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librustc: Disallow mutation and assignment in pattern guards, and modify #15989

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librustc: Disallow mutation and assignment in pattern guards, and modify #15989

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9 changes: 7 additions & 2 deletions src/libfmt_macros/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -352,8 +352,13 @@ impl<'a> Parser<'a> {
None => {
let tmp = self.cur.clone();
match self.word() {
word if word.len() > 0 && self.consume('$') => {
CountIsName(word)
word if word.len() > 0 => {
if self.consume('$') {
CountIsName(word)
} else {
self.cur = tmp;
CountImplied
}
}
_ => {
self.cur = tmp;
Expand Down
41 changes: 23 additions & 18 deletions src/librustc/middle/cfg/construct.rs
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Expand Up @@ -333,32 +333,37 @@ impl<'a> CFGBuilder<'a> {
// [discr]
// |
// v 2
// [guard1]
// [cond1]
// / \
// | \
// v 3 |
// [pat1] |
// |
// v 4 |
// [body1] v
// | [guard2]
// | / \
// | [body2] \
// | | ...
// | | |
// v 5 v v
// [....expr....]
// v 3 \
// [pat1] \
// | |
// v 4 |
// [guard1] |
// | |
// | |
// v 5 v
// [body1] [cond2]
// | / \
// | ... ...
// | | |
// v 6 v v
// [.....expr.....]
//
let discr_exit = self.expr(discr.clone(), pred); // 1

let expr_exit = self.add_node(expr.id, []);
let mut guard_exit = discr_exit;
let mut cond_exit = discr_exit;
for arm in arms.iter() {
guard_exit = self.opt_expr(arm.guard, guard_exit); // 2
cond_exit = self.add_dummy_node([cond_exit]); // 2
let pats_exit = self.pats_any(arm.pats.as_slice(),
guard_exit); // 3
let body_exit = self.expr(arm.body.clone(), pats_exit); // 4
self.add_contained_edge(body_exit, expr_exit); // 5
cond_exit); // 3
let guard_exit = self.opt_expr(arm.guard,
pats_exit); // 4
let body_exit = self.expr(arm.body.clone(),
guard_exit); // 5
self.add_contained_edge(body_exit, expr_exit); // 6
}
expr_exit
}
Expand Down
65 changes: 64 additions & 1 deletion src/librustc/middle/check_match.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -11,6 +11,10 @@
use middle::const_eval::{compare_const_vals, const_bool, const_float, const_nil, const_val};
use middle::const_eval::{const_expr_to_pat, eval_const_expr, lookup_const_by_id};
use middle::def::*;
use middle::expr_use_visitor::{ConsumeMode, Delegate, ExprUseVisitor, Init};
use middle::expr_use_visitor::{JustWrite, LoanCause, MutateMode};
use middle::expr_use_visitor::{WriteAndRead};
use middle::mem_categorization::cmt;
use middle::pat_util::*;
use middle::ty::*;
use middle::ty;
Expand Down Expand Up @@ -143,7 +147,16 @@ fn check_expr(cx: &mut MatchCheckCtxt, ex: &Expr) {
arm.pats.as_slice());
}

// Second, check for unreachable arms.
// Second, if there is a guard on each arm, make sure it isn't
// assigning or borrowing anything mutably.
for arm in arms.iter() {
match arm.guard {
Some(guard) => check_for_mutation_in_guard(cx, &*guard),
None => {}
}
}

// Third, check for unreachable arms.
check_arms(cx, arms.as_slice());

// Finally, check if the whole match expression is exhaustive.
Expand Down Expand Up @@ -903,3 +916,53 @@ fn check_legality_of_move_bindings(cx: &MatchCheckCtxt,
});
}
}

/// Ensures that a pattern guard doesn't borrow by mutable reference or
/// assign.
fn check_for_mutation_in_guard<'a>(cx: &'a MatchCheckCtxt<'a>, guard: &Expr) {
let mut checker = MutationChecker {
cx: cx,
};
let mut visitor = ExprUseVisitor::new(&mut checker, checker.cx.tcx);
visitor.walk_expr(guard);
}

struct MutationChecker<'a> {
cx: &'a MatchCheckCtxt<'a>,
}

impl<'a> Delegate for MutationChecker<'a> {
fn consume(&mut self, _: NodeId, _: Span, _: cmt, _: ConsumeMode) {}
fn consume_pat(&mut self, _: &Pat, _: cmt, _: ConsumeMode) {}
fn borrow(&mut self,
_: NodeId,
span: Span,
_: cmt,
_: Region,
kind: BorrowKind,
_: LoanCause) {
match kind {
MutBorrow => {
self.cx
.tcx
.sess
.span_err(span,
"cannot mutably borrow in a pattern guard")
}
ImmBorrow | UniqueImmBorrow => {}
}
}
fn decl_without_init(&mut self, _: NodeId, _: Span) {}
fn mutate(&mut self, _: NodeId, span: Span, _: cmt, mode: MutateMode) {
match mode {
JustWrite | WriteAndRead => {
self.cx
.tcx
.sess
.span_err(span, "cannot assign in a pattern guard")
}
Init => {}
}
}
}

2 changes: 1 addition & 1 deletion src/librustc/middle/expr_use_visitor.rs
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Expand Up @@ -292,7 +292,7 @@ impl<'d,'t,TYPER:mc::Typer> ExprUseVisitor<'d,'t,TYPER> {
self.walk_expr(expr)
}

fn walk_expr(&mut self, expr: &ast::Expr) {
pub fn walk_expr(&mut self, expr: &ast::Expr) {
debug!("walk_expr(expr={})", expr.repr(self.tcx()));

self.walk_adjustment(expr);
Expand Down
22 changes: 12 additions & 10 deletions src/librustdoc/html/render.rs
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Expand Up @@ -1730,17 +1730,19 @@ fn item_struct(w: &mut fmt::Formatter, it: &clean::Item,
}
}).peekable();
match s.struct_type {
doctree::Plain if fields.peek().is_some() => {
try!(write!(w, "<h2 class='fields'>Fields</h2>\n<table>"));
for field in fields {
try!(write!(w, "<tr><td id='structfield.{name}'>\
{stab}<code>{name}</code></td><td>",
stab = ConciseStability(&field.stability),
name = field.name.get_ref().as_slice()));
try!(document(w, field));
try!(write!(w, "</td></tr>"));
doctree::Plain => {
if fields.peek().is_some() {
try!(write!(w, "<h2 class='fields'>Fields</h2>\n<table>"));
for field in fields {
try!(write!(w, "<tr><td id='structfield.{name}'>\
{stab}<code>{name}</code></td><td>",
stab = ConciseStability(&field.stability),
name = field.name.get_ref().as_slice()));
try!(document(w, field));
try!(write!(w, "</td></tr>"));
}
try!(write!(w, "</table>"));
}
try!(write!(w, "</table>"));
}
_ => {}
}
Expand Down
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