Remove `StringReader::col`.

It only has a single use, within code handling indented block comments.
We can replace that with the new `FileMap::col_pos()`, which computes
the col position (BytePos instead of CharPos) based on the record of the
last newline char (which we already record).

This is actually an improvement, because
`trim_whitespace_prefix_and_push_line()` was using `col`, which is a
`CharPos`, as a slice index, which is a byte/char confusion.

2 files changed, 13 insertions, 7 deletions

diff --git a/src/libsyntax/parse/lexer/comments.rs b/src/libsyntax/parse/lexer/comments.rs
index 63aa5d28ce8..672b0b9bbd1 100644
--- a/src/libsyntax/parse/lexer/comments.rs
+++ b/src/libsyntax/parse/lexer/comments.rs
@@ -238,7 +238,19 @@ fn read_block_comment(rdr: &mut StringReader,
     debug!(">>> block comment");
     let p = rdr.pos;
     let mut lines: Vec<String> = Vec::new();
-    let col = rdr.col;
+
+    // Count the number of chars since the start of the line by rescanning.
+    let mut src_index = rdr.src_index(rdr.filemap.line_begin_pos());
+    let end_src_index = rdr.src_index(rdr.pos);
+    assert!(src_index <= end_src_index);
+    let mut n = 0;
+    while src_index < end_src_index {
+        let c = char_at(&rdr.src, src_index);
+        src_index += c.len_utf8();
+        n += 1;
+    }
+    let col = CharPos(n);
+
     rdr.bump();
     rdr.bump();
 
diff --git a/src/libsyntax/parse/lexer/mod.rs b/src/libsyntax/parse/lexer/mod.rs
index 3968b7f113b..566e0c213b1 100644
--- a/src/libsyntax/parse/lexer/mod.rs
+++ b/src/libsyntax/parse/lexer/mod.rs
@@ -44,8 +44,6 @@ pub struct StringReader<'a> {
     pub next_pos: BytePos,
     /// The absolute offset within the codemap of the current character
     pub pos: BytePos,
-    /// The column of the next character to read
-    pub col: CharPos,
     /// The current character (which has been read from self.pos)
     pub ch: Option<char>,
     pub filemap: Lrc<syntax_pos::FileMap>,
@@ -175,7 +173,6 @@ impl<'a> StringReader<'a> {
             sess,
             next_pos: filemap.start_pos,
             pos: filemap.start_pos,
-            col: CharPos(0),
             ch: Some('\n'),
             filemap,
             end_src_index: src.len(),
@@ -442,9 +439,6 @@ impl<'a> StringReader<'a> {
                 if self.save_new_lines_and_multibyte {
                     self.filemap.next_line(self.next_pos);
                 }
-                self.col = CharPos(0);
-            } else {
-                self.col = self.col + CharPos(1);
             }
             if next_ch_len > 1 {
                 if self.save_new_lines_and_multibyte {