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go/types: assertion failure: Sizeof Basic T is typed #20237

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josharian opened this issue May 4, 2017 · 1 comment
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go/types: assertion failure: Sizeof Basic T is typed #20237

josharian opened this issue May 4, 2017 · 1 comment
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@josharian
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@josharian josharian commented May 4, 2017

The following test, which is identical to TestIssue16902 aside from src, fails.

func TestShift(t *testing.T) {
	const src = `
package p

const x = 1>>1`
	fset := token.NewFileSet()
	f, err := parser.ParseFile(fset, "x.go", src, 0)
	if err != nil {
		t.Fatal(err)
	}
	info := types.Info{Types: make(map[ast.Expr]types.TypeAndValue)}
	conf := types.Config{
		Importer: importer.Default(),
		Sizes:    &types.StdSizes{WordSize: 8, MaxAlign: 8},
	}
	_, err = conf.Check("x", fset, []*ast.File{f}, &info)
	if err != nil {
		t.Fatal(err)
	}
	for _, tv := range info.Types {
		_ = conf.Sizes.Sizeof(tv.Type)
		_ = conf.Sizes.Alignof(tv.Type)
	}
}

Result:

panic: assertion failed [recovered]
	panic: assertion failed

goroutine 5 [running]:
testing.tRunner.func1(0xc4200de0f0)
	/Users/josh/go/tip/src/testing/testing.go:712 +0x256
panic(0x1291ac0, 0x1334970)
	/Users/josh/go/tip/src/runtime/panic.go:489 +0x259
go/types.assert(0x1468400)
	/Users/josh/go/tip/src/go/types/errors.go:18 +0x4c
go/types.(*StdSizes).Sizeof(0xc420014430, 0x14684e0, 0x147cd80, 0xc420058b40)
	/Users/josh/go/tip/src/go/types/sizes.go:123 +0x39d
go/types_test.TestZeroShiftOne(0xc4200de0f0)
	/Users/josh/go/tip/src/go/types/sizes_test.go:131 +0x485
testing.tRunner(0xc4200de0f0, 0x130c348)
	/Users/josh/go/tip/src/testing/testing.go:747 +0xd0
created by testing.(*T).Run
	/Users/josh/go/tip/src/testing/testing.go:789 +0x2de
exit status 2
FAIL	go/types	0.010s

The relevant assertion is near the beginning of StdSizes.SizeOf:

func (s *StdSizes) Sizeof(T Type) int64 {
	switch t := T.Underlying().(type) {
	case *Basic:
		assert(isTyped(T))  // HERE
		k := t.kind

When fixed, we should also test larger shifts, like 0>>1090, which currently produce a different error.

@griesemer

Found by go-fuzz.

@josharian josharian added this to the Go1.9 milestone May 4, 2017
@griesemer
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@griesemer griesemer commented May 5, 2017

@josharian FWIW, you wrote the old test when you fixed #16902... :-)

I don't believe there's anything wrong here: go/types.Sizes.Sizeof is supposed to be called with a typed value; so in this case the test is simply wrong/not applicable.

Trying a large shift count (0 >> 1080) after disabling the assertion (or removing the explicit calls to Sizeof) leads to the error

invalid operation: invalid shift count 1080 (untyped int constant)

which is perhaps not great, but ok: we don't support shift counts over a certain size.

Closing.

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@griesemer griesemer closed this May 5, 2017
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