[NFC] ParamDecl: Extract write of type-checked default expr into its own method

include/swift/AST/ASTSynthesis.h

@@ -361,7 +361,7 @@ void synthesizeDefaultArgumentFromExpr(SynthesisContext &SC, const S &s,
   // to render the default argument if you mess up the call.
   auto expr = synthesizeExpr(SC, s);
   param->setDefaultArgumentKind(DefaultArgumentKind::Normal);
-  param->setDefaultExpr(expr, /*type checked*/ false);
+  param->setDefaultExpr(expr);
 }
 
 /// Default arguments.
@@ -545,7 +545,7 @@ inline void synthesizeDefaultArgument(SynthesisContext &SC,
   case _nil: {
     auto expr = synthesizeExpr(SC, s);
     param->setDefaultArgumentKind(DefaultArgumentKind::NilLiteral);
-    param->setDefaultExpr(expr, /*type checked*/ false);
+    param->setDefaultExpr(expr);
     return;
   }
 

include/swift/AST/Decl.h

@@ -6784,13 +6784,19 @@ public:
   }
 
   /// Sets a new default argument expression for this parameter. This should
-  /// only be called internally by ParamDecl and AST walkers.
+  /// only be called internally by `ParamDecl` and `ASTWalker`.
   ///
   /// \param E The new default argument.
-  /// \param isTypeChecked Whether this argument should be used as the
-  /// parameter's fully type-checked default argument.
-  void setDefaultExpr(Expr *E, bool isTypeChecked);
+  void setDefaultExpr(Expr *E);
 
+  // FIXME: private:
+  /// Sets a type-checked default argument expression for this parameter. This
+  /// should only be called by the `DefaultArgumentExprRequest` request.
+  ///
+  /// \param E The type-checked default argument.
+  void setTypeCheckedDefaultExpr(Expr *E);
+
+public:
   /// Sets a type of default expression associated with this parameter.
   /// This should only be called by deserialization.
   void setDefaultExprType(Type type);

lib/AST/ASTWalker.cpp

@@ -370,7 +370,7 @@ class Traversal : public ASTVisitor<Traversal, Expr*, Stmt*,
     if (auto *E = P->getStructuralDefaultExpr()) {
       auto res = doIt(E);
       if (!res) return true;
-      P->setDefaultExpr(res, /*isTypeChecked*/ (bool)res->getType());
+      P->setDefaultExpr(res);
     }
 
     if (!Walker.shouldWalkAccessorsTheOldWay()) {

lib/AST/Decl.cpp

@@ -8361,7 +8361,7 @@ ParamDecl *ParamDecl::createParsed(ASTContext &Context, SourceLoc specifierLoc,
     defaultValue = nullptr;
   }
 
-  decl->setDefaultExpr(defaultValue, false);
+  decl->setDefaultExpr(defaultValue);
   decl->setDefaultArgumentKind(kind);
 
   return decl;
@@ -8615,28 +8615,39 @@ Type ParamDecl::getTypeOfDefaultExpr() const {
   return Type();
 }
 
-void ParamDecl::setDefaultExpr(Expr *E, bool isTypeChecked) {
-  if (!DefaultValueAndFlags.getPointer()) {
-    if (!E) return;
-
-    DefaultValueAndFlags.setPointer(
-        getASTContext().Allocate<StoredDefaultArgument>());
-  }
-
+void ParamDecl::setDefaultExpr(Expr *E) {
   auto *defaultInfo = DefaultValueAndFlags.getPointer();
+  if (defaultInfo) {
     assert(defaultInfo->DefaultArg.isNull() ||
            defaultInfo->DefaultArg.is<Expr *>());
 
-  if (!isTypeChecked) {
-    assert(!defaultInfo->InitContextAndIsTypeChecked.getInt() &&
-           "Can't overwrite type-checked default with un-type-checked default");
+    auto *const oldE = defaultInfo->DefaultArg.dyn_cast<Expr *>();
+    assert((bool)E == (bool)oldE && "Overwrite of non-null default with null");
+    assert((!oldE || !oldE->getType() || (bool)E->getType()) &&
+           "Overwrite of type-checked default with non-type-checked default");
+  } else {
+    if (!E) return;
+
+    defaultInfo = getASTContext().Allocate<StoredDefaultArgument>();
+    DefaultValueAndFlags.setPointer(defaultInfo);
+
+    defaultInfo->InitContextAndIsTypeChecked.setInt(false);
   }
+
   defaultInfo->DefaultArg = E;
-  // `Inherited` default arguments do not have an expression,
-  // so if the storage has been pre-allocated already we need
-  // to be careful requesting type here.
-  defaultInfo->ExprType = E ? E->getType() : Type();
-  defaultInfo->InitContextAndIsTypeChecked.setInt(isTypeChecked);
+}
+
+void ParamDecl::setTypeCheckedDefaultExpr(Expr *E) {
+  assert(E || getDefaultArgumentKind() == DefaultArgumentKind::Inherited);
+  setDefaultExpr(E);
+
+  auto *defaultInfo = DefaultValueAndFlags.getPointer();
+  if (!defaultInfo) {
+    defaultInfo = getASTContext().Allocate<StoredDefaultArgument>();
+    DefaultValueAndFlags.setPointer(defaultInfo);
+  }
+
+  defaultInfo->InitContextAndIsTypeChecked.setInt(true);
 }
 
 void ParamDecl::setDefaultExprType(Type type) {

lib/AST/TypeCheckRequests.cpp

@@ -1299,7 +1299,7 @@ std::optional<Expr *> DefaultArgumentExprRequest::getCachedResult() const {
 
 void DefaultArgumentExprRequest::cacheResult(Expr *expr) const {
   auto *param = std::get<0>(getStorage());
-  param->setDefaultExpr(expr, /*isTypeChecked*/ true);
+  param->setTypeCheckedDefaultExpr(expr);
 }
 
 //----------------------------------------------------------------------------//

lib/ClangImporter/ImportType.cpp

@@ -2609,7 +2609,7 @@ static ParamDecl *getParameterInfo(ClangImporter::Implementation *impl,
     if (CallExpr *defaultArgExpr = synthesizer.makeDefaultArgument(
             param, swiftParamTy, paramInfo->getParameterNameLoc())) {
       paramInfo->setDefaultArgumentKind(DefaultArgumentKind::Normal);
-      paramInfo->setDefaultExpr(defaultArgExpr, /*isTypeChecked*/ true);
+      paramInfo->setTypeCheckedDefaultExpr(defaultArgExpr);
       paramInfo->setDefaultValueStringRepresentation("cxxDefaultArg");
     }
   }