Add range-diff, a tbdiff lookalike

[dscho]

The incredibly useful git-tbdiff tool to compare patch series (say, to see what changed between two iterations sent to the Git mailing list) is slightly less useful for this developer due to the fact that it requires the hungarian and numpy Python packages which are for some reason really hard to build in MSYS2. So hard that I even had to give up, because it was simply easier to re-implement the whole shebang as a builtin command.

The project at https://github.com/trast/tbdiff seems to be dormant, anyway. Funny (and true) story: I looked at the open Pull Requests to see how active that project is, only to find to my surprise that I had submitted one in August 2015, and that it was still unanswered let alone merged.

While at it, I forward-ported AEvar's patch to force --decorate=no because git -p tbdiff would fail otherwise.

Side note: I work on implementing range-diff not only to make life easier for reviewers who have to suffer through v2, v3, ... of my patch series, but also to verify my changes before submitting a new iteration. And also, maybe even more importantly, I plan to use it to verify my merging-rebases of Git for
Windows (for which I previously used to redirect the pre-rebase/post-rebase diffs vs upstream and then compare them using git diff --no-index). And of course any interested person can see what changes were necessary e.g. in the merging-rebase of Git for Windows onto v2.17.0 by running a command like:

        base=^{/Start.the.merging-rebase}
        tag=v2.17.0.windows.1
        pre=$tag$base^2
        git range-diff $pre$base..$pre $tag$base..$tag

The command uses what it calls the "dual color mode" (can be disabled via --no-dual-color) which helps identifying what actually changed: it prefixes lines with a - (and red background) that correspond to the first commit range, and with a + (and green background) that correspond to the second range. The rest of the lines will be colored according to the original diffs.

Changes since v4:

• Fixed a typo in the commit message of "range-diff: add tests" that was introduced in v4.
• White-space fixes.
• Fixed the length of the first header underline in the man page.
• Changed the preprocessor guard in linear-assignment.h to reflect the new name (instead of the old name, which was hungarian.h).
• Likewise, changed the preprocessor guards in range-diff.h to hide the history of the thrice-renamed command.
• Fixed indentation in the completion.
• Instead of trying to paper over white-space error handling that does not apply to "diffs of diffs", dual color mode now simply disables all white-space warnings.
• When showing the "single arg must be symmetric range" error message, git range-diff now also shows the usage.
• Adjusted the commit message of "range-diff: adjust the output of the commit pairs" to avoid the surprise of the reviewer when onelines are printed all of a sudden, too.
• "range-diff: adjust the output of the commit pairs" is now using a simpler way to print onelines.
• We are now sandwiching the diff_opt_parse() loop between two parse_options(), to make sure that we caught all options, and that the -- separator is handled.
• Adjusted the lookup_commit_reference() call to the newest master (it now takes a the_repository parameter).

Changes since v3:

• The cover letter was adjusted to reflect the new reality (the command is called range-diff now, not branch-diff, and --dual-color is the default).
• The documentation was adjusted a bit more in the patch that makes --dual-color the default.
• Clarified the calculation of the cost matrix, as per Stefan Beller's request.
• The man page now spells out that merge commits are ignored in the commit ranges (not merges per se).
• The code in linear-assignment.c was adjusted to use the SWAP() macro.
• The commit message of the patch introducing the first rudimentary implementation no longer talks about the "Hungarian" algorithm, but about the "linear assignment algorithm" instead.
• A bogus indentation change was backed out from the patch introducing the first rudimentary implementation.
• Instead of merely warning about missing .. in the 2-parameter invocation, we now exit with the error message.
• The diff_opt_parse() function is allowed to return a value larger than 1, indicating that more than just one command-line parameter was parsed. We now advance by the indicated value instead of always advancing exactly 1 (which is still correct much of the time).
• A lengthy if...else if...else if...else was simplified (from a logical point of view) by reordering it.
• The unnecessarily static variable dashes was turned into a local variable of the caller.
• The commit message talking about the new man page still referred to git branch --diff, which has been fixed.
• A forgotten t7910 reference was changed to t3206.
• An unbalanced double-tick was fixed in the man page.
• Fixed grammar both of the commit message and the description of the --no-dual-color option.
• To fix the build, a blank man page is now introduced together with the new range-diff command, even if it is populated for real only at a later patch (i.e. at the same time as before).
• The headaches Junio fears would be incurred by that simple workaround to avoid bogus white-space error reporting are fended off: a more complex patch is now in place that adds (and uses) a new white-space flag. Sadly, as is all too common when Junio "encourages" me to replace a simple workaround by something "proper", it caused all kinds of headaches to get this right, so I am rather less certain that the "proper" fix will cause us less headaches than the simple workaround would have done. But whatever.
• The dual color mode now also dims the changes that are exclusively in the first specified commit range, and uses bold face on the changes exclusively in the second one. This matches the intuition when using range-diff to compare an older iteration of a patch series to a newer one: the changes from the previous iteration that were replaced by new ones "fade", while the changes that replace them are "shiny new".

Changes since v2:

• Right-aligned the patch numbers in the commit pairs.
• Used ALLOC_ARRAY() in hungarian.c instead of xmalloc(sizeof()*size).
• Changed compute_assignment()s return type from int to void, as it always succeeds.
• Changed the Hungarian Algorithm to use an integer cost matrix.
• Changed the --creation-weight option to --creation-factor where is an integer.
• Retitled 1/19 and 2/19 to better conform with the current conventions, as pointed out (and suggested) by Junio.
• Shut up Coverity, and at the same time avoided passing the unnecessary i and j parameters to output_pair_header().
• Removed support for the --no-patches option: we inherit diff_options' support for -s already (and much more).
• Removed the ugly _INV enum values, and introduced a beautiful GIT_COLOR_REVERSE instead. This way, whatever the user configured as color.diff.new (or .old) will be used in reverse in the dual color mode.
• Instead of overriding the fragment header color, the dual color mode will now reverse the "outer" fragment headers, too.
• Turned the stand-alone branch-diff command into the --diff option of git branch. Adjusted pretty much all commit messages to account for this. This change should no longer be visible: see below.
• Pretty much re-wrote the completion, to support the new --diff mode of git-branch. See below: it was reverted for range-diff.
• Renamed t7910 to t3206, to be closer to the git-branch tests.
• Ensured that git_diff_ui_config() gets called, and therefore color.diff.* respected.
• Avoided leaking four_spaces.
• Fixed a declaration in a for (;;) statement (which Junio had as a fixup! that I almost missed).
• Renamed branch --diff, which had been renamed from branch-diff (which was picked to avoid re-using tbdiff) to range-diff.
• Renamed hungarian.c and its header to linear-assignment.c
• Made --dual-color the default, and changed it to still auto-detect whether color should be used rather than forcing it

[gitgitgadget]

An error occurred while submitting:

Error: Branch f8c4e30c63bbfa7efec44ff0f6d0404326723d35 is not rebased to upstream/master

[dscho]

/submit

[gitgitgadget]

An error occurred while submitting:

Error: git tag -F - -a pr-1/dscho/branch-diff-v3 4a68b95 failed: 128,
fatal: tag 'pr-1/dscho/branch-diff-v3' already exists

[dscho]

/submit

[gitgitgadget]

Submitted as pull.1.v3.git.gitgitgadget@gmail.com

[dscho]

/submit

[gitgitgadget]

Submitted as pull.1.v4.git.gitgitgadget@gmail.com