[pre-commit.ci] pre-commit autoupdate

updates:
- [github.com/golangci/golangci-lint: v1.64.6 → v1.64.7](https://github.com/golangci/golangci-lint/compare/v1.64.6...v1.64.7)

.github/dependabot.yml

@@ -0,0 +1,16 @@
+# Doc: https://docs.github.com/code-security/dependabot/dependabot-version-updates/configuration-options-for-the-dependabot.yml-file
+
+version: 2
+updates:
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "monthly"
+    groups:
+      github-actions:
+        patterns:
+          - "*"  # Group all updates into a single larger pull request.
+  - package-ecosystem: "gomod"
+    directory: "/"
+    schedule:
+      interval: "monthly"

.github/workflows/go.yml

@@ -14,8 +14,9 @@ permissions:
 jobs:
   build:
     strategy:
+      fail-fast: false
       matrix:
-        go: ['1.21', '1.22']
+        go: [stable, oldstable]
         os: [macos-latest, windows-latest, ubuntu-latest]
     name: build
     runs-on: ${{ matrix.os }}
@@ -28,3 +29,21 @@ jobs:
         run: go build -v ./...
       - name: Test
         run: make test
+  coverage:
+    name: coverage
+    permissions:
+      contents: write
+    concurrency:
+      group: coverage
+    runs-on: ubuntu-latest
+    needs: [build]
+    steps:
+      - name: Update coverage report
+        uses: ncruces/go-coverage-report@v0
+        with:
+          report: true
+          chart: true
+          amend: true
+        if: |
+          github.event_name == 'push'
+        continue-on-error: true

.github/workflows/golangci-lint.yml

@@ -16,7 +16,7 @@ jobs:
   golangci:
     strategy:
       matrix:
-        go: ['1.21', '1.22']
+        go: [stable, oldstable]
     name: lint
     runs-on: ubuntu-latest
     steps:
@@ -25,6 +25,6 @@ jobs:
         with:
           go-version: ${{ matrix.go }}
       - name: golangci-lint
-        uses: golangci/golangci-lint-action@v4
+        uses: golangci/golangci-lint-action@v6
         with:
           version: latest

.github/workflows/goreleaser.yml

@@ -17,8 +17,10 @@ jobs:
           fetch-depth: 0
       - name: Set up Go
         uses: actions/setup-go@v5
+        with:
+          go-version: stable
       - name: Run GoReleaser
-        uses: goreleaser/goreleaser-action@v5
+        uses: goreleaser/goreleaser-action@v6
         with:
           distribution: goreleaser
           version: latest

.gitignore

@@ -1,3 +1,4 @@
 .idea
 
+/fatcontext
 dist/

.golangci.yml

@@ -1,3 +1,9 @@
 issues:
   exclude-dirs:
     - contrib
+linters:
+  enable:
+    - goimports
+linters-settings:
+  goimports:
+    local-prefixes: "github.com/Crocmagnon/fatcontext"

.goreleaser.yaml

@@ -1,12 +1,6 @@
-# This is an example .goreleaser.yml file with some sensible defaults.
-# Make sure to check the documentation at https://goreleaser.com
-
-# The lines below are called `modelines`. See `:help modeline`
-# Feel free to remove those if you don't want/need to use them.
 # yaml-language-server: $schema=https://goreleaser.com/static/schema.json
 # vim: set ts=2 sw=2 tw=0 fo=cnqoj
-
-version: 1
+version: 2
 
 force_token: github
 
@@ -45,3 +39,6 @@ changelog:
     exclude:
       - "^docs:"
       - "^test:"
+
+release:
+  draft: true

.pre-commit-config.yaml

@@ -3,13 +3,13 @@ ci:
 
 repos:
   - repo: https://github.com/pre-commit/pre-commit-hooks
-    rev: v2.3.0
+    rev: v5.0.0
     hooks:
       - id: check-yaml
       - id: end-of-file-fixer
       - id: trailing-whitespace
   - repo: https://github.com/golangci/golangci-lint
-    rev: v1.57.1
+    rev: v1.64.7
     hooks:
       - id: golangci-lint-full
   - repo: local

