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cmd/compile: incorrect error message when mixing named/unamed with an interface arg type #17382

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mitchellh opened this issue Oct 8, 2016 · 3 comments
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cmd/compile: incorrect error message when mixing named/unamed with an interface arg type #17382

mitchellh opened this issue Oct 8, 2016 · 3 comments
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@mitchellh
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mitchellh commented Oct 8, 2016 •
edited

What version of Go are you using (go version)?

go version go1.7.1 darwin/amd64

What operating system and processor architecture are you using (go env)?

GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
GOPATH="/Users/mitchellh/code/go"
GORACE=""
GOROOT="/Users/mitchellh/code/3rdparty/go"
GOTOOLDIR="/Users/mitchellh/code/3rdparty/go/pkg/tool/darwin_amd64"
CC="clang"
GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/3q/c37yygcs4vl7cvzq3k3wdnyr0000gn/T/go-build207171984=/tmp/go-build -gno-record-gcc-switches -fno-common"
CXX="clang++"
CGO_ENABLED="1"

What did you do?

https://play.golang.org/p/4UIQBFK6tm

What did you expect to see?

I expect this error message:

tmp/sandbox307788845/main.go:15: mixed named and unnamed function parameters

Which you get if you change the A parameter to a pointer to A (notice A just changed to *A):

https://play.golang.org/p/EoGX8zfkKj

What did you see instead?

I see this error message with the key point being the type signature just looks wrong:

tmp/sandbox076937847/main.go:15: cannot use new(Impl) (type *Impl) as type I in assignment:
    *Impl does not implement I (wrong type for F method)
        have F(*B, *B)
        want F(A, *B)

It says have F(*B, *B) but if you look at the source thats not what you see and its very confusing.
@odeke-em odeke-em changed the title Incorrect compiler error message when mixing named/unamed with an interface arg type cmd/compile: incorrect error message when mixing named/unamed with an interface arg type Oct 8, 2016
@odeke-em
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odeke-em commented Oct 8, 2016

/cc @griesemer @josharian

@cznic
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cznic commented Oct 8, 2016

It says have F(*B, *B) but if you look at the source thats not what you see and its very confusing.

The error message is correct. F(A, b *B) has signature F(*B, *B) because it has two named parameters, A and b, both of type *B.

@mitchellh
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Ahhhh, interesting.

I can see that now (I'm just so used to lowercase var names). That is really confusing but I can see how that's possible. I can see how this probably isn't a bug then and I'll close it.

@golang golang locked and limited conversation to collaborators Oct 8, 2017
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@mitchellh @cznic @odeke-em @gopherbot