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Improve error message where a closure escapes fn while trying to borrow

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from the current fn. Employ the new `span_suggestion` to show how you
can use `move`.
This commit is contained in:
Niko Matsakis 2015-04-09 14:49:03 -04:00
parent 906a9728ff
commit e313b3334b
8 changed files with 128 additions and 13 deletions
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62
src/librustc_borrowck/borrowck/mod.rs
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@ -522,6 +522,16 @@ impl<'a, 'tcx> BorrowckCtxt<'a, 'tcx> {
}
pub fn report(&self, err: BckError<'tcx>) {
// Catch and handle some particular cases.
match (&err.code, &err.cause) {
(&err_out_of_scope(ty::ReScope(_), ty::ReStatic), &euv::ClosureCapture(span)) |
(&err_out_of_scope(ty::ReScope(_), ty::ReFree(..)), &euv::ClosureCapture(span)) => {
return self.report_out_of_scope_escaping_closure_capture(&err, span);
}
_ => { }
}
// General fallback.
self.span_err(
err.span,
&self.bckerr_to_string(&err));
@ -796,16 +806,10 @@ impl<'a, 'tcx> BorrowckCtxt<'a, 'tcx> {
format!("{} does not live long enough", msg)
}
err_borrowed_pointer_too_short(..) => {
let descr = match opt_loan_path(&err.cmt) {
Some(lp) => {
format!("`{}`", self.loan_path_to_string(&*lp))
}
None => self.cmt_to_string(&*err.cmt),
};
let descr = self.cmt_to_path_or_string(&err.cmt);
format!("lifetime of {} is too short to guarantee \
its contents can be safely reborrowed",
descr)
its contents can be safely reborrowed",
descr)
}
}
}
@ -888,6 +892,39 @@ impl<'a, 'tcx> BorrowckCtxt<'a, 'tcx> {
}
}
fn report_out_of_scope_escaping_closure_capture(&self,
err: &BckError<'tcx>,
capture_span: Span)
{
let cmt_path_or_string = self.cmt_to_path_or_string(&err.cmt);
span_err!(
self.tcx.sess, err.span, E0373,
"closure may outlive the current function, \
but it borrows {}, \
which is owned by the current function",
cmt_path_or_string);
self.tcx.sess.span_note(
capture_span,
&format!("{} is borrowed here",
cmt_path_or_string));
let suggestion =
match self.tcx.sess.codemap().span_to_snippet(err.span) {
Ok(string) => format!("move {}", string),
Err(_) => format!("move |<args>| <body>")
};
self.tcx.sess.span_suggestion(
err.span,
&format!("to force the closure to take ownership of {} \
(and any other referenced variables), \
use the `move` keyword, as shown:",
cmt_path_or_string),
suggestion);
}
pub fn note_and_explain_bckerr(&self, err: BckError<'tcx>) {
let code = err.code;
match code {
@ -1035,6 +1072,13 @@ impl<'a, 'tcx> BorrowckCtxt<'a, 'tcx> {
pub fn cmt_to_string(&self, cmt: &mc::cmt_<'tcx>) -> String {
cmt.descriptive_string(self.tcx)
}
pub fn cmt_to_path_or_string(&self, cmt: &mc::cmt<'tcx>) -> String {
match opt_loan_path(cmt) {
Some(lp) => format!("`{}`", self.loan_path_to_string(&lp)),
None => self.cmt_to_string(cmt),
}
}
}
fn is_statement_scope(tcx: &ty::ctxt, region: ty::Region) -> bool {

17
src/librustc_borrowck/diagnostics.rs Normal file
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@ -0,0 +1,17 @@
// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
#![allow(non_snake_case)]
register_diagnostics! {
E0373 // closure may outlive current fn, but it borrows {}, which is owned by current fn
}
__build_diagnostic_array! { DIAGNOSTICS }

4
src/librustc_borrowck/lib.rs
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@ -40,6 +40,10 @@ pub use borrowck::check_crate;
pub use borrowck::build_borrowck_dataflow_data_for_fn;
pub use borrowck::FnPartsWithCFG;
// NB: This module needs to be declared first so diagnostics are
// registered before they are used.
pub mod diagnostics;
mod borrowck;
pub mod graphviz;

25
src/test/compile-fail/borrowck-escaping-closure-error-1.rs Normal file
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@ -0,0 +1,25 @@
// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
use std::thread::spawn;
// Test that we give a custom error (E0373) for the case where a
// closure is escaping current frame, and offer a suggested code edit.
// I refrained from including the precise message here, but the
// original text as of the time of this writing is:
//
// closure may outlive the current function, but it borrows `books`,
// which is owned by the current function
fn main() {
let mut books = vec![1,2,3];
spawn(|| books.push(4));
//~^ ERROR E0373
}

25
src/test/compile-fail/borrowck-escaping-closure-error-2.rs Normal file
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@ -0,0 +1,25 @@
// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
// Test that we give a custom error (E0373) for the case where a
// closure is escaping current frame, and offer a suggested code edit.
// I refrained from including the precise message here, but the
// original text as of the time of this writing is:
//
// closure may outlive the current function, but it borrows `books`,
// which is owned by the current function
fn foo<'a>(x: &'a i32) -> Box<FnMut()+'a> {
let mut books = vec![1,2,3];
Box::new(|| books.push(4))
//~^ ERROR E0373
}
fn main() { }

4
src/test/compile-fail/issue-16747.rs
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@ -18,10 +18,10 @@ trait Collection { fn len(&self) -> usize; }
struct List<'a, T: ListItem<'a>> {
//~^ ERROR the parameter type `T` may not live long enough
//~^^ NOTE ...so that the reference type `&'a [T]` does not outlive the data it points at
//~| HELP consider adding an explicit lifetime bound
//~| NOTE ...so that the reference type `&'a [T]` does not outlive the data it points at
slice: &'a [T]
}
//~^ HELP consider adding an explicit lifetime bound
impl<'a, T: ListItem<'a>> Collection for List<'a, T> {
fn len(&self) -> usize {
0

2
src/test/compile-fail/issue-4335.rs
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@ -15,7 +15,7 @@ fn id<T>(t: T) -> T { t }
fn f<'r, T>(v: &'r T) -> Box<FnMut() -> T + 'r> {
// FIXME (#22405): Replace `Box::new` with `box` here when/if possible.
id(Box::new(|| *v))
//~^ ERROR `v` does not live long enough
//~^ ERROR E0373
//~| ERROR cannot move out of borrowed content
}

2
src/test/compile-fail/regions-nested-fns-2.rs
View File

@ -13,7 +13,7 @@ fn ignore<F>(_f: F) where F: for<'z> FnOnce(&'z isize) -> &'z isize {}
fn nested() {
let y = 3;
ignore(
|z| { //~ ERROR `y` does not live long enough
|z| { //~ ERROR E0373
if false { &y } else { z }
});
}