From d2dc1af0e88d905b4ce7072fbbf576e8cccd0cfc Mon Sep 17 00:00:00 2001
From: Joe Savona <joesavona@fb.com>
Date: Fri, 6 Jun 2025 12:42:50 -0700
Subject: [PATCH] Update base for Update on "[compiler][newinference]
 Explicitly model StoreContext variables as mutable boxes"
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Context variables — in the {Declare,Store,Load}Context sense — are conceptually like mutable boxes that are stored into and read out of at various points. Previously some fixtures were failing in the new inference bc i wasn't fully modeling them this way, so this PR moves toward more explicitly modeling these variables exactly like a mutable object that we're storing into and reading out of.

One catch is that unlike with regular variables, a `StoreContext Let x = ...` may not be the initial declaration of a value — for hoisted bindings, they may be a `DeclareContext HoistedLet x` first. So we first do a scan over the HIR to determine which declaration ids have hoisted let/const/function bindings. Then we model the "first" declaration of each context declaration id as the creation of fresh mutable value (box), then model subsequent reassignments as mutations of that box plus capturing of a value into that box, and model loads as CreateFrom from the box. Thus StoreContext assignments have equivalent effects to PropertyStore and LoadContext has equivalent effects to PropertyLoad.

[ghstack-poisoned]