From 8bb574fdd301dbb6ff18bd2500ccf463ce8a19d4 Mon Sep 17 00:00:00 2001
From: Zalathar <Zalathar@users.noreply.github.com>
Date: Sun, 16 Feb 2025 21:10:04 +1100
Subject: [PATCH] Don't store a redundant span in user-type projections

This span is already present in the corresponding
`CanonicalUserTypeAnnotation`, and can be retrieved via the annotation's ID.
---
 compiler/rustc_borrowck/src/type_check/mod.rs | 11 +++++-----
 compiler/rustc_middle/src/mir/mod.rs          | 21 ++++++-------------
 compiler/rustc_middle/src/mir/visit.rs        |  2 +-
 .../src/builder/matches/mod.rs                |  3 +--
 4 files changed, 13 insertions(+), 24 deletions(-)

diff --git a/compiler/rustc_borrowck/src/type_check/mod.rs b/compiler/rustc_borrowck/src/type_check/mod.rs
index 21b0a62fe43..bd0d98028ae 100644
--- a/compiler/rustc_borrowck/src/type_check/mod.rs
+++ b/compiler/rustc_borrowck/src/type_check/mod.rs
@@ -456,12 +456,11 @@ impl<'a, 'b, 'tcx> Visitor<'tcx> for TypeVerifier<'a, 'b, 'tcx> {
     fn visit_local_decl(&mut self, local: Local, local_decl: &LocalDecl<'tcx>) {
         self.super_local_decl(local, local_decl);
 
-        for (user_ty, span) in local_decl
-            .user_ty
-            .as_deref()
-            .into_iter()
-            .flat_map(UserTypeProjections::projections_and_spans)
+        for user_ty in
+            local_decl.user_ty.as_deref().into_iter().flat_map(UserTypeProjections::projections)
         {
+            let span = self.typeck.user_type_annotations[user_ty.base].span;
+
             let ty = if local_decl.is_nonref_binding() {
                 local_decl.ty
             } else if let &ty::Ref(_, rty, _) = local_decl.ty.kind() {
@@ -477,7 +476,7 @@ impl<'a, 'b, 'tcx> Visitor<'tcx> for TypeVerifier<'a, 'b, 'tcx> {
                 ty,
                 ty::Invariant,
                 user_ty,
-                Locations::All(*span),
+                Locations::All(span),
                 ConstraintCategory::TypeAnnotation(AnnotationSource::Declaration),
             ) {
                 span_mirbug!(
diff --git a/compiler/rustc_middle/src/mir/mod.rs b/compiler/rustc_middle/src/mir/mod.rs
index d74a917f33c..71fed4b3e1e 100644
--- a/compiler/rustc_middle/src/mir/mod.rs
+++ b/compiler/rustc_middle/src/mir/mod.rs
@@ -1494,7 +1494,7 @@ pub struct SourceScopeLocalData {
 /// &'static str`.
 #[derive(Clone, Debug, TyEncodable, TyDecodable, HashStable, TypeFoldable, TypeVisitable)]
 pub struct UserTypeProjections {
-    pub contents: Vec<(UserTypeProjection, Span)>,
+    pub contents: Vec<UserTypeProjection>,
 }
 
 impl<'tcx> UserTypeProjections {
@@ -1506,26 +1506,17 @@ impl<'tcx> UserTypeProjections {
         self.contents.is_empty()
     }
 
-    pub fn projections_and_spans(
-        &self,
-    ) -> impl Iterator<Item = &(UserTypeProjection, Span)> + ExactSizeIterator {
+    pub fn projections(&self) -> impl Iterator<Item = &UserTypeProjection> + ExactSizeIterator {
         self.contents.iter()
     }
 
-    pub fn projections(&self) -> impl Iterator<Item = &UserTypeProjection> + ExactSizeIterator {
-        self.contents.iter().map(|&(ref user_type, _span)| user_type)
-    }
-
-    pub fn push_user_type(mut self, base_user_ty: UserTypeAnnotationIndex, span: Span) -> Self {
-        self.contents.push((UserTypeProjection { base: base_user_ty, projs: vec![] }, span));
+    pub fn push_user_type(mut self, base_user_type: UserTypeAnnotationIndex) -> Self {
+        self.contents.push(UserTypeProjection { base: base_user_type, projs: vec![] });
         self
     }
 
-    fn map_projections(
-        mut self,
-        mut f: impl FnMut(UserTypeProjection) -> UserTypeProjection,
-    ) -> Self {
-        self.contents = self.contents.into_iter().map(|(proj, span)| (f(proj), span)).collect();
+    fn map_projections(mut self, f: impl FnMut(UserTypeProjection) -> UserTypeProjection) -> Self {
+        self.contents = self.contents.into_iter().map(f).collect();
         self
     }
 
diff --git a/compiler/rustc_middle/src/mir/visit.rs b/compiler/rustc_middle/src/mir/visit.rs
index 193806f238b..98e8f269c57 100644
--- a/compiler/rustc_middle/src/mir/visit.rs
+++ b/compiler/rustc_middle/src/mir/visit.rs
@@ -857,7 +857,7 @@ macro_rules! make_mir_visitor {
                     source_info: *source_info,
                 });
                 if let Some(user_ty) = user_ty {
-                    for (user_ty, _) in & $($mutability)? user_ty.contents {
+                    for user_ty in & $($mutability)? user_ty.contents {
                         self.visit_user_type_projection(user_ty);
                     }
                 }
diff --git a/compiler/rustc_mir_build/src/builder/matches/mod.rs b/compiler/rustc_mir_build/src/builder/matches/mod.rs
index f551f0ceeda..6334612eced 100644
--- a/compiler/rustc_mir_build/src/builder/matches/mod.rs
+++ b/compiler/rustc_mir_build/src/builder/matches/mod.rs
@@ -927,8 +927,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 // of `user_ty` on any bindings contained with subpattern.
 
                 let base_user_ty = self.canonical_user_type_annotations.push(annotation.clone());
-                let subpattern_user_ty =
-                    pattern_user_ty.push_user_type(base_user_ty, annotation.span);
+                let subpattern_user_ty = pattern_user_ty.push_user_type(base_user_ty);
                 self.visit_primary_bindings(subpattern, subpattern_user_ty, f)
             }