Allow per test rules in neverallow_test.go

Makes testing individual rules easier by allowing them to be specified
per test rather than having to add them to the global defaults.

Bug: 138428610
Test: m nothing
Change-Id: Ic65a55dee2a02b6d33254753c047295dd5804408

android/neverallow.go

@@ -177,7 +177,7 @@ func neverallowMutator(ctx BottomUpMutatorContext) {
 
 	osClass := ctx.Module().Target().Os.Class
 
-	for _, r := range neverallows {
+	for _, r := range neverallowRules(ctx.Config()) {
 		n := r.(*rule)
 		if !n.appliesToPath(dir) {
 			continue
@@ -551,3 +551,19 @@ func matchValue(value reflect.Value, check func(string) bool) bool {
 
 	panic("Can't handle type: " + value.Kind().String())
 }
+
+var neverallowRulesKey = NewOnceKey("neverallowRules")
+
+func neverallowRules(config Config) []Rule {
+	return config.Once(neverallowRulesKey, func() interface{} {
+		// No test rules were set by setTestNeverallowRules, use the global rules
+		return neverallows
+	}).([]Rule)
+}
+
+// Overrides the default neverallow rules for the supplied config.
+//
+// For testing only.
+func setTestNeverallowRules(config Config, testRules []Rule) {
+	config.Once(neverallowRulesKey, func() interface{} { return testRules })
+}

android/neverallow_test.go

@@ -20,16 +20,19 @@ import (
 	"github.com/google/blueprint"
 )
 
-func init() {
-	// Add extra rules needed for testing.
-	AddNeverAllowRules(
-		NeverAllow().InDirectDeps("not_allowed_in_direct_deps"),
-	)
-}
-
 var neverallowTests = []struct {
+	// The name of the test.
 	name string
+
+	// Optional test specific rules. If specified then they are used instead of the default rules.
+	rules []Rule
+
+	// Additional contents to add to the virtual filesystem used by the tests.
 	fs map[string][]byte
+
+	// The expected error patterns. If empty then no errors are expected, otherwise each error
+	// reported must be matched by at least one of these patterns. A pattern matches if the error
+	// message contains the pattern. A pattern does not have to match the whole error message.
 	expectedErrors []string
 }{
 	// Test General Functionality
@@ -37,6 +40,9 @@ var neverallowTests = []struct {
 	// in direct deps tests
 	{
 		name: "not_allowed_in_direct_deps",
+		rules: []Rule{
+			NeverAllow().InDirectDeps("not_allowed_in_direct_deps"),
+		},
 		fs: map[string][]byte{
 			"top/Blueprints": []byte(`
 				cc_library {
@@ -53,7 +59,7 @@ var neverallowTests = []struct {
 		},
 	},
 
-	// Test specific rules
+	// Test android specific rules
 
 	// include_dir rule tests
 	{
@@ -247,11 +253,15 @@ var neverallowTests = []struct {
 }
 
 func TestNeverallow(t *testing.T) {
+	for _, test := range neverallowTests {
+		// Create a test per config to allow for test specific config, e.g. test rules.
 		config := TestConfig(buildDir, nil)
 
-	for _, test := range neverallowTests {
-
 		t.Run(test.name, func(t *testing.T) {
+			// If the test has its own rules then use them instead of the default ones.
+			if test.rules != nil {
+				setTestNeverallowRules(config, test.rules)
+			}
 			_, errs := testNeverallow(config, test.fs)
 			CheckErrorsAgainstExpectations(t, errs, test.expectedErrors)
 		})