build(deps): bump golangci/golangci-lint-action

Bumps the github-actions group with 1 update: [golangci/golangci-lint-action](https://github.com/golangci/golangci-lint-action).


Updates `golangci/golangci-lint-action` from 6 to 7
- [Release notes](https://github.com/golangci/golangci-lint-action/releases)
- [Commits](https://github.com/golangci/golangci-lint-action/compare/v6...v7)

---
updated-dependencies:
- dependency-name: golangci/golangci-lint-action
  dependency-version: '7'
  dependency-type: direct:production
  update-type: version-update:semver-major
  dependency-group: github-actions
...

Signed-off-by: dependabot[bot] <support@github.com>

.github/dependabot.yml

@@ -6,6 +6,10 @@ updates:
     directory: "/"
     schedule:
       interval: "monthly"
+    groups:
+      github-actions:
+        patterns:
+          - "*"  # Group all updates into a single larger pull request.
   - package-ecosystem: "gomod"
     directory: "/"
     schedule:

.github/workflows/go.yml

@@ -16,7 +16,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        go: ['1.22', '1.23']
+        go: [stable, oldstable]
         os: [macos-latest, windows-latest, ubuntu-latest]
     name: build
     runs-on: ${{ matrix.os }}
@@ -29,3 +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: ['1.22', '1.23']
+        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@v6
+        uses: golangci/golangci-lint-action@v7
         with:
           version: latest

.github/workflows/goreleaser.yml

@@ -17,6 +17,8 @@ jobs:
           fetch-depth: 0
       - name: Set up Go
         uses: actions/setup-go@v5
+        with:
+          go-version: stable
       - name: Run GoReleaser
         uses: goreleaser/goreleaser-action@v6
         with:

.golangci.yml

@@ -1,3 +1,18 @@
+version: "2"
 issues:
-  exclude-dirs:
+  fix: true
-    - contrib
+linters:
+  default: all
+  disable:
+    - depguard
+    - exhaustruct
+formatters:
+  enable:
+    - goimports
+    - gofmt
+    - gofumpt
+    - golines
+  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: 2
-version: 1
 
 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: v4.6.0
+    rev: v5.0.0
     hooks:
       - id: check-yaml
       - id: end-of-file-fixer
       - id: trailing-whitespace
   - repo: https://github.com/golangci/golangci-lint
-    rev: v1.60.3
+    rev: v2.0.2
     hooks:
       - id: golangci-lint-full
   - repo: local

README.md

@@ -1,5 +1,9 @@
 # fatcontext
 
+[![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/
 
@@ -12,8 +16,6 @@ go install github.com/Crocmagnon/fatcontext/cmd/fatcontext@latest
 fatcontext ./...
 ```
 
-There are no specific configuration options or custom command-line flags.
-
 ## Example
 
 ```go

cmd/fatcontext/main.go

@@ -1,10 +1,12 @@
+// Package main runs the analyzer. It's the CLI entrypoint.
 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

@@ -1,10 +1,10 @@
 module github.com/Crocmagnon/fatcontext
 
-go 1.22.0
+go 1.23.0
 
-require golang.org/x/tools v0.23.0
+require golang.org/x/tools v0.31.0
 
 require (
-	golang.org/x/mod v0.19.0 // indirect
+	golang.org/x/mod v0.24.0 // indirect
-	golang.org/x/sync v0.7.0 // indirect
+	golang.org/x/sync v0.12.0 // indirect
 )

