Auto merge of #27458 - mitaa:local_cpath, r=nikomatsakis

This changes the current behaviour for two cases (that I know of)
```rust
mod foo {
    extern crate bar;
}
// `bar::` changes to `foo::bar::`
```

```rust
extern crate bar as quux;
// `bar::` changes to `quux::`
```
For example:
```rust
mod foo {
    extern crate core;
}

fn assert_clone<T>() where T : Clone { }

fn main() {
    assert_clone::<foo::core::atomic::AtomicBool>();
    // error: the trait `core::clone::Clone` is not implemented for the type `core::atomic::AtomicBool` [E0277]
    // changes to
    // error: the trait `foo::core::clone::Clone` is not implemented for the type `foo::core::atomic::AtomicBool` [E0277]
}
```

Notably the following test case broke:
```rust
 #[bench]
 fn bar(x: isize) { }
 //~^ ERROR mismatched types
 //~| expected `fn(&mut test::Bencher)`
 // changed to
 //~| expected `fn(&mut __test::test::Bencher)`
```
If a crate is linked multiple times the path with the least segments is stored.
Partially addresses #1920. (this doesn't solve the issue raised about re-exports)

r? @nikomatsakis

Author: bors

src/librustc/metadata/creader.rs

@@ -34,14 +34,22 @@ use syntax::codemap::{self, Span, mk_sp, Pos};
 use syntax::parse;
 use syntax::parse::token::InternedString;
 use syntax::visit;
+use syntax::util::small_vector::SmallVector;
+use ast_map;
 use log;
 
+pub struct LocalCrateReader<'a, 'b:'a> {
+    sess: &'a Session,
+    creader: CrateReader<'a>,
+    ast_map: &'a ast_map::Map<'b>,
+}
+
 pub struct CrateReader<'a> {
     sess: &'a Session,
     next_crate_num: ast::CrateNum,
 }
 
-impl<'a, 'v> visit::Visitor<'v> for CrateReader<'a> {
+impl<'a, 'b, 'v> visit::Visitor<'v> for LocalCrateReader<'a, 'b> {
     fn visit_item(&mut self, a: &ast::Item) {
         self.process_item(a);
         visit::walk_item(self, a);
@@ -152,31 +160,6 @@ impl<'a> CrateReader<'a> {
         }
     }
 
-    // Traverses an AST, reading all the information about use'd crates and
-    // extern libraries necessary for later resolving, typechecking, linking,
-    // etc.
-    pub fn read_crates(&mut self, krate: &ast::Crate) {
-        self.process_crate(krate);
-        visit::walk_crate(self, krate);
-
-        if log_enabled!(log::DEBUG) {
-            dump_crates(&self.sess.cstore);
-        }
-
-        for &(ref name, kind) in &self.sess.opts.libs {
-            register_native_lib(self.sess, None, name.clone(), kind);
-        }
-    }
-
-    fn process_crate(&self, c: &ast::Crate) {
-        for a in c.attrs.iter().filter(|m| m.name() == "link_args") {
-            match a.value_str() {
-                Some(ref linkarg) => self.sess.cstore.add_used_link_args(&linkarg),
-                None => { /* fallthrough */ }
-            }
-        }
-    }
-
     fn extract_crate_info(&self, i: &ast::Item) -> Option<CrateInfo> {
         match i.node {
             ast::ItemExternCrate(ref path_opt) => {
@@ -201,103 +184,6 @@ impl<'a> CrateReader<'a> {
         }
     }
 
