9 @@ func (node *ForLoopOneVariableNode) Execute(state *runtime.State) (*BlockExitPay
 	// silent zero-pass. But maybe we should surface it as an error. Maybe
 	// with a "mlr put --errors" flag or something.
 	//	} else {
-	//		return nil, errors.New(
-	//			fmt.Sprintf(
-	//				"mlr: looped-over item is not a map or array; got %s",
-	//				indexMlrval.GetTypeName(),
-	//			),
+	//		return nil, fmt.Errorf(
+	//			"mlr: looped-over item is not a map or array; got %s",
+	//			indexMlrval.GetTypeName(),
 	//		)
 
 	return nil, nil
@@ -390,11 +388,9 @@ func (node *ForLoopTwoVariableNode) Execute(state *runtime.State) (*BlockExitPay
 	// silent zero-pass. But maybe we should surface it as an error. Maybe
 	// with a "mlr put --errors" flag or something.
 	//	} else {
-	//		return nil, errors.New(
-	//			fmt.Sprintf(
-	//				"mlr: looped-over item is not a map or array; got %s",
-	//				indexMlrval.GetTypeName(),
-	//			),
+	//		return nil, fmt.Errorf(
+	//			"mlr: looped-over item is not a map or array; got %s",
+	//			indexMlrval.GetTypeName(),
 	//		)
 
 	return nil, nil
@@ -605,11 +601,9 @@ func (node *ForLoopMultivariableNode) executeOuter(
 	// silent zero-pass. But maybe we should surface it as an error. Maybe
 	// with a "mlr put --errors" flag or something.
 	//	} else {
-	//		return nil, errors.New(
-	//			fmt.Sprintf(
-	//				"mlr: looped-over item is not a map or array; got %s",
-	//				mv.GetTypeName(),
-	//			),
+	//		return nil, fmt.Errorf(
+	//			"mlr: looped-over item is not a map or array; got %s",
+	//			mv.GetTypeName(),
 	//		)
 
 	return nil, nil
@@ -702,11 +696,9 @@ func (node *ForLoopMultivariableNode) executeInner(
 	// silent zero-pass. But maybe we should surface it as an error. Maybe
 	// with a "mlr put --errors" flag or something.
 	//	} else {
-	//		return nil, errors.New(
-	//			fmt.Sprintf(
-	//				"mlr: looped-over item is not a map or array; got %s",
-	//				mv.GetTypeName(),
-	//			),
+	//		return nil, fmt.Errorf(
+	//			"mlr: looped-over item is not a map or array; got %s",
+	//			mv.GetTypeName(),
 	//		)
 
 	return nil, nil
@@ -808,7 +800,7 @@ func (root *RootNode) BuildTripleForLoopNode(astNode *dsl.ASTNode) (*TripleForLo
 			precontinuationAssignments = make([]IExecutable, n-1)
 			for i := 0; i < n-1; i++ {
 				if continuationExpressionASTNode.Children[i].Type != dsl.NodeTypeAssignment {
-					return nil, errors.New(
+					return nil, fmt.Errorf(
 						"mlr: the non-final triple-for continutation statements must be assignments.",
 					)
 				}
@@ -825,11 +817,11 @@ func (root *RootNode) BuildTripleForLoopNode(astNode *dsl.ASTNode) (*TripleForLo
 		bareBooleanASTNode := continuationExpressionASTNode.Children[n-1]
 		if bareBooleanASTNode.Type != dsl.NodeTypeBareBoolean {
 			if n == 1 {
-				return nil, errors.New(
+				return nil, fmt.Errorf(
 					"mlr: the triple-for continutation statement must be a bare boolean.",
 				)
 			} else {
-				return nil, errors.New(
+				return nil, fmt.Errorf(
 					"mlr: the final triple-for continutation statement must be a bare boolean.",
 				)
 			}
@@ -902,7 +894,7 @@ func (node *TripleForLoopNode) Execute(state *runtime.State) (*BlockExitPayload,
 			boolValue, isBool := continuationValue.GetBoolValue()
 			if !isBool {
 				// TODO: propagate line-number context
-				return nil, errors.New("mlr: for-loop continuation did not evaluate to boolean.")
+				return nil, fmt.Errorf("mlr: for-loop continuation did not evaluate to boolean.")
 			}
 			if boolValue == false {
 				break

internal/pkg/dsl/cst/if.go

@@ -5,7 +5,7 @@
 package cst
 
 import (
-	"errors"
+	"fmt"
 
 	"github.com/johnkerl/miller/internal/pkg/dsl"
 	"github.com/johnkerl/miller/internal/pkg/lib"
@@ -127,7 +127,7 @@ func (node *IfChainNode) Execute(state *runtime.State) (*BlockExitPayload, error
 		boolValue, isBool := condition.GetBoolValue()
 		if !isBool {
 			// TODO: line-number/token info for the DSL expression.
-			return nil, errors.New("mlr: conditional expression did not evaluate to boolean.")
+			return nil, fmt.Errorf("mlr: conditional expression did not evaluate to boolean.")
 		}
 		if boolValue == true {
 			blockExitPayload, err := ifItem.statementBlockNode.Execute(state)

internal/pkg/dsl/cst/leaves.go

@@ -5,7 +5,7 @@
 package cst
 
 import (
-	"errors"
+	"fmt"
 	"math"
 
 	"github.com/johnkerl/miller/internal/pkg/dsl"
@@ -97,9 +97,7 @@ func (root *RootNode) BuildLeafNode(
 		break
 	}
 
-	return nil, errors.New(
-		"CST BuildLeafNode: unhandled AST node " + string(astNode.Type),
-	)
+	return nil, fmt.Errorf("at CST BuildLeafNode: unhandled AST node %s", string(astNode.Type))
 }
 
 // ----------------------------------------------------------------
@@ -443,9 +441,7 @@ func (root *RootNode) BuildContextVariableNode(astNode *dsl.ASTNode) (IEvaluable
 
 	}
 
-	return nil, errors.New(
-		"CST BuildContextVariableNode: unhandled context variable " + sval,
-	)
+	return nil, fmt.Errorf("at CST BuildContextVariableNode: unhandled context variable %s", sval)
 }
 
 // ----------------------------------------------------------------
@@ -620,9 +616,7 @@ func (root *RootNode) BuildConstantNode(astNode *dsl.ASTNode) (IEvaluable, error
 
 	}
 
-	return nil, errors.New(
-		"CST BuildContextVariableNode: unhandled context variable " + sval,
-	)
+	return nil, fmt.Errorf("at CST BuildContextVariableNode: unhandled context variable %s", sval)
 }
 
 // ----------------------------------------------------------------

internal/pkg/dsl/cst/lvalues.go

@@ -6,7 +6,6 @@
 package cst
 
 import (
-	"errors"
 	"fmt"
 	"os"
 
@@ -54,12 +53,12 @@ func (root *RootNode) BuildAssignableNode(
 		break
 
 	case dsl.NodeTypeArrayOrMapPositionalNameAccess:
-		return nil, errors.New(
+		return nil, fmt.Errorf(
 			"mlr: '[[...]]' is allowed on assignment left-hand sides only when immediately preceded by '$'.",
 		)
 		break
 	case dsl.NodeTypeArrayOrMapPositionalValueAccess:
-		return nil, errors.New(
+		return nil, fmt.Errorf(
 			"mlr: '[[[...]]]' is allowed on assignment left-hand sides only when immediately preceded by '$'.",
 		)
 		break
@@ -77,8 +76,8 @@ func (root *RootNode) BuildAssignableNode(
 		break
 	}
 
-	return nil, errors.New(
-		"CST BuildAssignableNode: unhandled AST node " + string(astNode.Type),
+	return nil, fmt.Errorf(
+		"at CST BuildAssignableNode: unhandled AST node " + string(astNode.Type),
 	)
 }
 
@@ -121,7 +120,7 @@ func (node *DirectFieldValueLvalueNode) AssignIndexed(
 	// print inrec attributes. Also, a UDF/UDS invoked from begin/end could try
 	// to access the inrec, and that would get past the validator.
 	if state.Inrec == nil {
-		return errors.New("There is no current record to assign to.")
+		return fmt.Errorf("there is no current record to assign to.")
 	}
 
