From 6a23949f07f4eba38086b656e7073ce3bf8cd2fe Mon Sep 17 00:00:00 2001
From: Yong He <yonghe@outlook.com>
Date: Fri, 13 Jun 2025 22:13:00 -0700
Subject: Allow interface methods to have default implementations. (#7439)

---
 source/slang/slang-check-expr.cpp | 29 ++++++++++++++++++++++++++++-
 1 file changed, 28 insertions(+), 1 deletion(-)

(limited to 'source/slang/slang-check-expr.cpp')

diff --git a/source/slang/slang-check-expr.cpp b/source/slang/slang-check-expr.cpp
index 9f5c1dc2e..4c6bf98d2 100644
--- a/source/slang/slang-check-expr.cpp
+++ b/source/slang/slang-check-expr.cpp
@@ -5346,6 +5346,12 @@ Expr* SemanticsExprVisitor::visitThisExpr(ThisExpr* expr)
             }
             return expr;
         }
+        else if (auto defaultImplDecl = as<InterfaceDefaultImplDecl>(containerDecl))
+        {
+            expr->type.type =
+                DeclRefType::create(m_astBuilder, DeclRef<Decl>(defaultImplDecl->thisTypeDecl));
+            return expr;
+        }
 #if 0
             else if (auto aggTypeDecl = as<AggTypeDecl>(containerDecl))
             {
@@ -5401,7 +5407,12 @@ Expr* SemanticsExprVisitor::visitThisTypeExpr(ThisTypeExpr* expr)
             expr->type.type = thisTypeType;
             return expr;
         }
-
+        else if (auto defaultImplDecl = as<InterfaceDefaultImplDecl>(containerDecl))
+        {
+            expr->type.type =
+                DeclRefType::create(m_astBuilder, DeclRef<Decl>(defaultImplDecl->thisTypeDecl));
+            return expr;
+        }
         scope = scope->parent;
     }
 
@@ -5409,6 +5420,22 @@ Expr* SemanticsExprVisitor::visitThisTypeExpr(ThisTypeExpr* expr)
     return CreateErrorExpr(expr);
 }
 
+Expr* SemanticsExprVisitor::visitThisInterfaceExpr(ThisInterfaceExpr* expr)
+{
+    auto scope = expr->scope;
+
+    auto containerDecl = findParentInterfaceDecl(scope->containerDecl);
+
+    // ThisInterfaceExpr can only be synthesized by the compiler during parsing
+    // an interface decl with default implementation, so container must always
+    // be an interface decl.
+    SLANG_ASSERT(containerDecl);
+    expr->declRef =
+        createDefaultSubstitutionsIfNeeded(m_astBuilder, this, getDefaultDeclRef(containerDecl));
+    expr->type = m_astBuilder->getTypeType(DeclRefType::create(m_astBuilder, expr->declRef));
+    return expr;
+}
+
 Expr* SemanticsExprVisitor::visitCastToSuperTypeExpr(CastToSuperTypeExpr* expr)
 {
     // CastToSuperType is effectively a struct field.
-- 
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