README.md

@@ -1,8 +1,21 @@
 # fatcontext
 
-`fatcontext` is a Go linter which detects potential fat contexts in loops.
+[![Go Reference](https://pkg.go.dev/badge/github.com/Crocmagnon/fatcontext.svg)](https://pkg.go.dev/github.com/Crocmagnon/fatcontext)
+[![Go Report Card](https://goreportcard.com/badge/github.com/Crocmagnon/fatcontext)](https://goreportcard.com/report/github.com/Crocmagnon/fatcontext)
+[![Go Coverage](https://github.com/Crocmagnon/fatcontext/wiki/coverage.svg)](https://github.com/Crocmagnon/fatcontext/wiki/Coverage)
+
+`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.
+
+```bash
+go install github.com/Crocmagnon/fatcontext/cmd/fatcontext@latest
+fatcontext ./...
+```
+
 ## Example
 
 ```go

cmd/fatcontext/main.go

@@ -1,10 +1,11 @@
 package main
 
 import (
-	"github.com/Crocmagnon/fatcontext/pkg/analyzer"
 	"golang.org/x/tools/go/analysis/singlechecker"
+
+	"github.com/Crocmagnon/fatcontext/pkg/analyzer"
 )
 
 func main() {
-	singlechecker.Main(analyzer.Analyzer)
+	singlechecker.Main(analyzer.NewAnalyzer())
 }

contrib/example.go

@@ -1,21 +0,0 @@
-package contrib
-
-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
-	}
-}

go.mod

@@ -1,7 +1,10 @@
 module github.com/Crocmagnon/fatcontext
 
-go 1.21
+go 1.22.0
 
-require golang.org/x/tools v0.19.0
+require golang.org/x/tools v0.30.0
 
-require golang.org/x/mod v0.16.0 // indirect
+require (
+	golang.org/x/mod v0.23.0 // indirect
+	golang.org/x/sync v0.11.0 // indirect
+)

go.sum

@@ -1,6 +1,8 @@
-golang.org/x/mod v0.16.0 h1:QX4fJ0Rr5cPQCF7O9lh9Se4pmwfwskqZfq5moyldzic=
-golang.org/x/mod v0.16.0/go.mod h1:hTbmBsO62+eylJbnUtE2MGJUyE7QWk4xUqPFrRgJ+7c=
-golang.org/x/sync v0.6.0 h1:5BMeUDZ7vkXGfEr1x9B4bRcTH4lpkTkpdh0T/J+qjbQ=
-golang.org/x/sync v0.6.0/go.mod h1:Czt+wKu1gCyEFDUtn0jG5QVvpJ6rzVqr5aXyt9drQfk=
-golang.org/x/tools v0.19.0 h1:tfGCXNR1OsFG+sVdLAitlpjAvD/I6dHDKnYrpEZUHkw=
-golang.org/x/tools v0.19.0/go.mod h1:qoJWxmGSIBmAeriMx19ogtrEPrGtDbPK634QFIcLAhc=
+github.com/google/go-cmp v0.6.0 h1:ofyhxvXcZhMsU5ulbFiLKl/XBFqE1GSq7atu8tAmTRI=
+github.com/google/go-cmp v0.6.0/go.mod h1:17dUlkBOakJ0+DkrSSNjCkIjxS6bF9zb3elmeNGIjoY=
+golang.org/x/mod v0.23.0 h1:Zb7khfcRGKk+kqfxFaP5tZqCnDZMjC5VtUBs87Hr6QM=
+golang.org/x/mod v0.23.0/go.mod h1:6SkKJ3Xj0I0BrPOZoBy3bdMptDDU9oJrpohJ3eWZ1fY=
+golang.org/x/sync v0.11.0 h1:GGz8+XQP4FvTTrjZPzNKTMFtSXH80RAzG+5ghFPgK9w=
+golang.org/x/sync v0.11.0/go.mod h1:Czt+wKu1gCyEFDUtn0jG5QVvpJ6rzVqr5aXyt9drQfk=
+golang.org/x/tools v0.30.0 h1:BgcpHewrV5AUp2G9MebG4XPFI1E2W41zU1SaqVA9vJY=
+golang.org/x/tools v0.30.0/go.mod h1:c347cR/OJfw5TI+GfX7RUPNMdDRRbjvYTS0jPyvsVtY=

pkg/analyzer/analyzer.go

@@ -3,30 +3,57 @@ package analyzer
 import (
 	"bytes"
 	"errors"
+	"flag"
 	"fmt"
 	"go/ast"
 	"go/printer"
 	"go/token"
+	"slices"
+
 	"golang.org/x/tools/go/analysis"
 	"golang.org/x/tools/go/analysis/passes/inspect"
 	"golang.org/x/tools/go/ast/inspector"
 )
 
-var Analyzer = &analysis.Analyzer{
-	Name:     "fatcontext",
-	Doc:      "detects nested contexts in loops",
-	Run:      run,
-	Requires: []*analysis.Analyzer{inspect.Analyzer},
+const FlagCheckStructPointers = "check-struct-pointers"
+
+func NewAnalyzer() *analysis.Analyzer {
+	r := &runner{}
+
+	flags := flag.NewFlagSet("fatcontext", flag.ExitOnError)
+	flags.BoolVar(&r.DetectInStructPointers, FlagCheckStructPointers, false,
+		"set to true to detect potential fat contexts in struct pointers")
+
+	return &analysis.Analyzer{
+		Name:     "fatcontext",
+		Doc:      "detects nested contexts in loops and function literals",
+		Run:      r.run,
+		Flags:    *flags,
+		Requires: []*analysis.Analyzer{inspect.Analyzer},
+	}
 }
 
