Implement a file-path remapping feature in support of debuginfo and reproducible builds.

src/libsyntax/test_snippet.rs

@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-use codemap::CodeMap;
+use codemap::{CodeMap, FilePathMapping};
 use errors::Handler;
 use errors::emitter::EmitterWriter;
 use std::io;
@@ -47,8 +47,8 @@ impl<T: Write> Write for Shared<T> {
 fn test_harness(file_text: &str, span_labels: Vec<SpanLabel>, expected_output: &str) {
     let output = Arc::new(Mutex::new(Vec::new()));
 
-    let code_map = Rc::new(CodeMap::new());
-    code_map.new_filemap_and_lines("test.rs", None, &file_text);
+    let code_map = Rc::new(CodeMap::new(FilePathMapping::empty()));
+    code_map.new_filemap_and_lines("test.rs", &file_text);
 
     let primary_span = make_span(&file_text, &span_labels[0].start, &span_labels[0].end);
     let mut msp = MultiSpan::from_span(primary_span);