fmt: hide bad format in test from vet

Hide in the source code instead of in the separate whitelist.
Removes the only printf false positive in the standard library.

Change-Id: I99285e67588c7c93bd56d59ee768a03be7c301e7
Reviewed-on: https://go-review.googlesource.com/74590
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rob Pike <r@golang.org>

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

@@ -13,9 +13,6 @@ go/types/scope.go: method WriteTo(w io.Writer, n int, recurse bool) should have
 
 // False positives.
 
-// Test of how fmt handles nil.
-fmt/fmt_test.go: arg nil for printf verb %s of wrong type: untyped nil
-
 // Nothing much to do about cross-package assembly. Unfortunate.
 runtime/asm_ARCHSUFF.s: [GOARCH] cannot check cross-package assembly function: call is in package reflect
 runtime/asm_ARCHSUFF.s: [GOARCH] cannot check cross-package assembly function: Equal is in package bytes

src/fmt/fmt_test.go

@@ -1733,12 +1733,14 @@ func TestIsSpace(t *testing.T) {
 	}
 }
 
+func hideFromVet(s string) string { return s }
+
 func TestNilDoesNotBecomeTyped(t *testing.T) {
 	type A struct{}
 	type B struct{}
 	var a *A = nil
 	var b B = B{}
-	got := Sprintf("%s %s %s %s %s", nil, a, nil, b, nil) // go vet should complain about this line.
+	got := Sprintf(hideFromVet("%s %s %s %s %s"), nil, a, nil, b, nil)
 	const expect = "%!s(<nil>) %!s(*fmt_test.A=<nil>) %!s(<nil>) {} %!s(<nil>)"
 	if got != expect {
 		t.Errorf("expected:\n\t%q\ngot:\n\t%q", expect, got)