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Fix unused_assignments false positive #57302

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Jan 19, 2019
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29 changes: 6 additions & 23 deletions src/librustc/middle/liveness.rs
Original file line number Diff line number Diff line change
Expand Up @@ -911,17 +911,8 @@ impl<'a, 'tcx> Liveness<'a, 'tcx> {
}

fn compute(&mut self, body: &hir::Expr) -> LiveNode {
// if there is a `break` or `again` at the top level, then it's
// effectively a return---this only occurs in `for` loops,
// where the body is really a closure.

debug!("compute: using id for body, {}", self.ir.tcx.hir().node_to_pretty_string(body.id));

let exit_ln = self.s.exit_ln;

self.break_ln.insert(body.id, exit_ln);
self.cont_ln.insert(body.id, exit_ln);

// the fallthrough exit is only for those cases where we do not
// explicitly return:
let s = self.s;
Expand Down Expand Up @@ -1024,19 +1015,10 @@ impl<'a, 'tcx> Liveness<'a, 'tcx> {
self.propagate_through_expr(&e, succ)
}

hir::ExprKind::Closure(.., blk_id, _, _) => {
hir::ExprKind::Closure(..) => {
debug!("{} is an ExprKind::Closure",
self.ir.tcx.hir().node_to_pretty_string(expr.id));

// The next-node for a break is the successor of the entire
// loop. The next-node for a continue is the top of this loop.
let node = self.live_node(expr.hir_id, expr.span);

let break_ln = succ;
let cont_ln = node;
self.break_ln.insert(blk_id.node_id, break_ln);
self.cont_ln.insert(blk_id.node_id, cont_ln);

// the construction of a closure itself is not important,
// but we have to consider the closed over variables.
let caps = self.ir.capture_info_map.get(&expr.id).cloned().unwrap_or_else(||
Expand Down Expand Up @@ -1407,15 +1389,16 @@ impl<'a, 'tcx> Liveness<'a, 'tcx> {
debug!("propagate_through_loop: using id for loop body {} {}",
expr.id, self.ir.tcx.hir().node_to_pretty_string(body.id));

let break_ln = succ;
let cont_ln = ln;
self.break_ln.insert(expr.id, break_ln);
self.cont_ln.insert(expr.id, cont_ln);

self.break_ln.insert(expr.id, succ);

let cond_ln = match kind {
LoopLoop => ln,
WhileLoop(ref cond) => self.propagate_through_expr(&cond, ln),
};

self.cont_ln.insert(expr.id, cond_ln);

let body_ln = self.propagate_through_block(body, cond_ln);

// repeat until fixed point is reached:
Expand Down
9 changes: 9 additions & 0 deletions src/test/ui/liveness/liveness-dead.rs
Original file line number Diff line number Diff line change
Expand Up @@ -27,4 +27,13 @@ fn f5(mut x: i32) {
x = 4; //~ ERROR: value assigned to `x` is never read
}

// #22630
fn f6() {
let mut done = false;
while !done {
done = true; // no error
continue;
}
}

fn main() {}