From 5ce5e3c37425e370e61ec1e04ff1cfdbbe375c41 Mon Sep 17 00:00:00 2001
From: Niko Matsakis <niko@alum.mit.edu>
Date: Wed, 17 Apr 2024 17:41:16 -0400
Subject: [PATCH] track and assert struct ingredient indices

We need a cheap way to compute field indices.
---
 components/salsa-2022-macros/src/tracked_struct.rs |  2 +-
 components/salsa-2022/src/routes.rs                |  8 ++++++--
 components/salsa-2022/src/tracked_struct.rs        | 14 ++++++++++++++
 3 files changed, 21 insertions(+), 3 deletions(-)

diff --git a/components/salsa-2022-macros/src/tracked_struct.rs b/components/salsa-2022-macros/src/tracked_struct.rs
index 0a4bb9b9..9d0ec4f5 100644
--- a/components/salsa-2022-macros/src/tracked_struct.rs
+++ b/components/salsa-2022-macros/src/tracked_struct.rs
@@ -257,7 +257,7 @@ impl TrackedStruct {
                 where
                     DB: salsa::DbWithJar<Self::Jar> + salsa::storage::JarFromJars<Self::Jar>,
                 {
-                    let struct_ingredient =                         {
+                    let struct_ingredient = {
                         let index = routes.push(
                             |jars| {
                                 let jar = <DB as salsa::storage::JarFromJars<Self::Jar>>::jar_from_jars(jars);
diff --git a/components/salsa-2022/src/routes.rs b/components/salsa-2022/src/routes.rs
index 1226bc0a..d8e663c1 100644
--- a/components/salsa-2022/src/routes.rs
+++ b/components/salsa-2022/src/routes.rs
@@ -10,13 +10,17 @@ pub struct IngredientIndex(u32);
 
 impl IngredientIndex {
     /// Create an ingredient index from a usize.
-    fn from(v: usize) -> Self {
+    pub(crate) fn from(v: usize) -> Self {
         assert!(v < (std::u32::MAX as usize));
         Self(v as u32)
     }
 
+    pub(crate) fn as_u32(self) -> u32 {
+        self.0
+    }
+
     /// Convert the ingredient index back into a usize.
-    fn as_usize(self) -> usize {
+    pub(crate) fn as_usize(self) -> usize {
         self.0 as usize
     }
 }
diff --git a/components/salsa-2022/src/tracked_struct.rs b/components/salsa-2022/src/tracked_struct.rs
index 0a548060..15f8d08e 100644
--- a/components/salsa-2022/src/tracked_struct.rs
+++ b/components/salsa-2022/src/tracked_struct.rs
@@ -121,6 +121,10 @@ pub struct TrackedStructValue<C>
 where
     C: Configuration,
 {
+    /// Index of the struct ingredient.
+    #[allow(dead_code)]
+    struct_ingredient_index: IngredientIndex,
+
     /// The id of this struct in the ingredient.
     id: C::Id,
 
@@ -166,12 +170,21 @@ where
         }
     }
 
+    fn struct_ingredient_index(&self) -> IngredientIndex {
+        self.interned.ingredient_index()
+    }
+
     pub fn new_field_ingredient(
         &self,
         field_ingredient_index: IngredientIndex,
         field_index: u32,
         field_debug_name: &'static str,
     ) -> TrackedFieldIngredient<C> {
+        assert_eq!(
+            field_ingredient_index.as_u32() - self.struct_ingredient_index().as_u32() - 1,
+            field_index,
+        );
+
         TrackedFieldIngredient {
             ingredient_index: field_ingredient_index,
             field_index,
@@ -215,6 +228,7 @@ where
                 runtime,
                 TrackedStructValue {
                     id,
+                    struct_ingredient_index: self.struct_ingredient_index(),
                     created_at: current_revision,
                     durability: current_deps.durability,
                     fields,