From fc0abdeb5529f3bc942d090f50895cae88731b12 Mon Sep 17 00:00:00 2001
From: yukang <moorekang@gmail.com>
Date: Fri, 21 Jul 2023 23:57:28 +0800
Subject: [PATCH] More precisely point out what is immutable for E0596
---
.../src/diagnostics/mutability_errors.rs | 52 +++++++++++++++++--
tests/ui/borrowck/issue-111554.stderr | 10 +++-
tests/ui/borrowck/issue_113842.rs | 22 ++++++++
tests/ui/borrowck/issue_113842.stderr | 31 +++++++++++
...et-else-binding-explicit-mut-borrow.stderr | 10 +++-
tests/ui/nll/issue-51191.rs | 1 +
tests/ui/nll/issue-51191.stderr | 16 ++++--
7 files changed, 133 insertions(+), 9 deletions(-)
create mode 100644 tests/ui/borrowck/issue_113842.rs
create mode 100644 tests/ui/borrowck/issue_113842.stderr
diff --git a/compiler/rustc_borrowck/src/diagnostics/mutability_errors.rs b/compiler/rustc_borrowck/src/diagnostics/mutability_errors.rs
index e6bde6a8c54dc..efe6f9cd5ce5f 100644
--- a/compiler/rustc_borrowck/src/diagnostics/mutability_errors.rs
+++ b/compiler/rustc_borrowck/src/diagnostics/mutability_errors.rs
@@ -506,9 +506,8 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
self.expected_fn_found_fn_mut_call(&mut err, span, act);
}
- PlaceRef { local: _, projection: [.., ProjectionElem::Deref] } => {
- err.span_label(span, format!("cannot {act}"));
-
+ PlaceRef { local: _, projection: [proj_base @ .., ProjectionElem::Deref] } => {
+ let mut span = span;
match opt_source {
Some(BorrowedContentSource::OverloadedDeref(ty)) => {
err.help(format!(
@@ -523,8 +522,15 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
));
self.suggest_map_index_mut_alternatives(ty, &mut err, span);
}
+ Some(BorrowedContentSource::DerefSharedRef) => {
+ let place_ref =
+ PlaceRef { local: the_place_err.local, projection: proj_base };
+ let ty = place_ref.ty(self.body, self.infcx.tcx).ty;
+ self.suggest_detailed_hint_for_ref(ty, &mut err, &mut span);
+ }
_ => (),
}
+ err.span_label(span, format!("cannot {act}"));
}
_ => {
@@ -539,6 +545,46 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
}
}
+ fn suggest_detailed_hint_for_ref(&self, ty: Ty<'_>, err: &mut Diagnostic, span: &mut Span) {
+ struct ExprFinder {
+ span: Span,
+ hir_id: Option<hir::HirId>,
+ }
+
+ impl<'tcx> Visitor<'tcx> for ExprFinder {
+ fn visit_expr(&mut self, s: &'tcx hir::Expr<'tcx>) {
+ if s.span.contains(self.span) {
+ self.hir_id = Some(s.hir_id);
+ }
+ hir::intravisit::walk_expr(self, s);
+ }
+ }
+ let hir_map = self.infcx.tcx.hir();
+ let def_id = self.body.source.def_id();
+ let hir_id = if let Some(local_def_id) = def_id.as_local()
+ && let Some(body_id) = hir_map.maybe_body_owned_by(local_def_id) {
+ let body = hir_map.body(body_id);
+ let mut v = ExprFinder {
+ span: *span,
+ hir_id: None,
+ };
+ v.visit_body(body);
+ v.hir_id
+ } else {
+ None
+ };
+ let expr = if let Some(hir_id) = hir_id {
+ hir_map.expect_expr(hir_id)
+ } else {
+ return;
+ };
+ if let hir::ExprKind::AddrOf(hir::BorrowKind::Ref, Mutability::Mut, ex) = expr.kind
+ && !matches!(ex.kind, hir::ExprKind::Unary(hir::UnOp::Deref, _) | hir::ExprKind::Field(_, _) | hir::ExprKind::Lit(_)) {
+ *span = ex.span;
+ err.span_help(ex.span, format!("this expression is of type `{}`, which is an immutable reference", ty));
+ }
+ }
+
fn suggest_map_index_mut_alternatives(&self, ty: Ty<'tcx>, err: &mut Diagnostic, span: Span) {
let Some(adt) = ty.ty_adt_def() else { return };
let did = adt.did();
diff --git a/tests/ui/borrowck/issue-111554.stderr b/tests/ui/borrowck/issue-111554.stderr
index 6b7a42e495999..4779b573719c7 100644
--- a/tests/ui/borrowck/issue-111554.stderr
+++ b/tests/ui/borrowck/issue-111554.stderr
@@ -14,7 +14,15 @@ error[E0596]: cannot borrow data in a `&` reference as mutable
--> $DIR/issue-111554.rs:10:16
|
LL | || bar(&mut self);
- | ^^^^^^^^^ cannot borrow as mutable
+ | ^^^^^----
+ | |
+ | cannot borrow as mutable
+ |
+help: this expression is of type `&Foo`, which is an immutable reference
+ --> $DIR/issue-111554.rs:10:21
+ |
+LL | || bar(&mut self);
+ | ^^^^
error[E0596]: cannot borrow `self` as mutable, as it is not declared as mutable
--> $DIR/issue-111554.rs:21:16
