From 5c4909b8e18eb4fcc7e3b8b6826be5890aa8e529 Mon Sep 17 00:00:00 2001
From: Nadrieril <nadrieril+git@gmail.com>
Date: Thu, 4 Apr 2024 00:25:16 +0200
Subject: [PATCH] Track mutability of deref patterns

---
 compiler/rustc_middle/src/thir.rs                  | 5 +++--
 compiler/rustc_middle/src/thir/visit.rs            | 2 +-
 compiler/rustc_mir_build/src/build/matches/mod.rs  | 2 +-
 compiler/rustc_mir_build/src/build/matches/util.rs | 2 +-
 compiler/rustc_mir_build/src/thir/pattern/mod.rs   | 4 +++-
 compiler/rustc_mir_build/src/thir/print.rs         | 2 +-
 6 files changed, 10 insertions(+), 7 deletions(-)

diff --git a/compiler/rustc_middle/src/thir.rs b/compiler/rustc_middle/src/thir.rs
index 66130a8dde0..b55fd0a9231 100644
--- a/compiler/rustc_middle/src/thir.rs
+++ b/compiler/rustc_middle/src/thir.rs
@@ -642,7 +642,7 @@ fn walk_(&self, it: &mut impl FnMut(&Pat<'tcx>) -> bool) {
             AscribeUserType { subpattern, .. }
             | Binding { subpattern: Some(subpattern), .. }
             | Deref { subpattern }
-            | DerefPattern { subpattern }
+            | DerefPattern { subpattern, .. }
             | InlineConstant { subpattern, .. } => subpattern.walk_(it),
             Leaf { subpatterns } | Variant { subpatterns, .. } => {
                 subpatterns.iter().for_each(|field| field.pattern.walk_(it))
@@ -760,6 +760,7 @@ pub enum PatKind<'tcx> {
     /// Deref pattern, written `box P` for now.
     DerefPattern {
         subpattern: Box<Pat<'tcx>>,
+        mutability: hir::Mutability,
     },
 
     /// One of the following:
@@ -1163,7 +1164,7 @@ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
                 }
                 write!(f, "{subpattern}")
             }
-            PatKind::DerefPattern { ref subpattern } => {
+            PatKind::DerefPattern { ref subpattern, .. } => {
                 write!(f, "deref!({subpattern})")
             }
             PatKind::Constant { value } => write!(f, "{value}"),
diff --git a/compiler/rustc_middle/src/thir/visit.rs b/compiler/rustc_middle/src/thir/visit.rs
index e42b85530b5..f1988810437 100644
--- a/compiler/rustc_middle/src/thir/visit.rs
+++ b/compiler/rustc_middle/src/thir/visit.rs
@@ -229,7 +229,7 @@ pub fn walk_pat<'thir, 'tcx: 'thir, V: Visitor<'thir, 'tcx>>(
     match &pat.kind {
         AscribeUserType { subpattern, ascription: _ }
         | Deref { subpattern }
-        | DerefPattern { subpattern }
+        | DerefPattern { subpattern, .. }
         | Binding { subpattern: Some(subpattern), .. } => visitor.visit_pat(subpattern),
         Binding { .. } | Wild | Never | Error(_) => {}
         Variant { subpatterns, adt_def: _, args: _, variant_index: _ } | Leaf { subpatterns } => {
diff --git a/compiler/rustc_mir_build/src/build/matches/mod.rs b/compiler/rustc_mir_build/src/build/matches/mod.rs
index 6094c8e759c..2ac2c2546dd 100644
--- a/compiler/rustc_mir_build/src/build/matches/mod.rs
+++ b/compiler/rustc_mir_build/src/build/matches/mod.rs
@@ -938,7 +938,7 @@ pub(super) fn visit_primary_bindings(
                 self.visit_primary_bindings(subpattern, pattern_user_ty.deref(), f);
             }
 
-            PatKind::DerefPattern { ref subpattern } => {
+            PatKind::DerefPattern { ref subpattern, .. } => {
                 self.visit_primary_bindings(subpattern, UserTypeProjections::none(), f);
             }
 
diff --git a/compiler/rustc_mir_build/src/build/matches/util.rs b/compiler/rustc_mir_build/src/build/matches/util.rs
index 4d8248c0e39..3292ab1f1b7 100644
--- a/compiler/rustc_mir_build/src/build/matches/util.rs
+++ b/compiler/rustc_mir_build/src/build/matches/util.rs
@@ -249,7 +249,7 @@ pub(in crate::build) fn new(
                 default_irrefutable()
             }
 
-            PatKind::DerefPattern { ref subpattern } => {
+            PatKind::DerefPattern { ref subpattern, .. } => {
                 // Create a new temporary for each deref pattern.
                 // FIXME(deref_patterns): dedup temporaries to avoid multiple `deref()` calls?
                 let temp = cx.temp(
diff --git a/compiler/rustc_mir_build/src/thir/pattern/mod.rs b/compiler/rustc_mir_build/src/thir/pattern/mod.rs
index bcb43a00547..5c016682d8d 100644
--- a/compiler/rustc_mir_build/src/thir/pattern/mod.rs
+++ b/compiler/rustc_mir_build/src/thir/pattern/mod.rs
@@ -264,7 +264,9 @@ fn lower_pattern_unadjusted(&mut self, pat: &'tcx hir::Pat<'tcx>) -> Box<Pat<'tc
             }
 
             hir::PatKind::Deref(subpattern) => {
-                PatKind::DerefPattern { subpattern: self.lower_pattern(subpattern) }
+                let mutable = self.typeck_results.pat_has_ref_mut_binding(subpattern);
+                let mutability = if mutable { hir::Mutability::Mut } else { hir::Mutability::Not };
+                PatKind::DerefPattern { subpattern: self.lower_pattern(subpattern), mutability }
             }
             hir::PatKind::Ref(subpattern, _) | hir::PatKind::Box(subpattern) => {
                 PatKind::Deref { subpattern: self.lower_pattern(subpattern) }
diff --git a/compiler/rustc_mir_build/src/thir/print.rs b/compiler/rustc_mir_build/src/thir/print.rs
index 49e48427b65..619bfbcf43d 100644
--- a/compiler/rustc_mir_build/src/thir/print.rs
+++ b/compiler/rustc_mir_build/src/thir/print.rs
@@ -688,7 +688,7 @@ fn print_pat_kind(&mut self, pat_kind: &PatKind<'tcx>, depth_lvl: usize) {
                 self.print_pat(subpattern, depth_lvl + 2);
                 print_indented!(self, "}", depth_lvl + 1);
             }
-            PatKind::DerefPattern { subpattern } => {
+            PatKind::DerefPattern { subpattern, .. } => {
                 print_indented!(self, "DerefPattern { ", depth_lvl + 1);
                 print_indented!(self, "subpattern:", depth_lvl + 2);
                 self.print_pat(subpattern, depth_lvl + 2);