-    fn process_item(&mut self, i: &ast::Item) {
-        match i.node {
-            ast::ItemExternCrate(_) => {
-                if !should_link(i) {
-                    return;
-                }
-
-                match self.extract_crate_info(i) {
-                    Some(info) => {
-                        let (cnum, _, _) = self.resolve_crate(&None,
-                                                              &info.ident,
-                                                              &info.name,
-                                                              None,
-                                                              i.span,
-                                                              PathKind::Crate);
-                        self.sess.cstore.add_extern_mod_stmt_cnum(info.id, cnum);
-                    }
-                    None => ()
-                }
-            }
-            ast::ItemForeignMod(ref fm) => {
-                if fm.abi == abi::Rust || fm.abi == abi::RustIntrinsic {
-                    return;
-                }
-
-                // First, add all of the custom link_args attributes
-                let link_args = i.attrs.iter()
-                    .filter_map(|at| if at.name() == "link_args" {
-                        Some(at)
-                    } else {
-                        None
-                    })
-                    .collect::<Vec<&ast::Attribute>>();
-                for m in &link_args {
-                    match m.value_str() {
-                        Some(linkarg) => self.sess.cstore.add_used_link_args(&linkarg),
-                        None => { /* fallthrough */ }
-                    }
-                }
-
-                // Next, process all of the #[link(..)]-style arguments
-                let link_args = i.attrs.iter()
-                    .filter_map(|at| if at.name() == "link" {
-                        Some(at)
-                    } else {
-                        None
-                    })
-                    .collect::<Vec<&ast::Attribute>>();
-                for m in &link_args {
-                    match m.meta_item_list() {
-                        Some(items) => {
-                            let kind = items.iter().find(|k| {
-                                k.name() == "kind"
-                            }).and_then(|a| a.value_str());
-                            let kind = match kind {
-                                Some(k) => {
-                                    if k == "static" {
-                                        cstore::NativeStatic
-                                    } else if self.sess.target.target.options.is_like_osx
-                                              && k == "framework" {
-                                        cstore::NativeFramework
-                                    } else if k == "framework" {
-                                        cstore::NativeFramework
-                                    } else if k == "dylib" {
-                                        cstore::NativeUnknown
-                                    } else {
-                                        self.sess.span_err(m.span,
-                                            &format!("unknown kind: `{}`",
-                                                    k));
-                                        cstore::NativeUnknown
-                                    }
-                                }
-                                None => cstore::NativeUnknown
-                            };
-                            let n = items.iter().find(|n| {
-                                n.name() == "name"
-                            }).and_then(|a| a.value_str());
-                            let n = match n {
-                                Some(n) => n,
-                                None => {
-                                    self.sess.span_err(m.span,
-                                        "#[link(...)] specified without \
-                                         `name = \"foo\"`");
-                                    InternedString::new("foo")
-                                }
-                            };
-                            register_native_lib(self.sess, Some(m.span),
-                                                n.to_string(), kind);
-                        }
-                        None => {}
-                    }
-                }
-            }
-            _ => { }
-        }
-    }
-
     fn existing_match(&self, name: &str, hash: Option<&Svh>, kind: PathKind)
                       -> Option<ast::CrateNum> {
         let mut ret = None;
@@ -378,6 +264,7 @@ impl<'a> CrateReader<'a> {
 
         let cmeta = Rc::new( cstore::crate_metadata {
             name: name.to_string(),
+            local_path: RefCell::new(SmallVector::zero()),
             data: metadata,
             cnum_map: cnum_map,
             cnum: cnum,
@@ -592,6 +479,140 @@ impl<'a> CrateReader<'a> {
     }
 }
 
+impl<'a, 'b> LocalCrateReader<'a, 'b> {
+    pub fn new(sess: &'a Session, map: &'a ast_map::Map<'b>) -> LocalCrateReader<'a, 'b> {
+        LocalCrateReader {
+            sess: sess,
+            creader: CrateReader::new(sess),
+            ast_map: map,
+        }
+    }
+
+    // Traverses an AST, reading all the information about use'd crates and
+    // extern libraries necessary for later resolving, typechecking, linking,
+    // etc.
+    pub fn read_crates(&mut self, krate: &ast::Crate) {
+        self.process_crate(krate);
+        visit::walk_crate(self, krate);
+
+        if log_enabled!(log::DEBUG) {
+            dump_crates(&self.sess.cstore);
+        }
+
+        for &(ref name, kind) in &self.sess.opts.libs {
+            register_native_lib(self.sess, None, name.clone(), kind);
+        }
+    }
+
+    fn process_crate(&self, c: &ast::Crate) {
+        for a in c.attrs.iter().filter(|m| m.name() == "link_args") {
+            match a.value_str() {
+                Some(ref linkarg) => self.sess.cstore.add_used_link_args(&linkarg),
+                None => { /* fallthrough */ }
+            }
+        }
+    }
+
+    fn process_item(&mut self, i: &ast::Item) {
+        match i.node {
+            ast::ItemExternCrate(_) => {
+                if !should_link(i) {
+                    return;
+                }
+
+                match self.creader.extract_crate_info(i) {
+                    Some(info) => {
+                        let (cnum, cmeta, _) = self.creader.resolve_crate(&None,
+                                                              &info.ident,
+                                                              &info.name,
+                                                              None,
+                                                              i.span,
+                                                              PathKind::Crate);
+                        self.ast_map.with_path(i.id, |path|
+                            cmeta.update_local_path(path));
+                        self.sess.cstore.add_extern_mod_stmt_cnum(info.id, cnum);
+                    }
+                    None => ()
+                }
+            }
+            ast::ItemForeignMod(ref fm) => {
+                if fm.abi == abi::Rust || fm.abi == abi::RustIntrinsic {
+                    return;
+                }
+
+                // First, add all of the custom link_args attributes
+                let link_args = i.attrs.iter()
+                    .filter_map(|at| if at.name() == "link_args" {
+                        Some(at)
+                    } else {
+                        None
+                    })
+                    .collect::<Vec<&ast::Attribute>>();
+                for m in &link_args {
+                    match m.value_str() {
+                        Some(linkarg) => self.sess.cstore.add_used_link_args(&linkarg),
+                        None => { /* fallthrough */ }
+                    }
+                }
+
+                // Next, process all of the #[link(..)]-style arguments
+                let link_args = i.attrs.iter()
+                    .filter_map(|at| if at.name() == "link" {
+                        Some(at)
+                    } else {
+                        None
+                    })
+                    .collect::<Vec<&ast::Attribute>>();
+                for m in &link_args {
+                    match m.meta_item_list() {
+                        Some(items) => {
+                            let kind = items.iter().find(|k| {
+                                k.name() == "kind"
+                            }).and_then(|a| a.value_str());
+                            let kind = match kind {
+                                Some(k) => {
+                                    if k == "static" {
+                                        cstore::NativeStatic
+                                    } else if self.sess.target.target.options.is_like_osx
+                                              && k == "framework" {
+                                        cstore::NativeFramework
+                                    } else if k == "framework" {
+                                        cstore::NativeFramework
+                                    } else if k == "dylib" {
+                                        cstore::NativeUnknown
+                                    } else {
+                                        self.sess.span_err(m.span,
+                                            &format!("unknown kind: `{}`",
+                                                    k));
+                                        cstore::NativeUnknown
+                                    }
+                                }
+                                None => cstore::NativeUnknown
+                            };
+                            let n = items.iter().find(|n| {
+                                n.name() == "name"
+                            }).and_then(|a| a.value_str());
+                            let n = match n {
+                                Some(n) => n,
+                                None => {
+                                    self.sess.span_err(m.span,
+                                        "#[link(...)] specified without \
+                                         `name = \"foo\"`");
+                                    InternedString::new("foo")
+                                }
+                            };
+                            register_native_lib(self.sess, Some(m.span),
+                                                n.to_string(), kind);
+                        }
+                        None => {}
+                    }
+                }
+            }
+            _ => { }
+        }
+    }
+}
+
 /// Imports the codemap from an external crate into the codemap of the crate
 /// currently being compiled (the "local crate").
 ///

