Fix type aliases for instantiated generic types

Author: owen-mc

extractor/extractor.go

@@ -369,8 +369,10 @@ func extractObjects(tw *trap.Writer, scope *types.Scope, scopeLabel trap.Label)
 				populateTypeParamParents(tw, funcObj.Type().(*types.Signature).TypeParams(), obj)
 				populateTypeParamParents(tw, funcObj.Type().(*types.Signature).RecvTypeParams(), obj)
 			}
-			// Populate type parameter parents for named types.
-			if typeNameObj, ok := obj.(*types.TypeName); ok {
+			// Populate type parameter parents for named types. Note that we
+			// skip type aliases as the original type should be the parent
+			// of any type parameters.
+			if typeNameObj, ok := obj.(*types.TypeName); ok && !typeNameObj.IsAlias() {
 				if tp, ok := typeNameObj.Type().(*types.Named); ok {
 					populateTypeParamParents(tw, tp.TypeParams(), obj)
 				}

ql/test/library-tests/semmle/go/Types/GenericTypeInstantiationExpr.expected

@@ -16,3 +16,4 @@
 | generic.go:62:12:62:26 | generic type instantiation expression | generic.go:62:12:62:23 | GenericNamed | 0 | generic.go:62:25:62:25 | U |
 | generic.go:70:42:70:64 | generic type instantiation expression | generic.go:70:42:70:57 | GenericInterface | 0 | generic.go:70:59:70:63 | int32 |
 | generic.go:74:41:74:62 | generic type instantiation expression | generic.go:74:41:74:54 | GenericStruct1 | 0 | generic.go:74:56:74:61 | string |
+| generic.go:82:18:82:34 | generic type instantiation expression | generic.go:82:18:82:29 | GenericArray | 0 | generic.go:82:31:82:33 | int |

ql/test/library-tests/semmle/go/Types/QualifiedNames.expected

@@ -19,6 +19,7 @@
 | GenericMap2 | github.com/github/codeql-go/ql/test/library-tests/semmle/go/Types.GenericMap2 |
 | GenericNamed | github.com/github/codeql-go/ql/test/library-tests/semmle/go/Types.GenericNamed |
 | GenericPointer | github.com/github/codeql-go/ql/test/library-tests/semmle/go/Types.GenericPointer |
+| GenericSignature | github.com/github/codeql-go/ql/test/library-tests/semmle/go/Types.GenericSignature |
 | GenericSlice | github.com/github/codeql-go/ql/test/library-tests/semmle/go/Types.GenericSlice |
 | GenericStruct1 | github.com/github/codeql-go/ql/test/library-tests/semmle/go/Types.GenericStruct1 |
 | GenericStruct2 | github.com/github/codeql-go/ql/test/library-tests/semmle/go/Types.GenericStruct2 |

ql/test/library-tests/semmle/go/Types/Types.expected

@@ -19,6 +19,7 @@
 | GenericMap2 | GenericMap2 |
 | GenericNamed | GenericNamed |
 | GenericPointer | GenericPointer |
+| GenericSignature | GenericSignature |
 | GenericSlice | GenericSlice |
 | GenericStruct1 | GenericStruct1 |
 | GenericStruct2 | GenericStruct2 |

ql/test/library-tests/semmle/go/Types/generic.go

@@ -78,3 +78,8 @@ func accessFieldsOfInstantiatedStruct(x GenericStruct1[string]) {
 	_ = x.sliceField
 	_ = x.mapField
 }
+
+type TypeAlias = GenericArray[int]
+
+type GenericSignature[T any] func(t T) T
+type GenericSignatureAlias = GenericSignature[string]