Auto merge of #52948 - davidtwco:issue-52633-later-loop-iteration, r=pnkfelix
NLL: Better Diagnostic When "Later" means "A Future Loop Iteration" Part of #52663. r? @pnkfelix
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commit
e415b5ecc0
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@ -11,7 +11,7 @@
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use borrow_check::borrow_set::BorrowData;
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use borrow_check::nll::region_infer::Cause;
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use borrow_check::{Context, MirBorrowckCtxt, WriteKind};
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use rustc::mir::Place;
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use rustc::mir::{Location, Place, TerminatorKind};
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use rustc_errors::DiagnosticBuilder;
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mod find_use;
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@ -63,10 +63,17 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
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match find_use::find(mir, regioncx, tcx, region_sub, context.loc) {
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Some(Cause::LiveVar(_local, location)) => {
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err.span_label(
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mir.source_info(location).span,
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"borrow later used here".to_string(),
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);
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if self.is_borrow_location_in_loop(context.loc) {
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err.span_label(
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mir.source_info(location).span,
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"borrow used here in later iteration of loop".to_string(),
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);
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} else {
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err.span_label(
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mir.source_info(location).span,
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"borrow later used here".to_string(),
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);
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}
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}
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Some(Cause::DropVar(local, location)) => match &mir.local_decls[local].name {
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@ -107,4 +114,76 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
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}
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}
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}
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/// Check if a borrow location is within a loop.
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fn is_borrow_location_in_loop(
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&self,
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borrow_location: Location,
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) -> bool {
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let mut visited_locations = Vec::new();
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let mut pending_locations = vec![ borrow_location ];
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debug!("is_in_loop: borrow_location={:?}", borrow_location);
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while let Some(location) = pending_locations.pop() {
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debug!("is_in_loop: location={:?} pending_locations={:?} visited_locations={:?}",
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location, pending_locations, visited_locations);
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if location == borrow_location && visited_locations.contains(&borrow_location) {
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// We've managed to return to where we started (and this isn't the start of the
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// search).
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debug!("is_in_loop: found!");
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return true;
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}
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// Skip locations we've been.
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if visited_locations.contains(&location) { continue; }
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let block = &self.mir.basic_blocks()[location.block];
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if location.statement_index == block.statements.len() {
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// Add start location of the next blocks to pending locations.
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match block.terminator().kind {
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TerminatorKind::Goto { target } => {
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pending_locations.push(target.start_location());
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},
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TerminatorKind::SwitchInt { ref targets, .. } => {
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for target in targets {
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pending_locations.push(target.start_location());
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}
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},
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TerminatorKind::Drop { target, unwind, .. } |
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TerminatorKind::DropAndReplace { target, unwind, .. } |
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TerminatorKind::Assert { target, cleanup: unwind, .. } |
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TerminatorKind::Yield { resume: target, drop: unwind, .. } |
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TerminatorKind::FalseUnwind { real_target: target, unwind, .. } => {
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pending_locations.push(target.start_location());
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if let Some(unwind) = unwind {
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pending_locations.push(unwind.start_location());
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}
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},
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TerminatorKind::Call { ref destination, cleanup, .. } => {
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if let Some((_, destination)) = destination {
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pending_locations.push(destination.start_location());
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}
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if let Some(cleanup) = cleanup {
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pending_locations.push(cleanup.start_location());
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}
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},
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TerminatorKind::FalseEdges { real_target, ref imaginary_targets, .. } => {
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pending_locations.push(real_target.start_location());
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for target in imaginary_targets {
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pending_locations.push(target.start_location());
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}
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},
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_ => {},
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}
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} else {
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// Add the next statement to pending locations.
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pending_locations.push(location.successor_within_block());
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}
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// Keep track of where we have visited.
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visited_locations.push(location);
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}
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false
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}
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}
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@ -17,7 +17,7 @@ LL | let inner_second = &mut inner_void; //~ ERROR cannot borrow
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| ^^^^^^^^^^^^^^^ second mutable borrow occurs here
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LL | inner_second.use_mut();
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LL | inner_first.use_mut();
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| ----------- borrow later used here
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| ----------- borrow used here in later iteration of loop
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error: aborting due to 2 previous errors
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@ -5,7 +5,7 @@ LL | let v: Vec<&str> = line.split_whitespace().collect();
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| ^^^^ borrowed value does not live long enough
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LL | //~^ ERROR `line` does not live long enough
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LL | println!("accumulator before add_assign {:?}", acc.map);
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| ------- borrow later used here
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| ------- borrow used here in later iteration of loop
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...
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LL | }
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| - `line` dropped here while still borrowed
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@ -7,7 +7,7 @@ LL | foo.mutate();
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| ^^^^^^^^^^^^ mutable borrow occurs here
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LL | //~^ ERROR cannot borrow `foo` as mutable
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LL | println!("foo={:?}", *string);
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| ------- borrow later used here
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| ------- borrow used here in later iteration of loop
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error: aborting due to previous error
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@ -2,7 +2,7 @@ error[E0597]: `x` does not live long enough
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--> $DIR/regions-escape-loop-via-variable.rs:21:13
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LL | let x = 1 + *p;
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| -- borrow later used here
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| -- borrow used here in later iteration of loop
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LL | p = &x;
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| ^^ borrowed value does not live long enough
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LL | }
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@ -7,7 +7,7 @@ LL | while x < 10 { //~ ERROR cannot use `x` because it was mutably borrowed
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| ^ use of borrowed `x`
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LL | let mut z = x; //~ ERROR cannot use `x` because it was mutably borrowed
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LL | _y.push(&mut z);
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| -- borrow later used here
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| -- borrow used here in later iteration of loop
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error[E0503]: cannot use `x` because it was mutably borrowed
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--> $DIR/regions-escape-loop-via-vec.rs:16:21
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@ -18,7 +18,7 @@ LL | while x < 10 { //~ ERROR cannot use `x` because it was mutably borrowed
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LL | let mut z = x; //~ ERROR cannot use `x` because it was mutably borrowed
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| ^ use of borrowed `x`
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LL | _y.push(&mut z);
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| -- borrow later used here
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| -- borrow used here in later iteration of loop
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error[E0597]: `z` does not live long enough
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--> $DIR/regions-escape-loop-via-vec.rs:17:17
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@ -26,7 +26,7 @@ error[E0597]: `z` does not live long enough
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LL | _y.push(&mut z);
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| -- ^^^^^^ borrowed value does not live long enough
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| |
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| borrow later used here
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| borrow used here in later iteration of loop
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...
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LL | }
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| - `z` dropped here while still borrowed
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@ -38,7 +38,7 @@ LL | let mut _y = vec![&mut x];
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| ------ borrow of `x` occurs here
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...
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LL | _y.push(&mut z);
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| -- borrow later used here
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| -- borrow used here in later iteration of loop
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LL | //~^ ERROR `z` does not live long enough
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LL | x += 1; //~ ERROR cannot assign
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| ^^^^^^ use of borrowed `x`
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