x/tools/analysis/passes/printf: regression in format type checks

[kevinburke]

The following code is incorrect - I meant to write len(s) not s.

package main

import (
	"testing"
)

func TestStringFormat(t *testing.T) {
	s := make([]string, 0)
	if len(s) != 1 {
		// "s" below is a mistake; I meant to type "len(s)"
		//
		// I expect to get this error:
		// ./lib_test.go:26: Errorf format %d has arg s of wrong type []string
		t.Errorf("wrong length: want %d got %d", 1, s)
	}
}

In Go 1.10, running go test returns a vet error:

./lib_test.go:26: Errorf format %d has arg s of wrong type []string

However, in Go 1.11 and above, go test does not return an error - it instead returns:

lib_test.go:26: wrong length: want 1 got []

I added a repository to reproduce - you can see in the Travis CI build which fails on Go 1.10 but passes on Go 1.11 and tip. https://travis-ci.org/kevinburke/test-fmt-repro/builds/456666561

[kevinburke]

I tried to search whether this change was deliberate but couldn't find anything. It's possible it was deliberate.

[ALTree]

It appears that this was introduced in 98409a4 (cmd/vet: better align print warnings with fmt).

[mvdan]

This does look like a regression introduced by that commit of mine a while ago. Will have a look.

[mvdan]

Thanks for the report, @kevinburke. This turned out to uncover another batch of bugs in vet's printf checker, where it was fairly inconsistent with what fmt does. See https://go-review.googlesource.com/c/tools/+/149979.

In its defense, fmt is poorly documented when it comes to pointers. I've raised #28865 for that.

[alandonovan]

Thanks for the quick fix, Daniel.

[kevinburke]

OK - should we mark this as a release blocker?

[mvdan]

Certainly seems like something we can fix in 1.12 to me, but it's not a regression in tip, so I wouldn't call it a blocker. Will leave the decision to Alan.

[alandonovan]

I agree with Daniel: not a regression, not a release blocker. Shouldn't be hard to fix though.

[gopherbot]

Change https://golang.org/cl/152277 mentions this issue: cmd/vendor: update to golang.org/x/tools@e5f3ab76