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cmd/compile: error message refers to aliased type instead of the alias type name #67628

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griesemer opened this issue May 24, 2024 · 5 comments
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compiler/runtime Issues related to the Go compiler and/or runtime. NeedsFix The path to resolution is known, but the work has not been done.
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@griesemer
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package p

func f[P any](x P) P { return x }

func _() {
	type A = int
	var a A
	b := f(a) // type of B is A
	_ = b + "foo"
}

produces

...: invalid operation: b + "foo" (mismatched types int and untyped string)

It should say:

mismatched types A and untyped string

cc: @findleyr

@griesemer griesemer added the NeedsFix The path to resolution is known, but the work has not been done. label May 24, 2024
@griesemer griesemer added this to the Go1.23 milestone May 24, 2024
@griesemer griesemer self-assigned this May 24, 2024
@gopherbot gopherbot added the compiler/runtime Issues related to the Go compiler and/or runtime. label May 24, 2024
@griesemer
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Related to #67547.

@findleyr
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Presumably this is because the inference algorithm strips alias information. I would expect that the type of b is int, not A.
This may be difficult to fix.

@griesemer
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I would expect that the type of b is int, not A.

That's what the error message says. But I think it should say A. Not sure why you say it should be int.

@gopherbot
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Change https://go.dev/cl/588797 mentions this issue: go/types, types2: don't lose alias information during unification

@findleyr
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I would expect that the type of b is int, not A.

That's what the error message says. But I think it should say A. Not sure why you say it should be int.

I merely meant that the type is int, not that it should be int. In other words, the problem is inference, not the error message.

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compiler/runtime Issues related to the Go compiler and/or runtime. NeedsFix The path to resolution is known, but the work has not been done.
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