encoding: add fast path of from/toutf8b() for ASCII strings See the previous patch for why. The added test seems not making much sense because ASCII strings should never contain "\xed" and be valid UTF-8. (with mercurial repo) $ export HGRCPATH=/dev/null HGPLAIN= $ hg log --time --config experimental.stabilization=all -Tjson > /dev/null (original) time: real 6.830 secs (user 6.740+0.000 sys 0.080+0.000) time: real 6.690 secs (user 6.650+0.000 sys 0.040+0.000) time: real 6.700 secs (user 6.640+0.000 sys 0.060+0.000) (fast jsonescape) time: real 5.630 secs (user 5.550+0.000 sys 0.070+0.000) time: real 5.700 secs (user 5.650+0.000 sys 0.050+0.000) time: real 5.690 secs (user 5.640+0.000 sys 0.050+0.000) (this patch) time: real 5.190 secs (user 5.120+0.000 sys 0.070+0.000) time: real 5.230 secs (user 5.170+0.000 sys 0.050+0.000) time: real 5.220 secs (user 5.150+0.000 sys 0.070+0.000)

--- a/mercurial/encoding.py	Sun Apr 23 13:06:23 2017 +0900
+++ b/mercurial/encoding.py	Sun Apr 23 13:08:58 2017 +0900
@@ -494,6 +494,8 @@
     internal surrogate encoding as a UTF-8 string.)
     '''
 
+    if not isinstance(s, localstr) and isasciistr(s):
+        return s
     if "\xed" not in s:
         if isinstance(s, localstr):
             return s._utf8
@@ -544,6 +546,8 @@
     True
     '''
 
+    if isasciistr(s):
+        return s
     # fast path - look for uDxxx prefixes in s
     if "\xed" not in s:
         return s