src/librustc/metadata/csearch.rs

@@ -24,7 +24,6 @@ use syntax::ast;
 use syntax::attr;
 use syntax::attr::AttrMetaMethods;
 use syntax::diagnostic::expect;
-use syntax::parse::token;
 
 use std::collections::hash_map::HashMap;
 
@@ -89,11 +88,12 @@ pub fn get_item_path(tcx: &ty::ctxt, def: ast::DefId) -> Vec<ast_map::PathElem>
     let cdata = cstore.get_crate_data(def.krate);
     let path = decoder::get_item_path(&*cdata, def.node);
 
-    // FIXME #1920: This path is not always correct if the crate is not linked
-    // into the root namespace.
-    let mut r = vec![ast_map::PathMod(token::intern(&cdata.name))];
-    r.push_all(&path);
-    r
+    cdata.with_local_path(|cpath| {
+        let mut r = Vec::with_capacity(cpath.len() + path.len());
+        r.push_all(cpath);
+        r.push_all(&path);
+        r
+    })
 }
 
 pub enum FoundAst<'ast> {

src/librustc/metadata/cstore.rs

@@ -28,7 +28,10 @@ use std::path::PathBuf;
 use flate::Bytes;
 use syntax::ast;
 use syntax::codemap;
+use syntax::parse::token;
 use syntax::parse::token::IdentInterner;
+use syntax::util::small_vector::SmallVector;
+use ast_map;
 
 // A map from external crate numbers (as decoded from some crate file) to
 // local crate numbers (as generated during this session). Each external
@@ -54,6 +57,7 @@ pub struct ImportedFileMap {
 
 pub struct crate_metadata {
     pub name: String,
+    pub local_path: RefCell<SmallVector<ast_map::PathElem>>,
     pub data: MetadataBlob,
     pub cnum_map: cnum_map,
     pub cnum: ast::CrateNum,
@@ -255,6 +259,30 @@ impl crate_metadata {
             filemaps
         }
     }
+    pub fn with_local_path<T, F>(&self, f: F) -> T
+    where F: Fn(&[ast_map::PathElem]) -> T {
+        let cpath = self.local_path.borrow();
+        if cpath.is_empty() {
+            let name = ast_map::PathMod(token::intern(&self.name));
+            f(&[name])
+        } else {
+            f(cpath.as_slice())
+        }
+    }
+    pub fn update_local_path<'a, 'b>(&self, candidate: ast_map::PathElems<'a, 'b>) {
+        let mut cpath = self.local_path.borrow_mut();
+        let cap = cpath.len();
+        match cap {
+            0 => *cpath = candidate.collect(),
+            1 => (),
+            _ => {
+                let candidate: SmallVector<_> = candidate.collect();
+                if candidate.len() < cap {
+                    *cpath = candidate;
+                }
+            },
+        }
+    }
 }
 
 impl MetadataBlob {