inconsistent compiler behavior between gc and go/types

[zeebo]

Consider this program:

package main

import (
    "fmt"
    "go/ast"
    "go/parser"
    "go/token"

    _ "golang.org/x/tools/go/gcimporter"
    "golang.org/x/tools/go/types"
)

func foo() {
    var x int
    func() {
        x = 1
    }()
}

func main() {
    fset := token.NewFileSet()
    file, err := parser.ParseFile(fset, "./repro.go", nil, 0)
    if err != nil {
        panic(err)
    }

    _, err = types.Check("repro", fset, []*ast.File{file})
    fmt.Println("error:", err)
}

If you place it in $GOPATH/src/repro/repro.go then you can build it with gc (go version 1.4), but if you run it, golang.org/x/tools/go/types (most recent tip at time of issue report) fails to type check.

It seems like they disagree on if x is considered to be used or not.

[ianlancetaylor]

Dup of issue #3059.

[zeebo]

I appreciate that the behavior that gc is doing here is a dupe of #3059 but the more important part in my opinion is that go/types disagrees and considers it an error. It doesn't look like #3059 has that information. Where should that issue be tracked, or is that not an issue because this is implementation defined in the spec?

[ianlancetaylor]

Personally I think go/types is correct and cmd/gc is wrong, so I'm not sure what needs to be tracked.

[zeebo]

I agree. I'll just leave a comment on the other ticket describing the pain I experienced due to this to maybe help prioritize fixing it since it's not obvious how cmd/gc accepting these programs is harmful.