golang/go

cmd/compile: exponential compile-time with nested generic instantiations

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#78,342 opened on Mar 25, 2026

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Description

Go version

go 1.26.1 / tip

Output of go env in your module/workspace:

GOARCH=arm64

What did you do?

case 1:

package p

type T[P any] struct { _,_,_,_,_,_,_,_ P }

type U T[T[T[T[T[T[T[T[T[T[int]]]]]]]]]]

case 2:

package p

type T[P any] struct { _,_,_,_,_,_,_,_ P }

type U T[T[T[T[T[T[T[T[T[T[T[int]]]]]]]]]]]

case 3:

package p

type T[P any] struct { _,_,_,_,_,_,_,_ P }

type U T[T[T[T[T[T[T[T[T[T[T[T[int]]]]]]]]]]]]

Run go build on the above and measure the time.

What did you see happen?

Very long compile time.

What did you expect to see?

Fast compilation.

Contributor guide

Research direction
Investigate the compiler's handling of nested generic instantiations to identify why compile time grows exponentially. Trace the type checking or instantiation path and look for possible algorithmic inefficiencies.
Tech stack
go
Domain
backend
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
Gocompiler internals
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
30