From f4c5a958932d2e618882c8a7972820b909770db1 Mon Sep 17 00:00:00 2001
From: Googler <tanzhengwei@google.com>
Date: Mon, 6 Mar 2023 04:58:28 -0800
Subject: [PATCH] Do not use ImmutableList.copyOf whilst finding the innermost
 starlark function of a StarlarkThread.

RELNOTES: None.
PiperOrigin-RevId: 514374572
Change-Id: I719489ebb78fd8c9a230d09a962e1208dd01eda9
---
 src/main/java/net/starlark/java/eval/Module.java      |  7 +++----
 .../java/net/starlark/java/eval/StarlarkThread.java   | 11 +++++++++++
 2 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/src/main/java/net/starlark/java/eval/Module.java b/src/main/java/net/starlark/java/eval/Module.java
index e1640ab145b0c3..248cad55b3debd 100644
--- a/src/main/java/net/starlark/java/eval/Module.java
+++ b/src/main/java/net/starlark/java/eval/Module.java
@@ -104,10 +104,9 @@ public static Module create() {
    */
   @Nullable
   public static Module ofInnermostEnclosingStarlarkFunction(StarlarkThread thread) {
-    for (Debug.Frame fr : thread.getDebugCallStack().reverse()) {
-      if (fr.getFunction() instanceof StarlarkFunction) {
-        return ((StarlarkFunction) fr.getFunction()).getModule();
-      }
+    StarlarkFunction fn = thread.getInnermostEnclosingStarlarkFunction();
+    if (fn != null) {
+      return fn.getModule();
     }
     return null;
   }
diff --git a/src/main/java/net/starlark/java/eval/StarlarkThread.java b/src/main/java/net/starlark/java/eval/StarlarkThread.java
index b6816fdca6ba20..ea4d0ebcaa60c4 100644
--- a/src/main/java/net/starlark/java/eval/StarlarkThread.java
+++ b/src/main/java/net/starlark/java/eval/StarlarkThread.java
@@ -440,6 +440,17 @@ ImmutableList<Debug.Frame> getDebugCallStack() {
     return ImmutableList.copyOf(callstack);
   }
 
+  @Nullable
+  StarlarkFunction getInnermostEnclosingStarlarkFunction() {
+    for (int i = callstack.size() - 1; i >= 0; i--) {
+      Debug.Frame fr = callstack.get(i);
+      if (fr.getFunction() instanceof StarlarkFunction) {
+        return (StarlarkFunction) fr.getFunction();
+      }
+    }
+    return null;
+  }
+
   /** Returns the size of the callstack. This is needed for the debugger. */
   int getCallStackSize() {
     return callstack.size();