From 59dd341fe16d26180c76aedf18ac2918dbe426b8 Mon Sep 17 00:00:00 2001
From: "g. nicholas d'andrea" <nick@gnidan.org>
Date: Thu, 2 Apr 2026 05:21:13 -0400
Subject: [PATCH] Fix call stack display for recursive function calls

The call stack dedup logic compared only function name and
call type, causing recursive calls (e.g. count -> count) to
be collapsed into a single frame. Now also checks whether the
previous frame was pushed on the immediately preceding step,
which distinguishes the compiler's duplicate invoke contexts
(caller JUMP + callee JUMPDEST on consecutive steps) from
genuine recursive calls (same name but steps far apart).

Fixed in both programs-react buildCallStack and web
TraceDrawer's duplicated call stack logic.
---
 .../programs-react/src/utils/mockTrace.ts     | 20 +++++++++++--------
 .../src/theme/ProgramExample/TraceDrawer.tsx  | 18 ++++++++++-------
 2 files changed, 23 insertions(+), 15 deletions(-)

diff --git a/packages/programs-react/src/utils/mockTrace.ts b/packages/programs-react/src/utils/mockTrace.ts
index 78af909c3..23d8483ed 100644
--- a/packages/programs-react/src/utils/mockTrace.ts
+++ b/packages/programs-react/src/utils/mockTrace.ts
@@ -298,15 +298,19 @@ export function buildCallStack(
     }
 
     if (callInfo.kind === "invoke") {
-      // The compiler emits invoke on both the caller JUMP and
-      // callee entry JUMPDEST. Skip if the top frame already
-      // matches this call.
+      // The compiler emits invoke on both the caller JUMP
+      // and callee entry JUMPDEST for the same call. These
+      // occur on consecutive trace steps. Only skip if the
+      // top frame matches AND was pushed on the immediately
+      // preceding step — otherwise this is a new call (e.g.
+      // recursion with the same function name).
       const top = stack[stack.length - 1];
-      if (
-        !top ||
-        top.identifier !== callInfo.identifier ||
-        top.callType !== callInfo.callType
-      ) {
+      const isDuplicate =
+        top &&
+        top.identifier === callInfo.identifier &&
+        top.callType === callInfo.callType &&
+        top.stepIndex === i - 1;
+      if (!isDuplicate) {
         stack.push({
           identifier: callInfo.identifier,
           stepIndex: i,
diff --git a/packages/web/src/theme/ProgramExample/TraceDrawer.tsx b/packages/web/src/theme/ProgramExample/TraceDrawer.tsx
index 088fa8d3f..99cdea4b8 100644
--- a/packages/web/src/theme/ProgramExample/TraceDrawer.tsx
+++ b/packages/web/src/theme/ProgramExample/TraceDrawer.tsx
@@ -118,14 +118,18 @@ function TraceDrawerContent(): JSX.Element {
 
       if (info.kind === "invoke") {
         // The compiler emits invoke on both the caller
-        // JUMP and callee entry JUMPDEST. Skip if the
-        // top frame already matches this call.
+        // JUMP and callee entry JUMPDEST for the same
+        // call. These occur on consecutive trace steps.
+        // Only skip if the top frame matches AND was
+        // pushed on the immediately preceding step —
+        // otherwise this is a new call (e.g. recursion).
         const top = frames[frames.length - 1];
-        if (
-          !top ||
-          top.identifier !== info.identifier ||
-          top.callType !== info.callType
-        ) {
+        const isDuplicate =
+          top &&
+          top.identifier === info.identifier &&
+          top.callType === info.callType &&
+          top.stepIndex === i - 1;
+        if (!isDuplicate) {
           frames.push({
             identifier: info.identifier,
             stepIndex: i,