Merge pull request #8846 from RazvanN7/Issue_16633

Fix Issue 16633 - Case where an alias this is tried before the object itself

src/dmd/expressionsem.d

@@ -8705,9 +8705,59 @@ private extern (C++) final class ExpressionSemanticVisitor : Visitor
         }
         else
         {
+            // Try alias this on first operand
+            static Expression tryAliasThisForLhs(BinAssignExp exp, Scope* sc)
+            {
+                AggregateDeclaration ad1 = isAggregate(exp.e1.type);
+                if (!ad1 || !ad1.aliasthis)
+                    return null;
+
+                /* Rewrite (e1 op e2) as:
+                 *      (e1.aliasthis op e2)
+                 */
+                if (exp.att1 && exp.e1.type == exp.att1)
+                    return null;
+                //printf("att %s e1 = %s\n", Token::toChars(e.op), e.e1.type.toChars());
+                Expression e1 = new DotIdExp(exp.loc, exp.e1, ad1.aliasthis.ident);
+                BinExp be = cast(BinExp)exp.copy();
+                if (!be.att1 && exp.e1.type.checkAliasThisRec())
+                    be.att1 = exp.e1.type;
+                be.e1 = e1;
+                return be.trySemantic(sc);
+            }
+
+            // Try alias this on second operand
+            static Expression tryAliasThisForRhs(BinAssignExp exp, Scope* sc)
+            {
+                AggregateDeclaration ad2 = isAggregate(exp.e2.type);
+                if (!ad2 || !ad2.aliasthis)
+                    return null;
+                /* Rewrite (e1 op e2) as:
+                 *      (e1 op e2.aliasthis)
+                 */
+                if (exp.att2 && exp.e2.type == exp.att2)
+                    return null;
+                //printf("att %s e2 = %s\n", Token::toChars(e.op), e.e2.type.toChars());
+                Expression e2 = new DotIdExp(exp.loc, exp.e2, ad2.aliasthis.ident);
+                BinExp be = cast(BinExp)exp.copy();
+                if (!be.att2 && exp.e2.type.checkAliasThisRec())
+                    be.att2 = exp.e2.type;
+                be.e2 = e2;
+                return be.trySemantic(sc);
+            }
+
+            result = tryAliasThisForLhs(exp, sc);
+            if (result)
+                return;
+
+            result = tryAliasThisForRhs(exp, sc);
+            if (result)
+                return;
+
             exp.error("cannot append type `%s` to type `%s`", tb2.toChars(), tb1.toChars());
             return setError();
         }
+
         if (exp.e2.checkValue())
             return setError();
 

src/dmd/opover.d

@@ -456,7 +456,14 @@ private Expression checkAliasThisForLhs(AggregateDeclaration ad, Scope* sc, BinE
     if (!be.att1 && e.e1.type.checkAliasThisRec())
         be.att1 = e.e1.type;
     be.e1 = e1;
-    return be.trySemantic(sc);
+
+    Expression result;
+    if (be.op == TOK.concatenateAssign)
+        result = be.op_overload(sc);
+    else
+        result = be.trySemantic(sc);
+
+    return result;
 }
 
 // Try alias this on second operand
@@ -475,7 +482,14 @@ private Expression checkAliasThisForRhs(AggregateDeclaration ad, Scope* sc, BinE
     if (!be.att2 && e.e2.type.checkAliasThisRec())
         be.att2 = e.e2.type;
     be.e2 = e2;
-    return be.trySemantic(sc);
+
+    Expression result;
+    if (be.op == TOK.concatenateAssign)
+        result = be.op_overload(sc);
+    else
+        result = be.trySemantic(sc);
+
+    return result;
 }
 
 /************************************

test/runnable/aliasthis.d

@@ -2057,6 +2057,25 @@ void test19284()
     assert(t.x == 5);
 }
 
+// 16633
+
+class Item
+{
+    alias children this;
+    Item[] children;
+    void populate()
+    {
+        children ~= new Item(); // Item is seen as []
+        assert(children.length == 1);
+    }
+}
+
+void test16633()
+{
+    Item root = new Item();
+    root.populate;
+}
+
 int main()
 {
     test1();
@@ -2114,6 +2133,7 @@ int main()
     test11355();
     test14806();
     test19284();
+    test16633();
 
     printf("Success\n");
     return 0;