Control: forwarded -1 https://debbugs.gnu.org/cgi/bugreport.cgi?bug=79546 Control: retitle -1 emacs: opening a diff file in diff-mode can be very slow Control: found -1 1:30.1+1-6 Control: found -1 1:30.1+1-9
On 2024-08-20 16:14:37 +0200, Santiago Vila wrote: > As pointed out by Paul Eggert in bug-diffutils, diff -d > is *inherently* slow. This is documented in the diff --help > output: > > -d, --minimal try *hard* to find a smaller set of changes > > and also in the texinfo manual: > > '-d' > '--minimal' > Change the algorithm perhaps find a smaller set of changes. This > makes 'diff' slower (sometimes much slower). > > Since I can't control how emacs calls diff, there is nothing I can > reasonably do on the diffutils packaging side. So I've reported the bug against GNU Emacs upstream: https://debbugs.gnu.org/cgi/bugreport.cgi?bug=79546 with a simpler testcase: $ echo . > file1 $ seq 50000 > file2 $ diff -u file1 file2 > file.diff $ emacs -Q file.diff takes 17 seconds on my machine. With 100000 instead of 50000, this takes 72 seconds, i.e. about 4 times as much. But I think that the best solution would be a limit detection in diff, above which the faster (but not giving a minimal diff) algorithm should be used. -- Vincent Lefèvre <[email protected]> - Web: <https://www.vinc17.net/> 100% accessible validated (X)HTML - Blog: <https://www.vinc17.net/blog/> Work: CR INRIA - computer arithmetic / Pascaline project (LIP, ENS-Lyon)
