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limit the length of types in monomorphization
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This adds the new insta-stable `#![type_size_limit]` crate attribute to control
the limit, and is obviously a [breaking-change] fixable by that.
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arielb1 committed Dec 1, 2016
1 parent 908dba0 commit 242cd7e
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Showing 9 changed files with 137 additions and 7 deletions.
21 changes: 16 additions & 5 deletions src/librustc/middle/recursion_limit.rs
Original file line number Diff line number Diff line change
Expand Up @@ -18,20 +18,31 @@
use session::Session;
use syntax::ast;

pub fn update_recursion_limit(sess: &Session, krate: &ast::Crate) {
use std::cell::Cell;

pub fn update_limits(sess: &Session, krate: &ast::Crate) {
update_limit(sess, krate, &sess.recursion_limit, "recursion_limit",
"recursion limit");
update_limit(sess, krate, &sess.type_length_limit, "type_length_limit",
"type length limit");
}

fn update_limit(sess: &Session, krate: &ast::Crate, limit: &Cell<usize>,
name: &str, description: &str) {
for attr in &krate.attrs {
if !attr.check_name("recursion_limit") {
if !attr.check_name(name) {
continue;
}

if let Some(s) = attr.value_str() {
if let Some(n) = s.as_str().parse().ok() {
sess.recursion_limit.set(n);
limit.set(n);
return;
}
}

span_err!(sess, attr.span, E0296, "malformed recursion limit attribute, \
expected #![recursion_limit=\"N\"]");
span_err!(sess, attr.span, E0296,
"malformed {} attribute, expected #![{}=\"N\"]",
description, name);
}
}
4 changes: 4 additions & 0 deletions src/librustc/session/mod.rs
Original file line number Diff line number Diff line change
Expand Up @@ -100,6 +100,9 @@ pub struct Session {
/// operations such as auto-dereference and monomorphization.
pub recursion_limit: Cell<usize>,

/// The maximum length of types during monomorphization.
pub type_length_limit: Cell<usize>,

/// The metadata::creader module may inject an allocator/panic_runtime
/// dependency if it didn't already find one, and this tracks what was
/// injected.
Expand Down Expand Up @@ -620,6 +623,7 @@ pub fn build_session_(sopts: config::Options,
crate_disambiguator: RefCell::new(Symbol::intern("")),
features: RefCell::new(feature_gate::Features::new()),
recursion_limit: Cell::new(64),
type_length_limit: Cell::new(1048576),
next_node_id: Cell::new(NodeId::new(1)),
injected_allocator: Cell::new(None),
injected_panic_runtime: Cell::new(None),
Expand Down
2 changes: 1 addition & 1 deletion src/librustc_driver/driver.rs
Original file line number Diff line number Diff line change
Expand Up @@ -566,7 +566,7 @@ pub fn phase_2_configure_and_expand<F>(sess: &Session,
*sess.crate_disambiguator.borrow_mut() = Symbol::intern(&compute_crate_disambiguator(sess));

time(time_passes, "recursion limit", || {
middle::recursion_limit::update_recursion_limit(sess, &krate);
middle::recursion_limit::update_limits(sess, &krate);
});

krate = time(time_passes, "crate injection", || {
Expand Down
35 changes: 35 additions & 0 deletions src/librustc_trans/collector.rs
Original file line number Diff line number Diff line change
Expand Up @@ -361,6 +361,7 @@ fn collect_items_rec<'a, 'tcx: 'a>(scx: &SharedCrateContext<'a, 'tcx>,
recursion_depth_reset = Some(check_recursion_limit(scx.tcx(),
instance,
recursion_depths));
check_type_length_limit(scx.tcx(), instance);

// Scan the MIR in order to find function calls, closures, and
// drop-glue
Expand Down Expand Up @@ -432,6 +433,40 @@ fn check_recursion_limit<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
(instance.def, recursion_depth)
}

fn check_type_length_limit<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
instance: Instance<'tcx>)
{
let type_length = instance.substs.types().flat_map(|ty| ty.walk()).count();
debug!(" => type length={}", type_length);