 	// AssignmentNode checks for absent, so we just assign whatever we get
@@ -220,7 +219,7 @@ func (node *IndirectFieldValueLvalueNode) AssignIndexed(
 	// print inrec attributes. Also, a UDF/UDS invoked from begin/end could try
 	// to access the inrec, and that would get past the validator.
 	if state.Inrec == nil {
-		return errors.New("There is no current record to assign to.")
+		return fmt.Errorf("there is no current record to assign to.")
 	}
 
 	lhsFieldName := node.lhsFieldNameExpression.Evaluate(state)
@@ -313,7 +312,7 @@ func (node *PositionalFieldNameLvalueNode) Assign(
 	// print inrec attributes. Also, a UDF/UDS invoked from begin/end could try
 	// to access the inrec, and that would get past the validator.
 	if state.Inrec == nil {
-		return errors.New("There is no current record to assign to.")
+		return fmt.Errorf("there is no current record to assign to.")
 	}
 
 	lhsFieldIndex := node.lhsFieldIndexExpression.Evaluate(state)
@@ -324,11 +323,9 @@ func (node *PositionalFieldNameLvalueNode) Assign(
 		state.Inrec.PutNameWithPositionalIndex(index, rvalue)
 		return nil
 	} else {
-		return errors.New(
-			fmt.Sprintf(
-				"mlr: positional index for $[[...]] assignment must be integer; got %s.",
-				lhsFieldIndex.GetTypeName(),
-			),
+		return fmt.Errorf(
+			"mlr: positional index for $[[...]] assignment must be integer; got %s.",
+			lhsFieldIndex.GetTypeName(),
 		)
 	}
 }
@@ -340,7 +337,7 @@ func (node *PositionalFieldNameLvalueNode) AssignIndexed(
 ) error {
 	// TODO: reconsider this if /when we decide to allow string-slice
 	// assignments.
-	return errors.New(
+	return fmt.Errorf(
 		"mlr: $[[...]] = ... expressions are not indexable.",
 	)
 }
@@ -433,7 +430,7 @@ func (node *PositionalFieldValueLvalueNode) AssignIndexed(
 	// print inrec attributes. Also, a UDF/UDS invoked from begin/end could try
 	// to access the inrec, and that would get past the validator.
 	if state.Inrec == nil {
-		return errors.New("There is no current record to assign to.")
+		return fmt.Errorf("there is no current record to assign to.")
 	}
 
 	lhsFieldIndex := node.lhsFieldIndexExpression.Evaluate(state)
@@ -450,11 +447,9 @@ func (node *PositionalFieldValueLvalueNode) AssignIndexed(
 			state.Inrec.PutCopyWithPositionalIndex(index, rvalue)
 			return nil
 		} else {
-			return errors.New(
-				fmt.Sprintf(
-					"mlr: positional index for $[[[...]]] assignment must be integer; got %s.",
-					lhsFieldIndex.GetTypeName(),
-				),
+			return fmt.Errorf(
+				"mlr: positional index for $[[[...]]] assignment must be integer; got %s.",
+				lhsFieldIndex.GetTypeName(),
 			)
 		}
 	} else {
@@ -536,7 +531,7 @@ func (node *FullSrecLvalueNode) AssignIndexed(
 	// print inrec attributes. Also, a UDF/UDS invoked from begin/end could try
 	// to access the inrec, and that would get past the validator.
 	if state.Inrec == nil {
-		return errors.New("There is no current record to assign to.")
+		return fmt.Errorf("there is no current record to assign to.")
 	}
 
 	// AssignmentNode checks for absentness of the rvalue, so we just assign
@@ -1095,12 +1090,10 @@ func (node *EnvironmentVariableLvalueNode) Assign(
 	}
 
 	if !name.IsString() {
-		return errors.New(
-			fmt.Sprintf(
-				"ENV[...] assignments must have string names; got %s \"%s\"\n",
-				name.GetTypeName(),
-				name.String(),
-			),
+		return fmt.Errorf(
+			"assignments to ENV[...] must have string names; got %s \"%s\"\n",
+			name.GetTypeName(),
+			name.String(),
 		)
 	}
 
@@ -1118,7 +1111,7 @@ func (node *EnvironmentVariableLvalueNode) AssignIndexed(
 	indices []*mlrval.Mlrval,
 	state *runtime.State,
 ) error {
-	return errors.New("mlr: ENV[...] cannot be indexed.")
+	return fmt.Errorf("mlr: ENV[...] cannot be indexed.")
 }
 
 func (node *EnvironmentVariableLvalueNode) Unassign(

internal/pkg/dsl/cst/print.go

@@ -6,7 +6,6 @@ package cst
 
 import (
 	"bytes"
-	"errors"
 	"fmt"
 	"os"
 
@@ -281,12 +280,7 @@ func (root *RootNode) buildPrintxStatementNode(
 			} else if redirectorNode.Type == dsl.NodeTypeRedirectPipe {
 				retval.outputHandlerManager = output.NewPipeWriteHandlerManager(root.recordWriterOptions)
 			} else {
-				return nil, errors.New(
-					fmt.Sprintf(
-						"%s: unhandled redirector node type %s.",
-						"mlr", string(redirectorNode.Type),
-					),
-				)
+				return nil, fmt.Errorf("mlr: unhandled redirector node type %s.", string(redirectorNode.Type))
 			}
 		}
 	}
@@ -362,12 +356,7 @@ func (node *PrintStatementNode) printToFileOrPipe(
 ) error {
 	redirectorTarget := node.redirectorTargetEvaluable.Evaluate(state)
 	if !redirectorTarget.IsString() {
-		return errors.New(
-			fmt.Sprintf(
-				"%s: output redirection yielded %s, not string.",
-				"mlr", redirectorTarget.GetTypeName(),
-			),
-		)
+		return fmt.Errorf("mlr: output redirection yielded %s, not string.", redirectorTarget.GetTypeName())
 	}
 	outputFileName := redirectorTarget.String()
 

internal/pkg/dsl/cst/root.go

@@ -7,7 +7,6 @@ package cst
 
 import (
 	"container/list"
-	"errors"
 	"fmt"
 	"os"
 	"strings"
@@ -148,7 +147,7 @@ func (root *RootNode) IngestAST(
 	warningsAreFatal bool,
 ) error {
 	if ast.RootNode == nil {
-		return errors.New("Cannot build CST from nil AST root")
+		return fmt.Errorf("cannot build CST from nil AST root")
 	}
 
 	// Check for things that are syntax errors but not done in the AST for
@@ -283,9 +282,7 @@ func (root *RootNode) regexProtectPrePassAux(astNode *dsl.ASTNode) {
 func (root *RootNode) buildMainPass(ast *dsl.AST, isReplImmediate bool) error {
 
 	if ast.RootNode.Type != dsl.NodeTypeStatementBlock {
-		return errors.New(
-			"CST root build: non-statement-block AST root node unhandled",
-		)
+		return fmt.Errorf("at CST root build: non-statement-block AST root node unhandled")
 	}
 	astChildren := ast.RootNode.Children
 
@@ -411,9 +408,7 @@ func (root *RootNode) resolveSubroutineCallsites() error {
 			return err
 		}
 		if uds == nil {
-			return errors.New(
-				"mlr: subroutine name not found: " + subroutineName,
-			)
+			return fmt.Errorf("mlr: subroutine name not found: " + subroutineName)
 		}
 
 		unresolvedSubroutineCallsite.uds = uds

internal/pkg/dsl/cst/statements.go

@@ -6,7 +6,7 @@
 package cst
 
 import (
-	"errors"
+	"fmt"
 
 	"github.com/johnkerl/miller/internal/pkg/dsl"
 )
@@ -67,13 +67,9 @@ func (root *RootNode) BuildStatementNode(
 		return root.BuildEmitPStatementNode(astNode)
 
 	case dsl.NodeTypeBeginBlock:
-		return nil, errors.New(
-			"mlr: begin blocks may only be declared at top level.",
-		)
+		return nil, fmt.Errorf("mlr: begin blocks may only be declared at top level.")
 	case dsl.NodeTypeEndBlock:
-		return nil, errors.New(
-			"mlr: end blocks may only be declared at top level.",
-		)
+		return nil, fmt.Errorf("mlr: end blocks may only be declared at top level.")
 
 	case dsl.NodeTypeIfChain:
 		return root.BuildIfChainNode(astNode)
@@ -93,13 +89,9 @@ func (root *RootNode) BuildStatementNode(
 		return root.BuildTripleForLoopNode(astNode)
 
 	case dsl.NodeTypeNamedFunctionDefinition:
-		return nil, errors.New(
-			"mlr: functions may only be declared at top level.",
-		)
+		return nil, fmt.Errorf("mlr: functions may only be declared at top level.")
 	case dsl.NodeTypeSubroutineDefinition:
-		return nil, errors.New(
-			"mlr: subroutines may only be declared at top level.",
-		)
+		return nil, fmt.Errorf("mlr: subroutines may only be declared at top level.")
 	case dsl.NodeTypeSubroutineCallsite:
 		return root.BuildSubroutineCallsiteNode(astNode)
 
