cmd/vet/all: in case of vet panic, don't filter stacktrace

Fixes #20839.

Change-Id: I125460c5da09b7fa0cf470ff5be436f8d650cde7
Reviewed-on: https://go-review.googlesource.com/47253
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/vet/all/main.go

@@ -17,6 +17,7 @@ import (
 	"go/build"
 	"go/types"
 	"internal/testenv"
+	"io"
 	"log"
 	"os"
 	"os/exec"
@@ -227,6 +228,15 @@ NextLine:
 			continue
 		}
 
+		if strings.HasPrefix(line, "panic: ") {
+			// Panic in vet. Don't filter anything, we want the complete output.
+			parseFailed = true
+			fmt.Fprintf(os.Stderr, "panic in vet (to reproduce: go run main.go -p %s):\n", p)
+			fmt.Fprintln(os.Stderr, line)
+			io.Copy(os.Stderr, stderr)
+			break
+		}
+
 		fields := strings.SplitN(line, ":", 3)
 		var file, lineno, msg string
 		switch len(fields) {