From 01c974ff98a293c9792779bbe4428f1e9b55a05b Mon Sep 17 00:00:00 2001
From: Michael Goulet <michael@errs.io>
Date: Wed, 14 Feb 2024 18:02:55 +0000
Subject: [PATCH] Do not report overflow errors on ConstArgHasType goals

---
 .../src/traits/fulfill.rs                     | 27 ++++++++++--------
 tests/ui/codegen/overflow-during-mono.rs      | 28 +++++++++++++++++++
 tests/ui/codegen/overflow-during-mono.stderr  | 11 ++++++++
 3 files changed, 54 insertions(+), 12 deletions(-)
 create mode 100644 tests/ui/codegen/overflow-during-mono.rs
 create mode 100644 tests/ui/codegen/overflow-during-mono.stderr

diff --git a/compiler/rustc_trait_selection/src/traits/fulfill.rs b/compiler/rustc_trait_selection/src/traits/fulfill.rs
index 5ef7a202a1253..7ad9427463418 100644
--- a/compiler/rustc_trait_selection/src/traits/fulfill.rs
+++ b/compiler/rustc_trait_selection/src/traits/fulfill.rs
@@ -423,6 +423,21 @@ impl<'a, 'tcx> ObligationProcessor for FulfillProcessor<'a, 'tcx> {
                 ty::PredicateKind::AliasRelate(..) => {
                     bug!("AliasRelate is only used by the new solver")
                 }
+                // Compute `ConstArgHasType` above the overflow check below.
+                // This is because this is not ever a useful obligation to report
+                // as the cause of an overflow.
+                ty::PredicateKind::Clause(ty::ClauseKind::ConstArgHasType(ct, ty)) => {
+                    match self.selcx.infcx.at(&obligation.cause, obligation.param_env).eq(
+                        DefineOpaqueTypes::No,
+                        ct.ty(),
+                        ty,
+                    ) {
+                        Ok(inf_ok) => ProcessResult::Changed(mk_pending(inf_ok.into_obligations())),
+                        Err(_) => ProcessResult::Error(FulfillmentErrorCode::SelectionError(
+                            SelectionError::Unimplemented,
+                        )),
+                    }
+                }
 
                 // General case overflow check. Allow `process_trait_obligation`
                 // and `process_projection_obligation` to handle checking for
@@ -650,18 +665,6 @@ impl<'a, 'tcx> ObligationProcessor for FulfillProcessor<'a, 'tcx> {
                         }
                     }
                 }
-                ty::PredicateKind::Clause(ty::ClauseKind::ConstArgHasType(ct, ty)) => {
-                    match self.selcx.infcx.at(&obligation.cause, obligation.param_env).eq(
-                        DefineOpaqueTypes::No,
-                        ct.ty(),
-                        ty,
-                    ) {
-                        Ok(inf_ok) => ProcessResult::Changed(mk_pending(inf_ok.into_obligations())),
-                        Err(_) => ProcessResult::Error(FulfillmentErrorCode::SelectionError(
-                            SelectionError::Unimplemented,
-                        )),
-                    }
-                }
             },
         }
     }
diff --git a/tests/ui/codegen/overflow-during-mono.rs b/tests/ui/codegen/overflow-during-mono.rs
new file mode 100644
index 0000000000000..e45db18e4074f
--- /dev/null
+++ b/tests/ui/codegen/overflow-during-mono.rs
@@ -0,0 +1,28 @@
+// build-fail
+//~^ ERROR overflow evaluating the requirement
+
+#![recursion_limit = "32"]
+
+fn quicksort<It: Clone + Iterator<Item = T>, I: IntoIterator<IntoIter = It>, T: Ord>(
+    i: I,
+) -> Vec<T> {
+    let mut i = i.into_iter();
+
+    match i.next() {
+        Some(x) => {
+            let less = i.clone().filter(|y| y < &x);
+            let greater = i.filter(|y| &x <= y);
+
+            let mut v = quicksort(less);
+            let u = quicksort(greater);
+            v.push(x);
+            v.extend(u);
+            v
+        }
+        None => vec![],
+    }
+}
+
+fn main() {
+    println!("{:?}", quicksort([5i32, 1, 6, 3, 6, 1, 9, 0, -1, 6, 8]));
+}
diff --git a/tests/ui/codegen/overflow-during-mono.stderr b/tests/ui/codegen/overflow-during-mono.stderr
new file mode 100644
index 0000000000000..f7a3e2df3dbaa
--- /dev/null
+++ b/tests/ui/codegen/overflow-during-mono.stderr
@@ -0,0 +1,11 @@
+error[E0275]: overflow evaluating the requirement `{closure@$DIR/overflow-during-mono.rs:13:41: 13:44}: Sized`
+   |
+   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "64"]` attribute to your crate (`overflow_during_mono`)
+   = note: required for `Filter<std::array::IntoIter<i32, 11>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>` to implement `Iterator`
+   = note: 31 redundant requirements hidden
+   = note: required for `Filter<Filter<Filter<Filter<Filter<Filter<Filter<Filter<Filter<Filter<Filter<Filter<Filter<Filter<Filter<Filter<Filter<Filter<Filter<Filter<Filter<Filter<Filter<Filter<Filter<Filter<Filter<Filter<Filter<Filter<Filter<Filter<std::array::IntoIter<i32, 11>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>` to implement `Iterator`
+   = note: required for `Filter<Filter<Filter<Filter<Filter<Filter<Filter<Filter<Filter<Filter<Filter<Filter<Filter<Filter<Filter<Filter<Filter<Filter<Filter<Filter<Filter<Filter<Filter<Filter<Filter<Filter<Filter<Filter<Filter<Filter<Filter<Filter<std::array::IntoIter<i32, 11>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>` to implement `IntoIterator`
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0275`.