@@ -111,9 +103,7 @@ func (root *RootNode) BuildStatementNode(
 		return root.BuildReturnNode(astNode)
 
 	default:
-		return nil, errors.New(
-			"CST BuildStatementNode: unhandled AST node " + string(astNode.Type),
-		)
+		return nil, fmt.Errorf("at CST BuildStatementNode: unhandled AST node %s", string(astNode.Type))
 		break
 	}
 	return statement, nil

internal/pkg/dsl/cst/tee.go

@@ -5,7 +5,6 @@
 package cst
 
 import (
-	"errors"
 	"fmt"
 
 	"github.com/johnkerl/miller/internal/pkg/dsl"
@@ -122,12 +121,7 @@ func (root *RootNode) BuildTeeStatementNode(astNode *dsl.ASTNode) (IExecutable,
 		} else if redirectorNode.Type == dsl.NodeTypeRedirectPipe {
 			retval.outputHandlerManager = output.NewPipeWriteHandlerManager(root.recordWriterOptions)
 		} else {
-			return nil, errors.New(
-				fmt.Sprintf(
-					"%s: unhandled redirector node type %s.",
-					"mlr", string(redirectorNode.Type),
-				),
-			)
+			return nil, fmt.Errorf("mlr: unhandled redirector node type %s.", string(redirectorNode.Type))
 		}
 	}
 
@@ -144,12 +138,7 @@ func (root *RootNode) BuildTeeStatementNode(astNode *dsl.ASTNode) (IExecutable,
 func (node *TeeStatementNode) Execute(state *runtime.State) (*BlockExitPayload, error) {
 	expression := node.expressionEvaluable.Evaluate(state)
 	if !expression.IsMap() {
-		return nil, errors.New(
-			fmt.Sprintf(
-				"%s: tee-evaluaiton yielded %s, not map.",
-				"mlr", expression.GetTypeName(),
-			),
-		)
+		return nil, fmt.Errorf("mlr: tee-evaluaiton yielded %s, not map.", expression.GetTypeName())
 	}
 	err := node.teeToRedirectFunc(expression.GetMap(), state)
 	return nil, err
@@ -162,12 +151,7 @@ func (node *TeeStatementNode) teeToFileOrPipe(
 ) error {
 	redirectorTarget := node.redirectorTargetEvaluable.Evaluate(state)
 	if !redirectorTarget.IsString() {
-		return errors.New(
-			fmt.Sprintf(
-				"%s: output redirection yielded %s, not string.",
-				"mlr", redirectorTarget.GetTypeName(),
-			),
-		)
+		return fmt.Errorf("mlr: output redirection yielded %s, not string.", redirectorTarget.GetTypeName())
 	}
 	outputFileName := redirectorTarget.String()
 

internal/pkg/dsl/cst/udf.go

@@ -5,7 +5,6 @@
 package cst
 
 import (
-	"errors"
 	"fmt"
 	"os"
 
@@ -324,14 +323,12 @@ func (manager *UDFManager) LookUp(functionName string, callsiteArity int) (*UDF,
 		return nil, nil
 	}
 	if udf.signature.arity != callsiteArity {
-		return nil, errors.New(
-			fmt.Sprintf(
-				"mlr: function %s invoked with %d argument%s; expected %d",
-				functionName,
-				callsiteArity,
-				lib.Plural(callsiteArity),
-				udf.signature.arity,
-			),
+		return nil, fmt.Errorf(
+			"mlr: function %s invoked with %d argument%s; expected %d",
+			functionName,
+			callsiteArity,
+			lib.Plural(callsiteArity),
+			udf.signature.arity,
 		)
 	}
 	return udf, nil
@@ -391,21 +388,17 @@ func (root *RootNode) BuildAndInstallUDF(astNode *dsl.ASTNode) error {
 	functionName := string(astNode.Token.Lit)
 
 	if BuiltinFunctionManagerInstance.LookUp(functionName) != nil {
-		return errors.New(
-			fmt.Sprintf(
-				"mlr: function named \"%s\" must not override a built-in function of the same name.",
-				functionName,
-			),
+		return fmt.Errorf(
+			"mlr: function named \"%s\" must not override a built-in function of the same name.",
+			functionName,
 		)
 	}
 
 	if !root.allowUDFUDSRedefinitions {
 		if root.udfManager.ExistsByName(functionName) {
-			return errors.New(
-				fmt.Sprintf(
-					"mlr: function named \"%s\" has already been defined.",
-					functionName,
-				),
+			return fmt.Errorf(
+				"mlr: function named \"%s\" has already been defined.",
+				functionName,
 			)
 		}
 	}

internal/pkg/dsl/cst/uds.go

@@ -5,7 +5,6 @@
 package cst
 
 import (
-	"errors"
 	"fmt"
 
 	"github.com/johnkerl/miller/internal/pkg/dsl"
@@ -174,14 +173,12 @@ func (manager *UDSManager) LookUp(subroutineName string, callsiteArity int) (*UD
 		return nil, nil
 	}
 	if uds.signature.arity != callsiteArity {
-		return nil, errors.New(
-			fmt.Sprintf(
-				"mlr: subroutine %s invoked with %d argument%s; expected %d",
-				subroutineName,
-				callsiteArity,
-				lib.Plural(callsiteArity),
-				uds.signature.arity,
-			),
+		return nil, fmt.Errorf(
+			"mlr: subroutine %s invoked with %d argument%s; expected %d",
+			subroutineName,
+			callsiteArity,
+			lib.Plural(callsiteArity),
+			uds.signature.arity,
 		)
 	}
 	return uds, nil
@@ -244,11 +241,9 @@ func (root *RootNode) BuildAndInstallUDS(astNode *dsl.ASTNode) error {
 
 	if !root.allowUDFUDSRedefinitions {
 		if root.udsManager.ExistsByName(subroutineName) {
-			return errors.New(
-				fmt.Sprintf(
-					"mlr: subroutine named \"%s\" has already been defined.",
-					subroutineName,
-				),
+			return fmt.Errorf(
+				"mlr: subroutine named \"%s\" has already been defined.",
+				subroutineName,
 			)
 		}
 	}

internal/pkg/dsl/cst/validate.go

@@ -7,7 +7,6 @@
 package cst
 
 import (
-	"errors"
 	"fmt"
 
 	"github.com/johnkerl/miller/internal/pkg/dsl"
@@ -32,7 +31,7 @@ func ValidateAST(
 	// But filter '' is an error.
 	if ast.RootNode.Children == nil || len(ast.RootNode.Children) == 0 {
 		if dslInstanceType == DSLInstanceTypeFilter {
-			return errors.New("mlr: filter statement must not be empty.")
+			return fmt.Errorf("mlr: filter statement must not be empty.")
 		}
 	}
 
@@ -82,7 +81,7 @@ func validateASTAux(
 
 	if astNode.Type == dsl.NodeTypeFilterStatement {
 		if dslInstanceType == DSLInstanceTypeFilter {
-			return errors.New(
+			return fmt.Errorf(
 				"mlr: filter expressions must not also contain the \"filter\" keyword.",
 			)
 		}
@@ -91,21 +90,21 @@ func validateASTAux(
 	// Check: begin/end/func/subr must be at top-level
 	if astNode.Type == dsl.NodeTypeBeginBlock {
 		if !atTopLevel {
-			return errors.New(
+			return fmt.Errorf(
 				"mlr: begin blocks can only be at top level.",
 			)
 		}
 		nextLevelInBeginOrEnd = true
 	} else if astNode.Type == dsl.NodeTypeEndBlock {
 		if !atTopLevel {
-			return errors.New(
+			return fmt.Errorf(
 				"mlr: end blocks can only be at top level.",
 			)
 		}
 		nextLevelInBeginOrEnd = true
 	} else if astNode.Type == dsl.NodeTypeNamedFunctionDefinition {
 		if !atTopLevel {
-			return errors.New(
+			return fmt.Errorf(
 				"mlr: func blocks can only be at top level.",
 			)
 		}
@@ -114,7 +113,7 @@ func validateASTAux(
 		nextLevelInUDF = true
 	} else if astNode.Type == dsl.NodeTypeSubroutineDefinition {
 		if !atTopLevel {
-			return errors.New(
+			return fmt.Errorf(
 				"mlr: subr blocks can only be at top level.",
 			)
 		}
@@ -136,7 +135,7 @@ func validateASTAux(
 		if astNode.Type == dsl.NodeTypeDirectFieldValue ||
 			astNode.Type == dsl.NodeTypeIndirectFieldValue ||
 			astNode.Type == dsl.NodeTypeFullSrec {
-			return errors.New(
+			return fmt.Errorf(
 				"mlr: begin/end blocks cannot refer to records via $x, $*, etc.",
 			)
 		}
@@ -145,7 +144,7 @@ func validateASTAux(
 	// Check: break/continue outside of loop
 	if !inLoop {
 		if astNode.Type == dsl.NodeTypeBreak {
-			return errors.New(
+			return fmt.Errorf(
 				"mlr: break statements are only valid within for/do/while loops.",
 			)
 		}
@@ -153,7 +152,7 @@ func validateASTAux(
 
 	if !inLoop {
 		if astNode.Type == dsl.NodeTypeContinue {
-			return errors.New(
+			return fmt.Errorf(
 				"mlr: break statements are only valid within for/do/while loops.",
 			)
 		}
@@ -171,7 +170,7 @@ func validateASTAux(
 	// Check: return outside of func/subr
 	if !inUDF && !inUDS {
 		if astNode.Type == dsl.NodeTypeReturn {
-			return errors.New(
+			return fmt.Errorf(
 				"mlr: return statements are only valid within func/subr blocks.",
 			)
 		}
@@ -181,14 +180,14 @@ func validateASTAux(
 	if astNode.Type == dsl.NodeTypeReturn {
 		if inUDF {
 			if len(astNode.Children) != 1 {
-				return errors.New(
+				return fmt.Errorf(
 					"mlr: return statements in func blocks must return a value.",
 				)
 			}
 		}
 		if inUDS {
 			if len(astNode.Children) != 0 {
-				return errors.New(
+				return fmt.Errorf(
 					"mlr: return statements in subr blocks must not return a value.",
 				)
 			}
@@ -199,11 +198,9 @@ func validateASTAux(
 	if isAssignmentLHS {
 		ok := VALID_LHS_NODE_TYPES[astNode.Type]
 		if !ok {
-			return errors.New(
-				fmt.Sprintf(
-					"mlr: %s is not valid on the left-hand side of an assignment.",
-					astNode.Type,
-				),
+			return fmt.Errorf(
+				"mlr: %s is not valid on the left-hand side of an assignment.",
+				astNode.Type,
 			)
 		}
 	}
@@ -212,11 +209,9 @@ func validateASTAux(
 	if isUnset {
 		ok := VALID_LHS_NODE_TYPES[astNode.Type]
 		if !ok {
-			return errors.New(
-				fmt.Sprintf(
-					"mlr: %s is not valid for unset statement.",
-					astNode.Type,
-				),
+			return fmt.Errorf(
+				"mlr: %s is not valid for unset statement.",
+				astNode.Type,
 			)
 		}
 	}
@@ -268,13 +263,7 @@ func validateForLoopTwoVariableUniqueNames(astNode *dsl.ASTNode) error {
 	keyVarName := string(keyVarNode.Token.Lit)
 	valVarName := string(valVarNode.Token.Lit)
 	if keyVarName == valVarName {
-		return errors.New(
-			fmt.Sprintf(
-				"%s: redefinition of variable %s in the same scope.",
-				"mlr",
-				keyVarName,
-			),
-		)
+		return fmt.Errorf("mlr: redefinition of variable %s in the same scope.", keyVarName)
 	} else {
 		return nil
 	}
@@ -304,26 +293,14 @@ func validateForLoopMultivariableUniqueNames(astNode *dsl.ASTNode) error {
 		name := string(keyVarNode.Token.Lit)
 		_, present := seen[name]
 		if present {
-			return errors.New(
-				fmt.Sprintf(
-					"%s: redefinition of variable %s in the same scope.",
-					"mlr",
-					name,
-				),
-			)
+			return fmt.Errorf("mlr: redefinition of variable %s in the same scope.", name)
 		}
 		seen[name] = true
 	}
 
 	valVarName := string(valVarNode.Token.Lit)
 	if seen[valVarName] {
-		return errors.New(
-			fmt.Sprintf(
-				"%s: redefinition of variable %s in the same scope.",
-				"mlr",
-				valVarName,
-			),
-		)
+		return fmt.Errorf("mlr: redefinition of variable %s in the same scope.", valVarName)
 	}
 
 	return nil

internal/pkg/dsl/cst/while.go

@@ -5,7 +5,7 @@
 package cst
 
 import (
-	"errors"
+	"fmt"
 
 	"github.com/johnkerl/miller/internal/pkg/dsl"
 	"github.com/johnkerl/miller/internal/pkg/lib"
@@ -54,7 +54,7 @@ func (node *WhileLoopNode) Execute(state *runtime.State) (*BlockExitPayload, err
 		boolValue, isBool := condition.GetBoolValue()
 		if !isBool {
 			// TODO: line-number/token info for the DSL expression.
-			return nil, errors.New("mlr: conditional expression did not evaluate to boolean.")
+			return nil, fmt.Errorf("mlr: conditional expression did not evaluate to boolean.")
 		}
 		if boolValue != true {
 			break
@@ -144,7 +144,7 @@ func (node *DoWhileLoopNode) Execute(state *runtime.State) (*BlockExitPayload, e
 		boolValue, isBool := condition.GetBoolValue()
 		if !isBool {
 			// TODO: line-number/token info for the DSL expression.
-			return nil, errors.New("mlr: conditional expression did not evaluate to boolean.")
+			return nil, fmt.Errorf("mlr: conditional expression did not evaluate to boolean.")
 		}
 		if boolValue == false {
 			break

internal/pkg/input/pseudo_reader_gen.go

@@ -2,7 +2,6 @@ package input
 
 import (
 	"container/list"
-	"errors"
 	"fmt"
 
 	"github.com/johnkerl/miller/internal/pkg/bifs"
@@ -124,9 +123,7 @@ func (reader *PseudoReaderGen) tryParse(
 ) (*mlrval.Mlrval, error) {
 	mvalue := mlrval.FromDeferredType(svalue)
 	if mvalue == nil || !mvalue.IsNumeric() {
-		return nil, errors.New(
-			fmt.Sprintf("mlr: gen: %s \"%s\" is not parseable as number", name, svalue),
-		)
+		return nil, fmt.Errorf("mlr: gen: %s \"%s\" is not parseable as number", name, svalue)
 	}
 	return mvalue, nil
 }

internal/pkg/input/record_reader_csv.go

@@ -4,7 +4,6 @@ import (
 	"bytes"
 	"container/list"
 	"encoding/csv"
-	"errors"
 	"fmt"
 	"io"
 	"strconv"
@@ -33,10 +32,10 @@ func NewRecordReaderCSV(
 	recordsPerBatch int,
 ) (*RecordReaderCSV, error) {
 	if readerOptions.IRS != "\n" && readerOptions.IRS != "\r\n" {
-		return nil, errors.New("CSV IRS cannot be altered; LF vs CR/LF is autodetected")
+		return nil, fmt.Errorf("for CSV, IRS cannot be altered; LF vs CR/LF is autodetected")
 	}
 	if len(readerOptions.IFS) != 1 {
-		return nil, errors.New("CSV IFS can only be a single character")
+		return nil, fmt.Errorf("for CSV, IFS can only be a single character")
 	}
 	return &RecordReaderCSV{
 		readerOptions:   readerOptions,
@@ -236,12 +235,10 @@ func (reader *RecordReaderCSV) getRecordBatch(
 
