Handle newly-introduced types.Alias type (#286)

Go 1.22 [1] introduces a proper `types.Alias` type for type aliases.
This PR adds handling (by simply unwrapping alias node - effectively
restoring previous behavior) for such a type.

Further simplification and refactors will be in future PRs.

annotation/helper_test.go

@@ -139,7 +139,7 @@ func collectMethods(t *types.Named, visitedMethods map[string]*types.Func, visit
 		for i := 0; i < s.NumFields(); i++ {
 			f := s.Field(i)
 			if f.Embedded() {
-				if n, ok := util.UnwrapPtr(f.Type()).(*types.Named); ok {
+				if n, ok := util.UnwrapPtr(types.Unalias(f.Type())).(*types.Named); ok {
 					collectMethods(n, visitedMethods, visitedStructs)
 				}
 			}
@@ -197,7 +197,7 @@ func structsImplementingInterface(interfaceName string, packageName ...string) m
 							if sObj == nil {
 								return true
 							}
-							sType, ok := sObj.Type().(*types.Named)
+							sType, ok := types.Unalias(sObj.Type()).(*types.Named)
 							if !ok {
 								return true
 							}

assertion/function/assertiontree/backprop.go

@@ -410,7 +410,7 @@ func backpropAcrossRange(rootNode *RootAssertionNode, lhs []ast.Expr, rhs ast.Ex
 		}
 	}
 
-	rhsType := rootNode.Pass().TypesInfo.Types[rhs].Type
+	rhsType := types.Unalias(rootNode.Pass().TypesInfo.Types[rhs].Type)
 
 	// This block breaks down the cases for the `range` statement being analyzed,
 	// starting by switching on how many left-hand operands there are

nilaway_test.go

@@ -12,6 +12,13 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+// Go 1.22 [1] introduces a proper `types.Alias` type for type aliases. The current default is
+// disabling such a feature. However, Go official doc suggests that it will be enabled in future Go
+// releases. Therefore, here we explicitly set this to `1` to enable the feature to test NilAway's
+// ability to handle it.
+// [1]: https://tip.golang.org/doc/go1.22
+//go:debug gotypesalias=1
+
 package nilaway
 
 import (

testdata/src/go.uber.org/looprange/looprange.go

@@ -196,3 +196,14 @@ func testRangeOverBasicTypes(j int) {
 		}
 	}
 }
+
+type Set map[string]bool
+
+type MyAlias = Set
+
+//nilable(s)
+func testAlias(s MyAlias) {
+	for myStr := range s {
+		print(myStr)
+	}
+}

util/util.go

@@ -145,7 +145,7 @@ func TypeAsDeeplyStruct(typ types.Type) *types.Struct {
 	}
 
 	if ptType, ok := typ.(*types.Pointer); ok {
-		if namedType, ok := ptType.Elem().(*types.Named); ok {
+		if namedType, ok := types.Unalias(ptType.Elem()).(*types.Named); ok {
 			if resType, ok := namedType.Underlying().(*types.Struct); ok {
 				return resType
 			}
@@ -262,7 +262,7 @@ func TypeBarsNilness(t types.Type) bool {
 		return false
 	case *types.Chan:
 		return false
-	case *types.Named:
+	case *types.Alias, *types.Named:
 		return TypeBarsNilness(t.Underlying())
 	case *types.Interface:
 		return false
@@ -314,11 +314,11 @@ func funcIsRichCheckEffectReturning(fdecl *types.Func, expectedType types.Type)
 	if n == 0 {
 		return false
 	}
-	if results.At(n-1).Type() != expectedType {
+	if !types.Identical(results.At(n-1).Type(), expectedType) {
 		return false
 	}
 	for i := 0; i < n-1; i++ {
-		if results.At(i).Type() == expectedType {
+		if types.Identical(results.At(i).Type(), expectedType) {
 			return false
 		}
 	}