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Check for shadowing between lifetimes and loop labels in function bodies.

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Note: this Warns rather than error on shadowing problems involving labels.
We took this more conservative option mostly due to issues with
hygiene being broken for labels and/or lifetimes.

Add FIXME regarding non-hygienic comparison.
This commit is contained in:
Felix S. Klock II 2015-04-03 02:51:38 +02:00
parent 77acda1c8e
commit dd24070799
1 changed files with 201 additions and 12 deletions
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213
src/librustc/middle/resolve_lifetime.rs
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@ -24,6 +24,7 @@ use middle::region;
use middle::subst;
use middle::ty;
use std::fmt;
use std::mem::replace;
use syntax::ast;
use syntax::codemap::Span;
use syntax::parse::token::special_idents;
@ -70,6 +71,9 @@ struct LifetimeContext<'a> {
// I'm sorry.
trait_ref_hack: bool,
// List of labels in the function/method currently under analysis.
labels_in_fn: Vec<(ast::Ident, Span)>,
}
enum ScopeChain<'a> {
@ -97,6 +101,7 @@ pub fn krate(sess: &Session, krate: &ast::Crate, def_map: &DefMap) -> NamedRegio
scope: &ROOT_SCOPE,
def_map: def_map,
trait_ref_hack: false,
labels_in_fn: vec![],
}, krate);
sess.abort_if_errors();
named_region_map
@ -104,6 +109,10 @@ pub fn krate(sess: &Session, krate: &ast::Crate, def_map: &DefMap) -> NamedRegio
impl<'a, 'v> Visitor<'v> for LifetimeContext<'a> {
fn visit_item(&mut self, item: &ast::Item) {
// Items save/restore the set of labels. This way innner items
// can freely reuse names, be they loop labels or lifetimes.
let saved = replace(&mut self.labels_in_fn, vec![]);
// Items always introduce a new root scope
self.with(RootScope, |_, this| {
match item.node {
@ -137,6 +146,9 @@ impl<'a, 'v> Visitor<'v> for LifetimeContext<'a> {
}
}
});
// Done traversing the item; restore saved set of labels.
replace(&mut self.labels_in_fn, saved);
}
fn visit_fn(&mut self, fk: visit::FnKind<'v>, fd: &'v ast::FnDecl,
@ -144,16 +156,16 @@ impl<'a, 'v> Visitor<'v> for LifetimeContext<'a> {
match fk {
visit::FkItemFn(_, generics, _, _, _) => {
self.visit_early_late(subst::FnSpace, generics, |this| {
visit::walk_fn(this, fk, fd, b, s)
this.walk_fn(fk, fd, b, s)
})
}
visit::FkMethod(_, sig, _) => {
self.visit_early_late(subst::FnSpace, &sig.generics, |this| {
visit::walk_fn(this, fk, fd, b, s)
this.walk_fn(fk, fd, b, s)
})
}
visit::FkFnBlock(..) => {
visit::walk_fn(self, fk, fd, b, s)
self.walk_fn(fk, fd, b, s)
}
}
}
@ -190,6 +202,10 @@ impl<'a, 'v> Visitor<'v> for LifetimeContext<'a> {
}
fn visit_trait_item(&mut self, trait_item: &ast::TraitItem) {
// We reset the labels on every trait item, so that different
// methods in an impl can reuse label names.
let saved = replace(&mut self.labels_in_fn, vec![]);
if let ast::MethodTraitItem(ref sig, None) = trait_item.node {
self.visit_early_late(
subst::FnSpace, &sig.generics,
@ -197,6 +213,8 @@ impl<'a, 'v> Visitor<'v> for LifetimeContext<'a> {
} else {
visit::walk_trait_item(self, trait_item);
}
replace(&mut self.labels_in_fn, saved);
}
fn visit_block(&mut self, b: &ast::Block) {
@ -286,7 +304,170 @@ impl<'a, 'v> Visitor<'v> for LifetimeContext<'a> {
}
}
#[derive(Copy, Clone, PartialEq)]
enum ShadowKind { Label, Lifetime }
struct Original { kind: ShadowKind, span: Span }
struct Shadower { kind: ShadowKind, span: Span }
fn original_label(span: Span) -> Original {
Original { kind: ShadowKind::Label, span: span }
}
fn shadower_label(span: Span) -> Shadower {
Shadower { kind: ShadowKind::Label, span: span }
}
fn original_lifetime(l: &ast::Lifetime) -> Original {
Original { kind: ShadowKind::Lifetime, span: l.span }
}
fn shadower_lifetime(l: &ast::Lifetime) -> Shadower {
Shadower { kind: ShadowKind::Lifetime, span: l.span }
}
impl ShadowKind {
fn desc(&self) -> &'static str {
match *self {
ShadowKind::Label => "label",
ShadowKind::Lifetime => "lifetime",
}
}
}
fn signal_shadowing_problem(
sess: &Session, name: ast::Name, orig: Original, shadower: Shadower) {
if let (ShadowKind::Lifetime, ShadowKind::Lifetime) = (orig.kind, shadower.kind) {
// lifetime/lifetime shadowing is an error
sess.span_err(shadower.span,
&format!("{} name `{}` shadows a \
{} name that is already in scope",
shadower.kind.desc(), name, orig.kind.desc()));
} else {
// shadowing involving a label is only a warning, due to issues with
// labels and lifetimes not being macro-hygienic.
