Fix bug on DSL comment with no final newline (#1216)

internal/pkg/dsl/cst/root.go

@@ -127,6 +127,14 @@ func buildASTFromString(dslString string) (*dsl.AST, error) {
 		dslString = dslString[1 : len(dslString)-1]
 	}
 
+	// The comment-stripping lex expression in Miller's GOCC grammar matches from '#' to '\n' ... in
+	// the case where there is a '#', then comment text, then end-of-string without any final
+	// newline, the comment text does _not_ get stripped out and is a parse error.
+	// It's simplest to ensure, here, that DSL-expression strings have a final newline.
+	if !strings.HasSuffix(dslString, "\n") {
+		dslString += "\n"
+	}
+
 	theLexer := lexer.NewLexer([]byte(dslString))
 	theParser := parser.NewParser()
 	interfaceAST, err := theParser.Parse(theLexer)

test/cases/dsl-parse/0121/cmd

@@ -0,0 +1 @@
+mlr --from test/input/abixy put '$z = NR # test'

test/cases/dsl-parse/0121/expout

@@ -0,0 +1,10 @@
+a=pan,b=pan,i=1,x=0.34679014,y=0.72680286,z=1
+a=eks,b=pan,i=2,x=0.75867996,y=0.52215111,z=2
+a=wye,b=wye,i=3,x=0.20460331,y=0.33831853,z=3
+a=eks,b=wye,i=4,x=0.38139939,y=0.13418874,z=4
+a=wye,b=pan,i=5,x=0.57328892,y=0.86362447,z=5
+a=zee,b=pan,i=6,x=0.52712616,y=0.49322129,z=6
+a=eks,b=zee,i=7,x=0.61178406,y=0.18788492,z=7
+a=zee,b=wye,i=8,x=0.59855401,y=0.97618139,z=8
+a=hat,b=wye,i=9,x=0.03144188,y=0.74955076,z=9
+a=pan,b=wye,i=10,x=0.50262601,y=0.95261836,z=10