Auto merge of #81717 - Aaron1011:fix/closure-diag, r=estebank

bors · bors · commit e708cbd91c9c · 2021-02-03T20:53:08.000Z
Fix panic when emitting diagnostic for closure mutable binding error Fixes #81700 The upvar borrow kind may be `ty::BorrowKind::UniqueImmBorrow`, which is still a mutable borrow for the purposes of this diagnostic code.
diff --git a/compiler/rustc_mir/src/borrow_check/diagnostics/mutability_errors.rs b/compiler/rustc_mir/src/borrow_check/diagnostics/mutability_errors.rs
@@ -514,15 +514,15 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
             let upvar = ty::place_to_string_for_capture(tcx, place);
             match tables.upvar_capture(upvar_id) {
                 ty::UpvarCapture::ByRef(ty::UpvarBorrow {
-                    kind: ty::BorrowKind::MutBorrow,
+                    kind: ty::BorrowKind::MutBorrow | ty::BorrowKind::UniqueImmBorrow,
                     ..
                 }) => {
                     format!("mutable borrow of `{}`", upvar)
                 }
                 ty::UpvarCapture::ByValue(_) => {
                     format!("possible mutation of `{}`", upvar)
                 }
-                _ => bug!("upvar `{}` borrowed, but not mutably", upvar),
+                val => bug!("upvar `{}` borrowed, but not mutably: {:?}", upvar, val),
             }
         } else {
             bug!("not an upvar")
diff --git a/src/test/ui/closures/issue-81700-mut-borrow.rs b/src/test/ui/closures/issue-81700-mut-borrow.rs
@@ -0,0 +1,5 @@
+fn foo(x: &mut u32) {
+    let bar = || { foo(x); };
+    bar(); //~ ERROR cannot borrow
+}
+fn main() {}
diff --git a/src/test/ui/closures/issue-81700-mut-borrow.stderr b/src/test/ui/closures/issue-81700-mut-borrow.stderr
@@ -0,0 +1,13 @@
+error[E0596]: cannot borrow `bar` as mutable, as it is not declared as mutable
+  --> $DIR/issue-81700-mut-borrow.rs:3:5
+   |
+LL |     let bar = || { foo(x); };
+   |         ---            - calling `bar` requires mutable binding due to mutable borrow of `x`
+   |         |
+   |         help: consider changing this to be mutable: `mut bar`
+LL |     bar();
+   |     ^^^ cannot borrow as mutable
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0596`.

Original file line number	Diff line number	Diff line change
`@@ -514,15 +514,15 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {`
`514`	`514`	`let upvar = ty::place_to_string_for_capture(tcx, place);`
`515`	`515`	`match tables.upvar_capture(upvar_id) {`
`516`	`516`	`ty::UpvarCapture::ByRef(ty::UpvarBorrow {`
`517`		`- kind: ty::BorrowKind::MutBorrow,`
	`517`	`+ kind: ty::BorrowKind::MutBorrow \| ty::BorrowKind::UniqueImmBorrow,`
`518`	`518`	`..`
`519`	`519`	`}) => {`
`520`	`520`	format!("mutable borrow of `{}`", upvar)
`521`	`521`	`}`
`522`	`522`	`ty::UpvarCapture::ByValue(_) => {`
`523`	`523`	format!("possible mutation of `{}`", upvar)
`524`	`524`	`}`
`525`		- _ => bug!("upvar `{}` borrowed, but not mutably", upvar),
	`525`	+ val => bug!("upvar `{}` borrowed, but not mutably: {:?}", upvar, val),
`526`	`526`	`}`
`527`	`527`	`} else {`
`528`	`528`	`bug!("not an upvar")`