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text/scanner: don't crash when calling TokenText in error handler

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Make sure Scanner.tokEnd is set before we call Scanner.Error
and update documentation accordingly.
(Until now tokEnd was only set before returning from Scan,
so a call to TokenText during error handling may have crashed.)

While at it, tighten a check in Scanner.TokenText to ensure
Scanner.tokEnd >= Scanner.tokPos if we have a token.

Also, silence error messages to Stderr in unrelated TestIllegalExponent.

Fixes #29723.

Change-Id: Ia97beeae91eaf9e0ed3dada0a806f1f7122461cc
Reviewed-on: https://go-review.googlesource.com/c/157819
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>
This commit is contained in:
Robert Griesemer 2019-01-14 13:34:42 -08:00
parent 69de40c9af
commit 85c1798ac6
2 changed files with 23 additions and 2 deletions
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6
src/text/scanner/scanner.go
View File

@ -322,6 +322,7 @@ func (s *Scanner) Peek() rune {
}
func (s *Scanner) error(msg string) {
s.tokEnd = s.srcPos - s.lastCharLen // make sure token text is terminated
s.ErrorCount++
if s.Error != nil {
s.Error(s, msg)
@ -664,17 +665,18 @@ func (s *Scanner) Pos() (pos Position) {
}
// TokenText returns the string corresponding to the most recently scanned token.
// Valid after calling Scan().
// Valid after calling Scan and in calls of Scanner.Error.
func (s *Scanner) TokenText() string {
if s.tokPos < 0 {
// no token text
return ""
}
if s.tokEnd < 0 {
if s.tokEnd < s.tokPos {
// if EOF was reached, s.tokEnd is set to -1 (s.srcPos == 0)
s.tokEnd = s.tokPos
}
// s.tokEnd >= s.tokPos
if s.tokBuf.Len() == 0 {
// common case: the entire token text is still in srcBuf

19
src/text/scanner/scanner_test.go
View File

@ -293,6 +293,12 @@ func TestScan(t *testing.T) {
func TestIllegalExponent(t *testing.T) {
const src = "1.5e 1.5E 1e+ 1e- 1.5z"
s := new(Scanner).Init(strings.NewReader(src))
s.Error = func(s *Scanner, msg string) {
const want = "illegal exponent"
if msg != want {
t.Errorf("%s: got error %q; want %q", s.TokenText(), msg, want)
}
}
checkTokErr(t, s, 1, Float, "1.5e")
checkTokErr(t, s, 1, Float, "1.5E")
checkTokErr(t, s, 1, Float, "1e+")
@ -692,3 +698,16 @@ func TestScanEOFHandling(t *testing.T) {
t.Errorf("scanner called Read %d times, not once", r)
}
}
func TestIssue29723(t *testing.T) {
s := new(Scanner).Init(strings.NewReader(`x "`))
s.Error = func(s *Scanner, _ string) {
got := s.TokenText() // this call shouldn't panic
const want = `"`
if got != want {
t.Errorf("got %q; want %q", got, want)
}
}
for r := s.Scan(); r != EOF; r = s.Scan() {
}
}