Go 1.6 - panic: runtime error: cgo argument has Go pointer to Go pointer

[dzan]

Hi,

https://github.com/sbinet/go-clang/blob/master/cursor.go#L798

it seems like this line causes issues when passed a closure if building with go 1.6. Using GODEBUG=cgocheck=0 when running works but that's not really a good idea. Passing it a closure is the only way to actually pass arguments to your visitor I think, e.g.

// collectMatchKind collects all or one element name(s) in the sub AST-tree rooted at
// the provided cursor.
func collectMatchKind(entityCursor clang.Cursor, kind clang.CursorKind,
        collectAll bool) (names []string) {

        // Invoke the visitor with this closure.
        entityCursor.Visit(func(cursor, parent clang.Cursor) (
                status clang.ChildVisitResult) {

                if cursor.Kind() == kind {
                        names = append(names, cursor.DisplayName())
                        if !collectAll {
                                return clang.CVR_Break
                        }
                }
                return clang.CVR_Continue
        })
        return // named
}

panic: runtime error: cgo argument has Go pointer to Go pointer

goroutine 1 [running]:
panic(0x42247c0, 0xc82000eae0)
        /usr/local/Cellar/go/1.6/libexec/src/runtime/panic.go:464 +0x3e6
github.com/sbinet/go-clang._cgoCheckPointer0(0x41c8c80, 0xc82002c050, 0xc82000ead0, 0x1, 0x1, 0xc82002c048)
        ??:0 +0x4d
github.com/sbinet/go-clang.Cursor.Visit(0xb, 0x6e24080, 0x1, 0x6095c30, 0xc820014ec0, 0x4236f20)
        /Users/dzan/Source/go/src/github.com/sbinet/go-clang/cursor.go:798 +0x12f
main.collectMatchKind(0xb, 0x6e24080, 0x1, 0x6095c30, 0x28, 0x0, 0x0, 0x0)

[sbinet]

indeed, this needs to be fixed.
thanks for the report.

note to self: perhaps draw some inspiration from adg/notify@4268ed7 ?

[justinfx]

Hi. I was about to post a new issue surrounding this exact problem, and saw this existing one. I too have the same need to collect results during the visit routines. Currently I have had to resort to using global state. I can't seem to find a combination that works, to enable me to associate any kind of unique state collection with a particular visit.

I've tried using a method on a struct that can store state and also a function closing over identifiers. But everything I try seems to end up with this same cgo pointer limitation. Is there a concrete example that anyone can post which allows even some form of managing unique state for a visit operation?

Thanks so much for this binding btw. Its enabled me to write an awesome codegen tool at work. I just want to be able to make the codegen tool work in parallel, but I can't solve this need to have multiple visitors running.

[doppioandante]

Hello, any update on this? How can I work around this?
Is it difficult to fix the bug?

[justinfx]

Awesome! Thanks for this.