From c210f9bc25588b7eb19e4a8a3a007ca53693a203 Mon Sep 17 00:00:00 2001
From: Mike <mike@moonbot.pro>
Date: Sun, 6 Sep 2026 14:29:10 +0300
Subject: [PATCH] helpers: key distinct type aliases by their own identity
 (fixes upstream#41564)

The helper key for a record or object was built from the base
structure's symbol table, so several distinct aliases of one record
(type TA = type TB) shared a single key and lookup returned the helper
registered last for any of them.

For a df_unique def build the key from the def's own owner and name;
plain aliases keep sharing the structural key.

FPC issue: https://gitlab.com/freepascal.org/fpc/source/-/issues/41564

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
---
 compiler/symtable.pas   |  3 +-
 tests/webtbs/tw41564.pp | 80 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 82 insertions(+), 1 deletion(-)
 create mode 100644 tests/webtbs/tw41564.pp

diff --git a/compiler/symtable.pas b/compiler/symtable.pas
index 2faef4a312b..40747a75723 100644
--- a/compiler/symtable.pas
+++ b/compiler/symtable.pas
@@ -3243,7 +3243,8 @@         if defowner.typ=recorddef then
             assigned(tstoreddef(def).genericdef) and
             assigned(def.typesym) then
           result:=make_mangledname('',tstoreddef(def).genericdef.owner,def.typesym.name)
-        else if def.typ in [recorddef,objectdef] then
+        else if (def.typ in [recorddef,objectdef]) and
+           not (df_unique in def.defoptions) then
           result:=make_mangledname('',tabstractrecorddef(def).symtable,'')
         else
           result:=make_mangledname('',def.owner,def.typesym.name);
diff --git a/tests/webtbs/tw41564.pp b/tests/webtbs/tw41564.pp
new file mode 100644
index 00000000000..5ea8a976f8b
--- /dev/null
+++ b/tests/webtbs/tw41564.pp
@@ -0,0 +1,80 @@
+program tw41564;
+
+{$mode delphi}
+
+type
+  TBase = record
+    Value: Integer;
+  end;
+  TAlias = TBase;
+  TFirst = type TBase;
+  TSecond = type TBase;
+
+  TBaseHelper = record helper for TBase
+    function Marker: Integer;
+    class function StaticMarker: Integer; static;
+  end;
+
+  TFirstHelper = record helper for TFirst
+    function Marker: Integer;
+    class function StaticMarker: Integer; static;
+  end;
+
+  TSecondHelper = record helper for TSecond
+    function Marker: Integer;
+    class function StaticMarker: Integer; static;
+  end;
+
+function TBaseHelper.Marker: Integer;
+begin
+  Result := 10;
+end;
+
+class function TBaseHelper.StaticMarker: Integer;
+begin
+  Result := 20;
+end;
+
+function TFirstHelper.Marker: Integer;
+begin
+  Result := 11;
+end;
+
+class function TFirstHelper.StaticMarker: Integer;
+begin
+  Result := 21;
+end;
+
+function TSecondHelper.Marker: Integer;
+begin
+  Result := 12;
+end;
+
+class function TSecondHelper.StaticMarker: Integer;
+begin
+  Result := 22;
+end;
+
+var
+  Base: TBase;
+  AliasValue: TAlias;
+  First: TFirst;
+  Second: TSecond;
+begin
+  if Base.Marker <> 10 then
+    Halt(1);
+  if AliasValue.Marker <> 10 then
+    Halt(2);
+  if First.Marker <> 11 then
+    Halt(3);
+  if Second.Marker <> 12 then
+    Halt(4);
+  if TBase.StaticMarker <> 20 then
+    Halt(5);
+  if TAlias.StaticMarker <> 20 then
+    Halt(6);
+  if TFirst.StaticMarker <> 21 then
+    Halt(7);
+  if TSecond.StaticMarker <> 22 then
+    Halt(8);
+end.