// Rust code can easily create exponentially-long types using only a
// polynomial recursion depth. Even with the default recursion
// depth, you can easily get cases that take >2^60 steps to run,
// which means that rustc basically hangs.
//
// Bail out in these cases to avoid that bad user experience.
let type_length_limit = tcx.sess.type_length_limit.get();
if type_length > type_length_limit {
// The instance name is already known to be too long for rustc. Use
// `{:.64}` to avoid blasting the user's terminal with thousands of
// lines of type-name.
let instance_name = instance.to_string();
let msg = format!("reached the type-length limit while instantiating `{:.64}...`",
instance_name);
let mut diag = if let Some(node_id) = tcx.map.as_local_node_id(instance.def) {
tcx.sess.struct_span_fatal(tcx.map.span(node_id), &msg)
} else {
tcx.sess.struct_fatal(&msg)
};

diag.note(&format!(
"consider adding a `#![type_length_limit=\"{}\"]` attribute to your crate",
type_length_limit*2));
diag.emit();
tcx.sess.abort_if_errors();
}
}

struct MirNeighborCollector<'a, 'tcx: 'a> {
scx: &'a SharedCrateContext<'a, 'tcx>,
mir: &'a mir::Mir<'tcx>,
Expand Down
1 change: 1 addition & 0 deletions src/libsyntax/feature_gate.rs
Original file line number Diff line number Diff line change
Expand Up @@ -738,6 +738,7 @@ pub const BUILTIN_ATTRIBUTES: &'static [(&'static str, AttributeType, AttributeG
("no_main", CrateLevel, Ungated),
("no_builtins", CrateLevel, Ungated),
("recursion_limit", CrateLevel, Ungated),
("type_length_limit", CrateLevel, Ungated),
];

// cfg(...)'s that are feature gated
Expand Down
3 changes: 2 additions & 1 deletion src/test/compile-fail/issue-22638.rs
Original file line number Diff line number Diff line change
Expand Up @@ -10,7 +10,8 @@

#![allow(unused)]

#![recursion_limit = "32"]
#![recursion_limit = "20"]
#![type_length_limit = "20000000"]

#[derive(Clone)]
struct A (B);
Expand Down
35 changes: 35 additions & 0 deletions src/test/compile-fail/type_length_limit.rs
Original file line number Diff line number Diff line change
@@ -0,0 +1,35 @@
// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

// error-pattern: reached the type-length limit while instantiating

// Test that the type length limit can be changed.

#![allow(dead_code)]
#![type_length_limit="256"]

macro_rules! link {
($id:ident, $t:ty) => {
pub type $id = ($t, $t, $t);
}
}

link! { A, B }
link! { B, C }
link! { C, D }
link! { D, E }
link! { E, F }
link! { F, G }

pub struct G;

fn main() {
drop::<Option<A>>(None);
}
30 changes: 30 additions & 0 deletions src/test/ui/issue-37311-type-length-limit/issue-37311.rs
Original file line number Diff line number Diff line change
@@ -0,0 +1,30 @@
// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

trait Mirror {
type Image;
}

impl<T> Mirror for T { type Image = T; }

trait Foo {
fn recurse(&self);
}

impl<T> Foo for T {
#[allow(unconditional_recursion)]
fn recurse(&self) {
(self, self).recurse();
}
}

fn main() {
().recurse();
}
13 changes: 13 additions & 0 deletions src/test/ui/issue-37311-type-length-limit/issue-37311.stderr
Original file line number Diff line number Diff line change
@@ -0,0 +1,13 @@
error: reached the type-length limit while instantiating `<T as Foo><(&(&(&(&(&(&(&(&(&(&(&(&(&(&(&(&(&(&(&(), &()), &(&()...`
--> $DIR/issue-37311.rs:23:5
|
23 | fn recurse(&self) {
| _____^ starting here...
24 | | (self, self).recurse();
25 | | }
| |_____^ ...ending here
|
= note: consider adding a `#![type_length_limit="2097152"]` attribute to your crate

error: aborting due to previous error

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