io/fs, path, path/filepath, testing/fstest: validate patterns in Match, Glob

According to #28614, proposal review agreed in December 2018 that
Match should return an error for failed matches where the unmatched
part of the pattern has a syntax error. (The failed match has to date
caused the scan of the pattern to stop early.)

This change implements that behavior: the match loop continues
scanning to the end of the pattern, even after a confirmed mismatch,
to check whether the pattern is even well-formed.

The change applies to both path.Match and filepath.Match.
Then filepath.Glob and fs.Glob make a single validity-checking
call to Match before beginning their usual processing.

Also update fstest.TestFS to check for correct validation in custom
Glob implementations.

Fixes #28614.

Change-Id: Ic1d35a4bb9c3565184ae83dbefc425c5c96318e7
Reviewed-on: https://go-review.googlesource.com/c/go/+/264397
Trust: Russ Cox <rsc@golang.org>
Reviewed-by: Rob Pike <r@golang.org>

1 files changed, 8 insertions, 4 deletions

diff --git a/src/path/filepath/match_test.go b/src/path/filepath/match_test.go
index b8657626bc..1c3b567fa3 100644
--- a/src/path/filepath/match_test.go
+++ b/src/path/filepath/match_test.go
@@ -75,8 +75,10 @@ var matchTests = []MatchTest{
 	{"[", "a", false, ErrBadPattern},
 	{"[^", "a", false, ErrBadPattern},
 	{"[^bc", "a", false, ErrBadPattern},
-	{"a[", "a", false, nil},
+	{"a[", "a", false, ErrBadPattern},
 	{"a[", "ab", false, ErrBadPattern},
+	{"a[", "x", false, ErrBadPattern},
+	{"a/b[", "x", false, ErrBadPattern},
 	{"*x", "xxx", true, nil},
 }
 
@@ -155,9 +157,11 @@ func TestGlob(t *testing.T) {
 }
 
 func TestGlobError(t *testing.T) {
-	_, err := Glob("[]")
-	if err == nil {
-		t.Error("expected error for bad pattern; got none")
+	bad := []string{`[]`, `nonexist/[]`}
+	for _, pattern := range bad {
+		if _, err := Glob(pattern); err != ErrBadPattern {
+			t.Errorf("Glob(%#q) returned err=%v, want ErrBadPattern", pattern, err)
+		}
 	}
 }