Route the option for desugaring stdlib deps

 - "build-stdlib" controls whether we prune stdlib deps (explicit or not)
 - "stdlib-reop" allows one to override http://githhub.com/rust-lang/rust

src/cargo/util/rustc.rs

@@ -1,5 +1,7 @@
 use std::path::Path;
 
+use regex::Regex;
+
 use util::{self, CargoResult, internal, ChainError};
 
 pub struct Rustc {
@@ -28,18 +30,19 @@ impl Rustc {
         ret.verbose_version = try!(String::from_utf8(output.stdout).map_err(|_| {
             internal("rustc -v didn't return utf8 output")
         }));
-        ret.host = {
-            let triple = ret.verbose_version.lines().filter(|l| {
-                l.starts_with("host: ")
-            }).map(|l| &l[6..]).next();
-            let triple = try!(triple.chain_error(|| {
-                internal("rustc -v didn't have a line for `host:`")
-            }));
-            triple.to_string()
-        };
+        ret.host = try!({
+            version_get(&*ret.verbose_version, "host")
+                .chain_error(|| {
+                    internal("rustc -v didn't have a line for `host:`")
+                })
+        }).to_string();
         Ok(ret)
     }
 
+    pub fn version_get<'a>(&'a self, key: &str) -> Option<&'a str> {
+        version_get(&self.verbose_version, key)
+    }
+
     pub fn blank() -> Rustc {
         Rustc {
             verbose_version: String::new(),
@@ -48,3 +51,13 @@ impl Rustc {
         }
     }
 }
+
+fn version_get<'a>(verbose_version: &'a str, key: &str) -> Option<&'a str> {
+    let regex = Regex::new(&*format!(r"^{}: (.*)$", key)).unwrap();
+
+    verbose_version
+        .lines()
+        .filter_map(|l| regex.captures(l))
+        .next()
+        .and_then(|caps| caps.at(1))
+}

src/cargo/util/toml.rs

@@ -120,7 +120,34 @@ pub fn to_manifest(contents: &[u8],
         human(e.to_string())
     }));
 
-    let pair = try!(manifest.to_manifest(source_id, &layout, None, config));
+    let opt_stdlib_reference = if
+        try!(config.get_bool("build-stdlib")).map(|v| v.val).unwrap_or(false)
+    {
+        match config.rustc_info().version_get("commit-hash") {
+            Some("unknown") | None => None,
+            Some(hash) => Some(GitReference::Rev(hash.to_string())),
+        }.or_else(|| match config.rustc_info().version_get("release") {
+            Some("unknown") | None => None,
+            Some(release) => Some(GitReference::Tag(release.to_string())),
+        })
+    } else {
+        None
+    };
+
+    let opt_stdlib_repo = match opt_stdlib_reference {
+        None => None,
+        Some(reference) => {
+            let config = try!(config.get_string("stdlib-repo"));
+            let url = config.as_ref().map(|s| &s.val[..])
+                .unwrap_or("http://github.com/rust-lang/rust.git");
+            let loc = try!(url.to_url().map_err(human));
+            Some(SourceId::for_git(&loc, reference))
+        },
+    };
+
+    let pair = try!(manifest.to_manifest(source_id, &layout,
+                                         opt_stdlib_repo,
+                                         config));
     let (mut manifest, paths) = pair;
     match d.toml {
         Some(ref toml) => add_unused_keys(&mut manifest, toml, "".to_string()),