Fix bad line printing for parse errors

The code that extracted lines from partially-parsed files
was broken.

Closes #1848

src/comp/driver/diagnostic.rs

@@ -204,8 +204,7 @@ fn highlight_lines(cm: codemap::codemap, sp: span,
     // Print the offending lines
     for line: uint in display_lines {
         io::stderr().write_str(#fmt["%s:%u ", fm.name, line + 1u]);
-        let s = codemap::get_line(fm, line as int);
-        if !str::ends_with(s, "\n") { s += "\n"; }
+        let s = codemap::get_line(fm, line as int) + "\n";
         io::stderr().write_str(s);
     }
     if elided {

src/comp/syntax/codemap.rs

@@ -157,16 +157,11 @@ fn span_to_lines(sp: span, cm: codemap::codemap) -> @file_lines {
 
 fn get_line(fm: filemap, line: int) -> str unsafe {
     let begin: uint = fm.lines[line].byte - fm.start_pos.byte;
-    let end: uint;
-    if line as uint < vec::len(fm.lines) - 1u {
-        end = fm.lines[line + 1].byte - fm.start_pos.byte;
-        ret str::unsafe::slice_bytes(*fm.src, begin, end);
-    } else {
-        // If we're not done parsing the file, we're at the limit of what's
-        // parsed. If we just slice the rest of the string, we'll print out
-        // the remainder of the file, which is undesirable.
-        ret str::splitn_char(*fm.src, '\n', 1u)[0];
-    }
+    let end = alt str::byte_index(*fm.src, '\n' as u8, begin) {
+      some(e) { e }
+      none { str::len(*fm.src) }
+    };
+    str::unsafe::slice_bytes(*fm.src, begin, end)
 }
 
 fn lookup_byte_offset(cm: codemap::codemap, chpos: uint)

src/libcore/str.rs

@@ -68,6 +68,7 @@ export
 
    // Searching
    index,
+   byte_index,
    rindex,
    find,
    find_bytes,
@@ -852,6 +853,19 @@ fn index(ss: str, cc: char) -> option<uint> {
     ret option::none;
 }
 
+// Function: byte_index
+//
+// Returns the index of the first matching byte
+// (as option some/none)
+fn byte_index(s: str, b: u8, start: uint) -> option<uint> {
+    let i = start, l = len_bytes(s);
+    while i < l {
+        if s[i] == b { ret some(i); }
+        i += 1u;
+    }
+    ret none;
+}
+
 // Function: rindex
 //
 // Returns the index of the first matching char