Don't drop aggregate type qualifier for alias parameter

Fixes #17959.

Author: ntrel

compiler/src/dmd/templatesem.d

@@ -2656,7 +2656,10 @@ private MATCH matchArg(TemplateParameter tp, Scope* sc, RootObject oarg, size_t
         //printf("TemplateAliasParameter.matchArg('%s')\n", tap.ident.toChars());
         MATCH m = MATCH.exact;
         Type ta = isType(oarg);
-        RootObject sa = ta && !ta.deco ? null : getDsymbol(oarg);
+        // Note: Dsymbol doesn't have qualifiers, so avoid if ta.mod is set
+        // https://github.com/dlang/dmd/issues/17959
+        RootObject sa = ta && !ta.deco ? null :
+            ta && ta.mod /*&& sc.hasEdition(Edition.v2024)*/ ? oarg : getDsymbol(oarg);
         Expression ea = isExpression(oarg);
         if (ea)
         {

compiler/test/compilable/alias_param_qual.d

@@ -0,0 +1,9 @@
+module m 2024;
+
+alias t(alias a) = a;
+
+static assert(is(t!(const Object) == const Object));
+static assert(is(t!(shared(Object)) == shared Object));
+static assert(is(t!(immutable S) == immutable(S)));
+
+struct S {}