[release-branch.go1.20] go/printer: error out of Fprint when it would write a '/...

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

Updates #60516.
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/+/501819
Auto-Submit: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>

diff --git a/src/go/printer/printer.go b/src/go/printer/printer.go
index 741e3f782c1492f66285dbcf5cbea103d9e97324..46131c66971829106cb0e13083fca14690f23ac3 100644 (file)
--- a/src/go/printer/printer.go
+++ b/src/go/printer/printer.go
@@ -75,10 +75,11 @@ 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
@@ -196,6 +197,13 @@ 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)
@@ -1169,7 +1177,7 @@ 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)

diff --git a/src/go/printer/printer_test.go b/src/go/printer/printer_test.go
index cb62b3e4f35db0fa78377dec4d7a318c27503ecb..3a8ce6043164848555cb12b7d985346badfaf1c3 100644 (file)
--- a/src/go/printer/printer_test.go
+++ b/src/go/printer/printer_test.go
@@ -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())
+       }
+}