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[release-branch.go1.19] go/printer: error out of Fprint when it would…
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… write a '//line' directive with a multiline file path

Line directives do not provide a way to escape newline characters, so
source file paths containing newlines must not be written in them.

Updates #60515.
Updates #60167.

Change-Id: I30f8b381cc7d1df6914c27591544edf424a4b634
Reviewed-on: https://go-review.googlesource.com/c/go/+/501578
Reviewed-by: Robert Griesemer <gri@google.com>
Auto-Submit: Bryan Mills <bcmills@google.com>
Run-TryBot: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
(cherry picked from commit d1087efa42ea0b0f011283a87d7a732cba51e4ad)
Reviewed-on: https://go-review.googlesource.com/c/go/+/501823
Reviewed-by: Ian Lance Taylor <iant@google.com>
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Bryan C. Mills authored and prattmic committed Jun 13, 2023
1 parent 6d44c15 commit 0b0f86e
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Showing 2 changed files with 41 additions and 5 deletions.
18 changes: 13 additions & 5 deletions src/go/printer/printer.go
Original file line number Diff line number Diff line change
Expand Up @@ -74,10 +74,11 @@ type printer struct {
// white space). If there's a difference and SourcePos is set in
// ConfigMode, //line directives are used in the output to restore
// original source positions for a reader.
pos token.Position // current position in AST (source) space
out token.Position // current position in output space
last token.Position // value of pos after calling writeString
linePtr *int // if set, record out.Line for the next token in *linePtr
pos token.Position // current position in AST (source) space
out token.Position // current position in output space
last token.Position // value of pos after calling writeString
linePtr *int // if set, record out.Line for the next token in *linePtr
sourcePosErr error // if non-nil, the first error emitting a //line directive

// The list of all source comments, in order of appearance.
comments []*ast.CommentGroup // may be nil
Expand Down Expand Up @@ -205,6 +206,13 @@ func (p *printer) lineFor(pos token.Pos) int {
// writeLineDirective writes a //line directive if necessary.
func (p *printer) writeLineDirective(pos token.Position) {
if pos.IsValid() && (p.out.Line != pos.Line || p.out.Filename != pos.Filename) {
if strings.ContainsAny(pos.Filename, "\r\n") {
if p.sourcePosErr == nil {
p.sourcePosErr = fmt.Errorf("go/printer: source filename contains unexpected newline character: %q", pos.Filename)
}
return
}

p.output = append(p.output, tabwriter.Escape) // protect '\n' in //line from tabwriter interpretation
p.output = append(p.output, fmt.Sprintf("//line %s:%d\n", pos.Filename, pos.Line)...)
p.output = append(p.output, tabwriter.Escape)
Expand Down Expand Up @@ -1178,7 +1186,7 @@ func (p *printer) printNode(node any) error {
goto unsupported
}

return nil
return p.sourcePosErr

unsupported:
return fmt.Errorf("go/printer: unsupported node type %T", node)
Expand Down
28 changes: 28 additions & 0 deletions src/go/printer/printer_test.go
Original file line number Diff line number Diff line change
Expand Up @@ -797,3 +797,31 @@ func f() {
t.Fatalf("got %q, want %q", got, want)
}
}

func TestSourcePosNewline(t *testing.T) {
// We don't provide a syntax for escaping or unescaping characters in line
// directives (see https://go.dev/issue/24183#issuecomment-372449628).
// As a result, we cannot write a line directive with the correct path for a
// filename containing newlines. We should return an error rather than
// silently dropping or mangling it.

fname := "foo\nbar/bar.go"
src := `package bar`
fset := token.NewFileSet()
f, err := parser.ParseFile(fset, fname, src, parser.ParseComments|parser.AllErrors|parser.SkipObjectResolution)
if err != nil {
t.Fatal(err)
}

cfg := &Config{
Mode: SourcePos, // emit line comments
Tabwidth: 8,
}
var buf bytes.Buffer
if err := cfg.Fprint(&buf, fset, f); err == nil {
t.Errorf("Fprint did not error for source file path containing newline")
}
if buf.Len() != 0 {
t.Errorf("unexpected Fprint output:\n%s", buf.Bytes())
}
}

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