From d961f4438ef865028d289148d22e0fb5c0d8319a Mon Sep 17 00:00:00 2001
From: kaizhangNV <149626564+kaizhangNV@users.noreply.github.com>
Date: Thu, 15 May 2025 12:00:50 -0500
Subject: Implement C++ style default member initializer (#7087)

close #7069.

We just insert the assignment expression to the beginning of the user-defined ctor, where the assignee is the member with init expression.
---
 source/slang/slang-check-decl.cpp | 82 +++++++++++++++++++++++++++++++++------
 1 file changed, 70 insertions(+), 12 deletions(-)

(limited to 'source')

diff --git a/source/slang/slang-check-decl.cpp b/source/slang/slang-check-decl.cpp
index bdd59c2c5..e7ce8721a 100644
--- a/source/slang/slang-check-decl.cpp
+++ b/source/slang/slang-check-decl.cpp
@@ -380,8 +380,13 @@ private:
         bool isMemberInitCtor,
         Index& paramIndex);
 
-    MemberExpr* createMemberExpr(ThisExpr* thisExpr, Scope* scope, Decl* member);
+    AssignExpr* createMemberAssignmentExpr(
+        ThisExpr* thisExpr,
+        Scope* scope,
+        Decl* member,
+        Expr* rightHandSideExpr);
     Expr* createCtorParamExpr(ConstructorDecl* ctor, Index paramIndex);
+    void maybeInsertDefaultInitExpr(StructDecl* structDecl);
 };
 
 template<typename VisitorType>
@@ -9194,10 +9199,11 @@ static SeqStmt* _ensureCtorBodyIsSeqStmt(ASTBuilder* m_astBuilder, ConstructorDe
     return as<SeqStmt>(stmt->body);
 }
 
-MemberExpr* SemanticsDeclBodyVisitor::createMemberExpr(
+AssignExpr* SemanticsDeclBodyVisitor::createMemberAssignmentExpr(
     ThisExpr* thisExpr,
     Scope* scope,
-    Decl* member)
+    Decl* member,
+    Expr* rightHandSideExpr)
 {
     MemberExpr* memberExpr = m_astBuilder->create<MemberExpr>();
     memberExpr->baseExpression = thisExpr;
@@ -9207,7 +9213,15 @@ MemberExpr* SemanticsDeclBodyVisitor::createMemberExpr(
     memberExpr->name = member->getName();
     memberExpr->type = GetTypeForDeclRef(member->getDefaultDeclRef(), member->loc);
 
-    return memberExpr;
+    if (!memberExpr->type.isLeftValue)
+        return nullptr;
+
+    auto assign = m_astBuilder->create<AssignExpr>();
+    assign->left = memberExpr;
+    assign->right = rightHandSideExpr;
+    assign->loc = member->loc;
+
+    return assign;
 }
 
 Expr* SemanticsDeclBodyVisitor::createCtorParamExpr(ConstructorDecl* ctor, Index paramIndex)
@@ -9345,15 +9359,10 @@ void SemanticsDeclBodyVisitor::synthesizeCtorBodyForMember(
         }
     }
 
-    MemberExpr* memberExpr = createMemberExpr(thisExpr, ctor->ownedScope, member);
-    if (!memberExpr->type.isLeftValue)
+    auto assign = createMemberAssignmentExpr(thisExpr, ctor->ownedScope, member, initExpr);
+    if (!assign)
         return;
 
-    auto assign = m_astBuilder->create<AssignExpr>();
-    assign->left = memberExpr;
-    assign->right = initExpr;
-    assign->loc = member->loc;
-
     auto stmt = m_astBuilder->create<ExpressionStmt>();
     stmt->expression = assign;
     stmt->loc = member->loc;
@@ -9363,13 +9372,61 @@ void SemanticsDeclBodyVisitor::synthesizeCtorBodyForMember(
         checkedMemberVarExpr = cachedDeclToCheckedVar[member];
     else
     {
-        checkedMemberVarExpr = CheckTerm(memberExpr);
+        checkedMemberVarExpr = CheckTerm(assign->left);
         cachedDeclToCheckedVar.add({member, checkedMemberVarExpr});
     }
 
     seqStmtChild->stmts.add(stmt);
 }
 
+// This function inserts the default initialization expression for every member who
+// has init expression at beginning of the user-defined ctor. We don't need to do this
+// for synthesized ctor, because synthesized ctor already handle this at the function
+// parameters
+void SemanticsDeclBodyVisitor::maybeInsertDefaultInitExpr(StructDecl* structDecl)
+{
+    // If there is no explicit constructor, we don't need to do anything.
+    if (!_hasExplicitConstructor(structDecl, false))
+        return;
+
+    // traverse all the constructors and insert the default initialization expressions.
+    for (auto ctor : structDecl->getMembersOfType<ConstructorDecl>())
+    {
+        ThisExpr* thisExpr = m_astBuilder->create<ThisExpr>();
+        thisExpr->scope = ctor->ownedScope;
+        thisExpr->type = ctor->returnType.type;
+        auto seqStmtChild = m_astBuilder->create<SeqStmt>();
+        seqStmtChild->stmts.reserve(structDecl->members.getCount());
+
+        for (auto& member : structDecl->members)
+        {
+            if (auto varDeclBase = as<VarDeclBase>(member))
+            {
+                if (varDeclBase->hasModifier<HLSLStaticModifier>() ||
+                    varDeclBase->getName() == nullptr || varDeclBase->initExpr == nullptr)
+                    continue;
+
+                auto assign = createMemberAssignmentExpr(
+                    thisExpr,
+                    ctor->ownedScope,
+                    member,
+                    varDeclBase->initExpr);
+                if (!assign)
+                    continue;
+
+                auto stmt = m_astBuilder->create<ExpressionStmt>();
+                stmt->expression = assign;
+                stmt->loc = member->loc;
+                seqStmtChild->stmts.add(stmt);
+            }
+        }
+        if (seqStmtChild->stmts.getCount() != 0)
+        {
+            auto seqStmt = _ensureCtorBodyIsSeqStmt(m_astBuilder, ctor);
+            seqStmt->stmts.insert(0, seqStmtChild);
+        }
+    }
+}
 
 void SemanticsDeclBodyVisitor::synthesizeCtorBody(
     DeclAndCtorInfo& structDeclInfo,
@@ -9476,6 +9533,7 @@ void SemanticsDeclBodyVisitor::visitAggTypeDecl(AggTypeDecl* aggTypeDecl)
     }
 
     synthesizeCtorBody(structDeclInfo, inheritanceDefaultCtorList, structDecl);
+    maybeInsertDefaultInitExpr(structDecl);
 
     if (structDeclInfo.defaultCtor)
     {
-- 
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