 var errUnknown = errors.New("unknown node type")
 
-func run(pass *analysis.Pass) (interface{}, error) {
+const (
+	categoryInLoop          = "nested context in loop"
+	categoryInFuncLit       = "nested context in function literal"
+	categoryInStructPointer = "potential nested context in struct pointer"
+	categoryUnsupported     = "unsupported nested context type"
+)
+
+type runner struct {
+	DetectInStructPointers bool
+}
+
+func (r *runner) run(pass *analysis.Pass) (interface{}, error) {
 	inspctr := pass.ResultOf[inspect.Analyzer].(*inspector.Inspector)
 
 	nodeFilter := []ast.Node{
 		(*ast.ForStmt)(nil),
 		(*ast.RangeStmt)(nil),
+		(*ast.FuncLit)(nil),
+		(*ast.FuncDecl)(nil),
 	}
 
 	inspctr.Preorder(nodeFilter, func(node ast.Node) {
@@ -35,79 +62,241 @@ func run(pass *analysis.Pass) (interface{}, error) {
 			return
 		}
 
-		for _, stmt := range body.List {
-			assignStmt, ok := stmt.(*ast.AssignStmt)
-			if !ok {
-				continue
-			}
-
-			t := pass.TypesInfo.TypeOf(assignStmt.Lhs[0])
-			if t == nil {
-				continue
-			}
-
-			if t.String() != "context.Context" {
-				continue
-			}
-
-			if assignStmt.Tok == token.DEFINE {
-				break
-			}
-
-			suggestedStmt := ast.AssignStmt{
-				Lhs:    assignStmt.Lhs,
-				TokPos: assignStmt.TokPos,
-				Tok:    token.DEFINE,
-				Rhs:    assignStmt.Rhs,
-			}
-			suggested, err := render(pass.Fset, &suggestedStmt)
-
-			var fixes []analysis.SuggestedFix
-			if err == nil {
-				fixes = append(fixes, analysis.SuggestedFix{
-					Message: "replace `=` with `:=`",
-					TextEdits: []analysis.TextEdit{
-						{
-							Pos:     assignStmt.Pos(),
-							End:     assignStmt.End(),
-							NewText: []byte(suggested),
-						},
-					},
-				})
-			}
-
-			pass.Report(analysis.Diagnostic{
-				Pos:            assignStmt.Pos(),
-				Message:        "nested context in loop",
-				SuggestedFixes: fixes,
-			})
-
-			break
+		if body == nil {
+			return
 		}
+
+		assignStmt := findNestedContext(pass, node, body.List)
+		if assignStmt == nil {
+			return
+		}
+
+		category := getCategory(pass, node, assignStmt)
+
+		if r.shouldIgnoreReport(category) {
+			return
+		}
+
+		fixes := r.getSuggestedFixes(pass, assignStmt, category)
+
+		pass.Report(analysis.Diagnostic{
+			Pos:            assignStmt.Pos(),
+			Message:        category,
+			SuggestedFixes: fixes,
+		})
 	})
 
 	return nil, nil
 }
 
-func getBody(node ast.Node) (*ast.BlockStmt, error) {
-	forStmt, ok := node.(*ast.ForStmt)
-	if ok {
-		return forStmt.Body, nil
+func (r *runner) shouldIgnoreReport(category string) bool {
+	return category == categoryInStructPointer && !r.DetectInStructPointers
+}
+
+func (r *runner) getSuggestedFixes(pass *analysis.Pass, assignStmt *ast.AssignStmt, category string) []analysis.SuggestedFix {
+	switch category {
+	case categoryInStructPointer, categoryUnsupported:
+		return nil
 	}
 
-	rangeStmt, ok := node.(*ast.RangeStmt)
-	if ok {
-		return rangeStmt.Body, nil
+	suggestedStmt := ast.AssignStmt{
+		Lhs:    assignStmt.Lhs,
+		TokPos: assignStmt.TokPos,
+		Tok:    token.DEFINE,
+		Rhs:    assignStmt.Rhs,
+	}
+	suggested, err := render(pass.Fset, &suggestedStmt)
+
+	var fixes []analysis.SuggestedFix
+	if err == nil {
+		fixes = append(fixes, analysis.SuggestedFix{
+			Message: "replace `=` with `:=`",
+			TextEdits: []analysis.TextEdit{
+				{
+					Pos:     assignStmt.Pos(),
+					End:     assignStmt.End(),
+					NewText: suggested,
+				},
+			},
+		})
+	}
+
+	return fixes
+}
+
+func getCategory(pass *analysis.Pass, node ast.Node, assignStmt *ast.AssignStmt) string {
+	switch node.(type) {
+	case *ast.ForStmt, *ast.RangeStmt:
+		return categoryInLoop
