From c92342d58ddb8b653deaeda8eb7d775017291f9d Mon Sep 17 00:00:00 2001
From: Michael Goulet <michael@errs.io>
Date: Fri, 2 Jun 2023 03:21:26 +0000
Subject: [PATCH] Erase regions even if normalization fails in writeback

---
 compiler/rustc_hir_typeck/src/writeback.rs    | 11 ++++++--
 ...0605.stderr => issue-20605.current.stderr} |  2 +-
 tests/ui/issues/issue-20605.next.stderr       | 25 +++++++++++++++++++
 tests/ui/issues/issue-20605.rs                |  5 ++++
 4 files changed, 40 insertions(+), 3 deletions(-)
 rename tests/ui/issues/{issue-20605.stderr => issue-20605.current.stderr} (95%)
 create mode 100644 tests/ui/issues/issue-20605.next.stderr

diff --git a/compiler/rustc_hir_typeck/src/writeback.rs b/compiler/rustc_hir_typeck/src/writeback.rs
index a395858262f..29abe921bbd 100644
--- a/compiler/rustc_hir_typeck/src/writeback.rs
+++ b/compiler/rustc_hir_typeck/src/writeback.rs
@@ -136,7 +136,10 @@ fn tcx(&self) -> TyCtxt<'tcx> {
 
     fn write_ty_to_typeck_results(&mut self, hir_id: hir::HirId, ty: Ty<'tcx>) {
         debug!("write_ty_to_typeck_results({:?}, {:?})", hir_id, ty);
-        assert!(!ty.has_infer() && !ty.has_placeholders() && !ty.has_free_regions());
+        assert!(
+            !ty.has_infer() && !ty.has_placeholders() && !ty.has_free_regions(),
+            "{ty} can't be put into typeck results"
+        );
         self.typeck_results.node_types_mut().insert(hir_id, ty);
     }
 
@@ -803,7 +806,11 @@ fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
                 // We must normalize erasing regions here, since later lints
                 // expect that types that show up in the typeck are fully
                 // normalized.
-                self.fcx.tcx.try_normalize_erasing_regions(self.fcx.param_env, t).unwrap_or(t)
+                if let Ok(t) = self.fcx.tcx.try_normalize_erasing_regions(self.fcx.param_env, t) {
+                    t
+                } else {
+                    EraseEarlyRegions { tcx: self.fcx.tcx }.fold_ty(t)
+                }
             }
             Ok(t) => {
                 // Do not anonymize late-bound regions
diff --git a/tests/ui/issues/issue-20605.stderr b/tests/ui/issues/issue-20605.current.stderr
similarity index 95%
rename from tests/ui/issues/issue-20605.stderr
rename to tests/ui/issues/issue-20605.current.stderr
index e1858b63989..b9a53cbd4fc 100644
--- a/tests/ui/issues/issue-20605.stderr
+++ b/tests/ui/issues/issue-20605.current.stderr
@@ -1,5 +1,5 @@
 error[E0277]: the size for values of type `dyn Iterator<Item = &'a mut u8>` cannot be known at compilation time
-  --> $DIR/issue-20605.rs:2:17
+  --> $DIR/issue-20605.rs:5:17
    |
 LL |     for item in *things { *item = 0 }
    |                 ^^^^^^^ the trait `IntoIterator` is not implemented for `dyn Iterator<Item = &'a mut u8>`
diff --git a/tests/ui/issues/issue-20605.next.stderr b/tests/ui/issues/issue-20605.next.stderr
new file mode 100644
index 00000000000..5362a68c834
--- /dev/null
+++ b/tests/ui/issues/issue-20605.next.stderr
@@ -0,0 +1,25 @@
+error[E0277]: the trait bound `dyn Iterator<Item = &'a mut u8>: IntoIterator` is not satisfied
+  --> $DIR/issue-20605.rs:5:17
+   |
+LL |     for item in *things { *item = 0 }
+   |                 ^^^^^^^ the trait `IntoIterator` is not implemented for `dyn Iterator<Item = &'a mut u8>`
+
+error[E0277]: the size for values of type `<dyn Iterator<Item = &'a mut u8> as IntoIterator>::IntoIter` cannot be known at compilation time
+  --> $DIR/issue-20605.rs:5:17
+   |
+LL |     for item in *things { *item = 0 }
+   |                 ^^^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `<dyn Iterator<Item = &'a mut u8> as IntoIterator>::IntoIter`
+   = note: all local variables must have a statically known size
+   = help: unsized locals are gated as an unstable feature
+
+error: the type `<_ as IntoIterator>::IntoIter` is not well-formed
+  --> $DIR/issue-20605.rs:5:17
+   |
+LL |     for item in *things { *item = 0 }
+   |                 ^^^^^^^
+
+error: aborting due to 3 previous errors
+
+For more information about this error, try `rustc --explain E0277`.
diff --git a/tests/ui/issues/issue-20605.rs b/tests/ui/issues/issue-20605.rs
index 17b7d32ebf5..66bdc52e6b1 100644
--- a/tests/ui/issues/issue-20605.rs
+++ b/tests/ui/issues/issue-20605.rs
@@ -1,6 +1,11 @@
+// revisions: current next
+//[next] compile-flags: -Ztrait-solver=next
+
 fn changer<'a>(mut things: Box<dyn Iterator<Item=&'a mut u8>>) {
     for item in *things { *item = 0 }
 //~^ ERROR the size for values of type
+//[next]~^^ ERROR the type `<_ as IntoIterator>::IntoIter` is not well-formed
+//[next]~| ERROR the trait bound `dyn Iterator<Item = &'a mut u8>: IntoIterator` is not satisfied
 }
 
 fn main() {}