go.sum

@@ -1,8 +1,8 @@
 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 v0.19.0 h1:fEdghXQSo20giMthA7cd28ZC+jts4amQ3YMXiP5oMQ8=
+golang.org/x/mod v0.24.0 h1:ZfthKaKaT4NrhGVZHO1/WDTwGES4De8KtWO0SIbNJMU=
-golang.org/x/mod v0.19.0/go.mod h1:hTbmBsO62+eylJbnUtE2MGJUyE7QWk4xUqPFrRgJ+7c=
+golang.org/x/mod v0.24.0/go.mod h1:IXM97Txy2VM4PJ3gI61r1YEk/gAj6zAHN3AdZt6S9Ww=
-golang.org/x/sync v0.7.0 h1:YsImfSBoP9QPYL0xyKJPq0gcaJdG3rInoqxTWbfQu9M=
+golang.org/x/sync v0.12.0 h1:MHc5BpPuC30uJk597Ri8TV3CNZcTLu6B6z4lJy+g6Jw=
-golang.org/x/sync v0.7.0/go.mod h1:Czt+wKu1gCyEFDUtn0jG5QVvpJ6rzVqr5aXyt9drQfk=
+golang.org/x/sync v0.12.0/go.mod h1:1dzgHSNfp02xaA81J2MS99Qcpr2w7fw1gpm99rleRqA=
-golang.org/x/tools v0.23.0 h1:SGsXPZ+2l4JsgaCKkx+FQ9YZ5XEtA1GZYuoDjenLjvg=
+golang.org/x/tools v0.31.0 h1:0EedkvKDbh+qistFTd0Bcwe/YLh4vHwWEkiI0toFIBU=
-golang.org/x/tools v0.23.0/go.mod h1:pnu6ufv6vQkll6szChhK3C3L/ruaIv5eBeztNG8wtsI=
+golang.org/x/tools v0.31.0/go.mod h1:naFTU+Cev749tSJRXJlna0T3WxKvb1kWEx15xA4SdmQ=

pkg/analyzer/analyzer.go

@@ -1,35 +1,69 @@
+// Package analyzer contains everything related to the linter analysis.
 package analyzer
 
 import (
 	"bytes"
 	"errors"
+	"flag"
 	"fmt"
 	"go/ast"
 	"go/printer"
 	"go/token"
-	"go/types"
+	"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{
+// FlagCheckStructPointers is a possible flag for the analyzer.
+// Exported to make it usable in golangci-lint.
+const FlagCheckStructPointers = "check-struct-pointers"
+
+// NewAnalyzer returns a fatcontext analyzer.
+func NewAnalyzer() *analysis.Analyzer {
+	rnnr := &runner{}
+
+	flags := flag.NewFlagSet("fatcontext", flag.ExitOnError)
+	flags.BoolVar(&rnnr.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:      run,
+		Run:      rnnr.run,
+		Flags:    *flags,
 		Requires: []*analysis.Analyzer{inspect.Analyzer},
+	}
 }
 
-var errUnknown = errors.New("unknown node type")
+var (
+	errUnknown         = errors.New("unknown node type")
+	errInvalidAnalysis = errors.New("invalid analysis")
+)
 
-func run(pass *analysis.Pass) (interface{}, error) {
+const (
-	inspctr := pass.ResultOf[inspect.Analyzer].(*inspector.Inspector)
+	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, typeValid := pass.ResultOf[inspect.Analyzer].(*inspector.Inspector)
+	if !typeValid {
+		return nil, errInvalidAnalysis
+	}
 
 	nodeFilter := []ast.Node{
 		(*ast.ForStmt)(nil),
 		(*ast.RangeStmt)(nil),
 		(*ast.FuncLit)(nil),
+		(*ast.FuncDecl)(nil),
 	}
 
 	inspctr.Preorder(nodeFilter, func(node ast.Node) {
@@ -38,11 +72,47 @@ func run(pass *analysis.Pass) (interface{}, error) {
 			return
 		}
 
+		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 //nolint:nilnil // we have no result to send to other analyzers
+}
+
+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
+	}
+
 	suggestedStmt := ast.AssignStmt{
 		Lhs:    assignStmt.Lhs,
 		TokPos: assignStmt.TokPos,
@@ -59,47 +129,43 @@ func run(pass *analysis.Pass) (interface{}, error) {
 				{
 					Pos:     assignStmt.Pos(),
 					End:     assignStmt.End(),
-						NewText: []byte(suggested),
+					NewText: suggested,
 				},
 			},
 		})
 	}
 
-		pass.Report(analysis.Diagnostic{
+	return fixes
-			Pos:            assignStmt.Pos(),
-			Message:        getReportMessage(node),
-			SuggestedFixes: fixes,
-		})
-	})
-
-	return nil, nil
 }
 
