tools/syz-linter: define context.Context usage rules

1. It is the first parameter everywhere except tests.
2. It is the second param in the tests.
3. It is always named ctx.
4. For the cases with multiple contexts recommend to opt-out syz-linter.

Author: tarasmadan

tools/syz-linter/linter.go

@@ -68,6 +68,7 @@ func run(p *analysis.Pass) (any, error) {
 				pass.checkStringLenCompare(n)
 			case *ast.FuncDecl:
 				pass.checkFuncArgs(n)
+				pass.checkContextArgs(n)
 			case *ast.CallExpr:
 				pass.checkFlagDefinition(n)
 				pass.checkLogErrorFormat(n)
@@ -229,6 +230,43 @@ func (pass *Pass) reportFuncArgs(fields []*ast.Field, first, last int) {
 	pass.report(fields[first], "Use '%v %v'", names[2:], pass.typ(fields[first].Type))
 }
 
+func (pass *Pass) checkContextArgs(n *ast.FuncDecl) {
+	if n.Type.Params == nil {
+		return
+	}
+	expectedCtxPos := 0
+	if len(n.Type.Params.List) > 0 {
+		firstField := n.Type.Params.List[0]
+		if strings.HasSuffix(pass.typ(firstField.Type), "*testing.T") {
+			expectedCtxPos = 1
+		}
+	}
+	for fieldPos, field := range n.Type.Params.List {
+		isContext := pass.typ(field.Type) == "context.Context"
+		if isContext {
+			if fieldPos != expectedCtxPos {
+				if expectedCtxPos == 0 {
+					pass.report(field, "Context must be the first argument")
+				} else {
+					pass.report(field, "Context must be the second argument")
+				}
+			}
+			// Every type group may have a few variables.
+			if len(field.Names) > 1 {
+				// A few contexts are passed to the function
+				// It is very rare. Let's use nolint:syz-linter to opt-out.
+				pass.report(field, "multiple Contexts are passed, use nolint:syz-linter")
+			}
+			if len(field.Names) == 1 {
+				name := field.Names[0]
+				if name.Name != "ctx" && name.Name != "_" {
+					pass.report(name, "Context variable must be named 'ctx' or '_'")
+				}
+			}
+		}
+	}
+}
+
 func (pass *Pass) checkFlagDefinition(n *ast.CallExpr) {
 	fun, ok := n.Fun.(*ast.SelectorExpr)
 	if !ok {

tools/syz-linter/testdata/src/lintertest/lintertest.go

@@ -4,6 +4,7 @@
 package lintertest
 
 import (
+	"context"
 	"flag"
 	"fmt"
 	"log"
@@ -152,3 +153,24 @@ func anyInterface() interface{} {	// want "Use any instead of interface{}"
 	func(any) {} (y)
 	return v
 }
+
+func contextArgsGood1(ctx context.Context) {
+}
+
+func contextArgsBad1(c context.Context) { // want "Context variable must be named 'ctx'"
+}
+
+func contextArgsBad2(a int, ctx context.Context) { // want "Context must be the first argument"
+}
+
+func contextArgsGood2(ctx context.Context, a int) {
+}
+
+func TestContextArgsGood(t *testing.T, ctx context.Context) {
+}
+
+func TestContextArgsBad1(t *testing.T, c context.Context) { // want "Context variable must be named 'ctx'"
+}
+
+func TestContextArgsBad2(t *testing.T, a int, ctx context.Context) { // want "Context must be the second argument"
+}