cmd/go: ignore vet typecheck failure during go test

For Go 1.10, works around a go/types bug that can't typecheck
a corner-case type cycle. Once we are confident that bugs like
this are gone from go/types then we can stop ignoring these
failures.

For #22890.

Change-Id: I38da57e01a0636323e1af4484c30871786125df3
Reviewed-on: https://go-review.googlesource.com/81500
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/cmd/go/go_test.go

@@ -5115,6 +5115,9 @@ func TestTestVet(t *testing.T) {
 	tg.grepStdout(`\[no test files\]`, "did not print test summary")
 	tg.run("test", "-vet=off", filepath.Join(tg.tempdir, "p1.go"))
 	tg.grepStdout(`\[no test files\]`, "did not print test summary")
+
+	tg.setenv("GOPATH", filepath.Join(tg.pwd(), "testdata"))
+	tg.run("test", "vetcycle") // must not fail; #22890
 }
 
 func TestInstallDeps(t *testing.T) {

src/cmd/go/internal/work/exec.go

@@ -638,6 +638,8 @@ type vetConfig struct {
 	GoFiles     []string
 	ImportMap   map[string]string
 	PackageFile map[string]string
+
+	SucceedOnTypecheckFailure bool
 }
 
 // VetFlags are the flags to pass to vet.
@@ -663,6 +665,13 @@ func (b *Builder) vet(a *Action) error {
 		vcfg.PackageFile["fmt"] = a1.built
 	}
 
+	// During go test, ignore type-checking failures during vet.
+	// We only run vet if the compilation has succeeded,
+	// so at least for now assume the bug is in vet.
+	// We know of at least #18395.
+	// TODO(rsc,gri): Try to remove this for Go 1.11.
+	vcfg.SucceedOnTypecheckFailure = cfg.CmdName == "test"
+
 	js, err := json.MarshalIndent(vcfg, "", "\t")
 	if err != nil {
 		return fmt.Errorf("internal error marshaling vet config: %v", err)

src/cmd/go/testdata/src/vetcycle/p.go

+package p
+
+
+type (
+	_ interface{ m(B1) }
+	A1 interface{ a(D1) }
+	B1 interface{ A1 }
+	C1 interface{ B1 /* ERROR issue #18395 */ }
+	D1 interface{ C1 }
+)
+
+var _ A1 = C1 /* ERROR cannot use C1 */ (nil)

src/cmd/vet/main.go

@@ -35,6 +35,8 @@ var (
 	tagList = []string{} // exploded version of tags flag; set in main
 
 	mustTypecheck bool
+
+	succeedOnTypecheckFailure bool // during go test, we ignore potential bugs in go/types
 )
 
 var exitCode = 0
@@ -291,6 +293,8 @@ type vetConfig struct {
 	ImportMap   map[string]string
 	PackageFile map[string]string
 
+	SucceedOnTypecheckFailure bool
+
 	imp types.Importer
 }
 
@@ -336,6 +340,7 @@ func doPackageCfg(cfgFile string) {
 	if err := json.Unmarshal(js, &vcfg); err != nil {
 		errorf("parsing vet config %s: %v", cfgFile, err)
 	}
+	succeedOnTypecheckFailure = vcfg.SucceedOnTypecheckFailure
 	stdImporter = &vcfg
 	inittypes()
 	mustTypecheck = true
@@ -427,6 +432,9 @@ func doPackage(names []string, basePkg *Package) *Package {
 	// Type check the package.
 	errs := pkg.check(fs, astFiles)
 	if errs != nil {
+		if succeedOnTypecheckFailure {
+			os.Exit(0)
+		}
 		if *verbose || mustTypecheck {
 			for _, err := range errs {
 				fmt.Fprintf(os.Stderr, "%v\n", err)