From 09d71448b7bfa18dca8e3c94cde5914d25cdd607 Mon Sep 17 00:00:00 2001
From: Deadbeef <fee1-dead-beef@protonmail.com>
Date: Tue, 23 Mar 2021 10:45:34 +0800
Subject: [PATCH] Fix ICE of for-loop mut borrowck where no suggestions are
available
---
.../diagnostics/mutability_errors.rs | 17 ++++++----
.../issue-83309-ice-immut-in-for-loop.rs | 32 +++++++++++++++++++
.../issue-83309-ice-immut-in-for-loop.stderr | 12 +++++++
3 files changed, 54 insertions(+), 7 deletions(-)
create mode 100644 src/test/ui/borrowck/issue-83309-ice-immut-in-for-loop.rs
create mode 100644 src/test/ui/borrowck/issue-83309-ice-immut-in-for-loop.stderr
diff --git a/compiler/rustc_mir/src/borrow_check/diagnostics/mutability_errors.rs b/compiler/rustc_mir/src/borrow_check/diagnostics/mutability_errors.rs
index 28f6508cab2..d1fb999e518 100644
--- a/compiler/rustc_mir/src/borrow_check/diagnostics/mutability_errors.rs
+++ b/compiler/rustc_mir/src/borrow_check/diagnostics/mutability_errors.rs
@@ -642,15 +642,18 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
.starts_with(&original_method_ident.name.to_string())
})
.map(|ident| format!("{}()", ident))
+ .peekable()
});
- if let Some(suggestions) = opt_suggestions {
- err.span_suggestions(
- path_segment.ident.span,
- &format!("use mutable method"),
- suggestions,
- Applicability::MaybeIncorrect,
- );
+ if let Some(mut suggestions) = opt_suggestions {
+ if suggestions.peek().is_some() {
+ err.span_suggestions(
+ path_segment.ident.span,
+ &format!("use mutable method"),
+ suggestions,
+ Applicability::MaybeIncorrect,
+ );
+ }
}
}
};
diff --git a/src/test/ui/borrowck/issue-83309-ice-immut-in-for-loop.rs b/src/test/ui/borrowck/issue-83309-ice-immut-in-for-loop.rs
new file mode 100644
index 00000000000..6da88bed2c6
--- /dev/null
+++ b/src/test/ui/borrowck/issue-83309-ice-immut-in-for-loop.rs
@@ -0,0 +1,32 @@
+// rust-lang/rust#83309: The compiler tries to suggest potential
+// methods that return `&mut` items. However, when it doesn't
+// find such methods, it still tries to add suggestions
+// which then fails an assertion later because there was
+// no suggestions to make.
+
+
+fn main() {
+ for v in Query.iter_mut() {
+ //~^ NOTE this iterator yields `&` references
+ *v -= 1;
+ //~^ ERROR cannot assign to `*v` which is behind a `&` reference
+ //~| NOTE `v` is a `&` reference, so the data it refers to cannot be written
+ }
+}
+
+pub struct Query;
+pub struct QueryIter<'a>(&'a i32);
+
+impl Query {
+ pub fn iter_mut<'a>(&'a mut self) -> QueryIter<'a> {
+ todo!();
+ }
+}
+
+impl<'a> Iterator for QueryIter<'a> {
+ type Item = &'a i32;
+
+ fn next(&mut self) -> Option<Self::Item> {
+ todo!();
+ }
+}
diff --git a/src/test/ui/borrowck/issue-83309-ice-immut-in-for-loop.stderr b/src/test/ui/borrowck/issue-83309-ice-immut-in-for-loop.stderr
new file mode 100644
index 00000000000..143b74c39ba
--- /dev/null
+++ b/src/test/ui/borrowck/issue-83309-ice-immut-in-for-loop.stderr
@@ -0,0 +1,12 @@
+error[E0594]: cannot assign to `*v` which is behind a `&` reference
+ --> $DIR/issue-83309-ice-immut-in-for-loop.rs:11:9
+ |
+LL | for v in Query.iter_mut() {
+ | ---------------- this iterator yields `&` references
+LL |
+LL | *v -= 1;
+ | ^^^^^^^ `v` is a `&` reference, so the data it refers to cannot be written
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0594`.