NLL: Improve move error loop detection (was "First shot at #54015") #54343
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nikomatsakis
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nikomatsakis
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Sep 21, 2018
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Updates look good. It'd be nice, if you're up for it, to separate the "rustfmt run" into its own commit (I usually do this by rebasing and "inserting" a rustfmt commit before the "meat").
The main concern though is that the output looks wrong; but then I see there's a travis failure, maybe it just needs to be updated?
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| /// True if we traversed a back edge while walking from the point | ||
| /// of error to the move site. | ||
| traversed_back_edge: bool, |
| | ^ value used here after move | ||
| LL | while true { while true { while true { x = y; x.clone(); } } } | ||
| | - value moved here | ||
| | ^ value moved here in previous iteration of loop |
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Huh, interesting. This doesn't quite look right, since this location is not a move.
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Is this the current output?
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I expect to see "value used here after move", and the "value moved here..." annotation somewhere else.
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Ah, no, the travis failure is that the |
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joydeep$ rustc +stage2 src/test/ui/liveness/liveness-move-in-while.rs error: aborting due to previous error For more information about this error, try |
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That is the current error when we compile the file. Expected: But we are getting: It completely ate up this line |
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☔ The latest upstream changes (presumably #54229) made this pull request unmergeable. Please resolve the merge conflicts. |
let move_site_vec = self.get_moved_indexes(context, mpi);
debug!(
- "report_use_of_moved_or_uninitialized: mois={:?}",
+ "report_use_of_moved_or_uninitialized: vec<mois,back_edge>={:?}",
move_site_vec
);
- let mois = move_site_vec.clone().into_iter().map(|x| x.moi).collect();
+ let mois = move_site_vec
+ .clone()
+ .into_iter()
+ .map(|x| {
+ let location = self.move_data.moves[x.moi].source;
+ let span = self.mir.source_info(location).span;
+ debug!("moi {:?}: {:?}", x.moi, span);
+ x.moi
+ })
+ .collect();
if move_site_vec.is_empty() {
let root_place = self.prefixes(&place, PrefixSet::All).last().unwrap();
@@ -137,12 +146,19 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
""
};
- if move_site.traversed_back_edge {
+ // if move_site.traversed_back_edge {
+ // is_loop_move = true;
+ // err.span_label(
+ // span,
+ // format!("value moved{} here in previous iteration of loop", move_msg),
+ // );
+ // }
+ if span == move_span {
+ is_loop_move = true;
err.span_label(
span,
format!("value moved{} here in previous iteration of loop", move_msg),
);
- is_loop_move = true;
} else {
err.span_label(move_span, format!("value moved{} here", move_msg));
move_spans.var_span_label(&mut err, "variable moved due to use in closure"); |
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This change is basically the same error reporting with the back-edge calculation done (but not used). >$ rustc +stage2 ./src/test/ui/liveness/liveness-move-in-while.rs
error[E0382]: borrow of moved value: `y`
--> ./src/test/ui/liveness/liveness-move-in-while.rs:18:24
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18 | println!("{}", y); //~ ERROR borrow of moved value: `y`
| ^ value moved here in previous iteration of loop
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= note: move occurs because `y` has type `std::boxed::Box<isize>`, which does not implement the `Copy` trait
error: aborting due to previous error
For more information about this error, try `rustc --explain E0382`.Compiled with stage 1, this is the output: >$ rustc +stage1 ./src/test/ui/liveness/liveness-move-in-while.rs
error[E0382]: borrow of moved value: `y`
--> ./src/test/ui/liveness/liveness-move-in-while.rs:18:24
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18 | println!("{}", y); //~ ERROR borrow of moved value: `y`
| ^ value borrowed here after move
19 | while true { while true { while true { x = y; x.clone(); } } }
| - value moved here
|
= note: move occurs because `y` has type `std::boxed::Box<isize>`, which does not implement the `Copy` trait
error: aborting due to previous error
For more information about this error, try `rustc --explain E0382`. |
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davidtwco
reviewed
Sep 28, 2018
| debug!( | ||
| "report_use_of_moved_or_uninitialized: current_location={:?}", | ||
| l | ||
| location |
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nit: could you add is_back_edge to this debug! too? It's useful if someone else ever needs to make a change here and work out what is happening from the logging.
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Thank you. That is a good point.
| @@ -134,8 +152,16 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> { | |||
| format!("value moved{} here in previous iteration of loop", move_msg), | |||
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nit: perhaps add a comma in this message too.
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I couldn't this to the above review below since you didn't change these lines, but could you change the error message in the below snippet to have a comma so all of the "iteration of loop" messages are consistent? (I'm pretty sure this still makes sense gramatically) ie. rust/src/librustc_mir/borrow_check/nll/explain_borrow/mod.rs Lines 48 to 52 in c222479 |
Before this patch running the following command would generate the given output:
$ rustc +stage1 src/test/ui/liveness/liveness-move-in-while.rs -Zborrowck=mir -Ztwo-phase-borrows
error[E0382]: borrow of moved value: `y`
--> src/main.rs:8:24
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8 | println!("{}", y); //~ ERROR use of moved value: `y`
| ^ value borrowed here after move
9 | while true { while true { while true { x = y; x.clone(); } } }
| - value moved here
|
= note: move occurs because `y` has type `std::boxed::Box<isize>`, which does not implement the `Copy` trait
We want to give the user more hint by telling them that the value was moved in the previous iteration of the
loop. After this patch, the error message adds the phrase "in previous iteration of loop" and in totality
looks like this:
$ rustc +stage1 src/test/ui/liveness/liveness-move-in-while.rs -Zborrowck=mir -Ztwo-phase-borrows
error[E0382]: borrow of moved value: `y`
--> src/test/ui/liveness/liveness-move-in-while.rs:17:24
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17 | println!("{}", y); //~ ERROR use of moved value: `y`
| ^ value borrowed here after move
18 | while true { while true { while true { x = y; x.clone(); } } }
| - value moved here, in previous iteration of loop
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= note: move occurs because `y` has type `std::boxed::Box<isize>`, which does not implement the `Copy` trait
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@bors r |
nikomatsakis
approved these changes
Oct 2, 2018
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@bors r+ |
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📌 Commit 671e77d has been approved by |
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☀️ Test successful - status-appveyor, status-travis |
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Closes #54015