Added external crates' sources to FileMap.

They are now handled in their own member to prevent mutating access to
the `src` member. This way, we can safely load external sources, while
keeping the mutation of local source strings off-limits.

src/librustc/ich/impls_syntax.rs

@@ -337,6 +337,7 @@ impl<'a, 'gcx, 'tcx> HashStable<StableHashingContext<'a, 'gcx, 'tcx>> for FileMa
             // Do not hash the source as it is not encoded
             src: _,
             src_hash,
+            external_src: _,
             start_pos,
             end_pos: _,
             ref lines,

src/librustc_errors/lib.rs

@@ -103,6 +103,7 @@ pub trait CodeMapper {
     fn span_to_filename(&self, sp: Span) -> FileName;
     fn merge_spans(&self, sp_lhs: Span, sp_rhs: Span) -> Option<Span>;
     fn call_span_if_macro(&self, sp: Span) -> Span;
+    fn load_source_for_filemap(&mut self, file: FileName) -> bool;
 }
 
 impl CodeSuggestion {

src/libsyntax/codemap.rs

@@ -219,6 +219,7 @@ impl CodeMap {
             crate_of_origin: crate_of_origin,
             src: None,
             src_hash: src_hash,
+            external_src: RefCell::new(ExternalSource::AbsentOk),
             start_pos: start_pos,
             end_pos: end_pos,
             lines: RefCell::new(file_local_lines),
@@ -558,6 +559,25 @@ impl CodeMapper for CodeMap {
         }
         sp
     }
+    fn load_source_for_filemap(&mut self, filename: FileName) -> bool {
+        let file_map = if let Some(fm) = self.get_filemap(&filename) {
+            fm
+        } else {
+            return false;
+        };
+
+        if *file_map.external_src.borrow() == ExternalSource::AbsentOk {
+            let mut external_src = file_map.external_src.borrow_mut();
+            if let Ok(src) = self.file_loader.read_file(Path::new(&filename)) {
+                *external_src = ExternalSource::Present(src);
+                return true;
+            } else {
+                *external_src = ExternalSource::AbsentErr;
+            }
+        }
+
+        false
+    }
 }
 
 #[derive(Clone)]

src/libsyntax_pos/lib.rs

@@ -374,6 +374,14 @@ pub struct MultiByteChar {
     pub bytes: usize,
 }
 
+#[derive(PartialEq, Eq, Clone)]
+pub enum ExternalSource {
+    Present(String),
+    AbsentOk,
+    AbsentErr,
+    Unneeded,
+}
+
 /// A single source in the CodeMap.
 #[derive(Clone)]
 pub struct FileMap {
@@ -389,6 +397,9 @@ pub struct FileMap {
     pub src: Option<Rc<String>>,
     /// The source code's hash
     pub src_hash: u128,
+    /// The external source code (used for external crates, which will have a `None`
+    /// value as `self.src`.
+    pub external_src: RefCell<ExternalSource>,
     /// The start position of this source in the CodeMap
     pub start_pos: BytePos,
     /// The end position of this source in the CodeMap
@@ -513,6 +524,7 @@ impl Decodable for FileMap {
                 end_pos: end_pos,
                 src: None,
                 src_hash: src_hash,
+                external_src: RefCell::new(ExternalSource::AbsentOk),
                 lines: RefCell::new(lines),
                 multibyte_chars: RefCell::new(multibyte_chars)
             })
@@ -545,6 +557,7 @@ impl FileMap {
             crate_of_origin: 0,
             src: Some(Rc::new(src)),
             src_hash: src_hash,
+            external_src: RefCell::new(ExternalSource::Unneeded),
             start_pos: start_pos,
             end_pos: Pos::from_usize(end_pos),
             lines: RefCell::new(Vec::new()),