From f991372ea8468c734e634093e8c26087f9a899bd Mon Sep 17 00:00:00 2001
From: Boris Carvajal <boris2.9@gmail.com>
Date: Thu, 6 May 2021 18:58:17 -0400
Subject: [PATCH] Fix Issue 21898 - Qualifier ignored in alias definition if
 parentheses are not present

---
 src/dmd/dsymbolsem.d        | 7 +++++--
 test/compilable/test21898.d | 7 +++++++
 2 files changed, 12 insertions(+), 2 deletions(-)
 create mode 100644 test/compilable/test21898.d

diff --git a/src/dmd/dsymbolsem.d b/src/dmd/dsymbolsem.d
index 2988f26cdf58..1d55bb5be38b 100644
--- a/src/dmd/dsymbolsem.d
+++ b/src/dmd/dsymbolsem.d
@@ -6536,8 +6536,11 @@ void aliasInstanceSemantic(TemplateInstance tempinst, Scope* sc, TemplateDeclara
 
     TemplateTypeParameter ttp = (*tempdecl.parameters)[0].isTemplateTypeParameter();
     Type ta = tempinst.tdtypes[0].isType();
-    Declaration d = new AliasDeclaration(tempinst.loc, ttp.ident, ta.addMod(tempdecl.onemember.isAliasDeclaration.type.mod));
-    d.storage_class |= STC.templateparameter;
+    auto ad = tempdecl.onemember.isAliasDeclaration();
+
+    // Note: qualifiers can be in both 'ad.type.mod' and 'ad.storage_class'
+    Declaration d = new AliasDeclaration(tempinst.loc, ttp.ident, ta.addMod(ad.type.mod));
+    d.storage_class |= STC.templateparameter | ad.storage_class;
     d.dsymbolSemantic(sc);
 
     paramscope.pop();
diff --git a/test/compilable/test21898.d b/test/compilable/test21898.d
new file mode 100644
index 000000000000..9ac18b8cb6b4
--- /dev/null
+++ b/test/compilable/test21898.d
@@ -0,0 +1,7 @@
+// https://issues.dlang.org/show_bug.cgi?id=21898
+
+alias Works(T) = immutable(T);
+alias Fails(T) = immutable T;
+
+static assert(is(Works!int == immutable int));
+static assert(is(Fails!int == immutable int));