AST: Stricter invariants when constructing TypeAliasType

Author: slavapestov

lib/AST/ASTContext.cpp

@@ -3011,9 +3011,12 @@ TypeAliasType::TypeAliasType(TypeAliasDecl *typealias, Type parent,
 
   // Record the substitutions.
   if (substitutions) {
+    assert(typealias->getGenericSignature()->isEqual(
+        substitutions.getGenericSignature()));
     Bits.TypeAliasType.HasSubstitutionMap = true;
     *getTrailingObjects<SubstitutionMap>() = substitutions;
   } else {
+    assert(!typealias->isGenericContext());
     Bits.TypeAliasType.HasSubstitutionMap = false;
   }
 }

lib/IDE/CompletionLookup.cpp

@@ -1684,14 +1684,10 @@ void CompletionLookup::addTypeAliasRef(const TypeAliasDecl *TAD,
   Builder.addBaseName(TAD->getName().str());
   if (auto underlyingType = TAD->getUnderlyingType()) {
     if (underlyingType->hasError()) {
-      Type parentType;
-      if (auto nominal = TAD->getDeclContext()->getSelfNominalTypeDecl()) {
-        parentType = nominal->getDeclaredInterfaceType();
-      }
       addTypeAnnotation(Builder,
-                        TypeAliasType::get(const_cast<TypeAliasDecl *>(TAD),
-                                           parentType, SubstitutionMap(),
-                                           underlyingType));
+                        TAD->isGeneric()
+                        ? TAD->getUnboundGenericType()
+                        : TAD->getDeclaredInterfaceType());
 
     } else {
       addTypeAnnotation(Builder, underlyingType);

lib/Sema/ImportResolution.cpp

@@ -1045,8 +1045,7 @@ ScopedImportLookupRequest::evaluate(Evaluator &evaluator,
       emittedDiag.emplace(ctx.Diags.diagnose(
           importLoc, diag::imported_decl_is_wrong_kind_typealias,
           typealias->getDescriptiveKind(),
-          TypeAliasType::get(typealias, Type(), SubstitutionMap(),
-                             typealias->getUnderlyingType()),
+          typealias->getDeclaredInterfaceType(),
           getImportKindString(importKind)));
     } else {
       emittedDiag.emplace(ctx.Diags.diagnose(

test/ImportResolution/import-specific-fixits.swift

@@ -36,7 +36,7 @@ import struct DeclsUsedWrongly.Choice // expected-error {{'Choice' was imported
 import struct DeclsUsedWrongly.Callback // expected-error {{type alias 'Callback' (aka '() -> ()') cannot be imported as 'struct'}} {{8-14=typealias}}
 import var DeclsUsedWrongly.Callback // expected-error {{'Callback' was imported as 'var', but is a type}} {{8-11=typealias}}
 
-import struct DeclsUsedWrongly.Pair // expected-error {{type alias 'Pair' (aka '(T, T)') cannot be imported as 'struct'}} {{8-14=typealias}}
+import struct DeclsUsedWrongly.Pair // expected-error {{type alias 'Pair<T>' (aka '(T, T)') cannot be imported as 'struct'}} {{8-14=typealias}}
 import var DeclsUsedWrongly.Pair // expected-error {{'Pair' was imported as 'var', but is a type}} {{8-11=typealias}}
 
 import struct Swift.print // expected-error {{'print' was imported as 'struct', but is a function}} {{8-14=func}}