stringutil: try to avoid running `splitlines()` only to get first line
It's wasteful to call `splitlines()` and only get the first line from
it. However, Python doesn't seem to provide a built-in way of doing
just one split based on the set of bytes used by `splitlines()`. As a
workaround, we do an initial split on just LF and then call
`splitlines()` on the result. Thanks to Joerg for this suggestion. I
didn't bother to also split on CR, so users with old Mac editors (or
repos created by such editors) will not get this performance
improvement.
Differential Revision: https://phab.mercurial-scm.org/D12413
--- a/mercurial/utils/stringutil.py Thu Mar 24 22:05:49 2022 -0700
+++ b/mercurial/utils/stringutil.py Fri Mar 25 08:33:03 2022 -0700
@@ -687,6 +687,10 @@
def firstline(text):
"""Return the first line of the input"""
+ # Try to avoid running splitlines() on the whole string
+ i = text.find(b'\n')
+ if i != -1:
+ text = text[:i]
try:
return text.splitlines()[0]
except IndexError: