Remove os.Exit callsites below the entrypoint: phase 4 (plans/exit.md) (#2205)

Phase 4 of plans/exit.md: the aux/terminal sub-entrypoints. pkg/auxents and
pkg/terminals are now os.Exit-free; even the dispatchers return exit codes
instead of exiting.

- auxents.Dispatch returns (handled bool, exitCode int); entrypoint.Main --
  the one sanctioned exit point -- exits with the code.
- terminals.Dispatch returns an exit code; the climain caller wraps it in a
  lib.ExitRequest, which also retires the 'terminal did not exit the process'
  panic.
- Usage functions (hex, unhex, lecat, termcvt, repl, script, regtest) no
  longer take an exitCode parameter and exit; call sites print usage and
  return the code explicitly.
- Inner I/O helpers (hexDumpFile, unhexFile, lecatFile, termcvtFile) return
  errors; each sub-main prints 'mlr {verb}: ...' as before and returns 1.
  lecatFile formerly looped forever on a non-EOF read error; it now returns
  the error.
- The regtest directory walk (Execute / executeSinglePath /
  executeSingleDirectory / hasCaseSubdirectories) plumbs errors up to
  RegTestMain; regression_test.go updated for the new Execute signature.

Stderr messages and exit codes are unchanged across mlr aux-list, hex, unhex,
lecat, termcvt, help, version, repl, script, and regtest surfaces (checked by
hand); all 4779 regression cases pass; make lint is clean; docs rebuild with
zero churn.

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

pkg/auxents/auxents.go

@@ -32,22 +32,23 @@ func init() {
 	}
 }
 
-// Dispatch is called from Miller main. Here we indicate if argv[1] is handled
+// Dispatch is called from Miller main. The boolean return says whether
-// by us, or not. If so, we handle it and exit, not returning control to Miller
+// argv[1] named an auxent handled here; if so, the int is the process exit
-// main.
+// code for the entrypoint layer to exit with. Otherwise control returns to
-func Dispatch(args []string) {
+// main for the rest of Miller.
+func Dispatch(args []string) (bool, int) {
 	if len(args) < 2 {
-		return
+		return false, 0
 	}
 	verb := args[1]
 
 	for _, entry := range _AUX_LOOKUP_TABLE {
 		if verb == entry.name {
-			os.Exit(entry.main(args))
+			return true, entry.main(args)
 		}
 	}
 
-	// Else, return control to main for the rest of Miller.
+	return false, 0
 }
 
 // auxListMain is the handler for 'mlr aux-list'.

pkg/auxents/hex.go

@@ -23,14 +23,13 @@ import (
 // 00000060: 60 61 62 63  64 65 66 67  68 69 6a 6b  6c 6d 6e 6f |`abcdefghijklmno|
 // 00000070: 70 71 72 73  74 75 76 77  78 79 7a 7b  7c 7d 7e 7f |pqrstuvwxyz{|}~.|
 
-func hexUsage(verbName string, o *os.File, exitCode int) {
+func hexUsage(verbName string, o *os.File) {
 	fmt.Fprintf(o, "Usage: mlr %s [options] {zero or more file names}\n", verbName)
 	fmt.Fprintf(o, "Simple hex-dump.\n")
 	fmt.Fprintf(o, "If zero file names are supplied, standard input is read.\n")
 	fmt.Fprintf(o, "Options:\n")
 	fmt.Fprintf(o, "-r: print only raw hex without leading offset indicators or trailing ASCII dump.\n")
 	fmt.Fprintf(o, "-h or --help: print this message\n")
-	os.Exit(exitCode)
 }
 
 func hexMain(args []string) int {
@@ -45,12 +44,16 @@ func hexMain(args []string) int {
 			doRaw = true
 			args = args[1:]
 		case "-h", "--help":
-			hexUsage(verb, os.Stdout, 0)
+			hexUsage(verb, os.Stdout)
+			return 0
 		}
 	}
 
 	if len(args) == 0 {
-		hexDumpFile(os.Stdin, doRaw)
+		if err := hexDumpFile(os.Stdin, doRaw); err != nil {
+			fmt.Fprintf(os.Stderr, "mlr hex: %v\n", err)
+			return 1
+		}
 	} else {
 		for _, filename := range args {
 			// Print filename if there is more than one file, unless raw output
@@ -61,14 +64,17 @@ func hexMain(args []string) int {
 
 			istream, err := os.Open(filename)
 			if err != nil {
-				// TODO: "mlr"
 				fmt.Fprintf(os.Stderr, "mlr hex: %v\n", err)
-				os.Exit(1)
+				return 1
 			}
 
-			hexDumpFile(istream, doRaw)
+			err = hexDumpFile(istream, doRaw)
-
 			_ = istream.Close()
+			if err != nil {
+				fmt.Fprintf(os.Stderr, "mlr hex: %v\n", err)
+				return 1
+			}
+
 			if !doRaw && len(args) > 1 {
 				fmt.Println()
 			}
@@ -78,7 +84,7 @@ func hexMain(args []string) int {
 	return 0
 }
 
-func hexDumpFile(istream *os.File, doRaw bool) {
+func hexDumpFile(istream *os.File, doRaw bool) error {
 	const bytesPerClump = 4
 	const clumpsPerLine = 4
 	const bufferSize = bytesPerClump * clumpsPerLine
@@ -97,8 +103,7 @@ func hexDumpFile(istream *os.File, doRaw bool) {
 		// exact multiple of our buffer size. We'll break the loop after
 		// hex-dumping this last, partial fragment.
 		if err != nil && err != io.ErrUnexpectedEOF {
-			fmt.Fprintf(os.Stderr, "mlr hex: %v\n", err)
+			return err
-			os.Exit(1)
 		}
 
 		// Print offset "pre" part
@@ -148,4 +153,5 @@ func hexDumpFile(istream *os.File, doRaw bool) {
 
 		offset += numBytesRead
 	}
+	return nil
 }

pkg/auxents/lecat.go

@@ -7,14 +7,13 @@ import (
 	"os"
 )
 
-func lecatUsage(verbName string, o *os.File, exitCode int) {
+func lecatUsage(verbName string, o *os.File) {
 	fmt.Fprintf(o, "Usage: mlr %s [options] {zero or more file names}\n", verbName)
 	fmt.Fprintf(o, "Simply echoes input, but flags CR characters in red and LF characters in green.\n")
 	fmt.Fprintf(o, "If zero file names are supplied, standard input is read.\n")
 	fmt.Fprintf(o, "Options:\n")
 	fmt.Fprintf(o, "--mono: don't try to colorize the output\n")
 	fmt.Fprintf(o, "-h or --help: print this message\n")
-	os.Exit(exitCode)
 }
 
 func lecatMain(args []string) int {
@@ -25,7 +24,8 @@ func lecatMain(args []string) int {
 	args = args[2:]
 	if len(args) >= 1 {
 		if args[0] == "-h" || args[0] == "--help" {
-			lecatUsage(verb, os.Stdout, 0)
+			lecatUsage(verb, os.Stdout)
+			return 0
 		}
 
 		if args[0][0] == '-' {
@@ -36,37 +36,46 @@ func lecatMain(args []string) int {
 				fmt.Fprintf(os.Stderr, "mlr %s: unrecognized option \"%s\".\n",
 					verb, args[0],
 				)
-				os.Exit(1)
+				return 1
 			}
 		}
 	}
 
 	if len(args) == 0 {
-		lecatFile(os.Stdin, doColor)
+		if err := lecatFile(os.Stdin, doColor); err != nil {
+			fmt.Fprintf(os.Stderr, "mlr lecat: %v\n", err)
+			return 1
+		}
 	} else {
 		for _, filename := range args {
 
 			istream, err := os.Open(filename)
 			if err != nil {
 				fmt.Fprintf(os.Stderr, "mlr lecat: %v\n", err)
-				os.Exit(1)
+				return 1
 			}
 
-			lecatFile(istream, doColor)
+			err = lecatFile(istream, doColor)
-
 			_ = istream.Close()
+			if err != nil {
+				fmt.Fprintf(os.Stderr, "mlr lecat: %v\n", err)
+				return 1
+			}
 		}
 	}
 	return 0
 }
 
-func lecatFile(istream *os.File, doColor bool) {
+func lecatFile(istream *os.File, doColor bool) error {
 	reader := bufio.NewReader(istream)
 	for {
 		c, err := reader.ReadByte()
 		if err == io.EOF {
 			break
 		}
+		if err != nil {
+			return err
+		}
 		switch c {
 		case '\r':
 			if doColor {
@@ -88,4 +97,5 @@ func lecatFile(istream *os.File, doColor bool) {
 			fmt.Printf("%c", c)
 		}
 	}
+	return nil
 }

pkg/auxents/termcvt.go

@@ -8,7 +8,7 @@ import (
 	"strings"
 )
 
-func termcvtUsage(verbName string, o *os.File, exitCode int) {
+func termcvtUsage(verbName string, o *os.File) {
 	fmt.Fprintf(o, "Usage: mlr %s [option] {zero or more file names}\n", verbName)
 	fmt.Fprintf(o, "Option (exactly one is required):\n")
 	fmt.Fprintf(o, "--cr2crlf\n")
@@ -21,7 +21,6 @@ func termcvtUsage(verbName string, o *os.File, exitCode int) {
 	fmt.Fprintf(o, "-h or --help: print this message\n")
 	fmt.Fprintf(o, "Zero file names means read from standard input.\n")
 	fmt.Fprintf(o, "Output is always to standard output; files are not written in-place.\n")
-	os.Exit(exitCode)
 }
 
 func termcvtMain(args []string) int {
@@ -33,7 +32,8 @@ func termcvtMain(args []string) int {
 	verb := args[1]
 	args = args[2:]
 	if len(args) < 1 {
-		termcvtUsage(verb, os.Stderr, 1)
+		termcvtUsage(verb, os.Stderr)
+		return 1
 	}
 
 	for len(args) >= 1 {
@@ -45,7 +45,8 @@ func termcvtMain(args []string) int {
 
 		switch opt {
 		case "-h", "--help":
-			termcvtUsage(verb, os.Stdout, 0)
+			termcvtUsage(verb, os.Stdout)
+			return 0
 		case "-I":
 			doInPlace = true
 		case "--cr2crlf":
@@ -67,12 +68,16 @@ func termcvtMain(args []string) int {
 			inputTerminator = "\r"
 			outputTerminator = "\n"
 		default:
-			termcvtUsage(verb, os.Stderr, 1)
+			termcvtUsage(verb, os.Stderr)
+			return 1
 		}
 	}
 
 	if len(args) == 0 {
-		termcvtFile(os.Stdin, os.Stdout, inputTerminator, outputTerminator)
+		if err := termcvtFile(os.Stdin, os.Stdout, inputTerminator, outputTerminator); err != nil {
+			fmt.Fprintf(os.Stderr, "mlr termcvt: %v\n", err)
+			return 1
+		}
 
 	} else if doInPlace {
 		for _, filename := range args {
@@ -82,31 +87,31 @@ func termcvtMain(args []string) int {
 
 			istream, err := os.Open(filename)
 			if err != nil {
-				// TODO: "mlr"
 				fmt.Fprintf(os.Stderr, "mlr termcvt: %v\n", err)
-				os.Exit(1)
+				return 1
 			}
 
 			ostream, err := os.Open(tempname)
 			if err != nil {
-				// TODO: "mlr"
 				fmt.Fprintf(os.Stderr, "mlr termcvt: %v\n", err)
-				os.Exit(1)
+				return 1
 			}
 
-			termcvtFile(istream, ostream, inputTerminator, outputTerminator)
+			if err := termcvtFile(istream, ostream, inputTerminator, outputTerminator); err != nil {
+				fmt.Fprintf(os.Stderr, "mlr termcvt: %v\n", err)
+				return 1
+			}
 
 			_ = istream.Close()
 			if err := ostream.Close(); err != nil {
 				fmt.Fprintf(os.Stderr, "mlr termcvt: %v\n", err)
-				os.Exit(1)
+				return 1
 			}
 
 			err = os.Rename(tempname, filename)
 			if err != nil {
-				// TODO: "mlr"
 				fmt.Fprintf(os.Stderr, "mlr termcvt: %v\n", err)
-				os.Exit(1)
+				return 1
 			}
 		}
 
@@ -115,20 +120,22 @@ func termcvtMain(args []string) int {
 
 			istream, err := os.Open(filename)
 			if err != nil {
-				// TODO: "mlr"
 				fmt.Fprintf(os.Stderr, "mlr termcvt: %v\n", err)
-				os.Exit(1)
+				return 1
 			}
 
-			termcvtFile(istream, os.Stdout, inputTerminator, outputTerminator)
+			err = termcvtFile(istream, os.Stdout, inputTerminator, outputTerminator)
-
 			_ = istream.Close()
+			if err != nil {
+				fmt.Fprintf(os.Stderr, "mlr termcvt: %v\n", err)
+				return 1
+			}
 		}
 	}
 	return 0
 }
 
-func termcvtFile(istream *os.File, ostream *os.File, inputTerminator string, outputTerminator string) {
+func termcvtFile(istream *os.File, ostream *os.File, inputTerminator string, outputTerminator string) error {
 	lineReader := bufio.NewReader(istream)
 	inputTerminatorBytes := []byte(inputTerminator[len(inputTerminator)-1:])[0] // bufio.Reader.ReadString takes char not string delimiter :(
 
@@ -139,16 +146,14 @@ func termcvtFile(istream *os.File, ostream *os.File, inputTerminator string, out
 		}
 
 		if err != nil {
-			// TODO: "mlr"
+			return err
-			fmt.Fprintf(os.Stderr, "mlr termcvt: %v\n", err)
-			os.Exit(1)
 		}
 
 		// This is how to do a chomp:
 		line = strings.TrimRight(line, inputTerminator)
 		if _, err := ostream.Write([]byte(line + outputTerminator)); err != nil {
-			fmt.Fprintf(os.Stderr, "mlr termcvt: %v\n", err)
+			return err
-			os.Exit(1)
 		}
 	}
+	return nil
 }

pkg/auxents/unhex.go

@@ -2,6 +2,7 @@ package auxents
 
 import (
 	"bufio"
+	"errors"
 	"fmt"
 	"io"
 	"os"
@@ -9,13 +10,12 @@ import (
 	"strings"
 )
 
-func unhexUsage(verbName string, o *os.File, exitCode int) {
+func unhexUsage(verbName string, o *os.File) {
 	fmt.Fprintf(o, "Usage: mlr %s [option] {zero or more file names}\n", verbName)
 	fmt.Fprintf(o, "Options:\n")
 	fmt.Fprintf(o, "-h or --help: print this message\n")
 	fmt.Fprintf(o, "Zero file names means read from standard input.\n")
 	fmt.Fprintf(o, "Output is always to standard output; files are not written in-place.\n")
-	os.Exit(exitCode)
 }
 
 func unhexMain(args []string) int {
@@ -25,28 +25,36 @@ func unhexMain(args []string) int {
 
 	if len(args) >= 1 {
 		if args[0] == "-h" || args[0] == "--help" {
-			unhexUsage(verb, os.Stdout, 0)
+			unhexUsage(verb, os.Stdout)
+			return 0
 		}
 	}
 
 	if len(args) == 0 {
-		unhexFile(os.Stdin, os.Stdout)
+		if err := unhexFile(os.Stdin, os.Stdout); err != nil {
+			fmt.Fprintf(os.Stderr, "mlr unhex: %v\n", err)
+			return 1
+		}
 	} else {
 		for _, filename := range args {
 			istream, err := os.Open(filename)
 			if err != nil {
 				fmt.Fprintf(os.Stderr, "mlr unhex: %v\n", err)
-				os.Exit(1)
+				return 1
 			}
-			unhexFile(istream, os.Stdout)
+			err = unhexFile(istream, os.Stdout)
 			_ = istream.Close()
+			if err != nil {
+				fmt.Fprintf(os.Stderr, "mlr unhex: %v\n", err)
+				return 1
+			}
 		}
 	}
 
 	return 0
 }
 
-func unhexFile(istream *os.File, ostream *os.File) {
+func unhexFile(istream *os.File, ostream *os.File) error {
 	// Key insight is os.File implements io.Reader
 	lineReader := bufio.NewReader(istream)
 
@@ -62,8 +70,7 @@ func unhexFile(istream *os.File, ostream *os.File) {
 			break
 		}
 		if err != nil {
-			fmt.Fprintf(os.Stderr, "mlr unhex: %v\n", err)
+			return err
-			os.Exit(1)
 		}
 
 		// This is how to do a chomp:
@@ -75,19 +82,17 @@ func unhexFile(istream *os.File, ostream *os.File) {
 			if field != "" {
 				n, err := fmt.Sscanf(field, "%x", &scanValue)
 				if err != nil {
-					fmt.Fprintf(os.Stderr, "mlr unhex: %v\n", err)
+					return err
-					os.Exit(1)
 				}
 				if n != 1 {
-					fmt.Fprintln(os.Stderr, "mlr unhex: internal coding error")
+					return errors.New("internal coding error")
-					os.Exit(1)
 				}
 				byteArray[0] = byte(scanValue)
 				if _, err := ostream.Write(byteArray); err != nil {
-					fmt.Fprintln(os.Stderr, "mlr unhex:", err)
+					return err
-					os.Exit(1)
 				}
 			}
 		}
 	}
+	return nil
 }

pkg/climain/mlrcli_parse.go

@@ -396,9 +396,9 @@ func parseCommandLinePassTwo(
 	}
 
 	if terminalSequence != nil {
-		terminals.Dispatch(terminalSequence)
+		// The terminal (help, repl, regtest, ...) runs here; its exit code
-		// They are expected to exit the process
+		// rides an ExitRequest up to the entrypoint layer.
-		panic("mlr: internal coding error: terminal did not exit the process")
+		return nil, nil, &lib.ExitRequest{Code: terminals.Dispatch(terminalSequence)}
 	}
 
 	// Now process the verb-sequences from pass one, with options-struct set up

pkg/entrypoint/entrypoint.go

@@ -38,8 +38,10 @@ func Main() MainReturn {
 
 	// 'mlr repl' or 'mlr lecat' or any other non-miller-per-se toolery which
 	// is delivered (for convenience) within the mlr executable. If argv[1] is
-	// found then this function will not return.
+	// an auxent name, it's run here and its exit code is the process's.
-	auxents.Dispatch(os.Args)
+	if handled, exitCode := auxents.Dispatch(os.Args); handled {
+		os.Exit(exitCode)
+	}
 
 	if lib.IsTruthyEnvValue(os.Getenv("MLR_NO_SHELL")) {
 		lib.DisableShellOut()

pkg/terminals/regtest/entry.go

@@ -11,7 +11,7 @@ import (
 
 const defaultPath = "./test/cases"
 
-func regTestUsage(verbName string, o *os.File, exitCode int) {
+func regTestUsage(verbName string, o *os.File) {
 	fmt.Fprintf(o, "Usage: mlr %s [options] [one or more directories/files]\n", verbName)
 	fmt.Fprintf(o, "If no directories/files are specified, the directory %s is used by default.\n", defaultPath)
 	fmt.Fprintf(o, "Recursively walks the directory/ies looking for foo.cmd files having Miller command-lines,\n")
@@ -30,7 +30,6 @@ func regTestUsage(verbName string, o *os.File, exitCode int) {
 	fmt.Fprintf(o, "-j       Just show the Miller command-line, put/filter script if any, and output.\n")
 	fmt.Fprintf(o, "-s {n}   After running tests, re-run first n failed .cmd files with verbosity level 3.\n")
 	fmt.Fprintf(o, "-S       After running tests, re-run all failed .cmd files with verbosity level 3.\n")
-	os.Exit(exitCode)
 }
 
 // Here the args are the full Miller command line: "mlr regtest --foo bar".
@@ -55,22 +54,26 @@ func RegTestMain(args []string) int {
 
 		switch arg {
 		case "-h", "--help":
-			regTestUsage(verbName, os.Stdout, 0)
+			regTestUsage(verbName, os.Stdout)
+			return 0
 
 		case "-m":
 			if argi >= argc {
-				regTestUsage(verbName, os.Stderr, 1)
+				regTestUsage(verbName, os.Stderr)
+				return 1
 			}
 			exeName = args[argi]
 			argi++
 
 		case "-s":
 			if argi >= argc {
-				regTestUsage(verbName, os.Stderr, 1)
+				regTestUsage(verbName, os.Stderr)
+				return 1
 			}
 			temp, err := strconv.Atoi(args[argi])
 			if err != nil {
-				regTestUsage(verbName, os.Stderr, 1)
+				regTestUsage(verbName, os.Stderr)
+				return 1
 			}
 			firstNFailsToShow = temp
 			argi++
@@ -88,7 +91,8 @@ func RegTestMain(args []string) int {
 			plainMode = true
 
 		default:
-			regTestUsage(verbName, os.Stderr, 1)
+			regTestUsage(verbName, os.Stderr)
+			return 1
 		}
 	}
 	casePaths := args[argi:]
@@ -104,7 +108,11 @@ func RegTestMain(args []string) int {
 		firstNFailsToShow,
 	)
 
-	ok := regtester.Execute(casePaths)
+	ok, err := regtester.Execute(casePaths)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "mlr %s: %v\n", verbName, err)
+		return 1
+	}
 
 	if !ok {
 		return 1

pkg/terminals/regtest/regtester.go

@@ -146,7 +146,7 @@ func (rt *RegTester) resetCounts() {
 
 func (rt *RegTester) Execute(
 	casePaths []string,
-) bool {
+) (bool, error) {
 	// Don't let the current user's settings affect expected results
 	for _, name := range envVarsToUnset {
 		_ = os.Unsetenv(name)
@@ -175,7 +175,9 @@ func (rt *RegTester) Execute(
 	}
 
 	for _, path := range casePaths {
-		rt.executeSinglePath(path)
+		if _, err := rt.executeSinglePath(path); err != nil {
+			return false, err
+		}
 	}
 
 	if len(rt.failCaseNames) > 0 && rt.firstNFailsToShow > 0 {
@@ -215,12 +217,12 @@ func (rt *RegTester) Execute(
 		if !rt.plainMode {
 			fmt.Printf("%s overall\n", colorizer.MaybeColorizePass("PASS", true))
 		}
-		return true
+		return true, nil
 	}
 	if !rt.plainMode {
 		fmt.Printf("%s overall\n", colorizer.MaybeColorizeFail("FAIL", true))
 	}
-	return false
+	return false, nil
 }
 
 // Recursively invoked routine to process either a single .cmd file, or a
@@ -228,15 +230,18 @@ func (rt *RegTester) Execute(
 
 func (rt *RegTester) executeSinglePath(
 	path string,
-) bool {
+) (bool, error) {
 	handle, err := os.Stat(path)
 	if err != nil {
 		fmt.Printf("%s: %v\n", path, err)
-		return false
+		return false, nil
 	}
 	mode := handle.Mode()
 	if mode.IsDir() {
-		passed, hasCaseSubdirectories := rt.executeSingleDirectory(path)
+		passed, hasCaseSubdirectories, err := rt.executeSingleDirectory(path)
+		if err != nil {
+			return false, err
+		}
 		if hasCaseSubdirectories {
 			if passed {
 				rt.directoryPassCount++
@@ -245,7 +250,7 @@ func (rt *RegTester) executeSinglePath(
 				rt.failDirNames = append(rt.failDirNames, path)
 			}
 		}
-		return passed
+		return passed, nil
 	} else if mode.IsRegular() {
 		basename := filepath.Base(path)
 		if basename == CmdName {
@@ -256,21 +261,24 @@ func (rt *RegTester) executeSinglePath(
 				rt.caseFailCount++
 				rt.failCaseNames = append(rt.failCaseNames, path)
 			}
-			return passed
+			return passed, nil
 		}
-		return true // No .cmd files directly inside
+		return true, nil // No .cmd files directly inside
 	}
 
 	fmt.Printf("%s: neither directory nor regular file.\n", path)
-	return false // fall-through
+	return false, nil // fall-through
 }
 
 func (rt *RegTester) executeSingleDirectory(
 	dirName string,
-) (bool, bool) {
+) (bool, bool, error) {
 	passed := true
 	// TODO: comment
-	fileNames, hasCaseSubdirectories := rt.hasCaseSubdirectories(dirName)
+	fileNames, hasCaseSubdirectories, err := rt.hasCaseSubdirectories(dirName)
+	if err != nil {
+		return false, false, err
+	}
 
 	if !rt.plainMode {
 		if hasCaseSubdirectories && rt.verbosityLevel >= 2 {
@@ -281,7 +289,10 @@ func (rt *RegTester) executeSingleDirectory(
 	for _, name := range fileNames {
 		path := dirName + "/" + name
 
-		ok := rt.executeSinglePath(path)
+		ok, err := rt.executeSinglePath(path)
+		if err != nil {
+			return false, false, err
+		}
 		if !ok {
 			passed = false
 		}
@@ -309,7 +320,7 @@ func (rt *RegTester) executeSingleDirectory(
 		}
 	}
 
-	return passed, hasCaseSubdirectories
+	return passed, hasCaseSubdirectories, nil
 }
 
 // Sees if a directory contains a single test case. If so, we don't want to
@@ -322,28 +333,26 @@ func (rt *RegTester) executeSingleDirectory(
 
 func (rt *RegTester) hasCaseSubdirectories(
 	dirName string,
-) ([]string, bool) {
+) ([]string, bool, error) {
 	f, err := os.Open(dirName)
 	if err != nil {
-		fmt.Printf("%s: %v\n", dirName, err)
+		return nil, false, err
-		os.Exit(1)
 	}
 	defer func() { _ = f.Close() }()
 
 	names, err := f.Readdirnames(-1)
 	if err != nil {
-		fmt.Printf("%s: %v\n", dirName, err)
+		return nil, false, err
-		os.Exit(1)
 	}
 	sort.Strings(names)
 
 	for _, name := range names {
 		path := dirName + string(filepath.Separator) + name
 		if rt.isCaseDirectory(path) {
-			return names, true
+			return names, true, nil
 		}
 	}
-	return names, false
+	return names, false, nil
 }
 
 func (rt *RegTester) isCaseDirectory(

pkg/terminals/repl/entry.go

@@ -30,7 +30,7 @@ import (
 	"github.com/johnkerl/miller/v6/pkg/lib"
 )
 
-func replUsage(verbName string, o *os.File, exitCode int) {
+func replUsage(verbName string, o *os.File) {
 	exeName := path.Base(os.Args[0])
 	fmt.Fprintf(o, "Usage: %s %s [options] {zero or more data-file names}\n", exeName, verbName)
 
@@ -72,8 +72,6 @@ Or any --icsv, --ojson, etc. reader/writer options as for the main Miller comman
 Any data-file names are opened just as if you had waited and typed :open {filenames}
 at the Miller REPL prompt.
 `)
-
-	os.Exit(exitCode)
 }
 
 // Here the args are the full Miller command line: if the latter was "mlr
@@ -97,7 +95,8 @@ func ReplMain(args []string) int {
 		}
 
 		if args[argi] == "-h" || args[argi] == "--help" {
-			replUsage(replName, os.Stdout, 0)
+			replUsage(replName, os.Stdout)
+			return 0
 
 		} else if args[argi] == "-q" {
 			showStartupBanner = false
@@ -124,14 +123,16 @@ func ReplMain(args []string) int {
 
 		} else if args[argi] == "--load" {
 			if argc-argi < 2 {
-				replUsage(replName, os.Stderr, 1)
+				replUsage(replName, os.Stderr)
+				return 1
 			}
 			options.DSLPreloadFileNames = append(options.DSLPreloadFileNames, args[argi+1])
 			argi += 2
 
 		} else if args[argi] == "--mload" {
 			if argc-argi < 2 {
-				replUsage(replName, os.Stderr, 1)
+				replUsage(replName, os.Stderr)
+				return 1
 			}
 			argi += 1
 			for argi < argc && args[argi] != "--" {
@@ -153,7 +154,8 @@ func ReplMain(args []string) int {
 		} else if handled {
 
 		} else {
-			replUsage(replName, os.Stderr, 1)
+			replUsage(replName, os.Stderr)
+			return 1
 		}
 	}
 
@@ -188,7 +190,7 @@ func ReplMain(args []string) int {
 	)
 	if err != nil {
 		fmt.Fprintf(os.Stderr, "mlr: %v\n", err)
-		os.Exit(1)
+		return 1
 	}
 
 	filenames := args[argi:]
@@ -199,18 +201,18 @@ func ReplMain(args []string) int {
 	err = repl.handleSession(os.Stdin)
 	if err != nil {
 		fmt.Fprintf(os.Stderr, "mlr %s: %v\n", repl.replName, err)
-		os.Exit(1)
+		return 1
 	}
 
 	err = repl.bufferedRecordOutputStream.Flush()
 	if err != nil {
 		fmt.Fprintf(os.Stderr, "mlr %s: %v\n", repl.replName, err)
-		os.Exit(1)
+		return 1
 	}
 	err = repl.closeBufferedOutputStream()
 	if err != nil {
 		fmt.Fprintf(os.Stderr, "mlr %s: %v\n", repl.replName, err)
-		os.Exit(1)
+		return 1
 	}
 	return 0
 }

pkg/terminals/script/entry.go

@@ -20,7 +20,7 @@ import (
 	"github.com/johnkerl/miller/v6/pkg/lib"
 )
 
-func scriptUsage(verbName string, o *os.File, exitCode int) {
+func scriptUsage(verbName string, o *os.File) {
 	exeName := path.Base(os.Args[0])
 	fmt.Fprintf(o, "Usage: %s %s [options] -f {script file} | -e {expression} [zero or more data-file names]\n", exeName, verbName)
 	fmt.Fprint(o,
@@ -39,7 +39,6 @@ Or any --icsv, --ojson, etc. reader/writer options.
 
 Data-file names (or stdin if none) are the record input stream.
 `)
-	os.Exit(exitCode)
 }
 
 func ScriptMain(args []string) int {
@@ -59,7 +58,8 @@ func ScriptMain(args []string) int {
 		}
 
 		if args[argi] == "-h" || args[argi] == "--help" {
-			scriptUsage(scriptName, os.Stdout, 0)
+			scriptUsage(scriptName, os.Stdout)
+			return 0
 		} else if args[argi] == "-w" {
 			doWarnings = true
 			argi++
@@ -68,42 +68,46 @@ func ScriptMain(args []string) int {
 			argi++
 		} else if args[argi] == "-f" {
 			if argc-argi < 2 {
-				scriptUsage(scriptName, os.Stderr, 1)
+				scriptUsage(scriptName, os.Stderr)
+				return 1
 			}
 			argi++
 			filename, err := cli.VerbGetStringArg("script", "-f", args, &argi, argc)
 			if err != nil {
 				fmt.Fprintf(os.Stderr, "mlr: %v\n", err)
-				os.Exit(1)
+				return 1
 			}
 			theseStrings, err := lib.LoadStringsFromFileOrDir(filename, ".mlr")
 			if err != nil {
 				fmt.Fprintf(os.Stderr, "mlr script: cannot load script from \"%s\": %v\n", filename, err)
-				os.Exit(1)
+				return 1
 			}
 			dslStrings = append(dslStrings, theseStrings...)
 			haveDSLStrings = true
 		} else if args[argi] == "-e" {
 			if argc-argi < 2 {
-				scriptUsage(scriptName, os.Stderr, 1)
+				scriptUsage(scriptName, os.Stderr)
+				return 1
 			}
 			argi++
 			expr, err := cli.VerbGetStringArg("script", "-e", args, &argi, argc)
 			if err != nil {
 				fmt.Fprintf(os.Stderr, "mlr: %v\n", err)
-				os.Exit(1)
+				return 1
 			}
 			dslStrings = append(dslStrings, expr)
 			haveDSLStrings = true
 		} else if args[argi] == "--load" {
 			if argc-argi < 2 {
-				scriptUsage(scriptName, os.Stderr, 1)
+				scriptUsage(scriptName, os.Stderr)
+				return 1
 			}
 			options.DSLPreloadFileNames = append(options.DSLPreloadFileNames, args[argi+1])
 			argi += 2
 		} else if args[argi] == "--mload" {
 			if argc-argi < 2 {
-				scriptUsage(scriptName, os.Stderr, 1)
+				scriptUsage(scriptName, os.Stderr)
+				return 1
 			}
 			argi++
 			for argi < argc && args[argi] != "--" {
@@ -122,13 +126,15 @@ func ScriptMain(args []string) int {
 			return 1
 		} else if handled {
 		} else {
-			scriptUsage(scriptName, os.Stderr, 1)
+			scriptUsage(scriptName, os.Stderr)
+			return 1
 		}
 	}
 
 	if !haveDSLStrings {
 		fmt.Fprintf(os.Stderr, "mlr script: -f or -e is required\n")
-		scriptUsage(scriptName, os.Stderr, 1)
+		scriptUsage(scriptName, os.Stderr)
+		return 1
 	}
 
 	if err := cli.FinalizeReaderOptions(&options.ReaderOptions); err != nil {
@@ -147,25 +153,25 @@ func ScriptMain(args []string) int {
 	scr, err := NewScript(options, doWarnings, strictMode, dslStrings)
 	if err != nil {
 		fmt.Fprintf(os.Stderr, "mlr script: %v\n", err)
-		os.Exit(1)
+		return 1
 	}
 
 	scr.openFiles(filenames)
 	err = scr.run()
 	if err != nil {
 		fmt.Fprintf(os.Stderr, "mlr script: %v\n", err)
-		os.Exit(1)
+		return 1
 	}
 
 	err = scr.bufferedRecordOutputStream.Flush()
 	if err != nil {
 		fmt.Fprintf(os.Stderr, "mlr script: %v\n", err)
-		os.Exit(1)
+		return 1
 	}
 	err = scr.closeBufferedOutputStream()
 	if err != nil {
 		fmt.Fprintf(os.Stderr, "mlr script: %v\n", err)
-		os.Exit(1)
+		return 1
 	}
 	return 0
 }

pkg/terminals/terminals.go

@@ -57,19 +57,24 @@ func Dispatchable(arg string) bool {
 	return false
 }
 
-func Dispatch(args []string) {
+// Dispatch runs the terminal named by args[0] and returns the process exit
+// code for the caller to propagate (via lib.ExitRequest) up to the entrypoint
+// layer.
+func Dispatch(args []string) int {
 	if len(args) < 1 {
-		return
+		// Can't happen: the climain caller passes a non-empty terminal sequence.
+		fmt.Fprintf(os.Stderr, "mlr: internal coding error: empty terminal sequence.\n")
+		return 1
 	}
 	terminal := args[0]
 
 	for _, entry := range _TERMINAL_LOOKUP_TABLE {
 		if terminal == entry.name {
-			os.Exit(entry.main(args))
+			return entry.main(args)
 		}
 	}
 	fmt.Fprintf(os.Stderr, "mlr: terminal \"%s\" not found.\n", terminal)
-	os.Exit(1)
+	return 1
 }
 
 // terminalListMain is the handler for 'mlr terminal-list'.

regression_test.go

@@ -65,7 +65,10 @@ func TestRegression(t *testing.T) {
 		firstNFailsToShow,
 	)
 
-	ok := regtester.Execute(casePaths)
+	ok, err := regtester.Execute(casePaths)
+	if err != nil {
+		t.Fatal(err)
+	}
 	if !ok {
 		t.Fatal()
 	}