+	}
+
+	if isPointer(pass, assignStmt.Lhs[0]) {
+		return categoryInStructPointer
+	}
+
+	switch node.(type) {
+	case *ast.FuncLit, *ast.FuncDecl:
+		return categoryInFuncLit
+	default:
+		return categoryUnsupported
+	}
+}
+
+func getBody(node ast.Node) (*ast.BlockStmt, error) {
+	switch typedNode := node.(type) {
+	case *ast.ForStmt:
+		return typedNode.Body, nil
+	case *ast.RangeStmt:
+		return typedNode.Body, nil
+	case *ast.FuncLit:
+		return typedNode.Body, nil
+	case *ast.FuncDecl:
+		return typedNode.Body, nil
 	}
 
 	return nil, errUnknown
 }
 
+func findNestedContext(pass *analysis.Pass, node ast.Node, stmts []ast.Stmt) *ast.AssignStmt {
+	for _, stmt := range stmts {
+		// Recurse if necessary
+		switch typedStmt := stmt.(type) {
+		case *ast.BlockStmt:
+			if found := findNestedContext(pass, node, typedStmt.List); found != nil {
+				return found
+			}
+		case *ast.IfStmt:
+			if found := findNestedContext(pass, node, typedStmt.Body.List); found != nil {
+				return found
+			}
+		case *ast.SwitchStmt:
+			if found := findNestedContext(pass, node, typedStmt.Body.List); found != nil {
+				return found
+			}
+		case *ast.CaseClause:
+			if found := findNestedContext(pass, node, typedStmt.Body); found != nil {
+				return found
+			}
+		case *ast.SelectStmt:
+			if found := findNestedContext(pass, node, typedStmt.Body.List); found != nil {
+				return found
+			}
+		case *ast.CommClause:
+			if found := findNestedContext(pass, node, typedStmt.Body); found != nil {
+				return found
+			}
+		}
+
+		// Actually check for nested context
+		assignStmt, ok := stmt.(*ast.AssignStmt)
+		if !ok {
+			continue
+		}
+
+		t := pass.TypesInfo.TypeOf(assignStmt.Lhs[0])
+		if t == nil {
+			continue
+		}
+
+		if t.String() != "context.Context" {
+			continue
+		}
+
+		if assignStmt.Tok == token.DEFINE {
+			continue
+		}
+
+		// Ignore [context.Background] & [context.TODO].
+		if isContextFunction(assignStmt.Rhs[0], "Background", "TODO") {
+			continue
+		}
+
+		if isPointer(pass, assignStmt.Lhs[0]) {
+			return assignStmt
+		}
+
+		// allow assignment to non-pointer children of values defined within the loop
+		if isWithinLoop(assignStmt.Lhs[0], node, pass) {
+			continue
+		}
+
+		return assignStmt
+	}
+
+	return nil
+}
+
 // render returns the pretty-print of the given node
-func render(fset *token.FileSet, x interface{}) (string, error) {
+func render(fset *token.FileSet, x interface{}) ([]byte, error) {
 	var buf bytes.Buffer
 	if err := printer.Fprint(&buf, fset, x); err != nil {
-		return "", fmt.Errorf("printing node: %w", err)
+		return nil, fmt.Errorf("printing node: %w", err)
 	}
-	return buf.String(), nil
+	return buf.Bytes(), nil
+}
+
+func isContextFunction(exp ast.Expr, fnName ...string) bool {
+	call, ok := exp.(*ast.CallExpr)
+	if !ok {
+		return false
+	}
+
+	selector, ok := call.Fun.(*ast.SelectorExpr)
+	if !ok {
+		return false
+	}
+
+	ident, ok := selector.X.(*ast.Ident)
+	if !ok {
+		return false
+	}
+
+	return ident.Name == "context" && slices.Contains(fnName, selector.Sel.Name)
+}
+
+func isWithinLoop(exp ast.Expr, node ast.Node, pass *analysis.Pass) bool {
+	lhs := getRootIdent(pass, exp)
+	if lhs == nil {
+		return false
+	}
+
+	obj := pass.TypesInfo.ObjectOf(lhs)
+	if obj == nil {
+		return false
+	}
+
+	scope := obj.Parent()
+	if scope == nil {
+		return false
+	}
+
+	return scope.Pos() >= node.Pos() && scope.End() <= node.End()
+}
+
+func getRootIdent(pass *analysis.Pass, node ast.Node) *ast.Ident {
+	for {
+		switch n := node.(type) {
+		case *ast.Ident:
+			return n
+		case *ast.IndexExpr:
+			node = n.X
+		case *ast.SelectorExpr:
+			if sel, ok := pass.TypesInfo.Selections[n]; ok && sel.Indirect() {
+				return nil // indirected (pointer) roots don't imply a (safe) copy
+			}
+			node = n.X
+		default:
+			return nil
+		}
+	}
+}
+
+func isPointer(pass *analysis.Pass, exp ast.Node) bool {
+	switch n := exp.(type) {
+	case *ast.SelectorExpr:
+		sel, ok := pass.TypesInfo.Selections[n]
+		return ok && sel.Indirect()
+	}
+
+	return false
 }

pkg/analyzer/analyzer_test.go

@@ -1,19 +1,63 @@
 package analyzer_test
 
 import (
-	"github.com/Crocmagnon/fatcontext/pkg/analyzer"
-	"golang.org/x/tools/go/analysis/analysistest"
-	"os"
-	"path/filepath"
 	"testing"
+
+	"golang.org/x/tools/go/analysis/analysistest"
+
+	"github.com/Crocmagnon/fatcontext/pkg/analyzer"
 )
 
-func TestAll(t *testing.T) {
-	wd, err := os.Getwd()
-	if err != nil {
-		t.Fatalf("Failed to get wd: %s", err)
+func TestAnalyzer(t *testing.T) {
+	testCases := []struct {
+		desc    string
+		dir     string
+		options map[string]string
+	}{
+		{
+			desc: "no func decl",
+			dir:  "common",
+		},
+		{
+			desc: "no func decl",
+			dir:  "no_structpointer",
+		},
+		{
+			desc: "func decl",
+			dir:  "common",
+			options: map[string]string{
+				analyzer.FlagCheckStructPointers: "true",
+			},
+		},
+		{
+			desc: "func decl",
+			dir:  "structpointer",
+			options: map[string]string{
+				analyzer.FlagCheckStructPointers: "true",
+			},
+		},
 	}
-	testdata := filepath.Join(filepath.Dir(filepath.Dir(wd)), "testdata")
 
-	analysistest.Run(t, testdata, analyzer.Analyzer, "./...")
+	for _, test := range testCases {
+		t.Run(test.desc+"_"+test.dir, func(t *testing.T) {
+			t.Parallel()
+
+			a := analyzer.NewAnalyzer()
+
+			for k, v := range test.options {
+				err := a.Flags.Set(k, v)
+				if err != nil {
+					t.Fatal(err)
+				}
+			}
+
+			analysistest.RunWithSuggestedFixes(t, analysistest.TestData(), a, test.dir)
+		})
+	}
+}
+
+func TestAnalyzer_cgo(t *testing.T) {
+	a := analyzer.NewAnalyzer()
+
+	analysistest.Run(t, analysistest.TestData(), a, "cgo")
 }

pkg/analyzer/testdata/src/cgo/cgo.go

@@ -1,8 +1,27 @@
-package src
+package cgo
 
-import "context"
+/*
+ #include <stdio.h>
+ #include <stdlib.h>
 
-func example() {
+ void myprint(char* s) {
+ 	printf("%d\n", s);
+ }
+*/
+import "C"
+
+import (
+	"context"
+	"unsafe"
+)
+
+func _() {
+	cs := C.CString("Hello from stdio\n")
+	C.myprint(cs)
+	C.free(unsafe.Pointer(cs))
+}
+
+func _() {
 	ctx := context.Background()
 
 	for i := 0; i < 10; i++ {

pkg/analyzer/testdata/src/common/example.go

@@ -0,0 +1,251 @@
+package common
+
+import (
+	"context"
+	"testing"
+)
+
+func example() {
+	ctx := context.Background()
+
+	for i := 0; i < 10; i++ {
+		ctx := context.WithValue(ctx, "key", i)
+		ctx = context.WithValue(ctx, "other", "val")
+	}
+
+	for i := 0; i < 10; i++ {
+		ctx = context.WithValue(ctx, "key", i) // want "nested context in loop"
+		ctx = context.WithValue(ctx, "other", "val")
+	}
+
+	for item := range []string{"one", "two", "three"} {
+		ctx = wrapContext(ctx) // want "nested context in loop"
+		ctx := context.WithValue(ctx, "key", item)
+		ctx = wrapContext(ctx)
+	}
+
+	for {
+		ctx = wrapContext(ctx) // want "nested context in loop"
+		break
+	}
+
+	// not fooled by shadowing in nested blocks
+	for {
+		err := doSomething()
+		if err != nil {
+			ctx := wrapContext(ctx)
+			ctx = wrapContext(ctx)
+		}
+
+		switch err {
+		case nil:
+			ctx := wrapContext(ctx)
+			ctx = wrapContext(ctx)
+		default:
+			ctx := wrapContext(ctx)
+			ctx = wrapContext(ctx)
+		}
+
+		{
+			ctx := wrapContext(ctx)
+			ctx = wrapContext(ctx)
+		}
+
+		select {
+		case <-ctx.Done():
+			ctx := wrapContext(ctx)
+			ctx = wrapContext(ctx)
