Rollup merge of #45221 - estebank:issue-41790, r=nikomatsakis
Point at immutable outer variable When attempting to mutate an immutable outer variable from a closure, point at the outer variable and suggest making it mutable. Fix #41790.
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2a6a4e7045
3 changed files with 45 additions and 1 deletions
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@ -759,7 +759,21 @@ impl<'a, 'tcx> BorrowckCtxt<'a, 'tcx> {
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let mut db = match err.cause {
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MutabilityViolation => {
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self.cannot_assign(error_span, &descr, Origin::Ast)
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let mut db = self.cannot_assign(error_span, &descr, Origin::Ast);
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if let mc::NoteClosureEnv(upvar_id) = err.cmt.note {
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let node_id = self.tcx.hir.hir_to_node_id(upvar_id.var_id);
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let sp = self.tcx.hir.span(node_id);
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match self.tcx.sess.codemap().span_to_snippet(sp) {
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Ok(snippet) => {
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let msg = &format!("consider making `{}` mutable", snippet);
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db.span_suggestion(sp, msg, format!("mut {}", snippet));
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}
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_ => {
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db.span_help(sp, "consider making this binding mutable");
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}
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}
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}
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db
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}
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BorrowViolation(euv::ClosureCapture(_)) => {
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struct_span_err!(self.tcx.sess, error_span, E0595,
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20
src/test/ui/suggestions/closure-immutable-outer-variable.rs
Normal file
20
src/test/ui/suggestions/closure-immutable-outer-variable.rs
Normal file
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@ -0,0 +1,20 @@
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// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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// Point at the captured immutable outer variable
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fn foo(mut f: Box<FnMut()>) {
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f();
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}
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fn main() {
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let y = true;
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foo(Box::new(move || y = false) as Box<_>);
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}
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@ -0,0 +1,10 @@
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error[E0594]: cannot assign to captured outer variable in an `FnMut` closure
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--> $DIR/closure-immutable-outer-variable.rs:19:26
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18 | let y = true;
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| - help: consider making `y` mutable: `mut y`
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19 | foo(Box::new(move || y = false) as Box<_>);
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| ^^^^^^^^^
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error: aborting due to previous error
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