fatcontext

fatcontext is a Go linter which detects potential fat contexts in loops or function literals. They can lead to performance issues, as documented here: https://gabnotes.org/fat-contexts/

Installation / usage

fatcontext is available in golangci-lint since v1.58.0.

go install go.augendre.info/fatcontext/cmd/fatcontext@latest
fatcontext ./...

Example

package main

import "context"

func ok() {
	ctx := context.Background()

	for i := 0; i < 10; i++ {
		ctx := context.WithValue(ctx, "key", i)
		_ = ctx
	}
}

func notOk() {
	ctx := context.Background()

	for i := 0; i < 10; i++ {
		ctx = context.WithValue(ctx, "key", i) // "nested context in loop"
		_ = ctx
	}
}

Configuration

The linter exposes the following options, all available on the command line:

Option	Default	Description
check-loops	true	Detect fat contexts created inside loops.
check-function-literals	true	Detect fat contexts created inside function literals.
check-struct-pointers	false	Detect potential fat contexts created through struct pointers.

# Disable loop detection (enabled by default)
fatcontext -check-loops=false ./...

# Disable function literal detection (enabled by default)
fatcontext -check-function-literals=false ./...

# Enable struct pointer detection (disabled by default)
fatcontext -check-struct-pointers ./...

When used through golangci-lint, these options are configured in the linter's settings rather than on the command line.

Development

Setup pre-commit locally:

pre-commit install

Run tests & linter:

mise run lint
mise run test

To release, just publish a git tag:

git tag -a v0.1.0 -m "v0.1.0"
git push --follow-tags