f.walk(ast1, ctxProg, (*File).saveExport)
	f.walk(ast2, ctxProg, (*File).saveExport2)

	f.Comments = ast1.Comments
	f.AST = ast2
}

// Like ast.CommentGroup's Text method but preserves
// leading blank lines, so that line numbers line up.
func commentText(g *ast.CommentGroup) string {
	var pieces []string
	for _, com := range g.List {
		c := com.Text
		// Remove comment markers.

	lineNum       int   // Line number in source file.
	errorLine     int   // Line number of last error.
	errorCount    int   // Number of errors.
	sawCode       bool  // saw code in this file (as opposed to comments and blank lines)
	pc            int64 // virtual PC; count of Progs; doesn't advance for GLOBL or DATA.
	input         []lex.Token
	inputPos      int
	pendingLabels []string // Labels to attach to next instruction.

		exitCode = 1
	}
	if filepath.Base(filename) == "go1.4.txt" {
		// No use for blank lines in api files, except go1.4.txt
		// used them in a reasonable way and we should let it be.
	} else if strings.HasPrefix(s, "\n") || strings.Contains(s, "\n\n") {
		log.Printf("%s: contains a blank line", filename)
		exitCode = 1
	}
	if s == "" {
		log.Printf("%s: empty file", filename)
		exitCode = 1

		}
		if len(output) > 0 && output[0] == want {
			output = output[1:]
		} else {
			t.Errorf("missing output: %q", want)
		}
	}
	for len(output) > 0 {
		if output[0] == "" {
			// spurious blank caused by Split on "\n"
			output = output[1:]
			continue
		}
		t.Errorf("unexpected output: %q", output[0])
		output = output[1:]
	}

	// Checked printing.
	// Now check machine code layout.