cmd/go: handle \r in input text

Remove carriage returns from //go:generate lines.
Carriage returns are the predecessor of BOMs and still
live on Windows.

Fixes golang#9264

Change-Id: I637748c74335c696b3630f52f2100061153fcdb4
Reviewed-on: https://go-review.googlesource.com/1564
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Andrew Gerrand <adg@golang.org>

src/cmd/go/generate.go

@@ -255,6 +255,10 @@ func (g *Generator) split(line string) []string {
 	// Parse line, obeying quoted strings.
 	var words []string
 	line = line[len("//go:generate ") : len(line)-1] // Drop preamble and final newline.
+	// There may still be a carriage return.
+	if len(line) > 0 && line[len(line)-1] == '\r' {
+		line = line[:len(line)-1]
+	}
 	// One (possibly quoted) word per iteration.
 Words:
 	for {

src/cmd/go/generate_test.go

@@ -40,9 +40,15 @@ func TestGenerateCommandParse(t *testing.T) {
 	}
 	g.setShorthand([]string{"-command", "yacc", "go", "tool", "yacc"})
 	for _, test := range splitTests {
+		// First with newlines.
 		got := g.split("//go:generate " + test.in + "\n")
 		if !reflect.DeepEqual(got, test.out) {
 			t.Errorf("split(%q): got %q expected %q", test.in, got, test.out)
 		}
+		// Then with CRLFs, thank you Windows.
+		got = g.split("//go:generate " + test.in + "\r\n")
+		if !reflect.DeepEqual(got, test.out) {
+			t.Errorf("split(%q): got %q expected %q", test.in, got, test.out)
+		}
 	}
 }