From c12575d3173eb6ba985482808a87e54f23ad328e Mon Sep 17 00:00:00 2001
From: Nilstrieb <48135649+Nilstrieb@users.noreply.github.com>
Date: Mon, 5 Jun 2023 08:34:06 +0000
Subject: [PATCH] Normalize in infcx instead of globally for `Option::as_deref`
 suggestion

The projection may contain inference variables. These inference
variables are local to the local inference context. Using
`tcx.normalize_erasing_regions` doesn't work here because this method is
global and does not have access to the inference context. It's therefore
unable to deal with the inference variables. We normalize in the local
inference context instead, which knowns about the inference variables.
---
 .../src/traits/error_reporting/suggestions.rs |  3 ++-
 .../suggest-option-asderef-inference-var.rs   |  9 +++++++
 ...uggest-option-asderef-inference-var.stderr | 24 +++++++++++++++++++
 3 files changed, 35 insertions(+), 1 deletion(-)
 create mode 100644 tests/ui/mismatched_types/suggest-option-asderef-inference-var.rs
 create mode 100644 tests/ui/mismatched_types/suggest-option-asderef-inference-var.stderr

diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
index 4ca83904f47..80d0faca670 100644
--- a/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
@@ -3592,7 +3592,8 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
             // Extract `<U as Deref>::Target` assoc type and check that it is `T`
             && let Some(deref_target_did) = tcx.lang_items().deref_target()
             && let projection = tcx.mk_projection(deref_target_did, tcx.mk_substs(&[ty::GenericArg::from(found_ty)]))
-            && let Ok(deref_target) = tcx.try_normalize_erasing_regions(param_env, projection)
+            && let InferOk { value: deref_target, obligations } = infcx.at(&ObligationCause::dummy(), param_env).normalize(projection)
+            && obligations.iter().all(|obligation| infcx.predicate_must_hold_modulo_regions(obligation))
             && infcx.can_eq(param_env, deref_target, target_ty)
         {
             let help = if let hir::Mutability::Mut = needs_mut
diff --git a/tests/ui/mismatched_types/suggest-option-asderef-inference-var.rs b/tests/ui/mismatched_types/suggest-option-asderef-inference-var.rs
new file mode 100644
index 00000000000..5febbbe392b
--- /dev/null
+++ b/tests/ui/mismatched_types/suggest-option-asderef-inference-var.rs
@@ -0,0 +1,9 @@
+fn deref_int(a: &i32) -> i32 {
+    *a
+}
+
+fn main() {
+    // https://github.com/rust-lang/rust/issues/112293
+    let _has_inference_vars: Option<i32> = Some(0).map(deref_int);
+    //~^ ERROR type mismatch in function arguments
+}
diff --git a/tests/ui/mismatched_types/suggest-option-asderef-inference-var.stderr b/tests/ui/mismatched_types/suggest-option-asderef-inference-var.stderr
new file mode 100644
index 00000000000..71c4729e310
--- /dev/null
+++ b/tests/ui/mismatched_types/suggest-option-asderef-inference-var.stderr
@@ -0,0 +1,24 @@
+error[E0631]: type mismatch in function arguments
+  --> $DIR/suggest-option-asderef-inference-var.rs:7:56
+   |
+LL | fn deref_int(a: &i32) -> i32 {
+   | ---------------------------- found signature defined here
+...
+LL |     let _has_inference_vars: Option<i32> = Some(0).map(deref_int);
+   |                                                    --- ^^^^^^^^^ expected due to this
+   |                                                    |
+   |                                                    required by a bound introduced by this call
+   |
+   = note: expected function signature `fn({integer}) -> _`
+              found function signature `for<'a> fn(&'a i32) -> _`
+note: required by a bound in `Option::<T>::map`
+  --> $SRC_DIR/core/src/option.rs:LL:COL
+help: do not borrow the argument
+   |
+LL - fn deref_int(a: &i32) -> i32 {
+LL + fn deref_int(a: i32) -> i32 {
+   |
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0631`.