+		default:
+		}
+
+		ctx = wrapContext(ctx) // want "nested context in loop"
+
+		break
+	}
+
+	// detects contexts wrapped in function literals (this is risky as function literals can be called multiple times)
+	_ = func() {
+		ctx = wrapContext(ctx) // want "nested context in function literal"
+	}
+
+	// this is fine because the context is created in the loop
+	for {
+		if ctx := context.Background(); doSomething() != nil {
+			ctx = wrapContext(ctx)
+		}
+	}
+
+	for {
+		ctx2 := context.Background()
+		ctx = wrapContext(ctx) // want "nested context in loop"
+		if doSomething() != nil {
+			ctx2 = wrapContext(ctx2)
+		}
+	}
+}
+
+func wrapContext(ctx context.Context) context.Context {
+	return context.WithoutCancel(ctx)
+}
+
+func doSomething() error {
+	return nil
+}
+
+// storing contexts in a struct isn't recommended, but local copies of a non-pointer struct should act like local copies of a context.
+func inStructs(ctx context.Context) {
+	for i := 0; i < 10; i++ {
+		c := struct{ Ctx context.Context }{ctx}
+		c.Ctx = context.WithValue(c.Ctx, "key", i)
+		c.Ctx = context.WithValue(c.Ctx, "other", "val")
+	}
+
+	for i := 0; i < 10; i++ {
+		c := []struct{ Ctx context.Context }{{ctx}}
+		c[0].Ctx = context.WithValue(c[0].Ctx, "key", i)
+		c[0].Ctx = context.WithValue(c[0].Ctx, "other", "val")
+	}
+
+	c := struct{ Ctx context.Context }{ctx}
+	for i := 0; i < 10; i++ {
+		c := c
+		c.Ctx = context.WithValue(c.Ctx, "key", i)
+		c.Ctx = context.WithValue(c.Ctx, "other", "val")
+	}
+
+	pc := &struct{ Ctx context.Context }{ctx}
+	for i := 0; i < 10; i++ {
+		c := pc
+		c.Ctx = context.WithValue(c.Ctx, "key", i) // want "nested context in loop"
+		c.Ctx = context.WithValue(c.Ctx, "other", "val")
+	}
+
+	r := []struct{ Ctx context.Context }{{ctx}}
+	for i := 0; i < 10; i++ {
+		r[0].Ctx = context.WithValue(r[0].Ctx, "key", i) // want "nested context in loop"
+		r[0].Ctx = context.WithValue(r[0].Ctx, "other", "val")
+	}
+
+	rp := []*struct{ Ctx context.Context }{{ctx}}
+	for i := 0; i < 10; i++ {
+		rp[0].Ctx = context.WithValue(rp[0].Ctx, "key", i) // want "nested context in loop"
+		rp[0].Ctx = context.WithValue(rp[0].Ctx, "other", "val")
+	}
+}
+
+func inVariousNestedBlocks(ctx context.Context) {
+	for {
+		err := doSomething()
+		if err != nil {
+			ctx = wrapContext(ctx) // want "nested context in loop"
+		}
+
+		break
+	}
+
+	for {
+		err := doSomething()
+		if err != nil {
+			if true {
+				ctx = wrapContext(ctx) // want "nested context in loop"
+			}
+		}
+
+		break
+	}
+
+	for {
+		err := doSomething()
+		switch err {
+		case nil:
+			ctx = wrapContext(ctx) // want "nested context in loop"
+		}
+
+		break
+	}
+
+	for {
+		err := doSomething()
+		switch err {
+		default:
+			ctx = wrapContext(ctx) // want "nested context in loop"
+		}
+
+		break
+	}
+
+	for {
+		ctx := wrapContext(ctx)
+
+		err := doSomething()
+		if err != nil {
+			ctx = wrapContext(ctx)
+		}
+
+		break
+	}
+
+	for {
+		{
+			ctx = wrapContext(ctx) // want "nested context in loop"
+		}
+
+		break
+	}
+
+	for {
+		select {
+		case <-ctx.Done():
+			ctx = wrapContext(ctx) // want "nested context in loop"
+		default:
+		}
+
+		break
+	}
+}
+
+// this middleware could run on every request, bloating the request parameter level context and causing a memory leak
+func badMiddleware(ctx context.Context) func() error {
+	return func() error {
+		ctx = wrapContext(ctx) // want "nested context in function literal"
+		return doSomethingWithCtx(ctx)
+	}
+}
+
+// this middleware is fine, as it doesn't modify the context of parent function
+func okMiddleware(ctx context.Context) func() error {
+	return func() error {
