Added source hashes to FileMap

We can use these to perform lazy loading of source files belonging to
external crates. That way we will be able to show the source code of
external spans that have been translated.

src/libsyntax/codemap.rs

@@ -27,9 +27,12 @@ use std::rc::Rc;
 
 use std::env;
 use std::fs;
+use std::hash::Hasher;
 use std::io::{self, Read};
 use errors::CodeMapper;
 
+use rustc_data_structures::stable_hasher::StableHasher;
+
 /// Return the span itself if it doesn't come from a macro expansion,
 /// otherwise return the call site span up to the `enclosing_sp` by
 /// following the `expn_info` chain.
@@ -171,11 +174,16 @@ impl CodeMap {
 
         let (filename, was_remapped) = self.path_mapping.map_prefix(filename);
 
+        let mut hasher: StableHasher<u128> = StableHasher::new();
+        hasher.write(src.as_bytes());
+        let src_hash = hasher.finish();
+
         let filemap = Rc::new(FileMap {
             name: filename,
             name_was_remapped: was_remapped,
             crate_of_origin: 0,
             src: Some(Rc::new(src)),
+            src_hash: src_hash,
             start_pos: Pos::from_usize(start_pos),
             end_pos: Pos::from_usize(end_pos),
             lines: RefCell::new(Vec::new()),
@@ -210,6 +218,7 @@ impl CodeMap {
                                 filename: FileName,
                                 name_was_remapped: bool,
                                 crate_of_origin: u32,
+                                src_hash: u128,
                                 source_len: usize,
                                 mut file_local_lines: Vec<BytePos>,
                                 mut file_local_multibyte_chars: Vec<MultiByteChar>)
@@ -233,6 +242,7 @@ impl CodeMap {
             name_was_remapped: name_was_remapped,
             crate_of_origin: crate_of_origin,
             src: None,
+            src_hash: src_hash,
             start_pos: start_pos,
             end_pos: end_pos,
             lines: RefCell::new(file_local_lines),