From bfbcfb0489e2b52657ceb117586fca4b6a89924e Mon Sep 17 00:00:00 2001
From: Andrew Haines <andrewd207@aol.com>
Date: Wed, 24 Jun 2026 18:16:14 -0400
Subject: [PATCH] fix(stdlib): release managed elements in generics.collections
 TList
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TList<T> stored its elements in a raw GetMem buffer and freed only the
buffer (Destroy did FreeMem with no element cleanup; Clear just reset
the count; Delete's shift left a duplicate ref on the vacated tail
slot). For a managed element type — a class (ARC) or a string — that
leaked every contained value: destroying or clearing the list never
released its items, so their destructors never ran.

Release each managed element by storing a zero-initialised T through
its slot before dropping it: the compiler's ARC discipline on the
managed store releases the previous value, so freeing the list cascades
to its items. For a non-managed T (e.g. Integer) the same store is a
harmless zero write, so TList<Integer> is unaffected.

Applied to Destroy (all elements), Clear (all elements), and Delete
(the vacated tail slot). The sibling containers (TStack, TQueue, TSet,
and the dictionaries) share the same raw-buffer pattern and leak
likewise; left as a follow-up.

Test: an e2e regression on both backends asserts a class element's
destructor fires on Clear and on Free (the cascade), and the existing
TList<Integer> coverage confirms the non-managed path is unchanged.
---
 .../src/test/pascal/cp.test.e2e.tlist.pas     | 41 +++++++++++++++++++
 .../src/main/pascal/generics.collections.pas  | 40 ++++++++++++++++--
 2 files changed, 77 insertions(+), 4 deletions(-)

diff --git a/compiler/src/test/pascal/cp.test.e2e.tlist.pas b/compiler/src/test/pascal/cp.test.e2e.tlist.pas
index e380d40..712fd59 100644
--- a/compiler/src/test/pascal/cp.test.e2e.tlist.pas
+++ b/compiler/src/test/pascal/cp.test.e2e.tlist.pas
@@ -38,6 +38,10 @@ type
     { Default array property: List[i] subscript for read and write. }
     procedure TestRun_TList_DefaultProperty_ReadWrite;
     procedure TestRun_TList_DefaultProperty_Polymorphic;
+
+    { Clear and Free release managed elements (ARC cascade): a class element's
+      destructor must run when the list is cleared or freed. }
+    procedure TestRun_TList_FreeAndClear_ReleasesElements;
   end;
 
 implementation
@@ -274,6 +278,43 @@ begin
   AssertEquals('List[i].Area (native)', '25' + #10, Output);
 end;
 
+const
+  SrcTListFreeClear = '''
+    program P;
+    uses generics.collections;
+    type
+      TC = class
+        N: Integer;
+        constructor Create(AN: Integer);
+        destructor Destroy; override;
+      end;
+    constructor TC.Create(AN: Integer);
+    begin N := AN end;
+    destructor TC.Destroy;
+    begin WriteLn('d', N) end;
+    var
+      L: TList<TC>;
+    begin
+      L := TList<TC>.Create();
+      L.Add(TC.Create(1));
+      L.Add(TC.Create(2));
+      L.Clear();
+      WriteLn('cleared');
+      L.Add(TC.Create(3));
+      L.Free();
+      WriteLn('done')
+    end.
+    ''';
+
+procedure TE2ETListTests.TestRun_TList_FreeAndClear_ReleasesElements;
+begin
+  if not ToolchainAvailable() then begin Ignore('toolchain unavailable'); Exit; end;
+  { Clear releases elements 1 and 2; the final Free releases element 3 — each
+    destructor fires, proving the managed-element release cascade. }
+  AssertRTLRunsOnAll(SrcTListFreeClear,
+    'd1' + #10 + 'd2' + #10 + 'cleared' + #10 + 'd3' + #10 + 'done' + #10, 0);
+end;
+
 initialization
   RegisterTest(TE2ETListTests);
 
diff --git a/stdlib/src/main/pascal/generics.collections.pas b/stdlib/src/main/pascal/generics.collections.pas
index 7c393dd..6199db5 100644
--- a/stdlib/src/main/pascal/generics.collections.pas
+++ b/stdlib/src/main/pascal/generics.collections.pas
@@ -302,9 +302,10 @@ end;
 
 procedure TList<T>.Delete(AIndex: Integer);
 var
-  Src: ^T;
-  Dst: ^T;
-  I:   Integer;
+  Src:   ^T;
+  Dst:   ^T;
+  I:     Integer;
+  Empty: T;
 begin
   I := AIndex;
   while I < Self.FCount - 1 do
@@ -314,16 +315,47 @@ begin
     Dst^ := Src^;
     I    := I + 1
   end;
-  Self.FCount := Self.FCount - 1
+  Self.FCount := Self.FCount - 1;
+  { The shift leaves the (now unused) tail slot holding a duplicate of the last
+    element; clear it so its managed ref is released, not leaked. }
+  Dst  := Self.FData + Self.FCount * SizeOf(T);
+  Dst^ := Empty
 end;
 
 procedure TList<T>.Clear;
+var
+  I:     Integer;
+  Slot:  ^T;
+  Empty: T;
 begin
+  { Release each managed element before dropping the count (see Destroy). }
+  I := 0;
+  while I < Self.FCount do
+  begin
+    Slot  := Self.FData + I * SizeOf(T);
+    Slot^ := Empty;
+    I     := I + 1
+  end;
   Self.FCount := 0
 end;
 
 procedure TList<T>.Destroy;
+var
+  I:     Integer;
+  Slot:  ^T;
+  Empty: T;
 begin
+  { Release each managed element so freeing the list cascades to its items
+    (Blaise is reference-counted): storing a zero-initialised T through the
+    slot runs the compiler's ARC discipline — the old element is released; for
+    a plain (non-managed) T the store is a harmless zero write. }
+  I := 0;
+  while I < Self.FCount do
+  begin
+    Slot  := Self.FData + I * SizeOf(T);
+    Slot^ := Empty;
+    I     := I + 1
+  end;
   FreeMem(Self.FData);
   Self.FData     := nil;
   Self.FCount    := 0;