From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Calvin Watford <cwatford@slack-corp.com>
Date: Wed, 17 Jul 2024 12:52:10 -0600
Subject: fix: disable scope reuse & associated dchecks

This change was introduced in https://crrev.com/c/5630974 which reuses
scope info objects across allocations. Unfortunately, this change seems
to be not yet fully cooked and causes crashes with normal usage of V8.

In particular, Node.js call's V8's `v8::ScriptCompiler::CompileFunction`
method. This ends up wrapping the source code in a function, which this
code is not yet prepared to handle. The generated function wrapper
(created by V8) has no source position, so it reports being at the start
of the source, which may overlap with other scopes that are in the
original source. This new feature adds a "UniqueIdInScript" concept that
is derived from the source position of a scope, along with the invariant
that inner scopes have a higher ID than outer scopes, which does not
hold for the above situation.

This patch is not intended to remain indefinitely. Once the upstream
feature stabilizes, we can remove this patch. Unfortunately, there is no
public tracking bug for this feature nor the crashes its been causing,
so we'll have to keep an eye on this for the time being.

diff --git a/src/ast/scopes.cc b/src/ast/scopes.cc
index 6c85e6734d40bbbe24d883b083f6712c474cc283..dc39bceb9b7c939eba8f4d2dd0c53395bde8fec4 100644
--- a/src/ast/scopes.cc
+++ b/src/ast/scopes.cc
@@ -2722,9 +2722,9 @@ void Scope::AllocateScopeInfosRecursively(
 
   // Allocate ScopeInfos for inner scopes.
   for (Scope* scope = inner_scope_; scope != nullptr; scope = scope->sibling_) {
-    DCHECK_GT(scope->UniqueIdInScript(), UniqueIdInScript());
-    DCHECK_IMPLIES(scope->sibling_, scope->sibling_->UniqueIdInScript() !=
-                                        scope->UniqueIdInScript());
+    // DCHECK_GT(scope->UniqueIdInScript(), UniqueIdInScript());
+    // DCHECK_IMPLIES(scope->sibling_, scope->sibling_->UniqueIdInScript() !=
+    //                                     scope->UniqueIdInScript());
     if (!scope->is_function_scope() ||
         scope->AsDeclarationScope()->ShouldEagerCompile()) {
       scope->AllocateScopeInfosRecursively(isolate, next_outer_scope,
diff --git a/src/flags/flag-definitions.h b/src/flags/flag-definitions.h
index 2ac4e74daa5e8837f459755d85b4f451a7f5bb31..326b42c92dc1f20b0abff4b9f49657df6489f78d 100644
--- a/src/flags/flag-definitions.h
+++ b/src/flags/flag-definitions.h
@@ -996,7 +996,12 @@ DEFINE_BOOL(trace_track_allocation_sites, false,
 DEFINE_BOOL(trace_migration, false, "trace object migration")
 DEFINE_BOOL(trace_generalization, false, "trace map generalization")
 
-DEFINE_BOOL(reuse_scope_infos, true, "reuse scope infos from previous compiles")
+// ELECTRON: The following flag should remain false by default until we can
+//   remove `fix_disable_scope_reuse_associated_dchecks.patch`
+DEFINE_BOOL(reuse_scope_infos, false,
+            "reuse scope infos from previous compiles")
+
+DEFINE_IMPLICATION(fuzzing, reuse_scope_infos)
 
 // Flags for Sparkplug
 #undef FLAG