golang/go

cmd/vet: govet sometimes wrong about whether a context gets cancelled

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#29,587 opened on Jan 6, 2019

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Description

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

Not sure, it's a toolchain. Most likely 1.11.

Does this issue reproduce with the latest release?

Yes, as of 1.12beta.

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

No idea, govet runs remotely on a language server.

What did you do?

ctx, cancel := context.WithCancel(context.Background())
defer cancel()
if true {
  // This makes govet think that the child context never gets cancelled,
  // when, in fact, it is cancelled by the parent's cancel().
  ctx, _ = context.WithTimeout(ctx, time.Second)
}

What did you expect to see?

govet should not claim that the child context leaks. (If it's a style question, it should be in the linter, not govet.)

What did you see instead?

govet incorrectly thinks the child context does not get cancelled.

Contributor guide

Research direction
Trace the vet pass for context cancellation in go/analysis/passes and identify why it misses parent cancellation propagation. Reproduce the issue with the provided example. Modify the analysis to detect that child contexts are effectively cancelled when the parent's cancel() is called, even if the child is overridden with a timeout.
Tech stack
go
Domain
developer experiencecli
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.
Stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
Gocontext
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
70