 		} else {
 			if !reader.readerOptions.AllowRaggedCSVInput {
-				err := errors.New(
-					fmt.Sprintf(
-						"mlr: CSV header/data length mismatch %d != %d "+
-							"at filename %s row %d.\n",
-						nh, nd, reader.filename, reader.rowNumber,
-					),
+				err := fmt.Errorf(
+					"mlr: CSV header/data length mismatch %d != %d "+
+						"at filename %s row %d.\n",
+					nh, nd, reader.filename, reader.rowNumber,
 				)
 				errorChannel <- err
 				return

internal/pkg/input/record_reader_csvlite.go

@@ -20,7 +20,6 @@ package input
 
 import (
 	"container/list"
-	"errors"
 	"fmt"
 	"io"
 	"strconv"
@@ -228,12 +227,10 @@ func getRecordBatchExplicitCSVHeader(
 			// Get data lines on subsequent loop iterations
 		} else {
 			if !reader.readerOptions.AllowRaggedCSVInput && len(reader.headerStrings) != len(fields) {
-				err := errors.New(
-					fmt.Sprintf(
-						"mlr: CSV header/data length mismatch %d != %d "+
-							"at filename %s line  %d.\n",
-						len(reader.headerStrings), len(fields), filename, reader.inputLineNumber,
-					),
+				err := fmt.Errorf(
+					"mlr: CSV header/data length mismatch %d != %d "+
+						"at filename %s line  %d.\n",
+					len(reader.headerStrings), len(fields), filename, reader.inputLineNumber,
 				)
 				errorChannel <- err
 				return
@@ -348,12 +345,10 @@ func getRecordBatchImplicitCSVHeader(
 			}
 		} else {
 			if !reader.readerOptions.AllowRaggedCSVInput && len(reader.headerStrings) != len(fields) {
-				err := errors.New(
-					fmt.Sprintf(
-						"mlr: CSV header/data length mismatch %d != %d "+
-							"at filename %s line  %d.\n",
-						len(reader.headerStrings), len(fields), filename, reader.inputLineNumber,
-					),
+				err := fmt.Errorf(
+					"mlr: CSV header/data length mismatch %d != %d "+
+						"at filename %s line  %d.\n",
+					len(reader.headerStrings), len(fields), filename, reader.inputLineNumber,
 				)
 				errorChannel <- err
 				return

internal/pkg/input/record_reader_factory.go

@@ -1,7 +1,6 @@
 package input
 
 import (
-	"errors"
 	"fmt"
 
 	"github.com/johnkerl/miller/internal/pkg/cli"
@@ -26,6 +25,6 @@ func Create(readerOptions *cli.TReaderOptions, recordsPerBatch int) (IRecordRead
 	case "gen":
 		return NewPseudoReaderGen(readerOptions, recordsPerBatch)
 	default:
-		return nil, errors.New(fmt.Sprintf("input file format \"%s\" not found", readerOptions.InputFileFormat))
+		return nil, fmt.Errorf("input file format \"%s\" not found", readerOptions.InputFileFormat)
 	}
 }

internal/pkg/input/record_reader_json.go

@@ -3,7 +3,6 @@ package input
 import (
 	"bufio"
 	"container/list"
-	"errors"
 	"fmt"
 	"io"
 	"strings"
@@ -126,7 +125,7 @@ func (reader *RecordReaderJSON) processHandle(
 			// TODO: make a helper method
 			record := mlrval.GetMap()
 			if record == nil {
-				errorChannel <- errors.New("Internal coding error detected in JSON record-reader")
+				errorChannel <- fmt.Errorf("internal coding error detected in JSON record-reader")
 				return
 			}
 			context.UpdateForInputRecord()
@@ -140,24 +139,22 @@ func (reader *RecordReaderJSON) processHandle(
 		} else if mlrval.IsArray() {
 			records := mlrval.GetArray()
 			if records == nil {
-				errorChannel <- errors.New("Internal coding error detected in JSON record-reader")
+				errorChannel <- fmt.Errorf("internal coding error detected in JSON record-reader")
 				return
 			}
 
 			for _, mlrval := range records {
 				if !mlrval.IsMap() {
 					// TODO: more context
-					errorChannel <- errors.New(
-						fmt.Sprintf(
-							"Valid but unmillerable JSON. Expected map (JSON object); got %s.",
-							mlrval.GetTypeName(),
-						),
+					errorChannel <- fmt.Errorf(
+						"valid but unmillerable JSON. Expected map (JSON object); got %s.",
+						mlrval.GetTypeName(),
 					)
 					return
 				}
 				record := mlrval.GetMap()
 				if record == nil {
-					errorChannel <- errors.New("Internal coding error detected in JSON record-reader")
+					errorChannel <- fmt.Errorf("internal coding error detected in JSON record-reader")
 					return
 				}
 				context.UpdateForInputRecord()
@@ -170,11 +167,9 @@ func (reader *RecordReaderJSON) processHandle(
 			}
 
 		} else {
-			errorChannel <- errors.New(
-				fmt.Sprintf(
-					"Valid but unmillerable JSON. Expected map (JSON object); got %s.",
-					mlrval.GetTypeName(),
-				),
+			errorChannel <- fmt.Errorf(
+				"valid but unmillerable JSON. Expected map (JSON object); got %s.",
+				mlrval.GetTypeName(),
 			)
 			return
 		}

internal/pkg/input/record_reader_xtab.go

@@ -3,7 +3,7 @@ package input
 import (
 	"bufio"
 	"container/list"
-	"errors"
+	"fmt"
 	"io"
 	"regexp"
 	"strings"
@@ -311,7 +311,7 @@ func (s *tXTABIPSSplitter) Split(input string) (key, value string, err error) {
 	// Empty string is a length-0 return value.
 	n := len(input)
 	if n == 0 {
-		return "", "", errors.New("mlr: internal coding error in XTAB reader")
+		return "", "", fmt.Errorf("internal coding error in XTAB reader")
 	}
 
 	// '   abc 123' splits as key '', value 'abc 123'.
@@ -360,12 +360,12 @@ type tXTABIPSRegexSplitter struct {
 func (s *tXTABIPSRegexSplitter) Split(input string) (key, value string, err error) {
 	kv := lib.RegexSplitString(s.ipsRegex, input, 2)
 	if len(kv) == 0 {
-		return "", "", errors.New("mlr: internal coding error in XTAB reader")
+		return "", "", fmt.Errorf("internal coding error in XTAB reader")
 	} else if len(kv) == 1 {
 		return kv[0], "", nil
 	} else if len(kv) == 2 {
 		return kv[0], kv[1], nil
 	} else {
-		return "", "", errors.New("mlr: internal coding error in XTAB reader")
+		return "", "", fmt.Errorf("internal coding error in XTAB reader")
 	}
 }

internal/pkg/lib/file-readers.go

@@ -24,7 +24,7 @@ import (
 	"compress/bzip2"
 	"compress/gzip"
 	"compress/zlib"
-	"errors"
+	"fmt"
 	"io"
 	"net/http"
 	"os"
@@ -236,10 +236,10 @@ func IsUpdateableInPlace(
 	if strings.HasPrefix(filename, "http://") ||
 		strings.HasPrefix(filename, "https://") ||
 		strings.HasPrefix(filename, "file://") {
-		return errors.New("http://, https://, and file:// URLs are not updateable in place.")
+		return fmt.Errorf("http://, https://, and file:// URLs are not updateable in place.")
 	}
 	if prepipe != "" {
-		return errors.New("input with --prepipe or --prepipex is not updateable in place.")
+		return fmt.Errorf("input with --prepipe or --prepipex is not updateable in place.")
 	}
 	return nil
 }
@@ -281,7 +281,7 @@ func WrapOutputHandle(
 ) (io.WriteCloser, bool, error) {
 	switch inputFileEncoding {
 	case FileInputEncodingBzip2:
-		return fileWriteHandle, false, errors.New("bzip2 is not currently supported for in-place mode.")
+		return fileWriteHandle, false, fmt.Errorf("bzip2 is not currently supported for in-place mode.")
 	case FileInputEncodingGzip:
 		return gzip.NewWriter(fileWriteHandle), true, nil
 	case FileInputEncodingZlib:

internal/pkg/mlrval/mlrmap_accessors.go

@@ -2,7 +2,6 @@ package mlrval
 
 import (
 	"bytes"
-	"errors"
 	"fmt"
 	"strconv"
 
@@ -84,9 +83,7 @@ func (mlrmap *Mlrmap) PutReferenceMaybeDedupe(key string, value *Mlrval, dedupe
 			return newKey, nil
 		}
 	}
-	return key, errors.New(
-		fmt.Sprintf("record has too many input fields named \"%s\"", key),
-	)
+	return key, fmt.Errorf("record has too many input fields named \"%s\"", key)
 }
 
