Added consumption logic for external sources in FileMap

We now fetch source lines from the `external_src` member as a secondary
fallback if no regular source is present, that is, if the file map
belongs to an external crate and the source has been fetched from disk.

Author: ibabushkin

src/librustc_errors/emitter.rs

@@ -17,6 +17,7 @@ use RenderSpan::*;
 use snippet::{Annotation, AnnotationType, Line, MultilineAnnotation, StyledString, Style};
 use styled_buffer::StyledBuffer;
 
+use std::borrow::Cow;
 use std::io::prelude::*;
 use std::io;
 use std::rc::Rc;
@@ -911,7 +912,8 @@ impl EmitterWriter {
         // Print out the annotate source lines that correspond with the error
         for annotated_file in annotated_files {
             // we can't annotate anything if the source is unavailable.
-            if annotated_file.file.src.is_none() {
+            if annotated_file.file.src.is_none()
+                    && annotated_file.file.external_src.borrow().is_absent() {
                 continue;
             }
 
@@ -1012,7 +1014,7 @@ impl EmitterWriter {
                     } else if line_idx_delta == 2 {
                         let unannotated_line = annotated_file.file
                             .get_line(annotated_file.lines[line_idx].line_index)
-                            .unwrap_or("");
+                            .unwrap_or_else(|| Cow::from(""));
 
                         let last_buffer_line_num = buffer.num_lines();
 

src/librustc_errors/lib.rs

@@ -37,6 +37,7 @@ use self::Level::*;
 
 use emitter::{Emitter, EmitterWriter};
 
+use std::borrow::Cow;
 use std::cell::{RefCell, Cell};
 use std::{error, fmt};
 use std::rc::Rc;
@@ -122,7 +123,7 @@ impl CodeSuggestion {
         use syntax_pos::{CharPos, Loc, Pos};
 
         fn push_trailing(buf: &mut String,
-                         line_opt: Option<&str>,
+                         line_opt: Option<&Cow<str>>,
                          lo: &Loc,
                          hi_opt: Option<&Loc>) {
             let (lo, hi_opt) = (lo.col.to_usize(), hi_opt.map(|hi| hi.col.to_usize()));
@@ -184,13 +185,13 @@ impl CodeSuggestion {
             let cur_lo = cm.lookup_char_pos(sp.lo);
             for (buf, substitute) in bufs.iter_mut().zip(substitutes) {
                 if prev_hi.line == cur_lo.line {
-                    push_trailing(buf, prev_line, &prev_hi, Some(&cur_lo));
+                    push_trailing(buf, prev_line.as_ref(), &prev_hi, Some(&cur_lo));
                 } else {
-                    push_trailing(buf, prev_line, &prev_hi, None);
+                    push_trailing(buf, prev_line.as_ref(), &prev_hi, None);
                     // push lines between the previous and current span (if any)
                     for idx in prev_hi.line..(cur_lo.line - 1) {
                         if let Some(line) = fm.get_line(idx) {
-                            buf.push_str(line);
+                            buf.push_str(line.as_ref());
                             buf.push('\n');
                         }
                     }
@@ -206,7 +207,7 @@ impl CodeSuggestion {
         for buf in &mut bufs {
             // if the replacement already ends with a newline, don't print the next line
             if !buf.ends_with('\n') {
-                push_trailing(buf, prev_line, &prev_hi, None);
+                push_trailing(buf, prev_line.as_ref(), &prev_hi, None);
             }
             // remove trailing newline
             buf.pop();

src/libsyntax/json.rs

@@ -314,7 +314,7 @@ impl DiagnosticSpanLine {
                          h_end: usize)
                          -> DiagnosticSpanLine {
         DiagnosticSpanLine {
-            text: fm.get_line(index).unwrap_or("").to_owned(),
+            text: fm.get_line(index).map_or(String::new(), |l| l.into_owned()),
             highlight_start: h_start,
             highlight_end: h_end,
         }

src/libsyntax_pos/lib.rs

@@ -33,6 +33,7 @@
 #![cfg_attr(stage0, feature(rustc_private))]
 #![cfg_attr(stage0, feature(staged_api))]
 
+use std::borrow::Cow;
 use std::cell::{Cell, RefCell};
 use std::ops::{Add, Sub};
 use std::rc::Rc;
@@ -605,24 +606,33 @@ impl FileMap {
 
     /// get a line from the list of pre-computed line-beginnings.
     /// line-number here is 0-based.
-    pub fn get_line(&self, line_number: usize) -> Option<&str> {
-        match self.src {
-            Some(ref src) => {
-                let lines = self.lines.borrow();
-                lines.get(line_number).map(|&line| {
-                    let begin: BytePos = line - self.start_pos;
-                    let begin = begin.to_usize();
-                    // We can't use `lines.get(line_number+1)` because we might
-                    // be parsing when we call this function and thus the current
-                    // line is the last one we have line info for.
-                    let slice = &src[begin..];
-                    match slice.find('\n') {
-                        Some(e) => &slice[..e],
-                        None => slice
-                    }
-                })
+    pub fn get_line(&self, line_number: usize) -> Option<Cow<str>> {
+        fn get_until_newline(src: &str, begin: usize) -> &str {
+            // We can't use `lines.get(line_number+1)` because we might
+            // be parsing when we call this function and thus the current
+            // line is the last one we have line info for.
+            let slice = &src[begin..];
+            match slice.find('\n') {
+                Some(e) => &slice[..e],
+                None => slice
             }
-            None => None
+        }
+
+        let lines = self.lines.borrow();
+        let line = if let Some(line) = lines.get(line_number) {
+            line
+        } else {
+            return None;
+        };
+        let begin: BytePos = *line - self.start_pos;
+        let begin = begin.to_usize();
+
+        if let Some(ref src) = self.src {
+            Some(Cow::from(get_until_newline(src, begin)))
+        } else if let Some(src) = self.external_src.borrow().get_source() {
+            Some(Cow::Owned(String::from(get_until_newline(src, begin))))
+        } else {
+            None
         }
     }
 
@@ -641,7 +651,7 @@ impl FileMap {
     }
 
     pub fn is_imported(&self) -> bool {
-        self.src.is_none() // TODO: change to something more sensible
+        self.src.is_none()
     }
 
     pub fn byte_length(&self) -> u32 {