cmd/compile/internal/syntax: skip GOROOT/misc in TestStdLib if it doesn't exist

cmd/distpack deletes GOROOT/misc from its distribution.

For #24904.

Change-Id: I47c60e9a6d39d015683dde7f44bf7c34517b6a8e
Reviewed-on: https://go-review.googlesource.com/c/go/+/504059
TryBot-Result: Gopher Robot <[email protected]>
Reviewed-by: Ian Lance Taylor <[email protected]>
Auto-Submit: Bryan Mills <[email protected]>
Run-TryBot: Bryan Mills <[email protected]>

Author: Bryan C. Mills

src/cmd/compile/internal/syntax/parser_test.go

@@ -70,6 +70,18 @@ func TestStdLib(t *testing.T) {
 			filepath.Join(goroot, "src"),
 			filepath.Join(goroot, "misc"),
 		} {
+			if filepath.Base(dir) == "misc" {
+				// cmd/distpack deletes GOROOT/misc, so skip that directory if it isn't present.
+				// cmd/distpack also requires GOROOT/VERSION to exist, so use that to
+				// suppress false-positive skips.
+				if _, err := os.Stat(dir); os.IsNotExist(err) {
+					if _, err := os.Stat(filepath.Join(testenv.GOROOT(t), "VERSION")); err == nil {
+						fmt.Printf("%s not present; skipping\n", dir)
+						continue
+					}
+				}
+			}
+
 			walkDirs(t, dir, func(filename string) {
 				if skipRx != nil && skipRx.MatchString(filename) {
 					// Always report skipped files since regexp