diff --git a/tests/ui/borrowck/issue_113842.rs b/tests/ui/borrowck/issue_113842.rs
new file mode 100644
index 0000000000000..adb7e40b267b1
--- /dev/null
+++ b/tests/ui/borrowck/issue_113842.rs
@@ -0,0 +1,22 @@
+mod some_library {
+ pub fn foo(_: &mut [i32]) {}
+ pub fn bar<'a>() -> &'a [i32] {
+ &[]
+ }
+ pub fn bar_mut<'a>() -> &'a mut [i32] {
+ &mut []
+ }
+}
+
+struct Foo {
+ pub x: i32,
+}
+
+fn foo() {
+ let foo = Foo { x: 0 };
+ let _y: &mut Foo = &mut &foo; //~ ERROR cannot borrow data in a `&` reference as mutable
+}
+
+fn main() {
+ some_library::foo(&mut some_library::bar()); //~ ERROR cannot borrow data in a `&` reference as mutable
+}
diff --git a/tests/ui/borrowck/issue_113842.stderr b/tests/ui/borrowck/issue_113842.stderr
new file mode 100644
index 0000000000000..164574b77f5bb
--- /dev/null
+++ b/tests/ui/borrowck/issue_113842.stderr
@@ -0,0 +1,31 @@
+error[E0596]: cannot borrow data in a `&` reference as mutable
+ --> $DIR/issue_113842.rs:17:24
+ |
+LL | let _y: &mut Foo = &mut &foo;
+ | ^^^^^----
+ | |
+ | cannot borrow as mutable
+ |
+help: this expression is of type `&Foo`, which is an immutable reference
+ --> $DIR/issue_113842.rs:17:29
+ |
+LL | let _y: &mut Foo = &mut &foo;
+ | ^^^^
+
+error[E0596]: cannot borrow data in a `&` reference as mutable
+ --> $DIR/issue_113842.rs:21:23
+ |
+LL | some_library::foo(&mut some_library::bar());
+ | ^^^^^-------------------
+ | |
+ | cannot borrow as mutable
+ |
+help: this expression is of type `&[i32]`, which is an immutable reference
+ --> $DIR/issue_113842.rs:21:28
+ |
+LL | some_library::foo(&mut some_library::bar());
+ | ^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0596`.
diff --git a/tests/ui/let-else/let-else-binding-explicit-mut-borrow.stderr b/tests/ui/let-else/let-else-binding-explicit-mut-borrow.stderr
index 023fab8fe4a3d..46e60d662de67 100644
--- a/tests/ui/let-else/let-else-binding-explicit-mut-borrow.stderr
+++ b/tests/ui/let-else/let-else-binding-explicit-mut-borrow.stderr
@@ -2,7 +2,15 @@ error[E0596]: cannot borrow data in a `&` reference as mutable
--> $DIR/let-else-binding-explicit-mut-borrow.rs:7:37
|
LL | let Some(n): &mut Option<i32> = &mut &Some(5i32) else {
- | ^^^^^^^^^^^^^^^^ cannot borrow as mutable
+ | ^^^^^-----------
+ | |
+ | cannot borrow as mutable
+ |
+help: this expression is of type `&Option<i32>`, which is an immutable reference
+ --> $DIR/let-else-binding-explicit-mut-borrow.rs:7:42
+ |
+LL | let Some(n): &mut Option<i32> = &mut &Some(5i32) else {
+ | ^^^^^^^^^^^
error: aborting due to previous error
diff --git a/tests/ui/nll/issue-51191.rs b/tests/ui/nll/issue-51191.rs
index 836587d93b84b..a2076b0db6188 100644
--- a/tests/ui/nll/issue-51191.rs
+++ b/tests/ui/nll/issue-51191.rs
@@ -22,6 +22,7 @@ impl Struct {
(&mut self).bar();
//~^ ERROR cannot borrow `self` as mutable, as it is not declared as mutable [E0596]
//~^^ ERROR cannot borrow data in a `&` reference as mutable [E0596]
+ //~^^^ HELP this expression is of type `&Struct`, which is an immutable reference
}
fn mtblref(&mut self) {
diff --git a/tests/ui/nll/issue-51191.stderr b/tests/ui/nll/issue-51191.stderr
index c14056c3a834b..5da92b2ad6e8f 100644
--- a/tests/ui/nll/issue-51191.stderr
+++ b/tests/ui/nll/issue-51191.stderr
@@ -48,21 +48,29 @@ error[E0596]: cannot borrow data in a `&` reference as mutable
--> $DIR/issue-51191.rs:22:9
|
LL | (&mut self).bar();
- | ^^^^^^^^^^^ cannot borrow as mutable
+ | ^^^^^^----^
+ | |
+ | cannot borrow as mutable
+ |
+help: this expression is of type `&Struct`, which is an immutable reference
+ --> $DIR/issue-51191.rs:22:15
+ |
+LL | (&mut self).bar();
+ | ^^^^
error[E0596]: cannot borrow `self` as mutable, as it is not declared as mutable
- --> $DIR/issue-51191.rs:28:9
+ --> $DIR/issue-51191.rs:29:9
|
LL | (&mut self).bar();
| ^^^^^^^^^^^ cannot borrow as mutable
|
note: the binding is already a mutable borrow
- --> $DIR/issue-51191.rs:27:16
+ --> $DIR/issue-51191.rs:28:16
|
LL | fn mtblref(&mut self) {
| ^^^^^^^^^
help: try removing `&mut` here
- --> $DIR/issue-51191.rs:28:9
+ --> $DIR/issue-51191.rs:29:9
|
LL | (&mut self).bar();
| ^^^^^^^^^^^