cmd/vet/all: work around vet printf checker deficiencies

cmd/vet has a known deficiency in its handling of fmt.Formatters.
This causes a spurious printf error only for non-host platforms.
Since cmd/vet/all may get run on any given platform,
whitelists cannot help here.

Work around the issue by skipping printf tests entirely
for non-host platforms.

Work around the one known acceptable false positive from vet
by whitelisting the file that contains it.

Change-Id: Id74b3d4db0519cf9a670a065683715f856266e45
Reviewed-on: https://go-review.googlesource.com/36936Reviewed-by: Rob Pike <r@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/vet/all/main.go

@@ -59,11 +59,12 @@ func main() {
 	case *flagAll:
 		vetPlatforms(allPlatforms())
 	default:
-		host := platform{os: build.Default.GOOS, arch: build.Default.GOARCH}
-		host.vet(runtime.GOMAXPROCS(-1))
+		hostPlatform.vet(runtime.GOMAXPROCS(-1))
 	}
 }
 
+var hostPlatform = platform{os: build.Default.GOOS, arch: build.Default.GOARCH}
+
 func allPlatforms() []platform {
 	var pp []platform
 	cmd := exec.Command(cmdGoPath, "tool", "dist", "list")
@@ -177,6 +178,14 @@ var ignorePathPrefixes = [...]string{
 	"cmd/go/testdata/",
 	"cmd/vet/testdata/",
 	"go/printer/testdata/",
+	// fmt_test contains a known bad format string.
+	// We cannot add it to any given whitelist,
+	// because it won't show up for any non-host platform,
+	// due to deficiencies in vet.
+	// Just whitelist the whole file.
+	// TODO: If vet ever uses go/loader and starts working off source,
+	// this problem will likely go away.
+	"fmt/fmt_test.go",
 }
 
 func vetPlatforms(pp []platform) {
@@ -224,7 +233,18 @@ func (p platform) vet(ncpus int) {
 	// and no clear way to improve vet to eliminate large chunks of them.
 	// And having them in the whitelists will just cause annoyance
 	// and churn when working on the runtime.
-	cmd = exec.Command(cmdGoPath, "tool", "vet", "-unsafeptr=false", ".")
+	args := []string{"tool", "vet", "-unsafeptr=false"}
+	if p != hostPlatform {
+		// When not checking the host platform, vet gets confused by
+		// the fmt.Formatters in cmd/compile,
+		// so just skip the printf checks on non-host platforms for now.
+		// There's not too much platform-specific code anyway.
+		// TODO: If vet ever uses go/loader and starts working off source,
+		// this problem will likely go away.
+		args = append(args, "-printf=false")
+	}
+	args = append(args, ".")
+	cmd = exec.Command(cmdGoPath, args...)
 	cmd.Dir = filepath.Join(runtime.GOROOT(), "src")
 	cmd.Env = env
 	stderr, err := cmd.StderrPipe()

src/cmd/vet/all/whitelist/all.txt

@@ -23,7 +23,6 @@ runtime/sys_GOOS_ARCHSUFF.s: [GOARCH] cannot check cross-package assembly functi
 // Legitimate vet complaints in which we are testing for correct runtime behavior
 // in bad situations that vet can also detect statically.
 cmd/cover/testdata/test.go: unreachable code
-fmt/fmt_test.go: arg nil for printf verb %s of wrong type: untyped nil
 encoding/json/decode_test.go: struct field m has json tag but is not exported
 encoding/json/decode_test.go: struct field m2 has json tag but is not exported
 encoding/json/tagkey_test.go: struct field tag `:"BadFormat"` not compatible with reflect.StructTag.Get: bad syntax for struct tag key