x/build/maintner: TestForeachRepo is failing on Go tip due to error change

[dmitshur]

With Go 1.12:

$ go test -v -run=TestForeachRepo -count=1 golang.org/x/build/maintner
=== RUN   TestForeachRepo
--- PASS: TestForeachRepo (0.00s)
    github_test.go:751: Tested Reviews
PASS
ok  	golang.org/x/build/maintner	0.146s

With Go tip (at commit df557fe):

$ gotip test -v -run=TestForeachRepo -count=1 golang.org/x/build/maintner
=== RUN   TestForeachRepo
--- FAIL: TestForeachRepo (0.00s)
    github_test.go:743: Will Error: ForeachReview errs differ. got: Planned Failure, want: Planned Failure
    github_test.go:743: Will Error Late: ForeachReview errs differ. got: Planned Failure, want: Planned Failure
    github_test.go:751: Tested Reviews
FAIL
FAIL	golang.org/x/build/maintner	0.148s

I suspect it's because of 6be6f11. It changed the internal representation of the result of fmt.Errorf, making it so that !deep.ReflectEqual no longer compares favorably in github_test.go#L742-L744:

if !reflect.DeepEqual(tt.wantErr, err) {
	t.Errorf("%s: ForeachReview errs differ. got: %s, want: %s", tt.name, err, tt.wantErr)
}

This makes trybots in x/build repo fail, e.g., https://go-review.googlesource.com/c/build/+/163205/2#message-8c683121b60291567babee1aed8cd19a0f83bfc6.

/cc @bradfitz

[bradfitz]

We could switch to using https://github.com/google/go-cmp instead of reflect.

[dmitshur]

That sounds like a good fix for the issue in x/build/maintner.

[dmitshur]

Since it was just two error values being compared, and not a more deeply nested struct, I went with a simpler solution in CL 164297 for now.

[gopherbot]

Change https://golang.org/cl/164297 mentions this issue: maintner: compare errors via their public API