From bd32c4c21ee30abc3795e5537245f157c31214e8 Mon Sep 17 00:00:00 2001
From: Nicholas Nethercote <n.nethercote@gmail.com>
Date: Mon, 17 Jun 2024 14:03:26 +1000
Subject: [PATCH] Convert a `span_bug` to a `span_delayed_bug`.

PR #121208 converted this from a `span_delayed_bug` to a `span_bug`
because nothing in the test suite caused execution to hit this path. But
now fuzzing has found a test case that does hit it. So this commit
converts it back to `span_delayed_bug` and adds the relevant test.

Fixes #126385.
---
 .../src/diagnostics/region_name.rs            |  4 +--
 tests/crashes/126385.rs                       | 10 ------
 .../unmatched-arg-and-hir-arg-issue-126385.rs | 14 ++++++++
 ...atched-arg-and-hir-arg-issue-126385.stderr | 34 +++++++++++++++++++
 4 files changed, 49 insertions(+), 13 deletions(-)
 delete mode 100644 tests/crashes/126385.rs
 create mode 100644 tests/ui/borrowck/unmatched-arg-and-hir-arg-issue-126385.rs
 create mode 100644 tests/ui/borrowck/unmatched-arg-and-hir-arg-issue-126385.stderr

diff --git a/compiler/rustc_borrowck/src/diagnostics/region_name.rs b/compiler/rustc_borrowck/src/diagnostics/region_name.rs
index 2cf548e28b18a..77fb9fb431518 100644
--- a/compiler/rustc_borrowck/src/diagnostics/region_name.rs
+++ b/compiler/rustc_borrowck/src/diagnostics/region_name.rs
@@ -628,9 +628,7 @@ impl<'tcx> MirBorrowckCtxt<'_, 'tcx> {
                     | GenericArgKind::Const(_),
                     _,
                 ) => {
-                    // This was previously a `span_delayed_bug` and could be
-                    // reached by the test for #82126, but no longer.
-                    self.dcx().span_bug(
+                    self.dcx().span_delayed_bug(
                         hir_arg.span(),
                         format!("unmatched arg and hir arg: found {kind:?} vs {hir_arg:?}"),
                     );
diff --git a/tests/crashes/126385.rs b/tests/crashes/126385.rs
deleted file mode 100644
index 9e74e88c1ffe1..0000000000000
--- a/tests/crashes/126385.rs
+++ /dev/null
@@ -1,10 +0,0 @@
-//@ known-bug: rust-lang/rust#126385
-pub struct MyStruct<'field> {
-    field: &'_ [u32],
-}
-
-impl MyStruct<'_> {
-    pub fn _<'a>(field: &'a[u32]) -> Self<new> {
-    Self{field}
-    }
-}
diff --git a/tests/ui/borrowck/unmatched-arg-and-hir-arg-issue-126385.rs b/tests/ui/borrowck/unmatched-arg-and-hir-arg-issue-126385.rs
new file mode 100644
index 0000000000000..637c47f29396d
--- /dev/null
+++ b/tests/ui/borrowck/unmatched-arg-and-hir-arg-issue-126385.rs
@@ -0,0 +1,14 @@
+// This test was triggering a `span_bug` crash, which was then fixed by
+// downgrading it to a `span_delayed_bug`.
+
+pub struct MyStruct<'field> {
+    field: &'field [u32],
+}
+
+impl MyStruct<'_> {
+    pub fn f(field: &[u32]) -> Self<u32> { //~ ERROR type arguments are not allowed on self type
+        Self { field }                     //~ ERROR lifetime may not live long enough
+    }
+}
+
+fn main() {}
diff --git a/tests/ui/borrowck/unmatched-arg-and-hir-arg-issue-126385.stderr b/tests/ui/borrowck/unmatched-arg-and-hir-arg-issue-126385.stderr
new file mode 100644
index 0000000000000..0ae301b2090ac
--- /dev/null
+++ b/tests/ui/borrowck/unmatched-arg-and-hir-arg-issue-126385.stderr
@@ -0,0 +1,34 @@
+error[E0109]: type arguments are not allowed on self type
+  --> $DIR/unmatched-arg-and-hir-arg-issue-126385.rs:9:37
+   |
+LL |     pub fn f(field: &[u32]) -> Self<u32> {
+   |                                ---- ^^^ type argument not allowed
+   |                                |
+   |                                not allowed on self type
+   |
+note: `Self` is of type `MyStruct<'_>`
+  --> $DIR/unmatched-arg-and-hir-arg-issue-126385.rs:4:12
+   |
+LL | pub struct MyStruct<'field> {
+   |            ^^^^^^^^ `Self` corresponds to this type
+...
+LL | impl MyStruct<'_> {
+   | ----------------- `Self` is on type `MyStruct` in this `impl`
+help: the `Self` type doesn't accept type parameters, use the concrete type's name `MyStruct` instead if you want to specify its type parameters
+   |
+LL |     pub fn f(field: &[u32]) -> MyStruct<u32> {
+   |                                ~~~~~~~~
+
+error: lifetime may not live long enough
+  --> $DIR/unmatched-arg-and-hir-arg-issue-126385.rs:10:9
+   |
+LL |     pub fn f(field: &[u32]) -> Self<u32> {
+   |                     -          --------- return type is MyStruct<'2>
+   |                     |
+   |                     let's call the lifetime of this reference `'1`
+LL |         Self { field }
+   |         ^^^^^^^^^^^^^^ associated function was supposed to return data with lifetime `'2` but it is returning data with lifetime `'1`
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0109`.