From 1cd9e683e8a43a427d141f82c580f47b07fce726 Mon Sep 17 00:00:00 2001
From: Chayim Refael Friedman <chayimfr@gmail.com>
Date: Thu, 27 Feb 2025 11:21:01 +0200
Subject: [PATCH] Normalize projections in evaluated const display and layout
 calculation

---
 crates/hir-ty/src/display.rs  |  2 ++
 crates/hir-ty/src/layout.rs   |  3 +++
 crates/ide/src/hover/tests.rs | 34 ++++++++++++++++++++++++++++++++++
 3 files changed, 39 insertions(+)

diff --git a/crates/hir-ty/src/display.rs b/crates/hir-ty/src/display.rs
index 6ee4780d20..b3613b372b 100644
--- a/crates/hir-ty/src/display.rs
+++ b/crates/hir-ty/src/display.rs
@@ -45,6 +45,7 @@ use crate::{
     db::{HirDatabase, InternedClosure},
     from_assoc_type_id, from_foreign_def_id, from_placeholder_idx,
     generics::generics,
+    infer::normalize,
     layout::Layout,
     lt_from_placeholder_idx,
     mapping::from_chalk,
@@ -657,6 +658,7 @@ fn render_const_scalar(
     // infrastructure and have it here as a field on `f`.
     let trait_env =
         TraitEnvironment::empty(*f.db.crate_graph().crates_in_topological_order().last().unwrap());
+    let ty = normalize(f.db, trait_env.clone(), ty.clone());
     match ty.kind(Interner) {
         TyKind::Scalar(s) => match s {
             Scalar::Bool => write!(f, "{}", b[0] != 0),
diff --git a/crates/hir-ty/src/layout.rs b/crates/hir-ty/src/layout.rs
index a4e49e0aa1..6b5c712159 100644
--- a/crates/hir-ty/src/layout.rs
+++ b/crates/hir-ty/src/layout.rs
@@ -435,6 +435,9 @@ pub fn layout_of_ty_query(
         TyKind::Error => return Err(LayoutError::HasErrorType),
         TyKind::AssociatedType(id, subst) => {
             // Try again with `TyKind::Alias` to normalize the associated type.
+            // Usually we should not try to normalize `TyKind::AssociatedType`, but layout calculation is used
+            // in monomorphized MIR where this is okay. If outside monomorphization, this will lead to cycle,
+            // which we will recover from with an error.
             let ty = TyKind::Alias(chalk_ir::AliasTy::Projection(ProjectionTy {
                 associated_ty_id: *id,
                 substitution: subst.clone(),
diff --git a/crates/ide/src/hover/tests.rs b/crates/ide/src/hover/tests.rs
index 7c720d97cb..964b1d7eb7 100644
--- a/crates/ide/src/hover/tests.rs
+++ b/crates/ide/src/hover/tests.rs
@@ -10947,3 +10947,37 @@ pub struct ManuallyDrop$0<T: ?Sized> {
         "#]],
     );
 }
+
+#[test]
+fn projection_const() {
+    check(
+        r#"
+pub trait PublicFlags {
+    type Internal;
+}
+
+pub struct NoteDialects(<NoteDialects as PublicFlags>::Internal);
+
+impl NoteDialects {
+    pub const CLAP$0: Self = Self(InternalBitFlags);
+}
+
+pub struct InternalBitFlags;
+
+impl PublicFlags for NoteDialects {
+    type Internal = InternalBitFlags;
+}
+    "#,
+        expect![[r#"
+            *CLAP*
+
+            ```rust
+            ra_test_fixture::NoteDialects
+            ```
+
+            ```rust
+            pub const CLAP: Self = NoteDialects(InternalBitFlags)
+            ```
+        "#]],
+    );
+}