patch: implement a new worddiff algorithm 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. Differential Revision: https://phab.mercurial-scm.org/D3212

patch: buffer lines for a same hunk Instead of yielding tokens directly, buffer them if they belong to a same hunk. This makes it easier for the upcoming new worddiff algorithm to only focus on the diff hunk, instead of having to worry about other contents. This breaks how the existing experimental worddiff algorithm works, so the algorithm was removed, and related tests are disabled for now. The next patch will add a new worddiff algorithm. Differential Revision: https://phab.mercurial-scm.org/D3211

patch: move yielding "\n" to the end of loop The original logic makes it harder to reason about - it yields the "\n" character belonging to the last line in the next loop iteration. The new code is in theory a little bit slower. But is more readable. It makes the following changes easier to read. Differential Revision: https://phab.mercurial-scm.org/D3210

context: clarify deprecation warning message I had one developer report that they couldn't find the message. This patch should make it clear where to find it. Differential Revision: https://phab.mercurial-scm.org/D3389

wireprotov2: add support for more response types This adds types to represent error and generator responses from server commands. Differential Revision: https://phab.mercurial-scm.org/D3388

wireprotov2: remove support for sending bytes response We recently declared that all responses must be CBOR. So remove support for sending a type that isn't CBOR data. Differential Revision: https://phab.mercurial-scm.org/D3387

wireprotov2: change behavior of error frame Now that we have a leading CBOR map in command response frames to indicate overall command result status, we don't need to use the error response frame to represent command errors. Instead, we can reserve it for protocol and server level errors. And for the special case of a command error that occurred after command response frames were emitted. The code for error handling still needs a ton of work. But we're slowly going in the right direction... Differential Revision: https://phab.mercurial-scm.org/D3386