-func getReportMessage(node ast.Node) string {
+func getCategory(pass *analysis.Pass, node ast.Node, assignStmt *ast.AssignStmt) string {
 	switch node.(type) {
 	case *ast.ForStmt, *ast.RangeStmt:
-		return "nested context in loop"
+		return categoryInLoop
-	case *ast.FuncLit:
+	}
-		return "nested context in function literal"
+
+	if isPointer(pass, assignStmt.Lhs[0]) {
+		return categoryInStructPointer
+	}
+
+	switch node.(type) {
+	case *ast.FuncLit, *ast.FuncDecl:
+		return categoryInFuncLit
 	default:
-		return "unsupported nested context type"
+		return categoryUnsupported
 	}
 }
 
 func getBody(node ast.Node) (*ast.BlockStmt, error) {
-	forStmt, ok := node.(*ast.ForStmt)
+	switch typedNode := node.(type) {
-	if ok {
+	case *ast.ForStmt:
-		return forStmt.Body, nil
+		return typedNode.Body, nil
-	}
+	case *ast.RangeStmt:
-
+		return typedNode.Body, nil
-	rangeStmt, ok := node.(*ast.RangeStmt)
+	case *ast.FuncLit:
-	if ok {
+		return typedNode.Body, nil
-		return rangeStmt.Body, nil
+	case *ast.FuncDecl:
-	}
+		return typedNode.Body, nil
-
-	funcLit, ok := node.(*ast.FuncLit)
-	if ok {
-		return funcLit.Body, nil
 	}
 
 	return nil, errUnknown
@@ -108,47 +174,10 @@ func getBody(node ast.Node) (*ast.BlockStmt, error) {
 func findNestedContext(pass *analysis.Pass, node ast.Node, stmts []ast.Stmt) *ast.AssignStmt {
 	for _, stmt := range stmts {
 		// Recurse if necessary
-		if inner, ok := stmt.(*ast.BlockStmt); ok {
+		stmtList := getStmtList(stmt)
-			found := findNestedContext(pass, node, inner.List)
+		if found := findNestedContext(pass, node, stmtList); found != nil {
-			if found != nil {
 			return found
 		}
-		}
-
-		if inner, ok := stmt.(*ast.IfStmt); ok {
-			found := findNestedContext(pass, node, inner.Body.List)
-			if found != nil {
-				return found
-			}
-		}
-
-		if inner, ok := stmt.(*ast.SwitchStmt); ok {
-			found := findNestedContext(pass, node, inner.Body.List)
-			if found != nil {
-				return found
-			}
-		}
-
-		if inner, ok := stmt.(*ast.CaseClause); ok {
-			found := findNestedContext(pass, node, inner.Body)
-			if found != nil {
-				return found
-			}
-		}
-
-		if inner, ok := stmt.(*ast.SelectStmt); ok {
-			found := findNestedContext(pass, node, inner.Body.List)
-			if found != nil {
-				return found
-			}
-		}
-
-		if inner, ok := stmt.(*ast.CommClause); ok {
-			found := findNestedContext(pass, node, inner.Body)
-			if found != nil {
-				return found
-			}
-		}
 
 		// Actually check for nested context
 		assignStmt, ok := stmt.(*ast.AssignStmt)
@@ -169,13 +198,18 @@ func findNestedContext(pass *analysis.Pass, node ast.Node, stmts []ast.Stmt) *as
 			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 lhs := getRootIdent(pass, assignStmt.Lhs[0]); lhs != nil {
+		if isWithinLoop(assignStmt.Lhs[0], node, pass) {
-			if obj := pass.TypesInfo.ObjectOf(lhs); obj != nil {
+			continue
-				if checkObjectScopeWithinNode(obj.Parent(), node) {
-					continue // definition is within the loop
-				}
-			}
 		}
 
 		return assignStmt
@@ -184,41 +218,99 @@ func findNestedContext(pass *analysis.Pass, node ast.Node, stmts []ast.Stmt) *as
 	return nil
 }
 