 // PutCopy copies the key and value (deep-copying in case the value is array/map).
@@ -250,8 +247,8 @@ func (mlrmap *Mlrmap) PutCopyWithMlrvalIndex(key *Mlrval, value *Mlrval) error {
 		mlrmap.PutCopy(key.String(), value)
 		return nil
 	} else {
-		return errors.New(
-			"mlr: record/map indices must be string, int, or array thereof; got " + key.GetTypeName(),
+		return fmt.Errorf(
+			"mlr: record/map indices must be string, int, or array thereof; got %s", key.GetTypeName(),
 		)
 	}
 }
@@ -352,9 +349,7 @@ func (mlrmap *Mlrmap) getWithMlrvalArrayIndex(index *Mlrval) (*Mlrval, error) {
 		}
 		if i < n-1 {
 			if !next.IsMap() {
-				return nil, errors.New(
-					"mlr: cannot multi-index non-map.",
-				)
+				return nil, fmt.Errorf("mlr: cannot multi-index non-map.")
 			}
 			current = next.mapval
 		} else {
@@ -371,8 +366,8 @@ func (mlrmap *Mlrmap) getWithMlrvalSingleIndex(index *Mlrval) (*Mlrval, error) {
 	} else if index.IsInt() {
 		return mlrmap.Get(index.String()), nil
 	} else {
-		return nil, errors.New(
-			"Record/map indices must be string, int, or array thereof; got " + index.GetTypeName(),
+		return nil, fmt.Errorf(
+			"Record/map indices must be string, int, or array thereof; got %s", index.GetTypeName(),
 		)
 	}
 }

internal/pkg/mlrval/mlrval_format.go

@@ -1,7 +1,6 @@
 package mlrval
 
 import (
-	"errors"
 	"fmt"
 	"strconv"
 	"strings"
@@ -85,13 +84,11 @@ func newFormatter(
 ) (IFormatter, error) {
 	numPercents := strings.Count(userLevelFormatString, "%")
 	if numPercents < 1 {
-		return nil, errors.New(
-			fmt.Sprintf("unhandled format string \"%s\": no leading \"%%\"", userLevelFormatString),
-		)
+		return nil, fmt.Errorf("unhandled format string \"%s\": no leading \"%%\"", userLevelFormatString)
 	}
 	if numPercents > 1 {
-		return nil, errors.New(
-			fmt.Sprintf("unhandled format string \"%s\": needs no \"%%\" after the first", userLevelFormatString),
+		return nil, fmt.Errorf(
+			"unhandled format string \"%s\": needs no \"%%\" after the first", userLevelFormatString,
 		)
 	}
 

internal/pkg/mlrval/mlrval_json.go

@@ -11,7 +11,7 @@ package mlrval
 import (
 	"bytes"
 	"encoding/json"
-	"errors"
+	"fmt"
 	"io"
 
 	"github.com/johnkerl/miller/internal/pkg/colorizer"
@@ -105,7 +105,7 @@ func (mv *Mlrval) UnmarshalJSON(inputBytes []byte) error {
 	decoder := json.NewDecoder(bytes.NewReader(inputBytes))
 	pmv, eof, err := MlrvalDecodeFromJSON(decoder)
 	if eof {
-		return errors.New("Miller JSON parser: unexpected premature EOF.")
+		return fmt.Errorf("mlr: JSON parser: unexpected premature EOF.")
 	}
 	if err != nil {
 		return err
@@ -155,8 +155,8 @@ func MlrvalDecodeFromJSON(decoder *json.Decoder) (
 			return mlrval, false, nil
 		}
 
-		return nil, false, errors.New(
-			"Miller JSON reader internal coding error: non-delimiter token unhandled",
+		return nil, false, fmt.Errorf(
+			"mlr: JSON reader internal coding error: non-delimiter token unhandled",
 		)
 
 	} else {
@@ -173,8 +173,8 @@ func MlrvalDecodeFromJSON(decoder *json.Decoder) (
 			expectedClosingDelimiter = '}'
 			collectionType = "JSON object`"
 		} else {
-			return nil, false, errors.New(
-				"Miller JSON reader: Unhandled opening delimiter \"" + string(delimiter) + "\"",
+			return nil, false, fmt.Errorf(
+				"mlr: JSON reader: Unhandled opening delimiter \"%s\"", string(delimiter),
 			)
 		}
 
@@ -186,7 +186,7 @@ func MlrvalDecodeFromJSON(decoder *json.Decoder) (
 				element, eof, err := MlrvalDecodeFromJSON(decoder)
 				if eof {
 					// xxx constify
-					return nil, false, errors.New("Miller JSON parser: unexpected premature EOF.")
+					return nil, false, fmt.Errorf("mlr: JSON parser: unexpected premature EOF.")
 				}
 				if err != nil {
 					return nil, false, err
@@ -201,22 +201,22 @@ func MlrvalDecodeFromJSON(decoder *json.Decoder) (
 				key, eof, err := MlrvalDecodeFromJSON(decoder)
 				if eof {
 					// xxx constify
-					return nil, false, errors.New("Miller JSON parser: unexpected premature EOF.")
+					return nil, false, fmt.Errorf("mlr: JSON parser: unexpected premature EOF.")
 				}
 				if err != nil {
 					return nil, false, err
 				}
 				if !key.IsString() {
-					return nil, false, errors.New(
+					return nil, false, fmt.Errorf(
 						// TODO: print out what was gotten
-						"Miller JSON reader: obejct keys must be string-valued.",
+						"mlr JSON reader: obejct keys must be string-valued.",
 					)
 				}
 
 				value, eof, err := MlrvalDecodeFromJSON(decoder)
 				if eof {
 					// xxx constify
-					return nil, false, errors.New("Miller JSON parser: unexpected premature EOF.")
+					return nil, false, fmt.Errorf("mlr: JSON parser: unexpected premature EOF.")
 				}
 				if err != nil {
 					return nil, false, err
@@ -227,16 +227,15 @@ func MlrvalDecodeFromJSON(decoder *json.Decoder) (
 			}
 		}
 
-		imbalanceError := errors.New(
-			"Miller JSON reader: did not find closing token '" +
-				string(expectedClosingDelimiter) +
-				"' for " +
-				collectionType,
+		imbalanceError := fmt.Errorf(
+			"mlr: JSON reader: did not find closing token \"%s\" for %s",
+			string(expectedClosingDelimiter),
+			collectionType,
 		)
 
 		endToken, err := decoder.Token()
 		if err == io.EOF {
-			return nil, false, errors.New("Miller JSON parser: unexpected premature EOF.")
+			return nil, false, fmt.Errorf("mlr: JSON parser: unexpected premature EOF.")
 		}
 		if err != nil {
 			return nil, false, err
@@ -255,7 +254,7 @@ func MlrvalDecodeFromJSON(decoder *json.Decoder) (
 		return mv, false, nil
 	}
 
-	return nil, false, errors.New("unimplemented")
+	return nil, false, fmt.Errorf("mlr: unimplemented")
 }
 
 // ================================================================
@@ -274,41 +273,30 @@ func (mv *Mlrval) marshalJSONAux(
 	switch mv.Type() {
 	case MT_PENDING:
 		return mv.marshalJSONPending(outputIsStdout)
-		break
 	case MT_ERROR:
 		return mv.marshalJSONError(outputIsStdout)
-		break
 	case MT_ABSENT:
 		return mv.marshalJSONAbsent(outputIsStdout)
-		break
 	case MT_NULL:
 		return mv.marshalJSONNull(outputIsStdout)
-		break
 	case MT_VOID:
 		return mv.marshalJSONVoid(outputIsStdout)
-		break
 	case MT_STRING:
 		return mv.marshalJSONString(outputIsStdout)
-		break
 	case MT_INT:
 		return mv.marshalJSONInt(outputIsStdout)
-		break
 	case MT_FLOAT:
 		return mv.marshalJSONFloat(outputIsStdout)
-		break
 	case MT_BOOL:
 		return mv.marshalJSONBool(outputIsStdout)
-		break
 	case MT_ARRAY:
 		return mv.marshalJSONArray(jsonFormatting, elementNestingDepth, outputIsStdout)
-		break
 	case MT_MAP:
 		return mv.marshalJSONMap(jsonFormatting, elementNestingDepth, outputIsStdout)
-		break
 	case MT_DIM: // MT_DIM is one past the last valid type
-		return "", errors.New("mlr: internal coding error detected")
+		return "", fmt.Errorf("mlr: internal coding error detected")
 	}
-	return "", errors.New("mlr: Internal coding error detected")
+	return "", fmt.Errorf("mlr: Internal coding error detected")
 }
 
 // ================================================================
@@ -317,8 +305,8 @@ func (mv *Mlrval) marshalJSONAux(
 // ----------------------------------------------------------------
 func (mv *Mlrval) marshalJSONPending(outputIsStdout bool) (string, error) {
 	lib.InternalCodingErrorIf(mv.mvtype != MT_PENDING)
-	return "", errors.New(
-		"Miller internal coding error: pending-values should not have been produced",
+	return "", fmt.Errorf(
+		"mlr: internal coding error: pending-values should not have been produced",
 	)
 }
 
