From 46923753890f04d12e1d9d230c6eb3b8af28bf40 Mon Sep 17 00:00:00 2001
From: Michael Goulet <michael@errs.io>
Date: Thu, 25 May 2023 01:41:13 +0000
Subject: [PATCH] Don't print newlines in APITs

---
 compiler/rustc_ast_lowering/src/lib.rs        | 11 +++++++++-
 .../arg-position-impl-trait-too-long.rs       | 22 +++++++++++++++++++
 .../arg-position-impl-trait-too-long.stderr   | 22 +++++++++++++++++++
 3 files changed, 54 insertions(+), 1 deletion(-)
 create mode 100644 tests/ui/impl-trait/arg-position-impl-trait-too-long.rs
 create mode 100644 tests/ui/impl-trait/arg-position-impl-trait-too-long.stderr

diff --git a/compiler/rustc_ast_lowering/src/lib.rs b/compiler/rustc_ast_lowering/src/lib.rs
index 211f5cb0a2a..8d4f96639ef 100644
--- a/compiler/rustc_ast_lowering/src/lib.rs
+++ b/compiler/rustc_ast_lowering/src/lib.rs
@@ -1425,7 +1425,16 @@ fn lower_ty_direct(&mut self, t: &Ty, itctx: &ImplTraitContext) -> hir::Ty<'hir>
                             DefPathData::ImplTrait,
                             span,
                         );
-                        let ident = Ident::from_str_and_span(&pprust::ty_to_string(t), span);
+
+                        // HACK: pprust breaks strings with newlines when the type
+                        // gets too long. We don't want these to show up in compiler
+                        // output or built artifacts, so replace them here...
+                        // Perhaps we should instead format APITs more robustly.
+                        let ident = Ident::from_str_and_span(
+                            &pprust::ty_to_string(t).replace('\n', " "),
+                            span,
+                        );
+
                         let (param, bounds, path) = self.lower_universal_param_and_bounds(
                             *def_node_id,
                             span,
diff --git a/tests/ui/impl-trait/arg-position-impl-trait-too-long.rs b/tests/ui/impl-trait/arg-position-impl-trait-too-long.rs
new file mode 100644
index 00000000000..8ef9281c9d3
--- /dev/null
+++ b/tests/ui/impl-trait/arg-position-impl-trait-too-long.rs
@@ -0,0 +1,22 @@
+struct Header;
+struct EntryMetadata;
+struct Entry<A, B>(A, B);
+
+trait Tr {
+    type EncodedKey;
+    type EncodedValue;
+}
+
+fn test<C: Tr, R>(
+    // This APIT is long, however we shouldn't render the type name with a newline in it.
+    y: impl FnOnce(
+        &mut Header,
+        &mut [EntryMetadata],
+        &mut [Entry<C::EncodedKey, C::EncodedValue>]
+    ) -> R,
+) {
+    let () = y;
+    //~^ ERROR mismatched types
+}
+
+fn main() {}
diff --git a/tests/ui/impl-trait/arg-position-impl-trait-too-long.stderr b/tests/ui/impl-trait/arg-position-impl-trait-too-long.stderr
new file mode 100644
index 00000000000..40446a3d339
--- /dev/null
+++ b/tests/ui/impl-trait/arg-position-impl-trait-too-long.stderr
@@ -0,0 +1,22 @@
+error[E0308]: mismatched types
+  --> $DIR/arg-position-impl-trait-too-long.rs:18:9
+   |
+LL |       y: impl FnOnce(
+   |  ________-
+LL | |         &mut Header,
+LL | |         &mut [EntryMetadata],
+LL | |         &mut [Entry<C::EncodedKey, C::EncodedValue>]
+LL | |     ) -> R,
+   | |__________- this type parameter
+LL |   ) {
+LL |       let () = y;
+   |           ^^   - this expression has type `impl FnOnce(&mut Header, &mut [EntryMetadata], &mut [Entry<C::EncodedKey, C::EncodedValue>]) -> R`
+   |           |
+   |           expected type parameter `impl FnOnce(&mut Header, &mut [EntryMetadata], &mut [Entry<C::EncodedKey, C::EncodedValue>]) -> R`, found `()`
+   |
+   = note: expected type parameter `impl FnOnce(&mut Header, &mut [EntryMetadata], &mut [Entry<C::EncodedKey, C::EncodedValue>]) -> R`
+                   found unit type `()`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0308`.