From 3fa1cceed8ee3e259c71508c9ef2fe96052051f1 Mon Sep 17 00:00:00 2001
From: Mofei Zhang <feifei0@meta.com>
Date: Thu, 13 Jun 2024 20:33:39 -0400
Subject: [PATCH] Update base for Update on "[compiler][rewrite] Patch logic
 for aligning scopes to non-value blocks"
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Our previous logic for aligning scopes to block scopes constructs a tree of block and scope nodes. We ensured that blocks always mapped to the same node as their fallthroughs. e.g.
```js
// source
a();
if (...) {
  b();
}
c();

// HIR
bb0:
a()
if test=... consequent=bb1 fallthrough=bb2

bb1:
b()
goto bb2

bb2:
c()

// AlignReactiveScopesToBlockScopesHIR nodes
Root node (maps to both bb0 and bb2)
  |- bb1
  |- ...
```

There are two issues with the existing implementation:
1. Only scopes that overlap with the beginning of a block are aligned correctly. This is because the traversal does not store information about the block-fallthrough pair for scopes that begin *within* the block-fallthrough range.
```
\# This case gets handled correctly
         ┌──────────────┐
         │              │
         block start    block end

scope start     scope end
│               │
└───────────────┘

\# But not this one!
┌──────────────┐
│              │
block start    block end

          scope start     scope end
          │               │
          └───────────────┘
```
2. Only scopes that are directly used by a block is considered. See the `align-scopes-nested-block-structure` fixture for details.

[ghstack-poisoned]