From d73c504efaaa724b30e97a11e3b5dacd4579fc30 Mon Sep 17 00:00:00 2001
From: Mike <mike@moonbot.pro>
Date: Sun, 6 Sep 2026 14:23:43 +0300
Subject: [PATCH] rtti: skip generic methods in the legacy VMT method table
 (fixes upstream#41410)

A published open generic method has no callable body, but the legacy
method table writer still counted it and emitted a reference to the
generic template symbol, so a valid class failed at link time with an
undefined symbol.

Make the counting and writing predicates symmetric and exclude
tprocdef.is_generic, as the extended RTTI writer already does. Ordinary
published methods and real specializations are unaffected.

FPC issue: https://gitlab.com/freepascal.org/fpc/source/-/issues/41410

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
---
 compiler/ncgvmt.pas     |  6 ++++--
 tests/webtbs/tw41410.pp | 44 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 48 insertions(+), 2 deletions(-)
 create mode 100644 tests/webtbs/tw41410.pp

diff --git a/compiler/ncgvmt.pas b/compiler/ncgvmt.pas
index 9762f1f505b..d5cdb1ab951 100644
--- a/compiler/ncgvmt.pas
+++ b/compiler/ncgvmt.pas
@@ -462,7 +462,8 @@              TMsgInt = record
           begin
             pd:=tprocdef(Tprocsym(p).ProcdefList[i]);
             if (pd.procsym=tsym(p)) and
-               (pd.visibility=vis_published) then
+               (pd.visibility=vis_published) and
+               not pd.is_generic then
               inc(plongint(arg)^);
           end;
       end;
@@ -490,7 +491,8 @@       tvmtasmoutput = record
           begin
             pd:=tprocdef(Tprocsym(p).ProcdefList[i]);
             if (pd.procsym=tsym(p)) and
-               (pd.visibility=vis_published) then
+               (pd.visibility=vis_published) and
+               not pd.is_generic then
               begin
                 { l: name_of_method }
                 lists^.pubmethodstcb.start_internal_data_builder(current_asmdata.AsmLists[al_const],sec_rodata,_class.vmt_mangledname,datatcb,l);
diff --git a/tests/webtbs/tw41410.pp b/tests/webtbs/tw41410.pp
new file mode 100644
index 00000000000..1a5596f0c79
--- /dev/null
+++ b/tests/webtbs/tw41410.pp
@@ -0,0 +1,44 @@
+program tw41410;
+
+{$mode delphi}
+
+type
+  {$M+}
+  TContainer = class
+  private
+    FValue: Integer;
+  published
+    procedure Ping;
+    procedure Test<T>(const AValue: T);
+  end;
+  {$M-}
+
+procedure TContainer.Ping;
+begin
+  FValue := 7;
+end;
+
+procedure TContainer.Test<T>(const AValue: T);
+begin
+  FValue := SizeOf(AValue);
+end;
+
+var
+  Container: TContainer;
+begin
+  Container := TContainer.Create;
+  try
+    if Container.MethodAddress('Ping') = nil then
+      Halt(1);
+    if Container.MethodAddress('Test') <> nil then
+      Halt(2);
+    Container.Ping;
+    if Container.FValue <> 7 then
+      Halt(3);
+    Container.Test<Int64>(42);
+    if Container.FValue <> SizeOf(Int64) then
+      Halt(4);
+  finally
+    Container.Free;
+  end;
+end.