+		ctx := wrapContext(ctx)
+		return doSomethingWithCtx(ctx)
+	}
+}
+
+// this middleware is fine, as it only modifies the context passed to it
+func okMiddleware2(ctx context.Context) func(ctx context.Context) error {
+	return func(ctx context.Context) error {
+		ctx = wrapContext(ctx)
+		return doSomethingWithCtx(ctx)
+	}
+}
+
+func doSomethingWithCtx(ctx context.Context) error {
+	return nil
+}
+
+func testCasesInit(t *testing.T) {
+	cases := []struct {
+		ctx context.Context
+	}{
+		{},
+		{
+			ctx: context.WithValue(context.Background(), "key", "value"),
+		},
+	}
+	for _, tc := range cases {
+		t.Run("some test", func(t *testing.T) {
+			if tc.ctx == nil {
+				tc.ctx = context.Background()
+			}
+		})
+	}
+}

pkg/analyzer/testdata/src/common/example.go.golden

@@ -0,0 +1,251 @@
+package common
+
+import (
+	"context"
+	"testing"
+)
+
+func example() {
+	ctx := context.Background()
+
+	for i := 0; i < 10; i++ {
+		ctx := context.WithValue(ctx, "key", i)
+		ctx = context.WithValue(ctx, "other", "val")
+	}
+
+	for i := 0; i < 10; i++ {
+		ctx := context.WithValue(ctx, "key", i) // want "nested context in loop"
+		ctx = context.WithValue(ctx, "other", "val")
+	}
+
+	for item := range []string{"one", "two", "three"} {
+		ctx := wrapContext(ctx) // want "nested context in loop"
+		ctx := context.WithValue(ctx, "key", item)
+		ctx = wrapContext(ctx)
+	}
+
+	for {
+		ctx := wrapContext(ctx) // want "nested context in loop"
+		break
+	}
+
+	// not fooled by shadowing in nested blocks
+	for {
+		err := doSomething()
+		if err != nil {
+			ctx := wrapContext(ctx)
+			ctx = wrapContext(ctx)
+		}
+
+		switch err {
+		case nil:
+			ctx := wrapContext(ctx)
+			ctx = wrapContext(ctx)
+		default:
+			ctx := wrapContext(ctx)
+			ctx = wrapContext(ctx)
+		}
+
+		{
+			ctx := wrapContext(ctx)
+			ctx = wrapContext(ctx)
+		}
+
+		select {
+		case <-ctx.Done():
+			ctx := wrapContext(ctx)
+			ctx = wrapContext(ctx)
+		default:
+		}
+
+		ctx := wrapContext(ctx) // want "nested context in loop"
+
+		break
+	}
+
+	// detects contexts wrapped in function literals (this is risky as function literals can be called multiple times)
+	_ = func() {
+		ctx := wrapContext(ctx) // want "nested context in function literal"
+	}
+
+	// this is fine because the context is created in the loop
+	for {
+		if ctx := context.Background(); doSomething() != nil {
+			ctx = wrapContext(ctx)
+		}
+	}
+
+	for {
+		ctx2 := context.Background()
+		ctx := wrapContext(ctx) // want "nested context in loop"
+		if doSomething() != nil {
+			ctx2 = wrapContext(ctx2)
+		}
+	}
+}
+
+func wrapContext(ctx context.Context) context.Context {
+	return context.WithoutCancel(ctx)
+}
+
+func doSomething() error {
+	return nil
+}
+
+// storing contexts in a struct isn't recommended, but local copies of a non-pointer struct should act like local copies of a context.
+func inStructs(ctx context.Context) {
+	for i := 0; i < 10; i++ {
+		c := struct{ Ctx context.Context }{ctx}
+		c.Ctx = context.WithValue(c.Ctx, "key", i)
+		c.Ctx = context.WithValue(c.Ctx, "other", "val")
+	}
+
+	for i := 0; i < 10; i++ {
+		c := []struct{ Ctx context.Context }{{ctx}}
+		c[0].Ctx = context.WithValue(c[0].Ctx, "key", i)
+		c[0].Ctx = context.WithValue(c[0].Ctx, "other", "val")
+	}
+
+	c := struct{ Ctx context.Context }{ctx}
+	for i := 0; i < 10; i++ {
+		c := c
+		c.Ctx = context.WithValue(c.Ctx, "key", i)
+		c.Ctx = context.WithValue(c.Ctx, "other", "val")
+	}
+
+	pc := &struct{ Ctx context.Context }{ctx}
+	for i := 0; i < 10; i++ {
+		c := pc
+		c.Ctx := context.WithValue(c.Ctx, "key", i) // want "nested context in loop"
