Fix dlang#19075 - Operator ^^= fails to compile for many numeric type combinations (dlang#23023)

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: dkorpel

compiler/src/dmd/expressionsem.d

@@ -13409,17 +13409,19 @@ private extern (C++) final class ExpressionSemanticVisitor : Visitor
 
             if (exp.e1.op == EXP.variable)
             {
-                // Rewrite: e1 = e1 ^^ e2
+                // Rewrite: e1 = cast(T)(e1 ^^ e2)
                 e = new PowExp(exp.loc, exp.e1.syntaxCopy(), exp.e2);
+                e = new CastExp(exp.loc, e, exp.e1.type);
                 e = new AssignExp(exp.loc, exp.e1, e);
             }
             else
             {
-                // Rewrite: ref tmp = e1; tmp = tmp ^^ e2
+                // Rewrite: ref tmp = e1; tmp = cast(T)(tmp ^^ e2)
                 auto v = copyToTemp(STC.ref_, "__powtmp", exp.e1);
                 auto de = new DeclarationExp(exp.e1.loc, v);
                 auto ve = new VarExp(exp.e1.loc, v);
                 e = new PowExp(exp.loc, ve, exp.e2);
+                e = new CastExp(exp.loc, e, exp.e1.type);
                 e = new AssignExp(exp.loc, new VarExp(exp.e1.loc, v), e);
                 e = new CommaExp(exp.loc, de, e);
             }

compiler/test/runnable/ctorpowtests.d

@@ -266,9 +266,34 @@ int anotherPowTest()
 
 /************************************/
 
+// https://github.com/dlang/dmd/issues/19075
+// ^^= must compile for small integer types
+
+void test19075()
+{
+    byte bw = 10;
+    bw ^^= 3;
+    assert(bw == cast(byte) 1000);
+
+    ubyte ubw = 10;
+    ubw ^^= 3;
+    assert(ubw == cast(ubyte) 1000);
+
+    short sw = 100;
+    sw ^^= 3;
+    assert(sw == cast(short) 1_000_000);
+
+    ushort usw = 100;
+    usw ^^= 3;
+    assert(usw == cast(ushort) 1_000_000);
+}
+
+/************************************/
+
 void main()
 {
     assert(!__ctfe);
     assert(magicVariable()==2);
     test11159();
+    test19075();
 }