-func checkObjectScopeWithinNode(scope *types.Scope, node ast.Node) bool {
+func getStmtList(stmt ast.Stmt) []ast.Stmt {
+	switch typedStmt := stmt.(type) {
+	case *ast.BlockStmt:
+		return typedStmt.List
+	case *ast.IfStmt:
+		return typedStmt.Body.List
+	case *ast.SwitchStmt:
+		return typedStmt.Body.List
+	case *ast.CaseClause:
+		return typedStmt.Body
+	case *ast.SelectStmt:
+		return typedStmt.Body.List
+	case *ast.CommClause:
+		return typedStmt.Body
+	}
+
+	return nil
+}
+
+// render returns the pretty-print of the given node.
+func render(fset *token.FileSet, x interface{}) ([]byte, error) {
+	var buf bytes.Buffer
+	if err := printer.Fprint(&buf, fset, x); err != nil {
+		return nil, fmt.Errorf("printing node: %w", err)
+	}
+
+	return buf.Bytes(), nil
+}
+
+func isContextFunction(exp ast.Expr, fnName ...string) bool {
+	call, typeValid := exp.(*ast.CallExpr)
+	if !typeValid {
+		return false
+	}
+
+	selector, typeValid := call.Fun.(*ast.SelectorExpr)
+	if !typeValid {
+		return false
+	}
+
+	ident, typeValid := selector.X.(*ast.Ident)
+	if !typeValid {
+		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
 	}
 
-	if scope.Pos() >= node.Pos() && scope.End() <= node.End() {
+	return scope.Pos() >= node.Pos() && scope.End() <= node.End()
-		return true
-	}
-
-	return false
 }
 
 func getRootIdent(pass *analysis.Pass, node ast.Node) *ast.Ident {
 	for {
-		switch n := node.(type) {
+		switch typedNode := node.(type) {
 		case *ast.Ident:
-			return n
+			return typedNode
 		case *ast.IndexExpr:
-			node = n.X
+			node = typedNode.X
 		case *ast.SelectorExpr:
-			if sel, ok := pass.TypesInfo.Selections[n]; ok && sel.Indirect() {
+			if sel, ok := pass.TypesInfo.Selections[typedNode]; ok && sel.Indirect() {
 				return nil // indirected (pointer) roots don't imply a (safe) copy
 			}
-			node = n.X
+
+			node = typedNode.X
 		default:
 			return nil
 		}
 	}
 }
 
-// render returns the pretty-print of the given node
+func isPointer(pass *analysis.Pass, exp ast.Node) bool {
-func render(fset *token.FileSet, x interface{}) (string, error) {
+	switch n := exp.(type) { //nolint:gocritic // Future-proofing with switch instead of if.
-	var buf bytes.Buffer
+	case *ast.SelectorExpr:
-	if err := printer.Fprint(&buf, fset, x); err != nil {
+		sel, ok := pass.TypesInfo.Selections[n]
-		return "", fmt.Errorf("printing node: %w", err)
+
+		return ok && sel.Indirect()
 	}
-	return buf.String(), nil
+
+	return false
 }

pkg/analyzer/analyzer_test.go

@@ -1,19 +1,67 @@
 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) {
+func TestAnalyzer(t *testing.T) {
-	wd, err := os.Getwd()
+	t.Parallel()
-	if err != nil {
-		t.Fatalf("Failed to get wd: %s", err)
-	}
-	testdata := filepath.Join(filepath.Dir(filepath.Dir(wd)), "testdata")
 
-	analysistest.Run(t, testdata, analyzer.Analyzer, "./...")
+	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",
+			},
+		},
+	}
+
+	for _, test := range testCases {
+		t.Run(test.desc+"_"+test.dir, func(t *testing.T) {
+			t.Parallel()
+
+			anlzr := analyzer.NewAnalyzer()
+
+			for k, v := range test.options {
+				err := anlzr.Flags.Set(k, v)
+				if err != nil {
+					t.Fatal(err)
+				}
+			}
+
+			analysistest.RunWithSuggestedFixes(t, analysistest.TestData(), anlzr, test.dir)
+		})
+	}
+}
+
+func TestAnalyzer_cgo(t *testing.T) {
+	t.Parallel()
+
+	a := analyzer.NewAnalyzer()
+
+	analysistest.Run(t, analysistest.TestData(), a, "cgo")
 }

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

@@ -0,0 +1,51 @@
+package cgo
+
+/*
+ #include <stdio.h>
+ #include <stdlib.h>
+
+ 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++ {
+		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
+	}
+}
+
+func wrapContext(ctx context.Context) context.Context {
+	return context.WithoutCancel(ctx)
+}

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

@@ -1,6 +1,9 @@
-package src
+package common
 
-import "context"
+import (
+	"context"
+	"testing"
+)
 
 func example() {
 	ctx := context.Background()
@@ -228,3 +231,21 @@ func okMiddleware2(ctx context.Context) func(ctx context.Context) error {
 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"
+}