+		c.Ctx = context.WithValue(c.Ctx, "other", "val")
+	}
+
+	r := []struct{ Ctx context.Context }{{ctx}}
+	for i := 0; i < 10; i++ {
+		r[0].Ctx := context.WithValue(r[0].Ctx, "key", i) // want "nested context in loop"
+		r[0].Ctx = context.WithValue(r[0].Ctx, "other", "val")
+	}
+
+	rp := []*struct{ Ctx context.Context }{{ctx}}
+	for i := 0; i < 10; i++ {
+		rp[0].Ctx := context.WithValue(rp[0].Ctx, "key", i) // want "nested context in loop"
+		rp[0].Ctx = context.WithValue(rp[0].Ctx, "other", "val")
+	}
+}
+
+func inVariousNestedBlocks(ctx context.Context) {
+	for {
+		err := doSomething()
+		if err != nil {
+			ctx := wrapContext(ctx) // want "nested context in loop"
+		}
+
+		break
+	}
+
+	for {
+		err := doSomething()
+		if err != nil {
+			if true {
+				ctx := wrapContext(ctx) // want "nested context in loop"
+			}
+		}
+
+		break
+	}
+
+	for {
+		err := doSomething()
+		switch err {
+		case nil:
+			ctx := wrapContext(ctx) // want "nested context in loop"
+		}
+
+		break
+	}
+
+	for {
+		err := doSomething()
+		switch err {
+		default:
+			ctx := wrapContext(ctx) // want "nested context in loop"
+		}
+
+		break
+	}
+
+	for {
+		ctx := wrapContext(ctx)
+
+		err := doSomething()
+		if err != nil {
+			ctx = wrapContext(ctx)
+		}
+
+		break
+	}
+
+	for {
+		{
+			ctx := wrapContext(ctx) // want "nested context in loop"
+		}
+
+		break
+	}
+
+	for {
+		select {
+		case <-ctx.Done():
+			ctx := wrapContext(ctx) // want "nested context in loop"
+		default:
+		}
+
+		break
+	}
+}
+
+// this middleware could run on every request, bloating the request parameter level context and causing a memory leak
+func badMiddleware(ctx context.Context) func() error {
+	return func() error {
+		ctx := wrapContext(ctx) // want "nested context in function literal"
+		return doSomethingWithCtx(ctx)
+	}
+}
+
+// this middleware is fine, as it doesn't modify the context of parent function
+func okMiddleware(ctx context.Context) func() error {
+	return func() error {
+		ctx := wrapContext(ctx)
+		return doSomethingWithCtx(ctx)
+	}
+}
+
+// this middleware is fine, as it only modifies the context passed to it
+func okMiddleware2(ctx context.Context) func(ctx context.Context) error {
+	return func(ctx context.Context) error {
+		ctx = wrapContext(ctx)
+		return doSomethingWithCtx(ctx)
+	}
+}
+
+func doSomethingWithCtx(ctx context.Context) error {
+	return nil
+}
+
+func testCasesInit(t *testing.T) {
+	cases := []struct {
+		ctx context.Context
+	}{
+		{},
+		{
+			ctx: context.WithValue(context.Background(), "key", "value"),
+		},
+	}
+	for _, tc := range cases {
+		t.Run("some test", func(t *testing.T) {
+			if tc.ctx == nil {
+				tc.ctx = context.Background()
+			}
+		})
+	}
+}

pkg/analyzer/testdata/src/no_structpointer/example.go

@@ -0,0 +1,23 @@
+package common
+
+import (
+	"context"
+)
+
+type Container struct {
+	Ctx context.Context
+}
+
+func something() func(*Container) {
+	return func(r *Container) {
+		ctx := r.Ctx
+		ctx = context.WithValue(ctx, "key", "val")
+		r.Ctx = ctx
+	}
+}
+
+func blah(r *Container) {
+	ctx := r.Ctx
+	ctx = context.WithValue(ctx, "key", "val")
+	r.Ctx = ctx
+}

pkg/analyzer/testdata/src/structpointer/example.go

@@ -0,0 +1,23 @@
+package common
+
+import (
+	"context"
+)
+
+type Container struct {
+	Ctx context.Context
+}
+
+func something() func(*Container) {
+	return func(r *Container) {
+		ctx := r.Ctx
+		ctx = context.WithValue(ctx, "key", "val")
+		r.Ctx = ctx // want "potential nested context in struct pointer"
+	}
+}
+
+func blah(r *Container) {
+	ctx := r.Ctx
+	ctx = context.WithValue(ctx, "key", "val")
+	r.Ctx = ctx // want "potential nested context in struct pointer"
+}