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go/types, types2: missing type due to delayed type-type inference #51489

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findleyr opened this issue Mar 4, 2022 · 4 comments
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go/types, types2: missing type due to delayed type-type inference #51489

findleyr opened this issue Mar 4, 2022 · 4 comments
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FrozenDueToAge NeedsFix The path to resolution is known, but the work has not been done.
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Go1.20

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@findleyr
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findleyr commented Mar 4, 2022

This is a follow-up on #51233: in type declarations, it is possible to substitute for type arguments before they are fully resolved.

While investigating this afternoon I was able to construct another crasher:
https://go.dev/play/p/V5Jl7-WDV4K?v=gotip

This may be complicated, but the mechanism is simple: force an expansion of T before R[int] is resolved. In this case, this is forced by the call to var x = T[int]{}.F. We currently lack controls to ensure that inference happens before substitution. I am not sure whether it is trivial to introduce such a mechanism.

CC @griesemer
@findleyr findleyr added this to the Go1.18 milestone Mar 4, 2022
@gopherbot
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Change https://go.dev/cl/390040 mentions this issue: go/types: add a check to detect invalid substitution for inferred types

@cagedmantis cagedmantis added the NeedsFix The path to resolution is known, but the work has not been done. label Mar 7, 2022
@findleyr findleyr mentioned this issue Mar 7, 2022
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@findleyr
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findleyr commented Mar 7, 2022

In #51527 we have disabled type-type inference for 1.18, so this can be moved to 1.19.

@findleyr findleyr modified the milestones: Go1.18, Go1.19 Mar 7, 2022
@ianlancetaylor
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Rolling forward to 1.20. Please comment if you disagree. Thanks.

@ianlancetaylor ianlancetaylor modified the milestones: Go1.19, Go1.20 Jun 24, 2022
@findleyr
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I don't think we're ever going to add type-type inference, and if we do the mechanism will be different. So I think this is no longer relevant.

@golang golang locked and limited conversation to collaborators Jun 24, 2023
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FrozenDueToAge NeedsFix The path to resolution is known, but the work has not been done.
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Go1.20
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@cagedmantis @ianlancetaylor @gopherbot @findleyr