The previous worddiff algorithm has many problems. The major problem is it
does a "similarity check" that selects a subset of matched lines to do
inline diffs. It is a bad idea because:
- The "similarity check" is non-obvious to users. For example, a simple change from "long long x" to "int64_t x" will fail the similarity check and won't be diff-ed as expected.
- Selecting "lines" to diff won't work as people expect if there are line wrapping changes.
- It has a sad time complexity if lines do not match, could be O(N^2)-ish.
There are other problems in implementation details.
- Lines can match across distant hunks (if the next hunk does not have "-" lines).
- "difflib" is slow.
The solution would be removing the "similarity check", and just diff all
words in a same hunk. So no content will be missed and everything will be
diff-ed as expected. This is similar to what code review tool like
Phabricator does.
This diff implements the word diff algorithm as described above. It also
avoids difflib to be faster.
Note about colors: To be consistent, "changed inserted" parts and "purely
insertion blocks" should have a same color, since they do not exist in the
previous version. Instead of highlighting differences, this patch chooses to
dim common parts. This is also more consistent with Phabricator or GitHub
webpage. That said, the labels are defined in a way that people can still
highlight changed parts and leave purely inserted/deleted hunks use the
"non-highlighted" color.
As one example, running:
hg log -pr df50b87d8f736aff8dc281f816bddcd6f306930c mercurial/commands.py \ --config experimental.worddiff=1 --color=debug --config diff.unified=0
The previous algorithm outputs:
[diff.file_a|--- a/mercurial/commands.py Fri Mar 09 15:53:41 2018 +0100]
[diff.file_b|+++ b/mercurial/commands.py Sat Mar 10 12:33:19 2018 +0530]
[diff.hunk|@@ -2039,1 +2039,4 @@]
[diff.deleted|-][diff.deleted.highlight|@command('^forget',][diff.deleted| ][diff.deleted.highlight|walkopts,][diff.deleted| _('[OPTION]... FILE...'), inferrepo=True)]
[diff.inserted|+@command(]
[diff.inserted|+ '^forget',]
[diff.inserted|+ walkopts + dryrunopts,]
[diff.inserted|+ ][diff.inserted.highlight| ][diff.inserted| _('[OPTION]... FILE...'), inferrepo=True)]
[diff.hunk|@@ -2074,1 +2077,3 @@]
[diff.deleted|- rejected = cmdutil.forget(ui, repo, m, prefix="",][diff.deleted.highlight| explicitonly=False)[0]]
[diff.inserted|+ dryrun = opts.get(r'dry_run')]
[diff.inserted|+ rejected = cmdutil.forget(ui, repo, m, prefix="",]
[diff.inserted|+ explicitonly=False, dryrun=dryrun)[0]]The new algorithm outputs:
[diff.file_a|--- a/mercurial/commands.py Fri Mar 09 15:53:41 2018 +0100]
[diff.file_b|+++ b/mercurial/commands.py Sat Mar 10 12:33:19 2018 +0530]
[diff.hunk|@@ -2039,1 +2039,4 @@]
[diff.deleted|-][diff.deleted.unchanged|@command(][diff.deleted.unchanged|'^forget',][diff.deleted.unchanged| ][diff.deleted.changed|walkopts][diff.deleted.unchanged|,][diff.deleted.changed| ][diff.deleted.unchanged|_('[OPTION]... FILE...'), inferrepo=True)]
[diff.inserted|+][diff.inserted.unchanged|@command(]
[diff.inserted|+][diff.inserted.changed| ][diff.inserted.unchanged|'^forget',]
[diff.inserted|+][diff.inserted.changed| walkopts][diff.inserted.unchanged| ][diff.inserted.changed|+ dryrunopts][diff.inserted.unchanged|,]
[diff.inserted|+][diff.inserted.changed| ][diff.inserted.unchanged|_('[OPTION]... FILE...'), inferrepo=True)]
[diff.hunk|@@ -2074,1 +2077,3 @@]
[diff.deleted|-][diff.deleted.unchanged| rejected = cmdutil.forget(ui, repo, m, prefix="",][diff.deleted.changed| ][diff.deleted.unchanged|explicitonly=False][diff.deleted.unchanged|)[0]]
[diff.inserted|+][diff.inserted.changed| dryrun = opts.get(r'dry_run')]
[diff.inserted|+][diff.inserted.unchanged| rejected = cmdutil.forget(ui, repo, m, prefix="",]
[diff.inserted|+][diff.inserted.changed| ][diff.inserted.unchanged|explicitonly=False][diff.inserted.changed|, dryrun=dryrun][diff.inserted.unchanged|)[0]]Practically, when diffing a 8k line change, the time spent on worddiff
reduces from 4 seconds to 0.14 seconds.
These are the first uses of 'dim' in the default set of things, and I don't think we can rely on it; for color.mode=auto, we really mean "ansi" (aka ecma48) (unless on windows), and don't do any detection of capabilities, so we just output \e[2m and some terminals just ignore that (like mine, rxvt-unicode v9.22). If using color.mode=terminfo, we at least get error messages (I did --config color.log.user='dim green'):
ignoring unknown color/effect 'dim' (configured in color.log.user)
Apparently cygwin doesn't advertise 'dim', and while the linux virtual console advertises it and supports it, it doesn't actually support a dim color (at least on my machine), it just always puts it in a weird blue :)
I think I'd prefer that changed be bold and unchanged be non-bold. For most terminals, that'll lead to a visible difference in intensity (bold being brighter unless using a weird palette), and for those that aren't configured for that, it'll at least be a heavier weight. It's better than having literally zero difference between them without any explanation why. I think it'll also be more obvious which lines have it; in your screenshot the difference between dim and regular is pretty subtle.