@@ -331,8 +319,8 @@ func (mv *Mlrval) marshalJSONError(outputIsStdout bool) (string, error) {
 // ----------------------------------------------------------------
 func (mv *Mlrval) marshalJSONAbsent(outputIsStdout bool) (string, error) {
 	lib.InternalCodingErrorIf(mv.mvtype != MT_ABSENT)
-	return "", errors.New(
-		"Miller internal coding error: absent-values should not have been assigned",
+	return "", fmt.Errorf(
+		"mlr: internal coding error: absent-values should not have been assigned",
 	)
 }
 

internal/pkg/mlrval/mlrval_output.go

@@ -42,33 +42,27 @@ func (mv *Mlrval) setPrintRep() {
 			// clearly visually if it should (buggily) slip through to
 			// user-level visibility.
 			mv.printrep = "(bug-if-you-see-this:case=3)" // xxx constdef at top of file
-			break
 
 		case MT_ERROR:
 			mv.printrep = "(error)" // xxx constdef at top of file
-			break
 
 		case MT_ABSENT:
 			// Callsites should be using absence to do non-assigns, so flag
 			// this clearly visually if it should (buggily) slip through to
 			// user-level visibility.
 			mv.printrep = "(bug-if-you-see-this:case=4)" // xxx constdef at top of file
-			break
 
 		case MT_VOID:
 			mv.printrep = "" // xxx constdef at top of file
-			break
 
 		case MT_STRING:
 			break
 
 		case MT_INT:
 			mv.printrep = strconv.Itoa(mv.intval)
-			break
 
 		case MT_FLOAT:
 			mv.printrep = strconv.FormatFloat(mv.floatval, 'f', -1, 64)
-			break
 
 		case MT_BOOL:
 			if mv.boolval == true {
@@ -76,7 +70,6 @@ func (mv *Mlrval) setPrintRep() {
 			} else {
 				mv.printrep = "false"
 			}
-			break
 
 		case MT_ARRAY:
 			bytes, err := mv.MarshalJSON(JSON_MULTILINE, false)
@@ -87,8 +80,6 @@ func (mv *Mlrval) setPrintRep() {
 			}
 			mv.printrep = string(bytes)
 
-			break
-
 		case MT_MAP:
 			bytes, err := mv.MarshalJSON(JSON_MULTILINE, false)
 			// maybe just InternalCodingErrorIf(err != nil)
@@ -97,8 +88,6 @@ func (mv *Mlrval) setPrintRep() {
 				os.Exit(1)
 			}
 			mv.printrep = string(bytes)
-
-			break
 		}
 		mv.printrepValid = true
 	}

internal/pkg/output/file-output-handlers.go

@@ -15,7 +15,6 @@ package output
 import (
 	"bufio"
 	"container/list"
-	"errors"
 	"fmt"
 	"io"
 	"os"
@@ -283,13 +282,7 @@ func NewPipeWriteOutputHandler(
 ) (*FileOutputHandler, error) {
 	writePipe, err := lib.OpenOutboundHalfPipe(commandString)
 	if err != nil {
-		return nil, errors.New(
-			fmt.Sprintf(
-				"%s: could not launch command \"%s\" for pipe-to.",
-				"mlr",
-				commandString,
-			),
-		)
+		return nil, fmt.Errorf("could not launch command \"%s\" for pipe-to.", commandString)
 	}
 
 	return newOutputHandlerCommon(

internal/pkg/output/record_writer_csv.go

@@ -3,7 +3,7 @@ package output
 import (
 	"bufio"
 	"encoding/csv"
-	"errors"
+	"fmt"
 	"strings"
 
 	"github.com/johnkerl/miller/internal/pkg/cli"
@@ -23,10 +23,10 @@ type RecordWriterCSV struct {
 
 func NewRecordWriterCSV(writerOptions *cli.TWriterOptions) (*RecordWriterCSV, error) {
 	if len(writerOptions.OFS) != 1 {
-		return nil, errors.New("CSV OFS can only be a single character")
+		return nil, fmt.Errorf("for CSV, OFS can only be a single character")
 	}
 	if writerOptions.ORS != "\n" && writerOptions.ORS != "\r\n" {
-		return nil, errors.New("CSV ORS cannot be altered")
+		return nil, fmt.Errorf("for CSV, ORS cannot be altered")
 	}
 	return &RecordWriterCSV{
 		writerOptions:      writerOptions,

internal/pkg/output/record_writer_factory.go

@@ -1,7 +1,6 @@
 package output
 
 import (
-	"errors"
 	"fmt"
 
 	"github.com/johnkerl/miller/internal/pkg/cli"
@@ -26,6 +25,6 @@ func Create(writerOptions *cli.TWriterOptions) (IRecordWriter, error) {
 	case "xtab":
 		return NewRecordWriterXTAB(writerOptions)
 	default:
-		return nil, errors.New(fmt.Sprintf("output file format \"%s\" not found", writerOptions.OutputFileFormat))
+		return nil, fmt.Errorf("output file format \"%s\" not found", writerOptions.OutputFileFormat)
 	}
 }

internal/pkg/output/record_writer_nidx.go

@@ -9,8 +9,6 @@ import (
 
 type RecordWriterNIDX struct {
 	writerOptions *cli.TWriterOptions
-	ofs           string
-	ors           string
 }
 
 func NewRecordWriterNIDX(writerOptions *cli.TWriterOptions) (*RecordWriterNIDX, error) {

internal/pkg/runtime/stack.go

@@ -27,7 +27,6 @@ package runtime
 
 import (
 	"container/list"
-	"errors"
 	"fmt"
 
 	"github.com/johnkerl/miller/internal/pkg/lib"
@@ -407,11 +406,9 @@ func (frame *StackFrame) defineTyped(
 		frame.namesToOffsets[stackVariable.name] = offsetInFrame
 		return nil
 	} else {
-		return errors.New(
-			fmt.Sprintf(
-				"%s: variable %s has already been defined in the same scope.",
-				"mlr", stackVariable.name,
-			),
+		return fmt.Errorf(
+			"%s: variable %s has already been defined in the same scope.",
+			"mlr", stackVariable.name,
 		)
 	}
 }
@@ -431,11 +428,9 @@ func (frame *StackFrame) setIndexed(
 			newval.PutIndexed(indices, mv)
 			return frame.set(stackVariable, newval)
 		} else {
-			return errors.New(
-				fmt.Sprintf(
-					"%s: map indices must be int or string; got %s.\n",
-					"mlr", leadingIndex.GetTypeName(),
-				),
+			return fmt.Errorf(
+				"%s: map indices must be int or string; got %s.\n",
+				"mlr", leadingIndex.GetTypeName(),
 			)
 		}
 	} else {

internal/pkg/transformers/label.go

@@ -2,7 +2,6 @@ package transformers
 
 import (
 	"container/list"
-	"errors"
 	"fmt"
 	"os"
 	"strings"
@@ -108,12 +107,7 @@ func NewTransformerLabel(
 	for _, newName := range newNames {
 		_, ok := uniquenessChecker[newName]
 		if ok {
-			return nil, errors.New(
-				fmt.Sprintf(
-					"mlr label: labels must be unique; got duplicate \"%s\"\n",
-					newName,
-				),
-			)
+			return nil, fmt.Errorf("mlr label: labels must be unique; got duplicate \"%s\"\n", newName)
 		}
 		uniquenessChecker[newName] = true
 	}

internal/pkg/transformers/merge-fields.go

@@ -2,7 +2,6 @@ package transformers
 
 import (
 	"container/list"
-	"errors"
 	"fmt"
 	"os"
 	"regexp"
@@ -257,11 +256,9 @@ func NewTransformerMergeFields(
 
 	for _, accumulatorName := range accumulatorNameList {
 		if !utils.ValidateStats1AccumulatorName(accumulatorName) {
-			return nil, errors.New(
-				fmt.Sprintf(
-					"%s %s: accumulator \"%s\" not found.\n",
-					"mlr", verbNameMergeFields, accumulatorName,
-				),
+			return nil, fmt.Errorf(
+				"mlr %s: accumulator \"%s\" not found.\n",
+				verbNameMergeFields, accumulatorName,
 			)
 		}
 	}

