auto merge of #19466 : nikomatsakis/rust/recursion-limit, r=eddyb

This is particularly important for deeply nested types, which generate deeply nested impls. This is a fix for #19318. It's possible we could also improve this particular case not to increment the recursion count, but it's worth being able to adjust the recursion limit anyhow.

cc @jdm 
r? @pcwalton

Author: bors

src/librustc/lib.rs

@@ -88,6 +88,7 @@ pub mod middle {
     pub mod privacy;
     pub mod reachable;
     pub mod region;
+    pub mod recursion_limit;
     pub mod resolve;
     pub mod resolve_lifetime;
     pub mod stability;

src/librustc/middle/recursion_limit.rs

@@ -0,0 +1,39 @@
+// Copyright 2012 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.
+
+// Recursion limit.
+//
+// There are various parts of the compiler that must impose arbitrary limits
+// on how deeply they recurse to prevent stack overflow. Users can override
+// this via an attribute on the crate like `#![recursion_limit(22)]`. This pass
+// just peeks and looks for that attribute.
+
+use session::Session;
+use syntax::ast;
+use syntax::attr::AttrMetaMethods;
+use std::str::FromStr;
+
+pub fn update_recursion_limit(sess: &Session, krate: &ast::Crate) {
+    for attr in krate.attrs.iter() {
+        if !attr.check_name("recursion_limit") {
+            continue;
+        }
+
+        if let Some(s) = attr.value_str() {
+            if let Some(n) = FromStr::from_str(s.get()) {
+                sess.recursion_limit.set(n);
+                return;
+            }
+        }
+
+        sess.span_err(attr.span, "malformed recursion limit attribute, \
+                                  expected #![recursion_limit(\"N\")]");
+    }
+}