test: avoid matching file names in errcheck

Fixes #17030.

Change-Id: Ic7f237ac7553ae0176929056e64b01667ed59066
Reviewed-on: https://go-review.googlesource.com/31351
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

test/fixedbugs/bug332.go

@@ -14,4 +14,4 @@ func main() {}
 
 // important: no newline on end of next line.
 // 6g used to print <epoch> instead of bug332.go:111
-func (t *T) F() {} // ERROR "bug332"
\ No newline at end of file
+func (t *T) F() {} // ERROR "undefined: T"
\ No newline at end of file

test/method2.go

@@ -33,5 +33,5 @@ var _ = (*Val).val // ERROR "method"
 var v Val
 var pv = &v
 
-var _ = pv.val() // ERROR "method"
-var _ = pv.val   // ERROR "method"
+var _ = pv.val() // ERROR "pv.val undefined"
+var _ = pv.val   // ERROR "pv.val undefined"

test/run.go

@@ -855,7 +855,13 @@ func (t *test) errorCheck(outStr string, wantAuto bool, fullshort ...string) (er
 		matched := false
 		n := len(out)
 		for _, errmsg := range errmsgs {
-			if we.re.MatchString(errmsg) {
+			// Assume errmsg says "file:line: foo".
+			// Cut leading "file:line: " to avoid accidental matching of file name instead of message.
+			text := errmsg
+			if i := strings.Index(text, " "); i >= 0 {
+				text = text[i+1:]
+			}
+			if we.re.MatchString(text) {
 				matched = true
 			} else {
 				out = append(out, errmsg)