sess.span_warn(shadower.span,
&format!("{} name `{}` shadows a \
{} name that is already in scope",
shadower.kind.desc(), name, orig.kind.desc()));
}
sess.span_note(orig.span,
&format!("shadowed {} `{}` declared here",
orig.kind.desc(), name));
}
// Adds all labels in `b` to `ctxt.labels_in_fn`, signalling a warning
// if one of the label shadows a lifetime or another label.
fn extract_labels<'v, 'a>(ctxt: &mut LifetimeContext<'a>, b: &'v ast::Block) {
struct GatherLabels<'a> {
sess: &'a Session,
scope: Scope<'a>,
labels_in_fn: &'a mut Vec<(ast::Ident, Span)>,
}
let mut gather = GatherLabels {
sess: ctxt.sess,
scope: ctxt.scope,
labels_in_fn: &mut ctxt.labels_in_fn,
};
gather.visit_block(b);
return;
impl<'v, 'a> Visitor<'v> for GatherLabels<'a> {
fn visit_expr(&mut self, ex: &'v ast::Expr) {
if let Some(label) = expression_label(ex) {
for &(prior, prior_span) in &self.labels_in_fn[..] {
// FIXME (#24278): non-hygienic comparision
if label.name == prior.name {
signal_shadowing_problem(self.sess,
label.name,
original_label(prior_span),
shadower_label(ex.span));
}
}
check_if_label_shadows_lifetime(self.sess,
self.scope,
label,
ex.span);
self.labels_in_fn.push((label, ex.span));
}
visit::walk_expr(self, ex)
}
fn visit_item(&mut self, _: &ast::Item) {
// do not recurse into items defined in the block
}
}
fn expression_label(ex: &ast::Expr) -> Option<ast::Ident> {
match ex.node {
ast::ExprWhile(_, _, Some(label)) |
ast::ExprWhileLet(_, _, _, Some(label)) |
ast::ExprForLoop(_, _, _, Some(label)) |
ast::ExprLoop(_, Some(label)) => Some(label),
_ => None,
}
}
fn check_if_label_shadows_lifetime<'a>(sess: &'a Session,
mut scope: Scope<'a>,
label: ast::Ident,
label_span: Span) {
loop {
match *scope {
BlockScope(_, s) => { scope = s; }
RootScope => { return; }
EarlyScope(_, lifetimes, s) |
LateScope(lifetimes, s) => {
for lifetime_def in lifetimes {
// FIXME (#24278): non-hygienic comparision
if label.name == lifetime_def.lifetime.name {
signal_shadowing_problem(
sess,
label.name,
original_lifetime(&lifetime_def.lifetime),
shadower_label(label_span));
return;
}
}
scope = s;
}
}
}
}
}
impl<'a> LifetimeContext<'a> {
// This is just like visit::walk_fn, except that it extracts the
// labels of the function body and swaps them in before visiting
// the function body itself.
fn walk_fn<'b>(&mut self,
fk: visit::FnKind,
fd: &ast::FnDecl,
fb: &'b ast::Block,
_span: Span) {
match fk {
visit::FkItemFn(_, generics, _, _, _) => {
visit::walk_fn_decl(self, fd);
self.visit_generics(generics);
}
visit::FkMethod(_, sig, _) => {
visit::walk_fn_decl(self, fd);
self.visit_generics(&sig.generics);
self.visit_explicit_self(&sig.explicit_self);
}
visit::FkFnBlock(..) => {
visit::walk_fn_decl(self, fd);
}
}
// After inpsecting the decl, add all labels from the body to
// `self.labels_in_fn`.
extract_labels(self, fb);
self.visit_block(fb);
}
fn with<F>(&mut self, wrap_scope: ScopeChain, f: F) where
F: FnOnce(Scope, &mut LifetimeContext),
{
@ -297,6 +478,7 @@ impl<'a> LifetimeContext<'a> {
scope: &wrap_scope,
def_map: self.def_map,
trait_ref_hack: self.trait_ref_hack,
labels_in_fn: self.labels_in_fn.clone(),
};
debug!("entering scope {:?}", this.scope);
f(self.scope, &mut this);
@ -494,6 +676,17 @@ impl<'a> LifetimeContext<'a> {
mut old_scope: Scope,
lifetime: &ast::Lifetime)
{
for &(label, label_span) in &self.labels_in_fn {
// FIXME (#24278): non-hygienic comparision
if lifetime.name == label.name {
signal_shadowing_problem(self.sess,
lifetime.name,
original_label(label_span),
shadower_lifetime(&lifetime));
return;
}
}
loop {
match *old_scope {
BlockScope(_, s) => {
@ -507,15 +700,11 @@ impl<'a> LifetimeContext<'a> {
EarlyScope(_, lifetimes, s) |
LateScope(lifetimes, s) => {
if let Some((_, lifetime_def)) = search_lifetimes(lifetimes, lifetime) {
self.sess.span_err(
lifetime.span,
&format!("lifetime name `{}` shadows another \
lifetime name that is already in scope",
token::get_name(lifetime.name)));
self.sess.span_note(
lifetime_def.span,
&format!("shadowed lifetime `{}` declared here",
token::get_name(lifetime.name)));
signal_shadowing_problem(
self.sess,
lifetime.name,
original_lifetime(&lifetime_def),
shadower_lifetime(&lifetime));
return;
}