# HG changeset patch
# User Anton Shestakov <av6@dwimlabs.net>
# Date 2015-08-02 11:18:35
# Node ID c35ee1bbbbdc1b31b514923ce92fa2e1d9e79f8d
# Parent  4dcc9b5d786a5f549bf999d0ca9e9babd27f93e4

highlight: exit early on textual and unknown files (issue3005)

When highlight extension encountered files that pygments didn't recognize, it
used to fall back to text lexer. Also, pygments uses TextLexer for .txt files.
This lexer is noop by design.

On bigger files, however, doing the noop highlighting resulted in noticeable
extra CPU work and memory usage: to show a 1 MB text file, hgweb required about
0.7s more (on top of ~3.8s, Q8400) and consumed about 100 MB of RAM more (on
top of ~150 MB).

Let's just exit the function when it's clear that nothing will be highlighted.

Due to how this pygmentize function works (it modifies the template in-place),
we can just return from it and everything else will work as if highlight
extension wasn't enabled.

diff --git a/hgext/highlight/highlight.py b/hgext/highlight/highlight.py
--- a/hgext/highlight/highlight.py
+++ b/hgext/highlight/highlight.py
@@ -49,7 +49,12 @@ def pygmentize(field, fctx, style, tmpl)
         try:
             lexer = guess_lexer(text[:1024], stripnl=False)
         except (ClassNotFound, ValueError):
-            lexer = TextLexer(stripnl=False)
+            # Don't highlight unknown files
+            return
+
+    # Don't highlight text files
+    if isinstance(lexer, TextLexer):
+        return
 
     formatter = HtmlFormatter(nowrap=True, style=style)