internal/pkg/transformers/put-or-filter.go

@@ -2,7 +2,6 @@ package transformers
 
 import (
 	"container/list"
-	"errors"
 	"fmt"
 	"os"
 	"strings"
@@ -447,12 +446,7 @@ func NewTransformerPut(
 		for _, preset := range presets {
 			pair := strings.SplitN(preset, "=", 2)
 			if len(pair) != 2 {
-				return nil, errors.New(
-					fmt.Sprintf(
-						"mlr: missing \"=\" in preset expression \"%s\".",
-						preset,
-					),
-				)
+				return nil, fmt.Errorf("missing \"=\" in preset expression \"%s\".", preset)
 			}
 			key := pair[0]
 			svalue := pair[1]

internal/pkg/transformers/rename.go

@@ -2,7 +2,6 @@ package transformers
 
 import (
 	"container/list"
-	"errors"
 	"fmt"
 	"os"
 	"regexp"
@@ -149,7 +148,7 @@ func NewTransformerRename(
 	doGsub bool,
 ) (*TransformerRename, error) {
 	if len(names)%2 != 0 {
-		return nil, errors.New("Rename: names string must have even length.")
+		return nil, fmt.Errorf("mlr rename: names string must have even length")
 	}
 
 	oldToNewNames := lib.NewOrderedMap()

internal/pkg/transformers/seqgen.go

@@ -2,7 +2,6 @@ package transformers
 
 import (
 	"container/list"
-	"errors"
 	"fmt"
 	"os"
 	"strings"
@@ -140,32 +139,17 @@ func NewTransformerSeqgen(
 
 	fstart, startIsNumeric := start.GetNumericToFloatValue()
 	if !startIsNumeric {
-		return nil, errors.New(
-			fmt.Sprintf(
-				"mlr seqgen: start value should be number; got \"%s\"",
-				startString,
-			),
-		)
+		return nil, fmt.Errorf("mlr seqgen: start value should be number; got \"%s\"", startString)
 	}
 
 	fstop, stopIsNumeric := stop.GetNumericToFloatValue()
 	if !stopIsNumeric {
-		return nil, errors.New(
-			fmt.Sprintf(
-				"mlr seqgen: stop value should be number; got \"%s\"",
-				stopString,
-			),
-		)
+		return nil, fmt.Errorf("mlr seqgen: stop value should be number; got \"%s\"", stopString)
 	}
 
 	fstep, stepIsNumeric := step.GetNumericToFloatValue()
 	if !stepIsNumeric {
-		return nil, errors.New(
-			fmt.Sprintf(
-				"mlr seqgen: step value should be number; got \"%s\"",
-				stepString,
-			),
-		)
+		return nil, fmt.Errorf("mlr seqgen: step value should be number; got \"%s\"", stepString)
 	}
 
 	if fstep > 0 {
@@ -176,9 +160,7 @@ func NewTransformerSeqgen(
 		if fstart == fstop {
 			doneComparator = bifs.BIF_equals
 		} else {
-			return nil, errors.New(
-				"mlr seqgen: step must not be zero unless start == stop.",
-			)
+			return nil, fmt.Errorf("mlr seqgen: step must not be zero unless start == stop.")
 		}
 	}
 

internal/pkg/transformers/stats1.go

@@ -3,7 +3,6 @@ package transformers
 import (
 	"bytes"
 	"container/list"
-	"errors"
 	"fmt"
 	"os"
 	"regexp"
@@ -316,12 +315,7 @@ func NewTransformerStats1(
 ) (*TransformerStats1, error) {
 	for _, name := range accumulatorNameList {
 		if !utils.ValidateStats1AccumulatorName(name) {
-			return nil, errors.New(
-				fmt.Sprintf(
-					"%s stats1: accumulator \"%s\" not found.\n",
-					"mlr", name,
-				),
-			)
+			return nil, fmt.Errorf("mlr stats1: accumulator \"%s\" not found.", name)
 		}
 	}
 

internal/pkg/transformers/stats2.go

@@ -2,7 +2,6 @@ package transformers
 
 import (
 	"container/list"
-	"errors"
 	"fmt"
 	"os"
 	"strings"
@@ -210,12 +209,7 @@ func NewTransformerStats2(
 ) (*TransformerStats2, error) {
 	for _, name := range accumulatorNameList {
 		if !utils.ValidateStats2AccumulatorName(name) {
-			return nil, errors.New(
-				fmt.Sprintf(
-					"%s stats2: accumulator \"%s\" not found.\n",
-					"mlr", name,
-				),
-			)
+			return nil, fmt.Errorf("mlr stats2: accumulator \"%s\" not found.", name)
 		}
 	}
 

internal/pkg/transformers/step.go

@@ -2,7 +2,6 @@ package transformers
 
 import (
 	"container/list"
-	"errors"
 	"fmt"
 	"os"
 	"strings"
@@ -180,16 +179,12 @@ func NewTransformerStep(
 ) (*TransformerStep, error) {
 
 	if len(stepperNames) == 0 || len(valueFieldNames) == 0 {
-		return nil, errors.New(
-			// TODO: parameterize verb here somehow
-			"mlr step: -a and -f are both required arguments.",
-		)
+		return nil, fmt.Errorf("mlr %s: -a and -f are both required arguments.", verbNameStep)
 	}
 	if len(stringAlphas) != 0 && len(ewmaSuffixes) != 0 {
 		if len(ewmaSuffixes) != len(stringAlphas) {
-			return nil, errors.New(
-				// TODO: parameterize verb here somehow
-				"mlr step: If -d and -o are provided, their values must have the same length.",
+			return nil, fmt.Errorf(
+				"mlr %s: If -d and -o are provided, their values must have the same length.", verbNameStep,
 			)
 		}
 	}

internal/pkg/transformers/utils/stats1-accumulators.go

@@ -219,16 +219,13 @@ func (factory *Stats1AccumulatorFactory) MakeNamedAccumulator(
 		valueFieldName,
 		doInterpolatedPercentiles,
 	)
-	// We don't return errors.New here. The nominal case is that the stats1
-	// verb has already pre-validated accumulator names, and this is just a
-	// fallback. The accumulators are instantiated for every unique combination
-	// of group-by field values in the record stream, only as those values are
-	// encountered: for example, with 'mlr stats1 -a count,sum -f x,y -g
-	// color,shape', we make a new accumulator the first time we find a record
-	// with 'color=blue,shape=square' and another the first time we find a
-	// record with 'color=red,shape=circle', and so on. The right thing is to
-	// pre-validate names once when the stats1 transformer is being
-	// instantiated.
+	// We don't return an error here -- we fatal. The nominal case is that the stats1 verb has already
+	// pre-validated accumulator names, and this is just a fallback. The accumulators are instantiated for
+	// every unique combination of group-by field values in the record stream, only as those values are
+	// encountered: for example, with 'mlr stats1 -a count,sum -f x,y -g color,shape', we make a new
+	// accumulator the first time we find a record with 'color=blue,shape=square' and another the first time
+	// we find a record with 'color=red,shape=circle', and so on. The right thing is to pre-validate names
+	// once when the stats1 transformer is being instantiated.
 	lib.InternalCodingErrorIf(accumulator == nil)
 
 	return NewStats1NamedAccumulator(

internal/pkg/types/mlrval_typing.go

@@ -6,7 +6,6 @@
 package types
 
 import (
-	"errors"
 	"fmt"
 
 	"github.com/johnkerl/miller/internal/pkg/mlrval"
@@ -25,11 +24,7 @@ func NewTypeGatedMlrvalName(
 ) (*TypeGatedMlrvalName, error) {
 	typeMask, ok := mlrval.TypeNameToMask(typeName)
 	if !ok {
-		return nil, errors.New(
-			fmt.Sprintf(
-				"mlr: couldn't resolve type name \"%s\".", typeName,
-			),
-		)
+		return nil, fmt.Errorf("mlr: couldn't resolve type name \"%s\".", typeName)
 	}
 	return &TypeGatedMlrvalName{
 		Name:     name,
@@ -43,11 +38,9 @@ func (tname *TypeGatedMlrvalName) Check(value *mlrval.Mlrval) error {
 	if bit&tname.TypeMask != 0 {
 		return nil
 	} else {
-		return errors.New(
-			fmt.Sprintf(
-				"mlr: couldn't assign variable %s %s from value %s %s\n",
-				tname.TypeName, tname.Name, value.GetTypeName(), value.String(),
-			),
+		return fmt.Errorf(
+			"mlr: couldn't assign variable %s %s from value %s %s\n",
+			tname.TypeName, tname.Name, value.GetTypeName(), value.String(),
 		)
 	}
 }

test/cases/verb-stats1/0018/experr

@@ -1,2 +1 @@
 mlr stats1: accumulator "nonesuch" not found.
-