🚀 Display percentage similarity for renamed and copied files

[dandavison]

See #392. cc @phil-blain

#392 (comment)

I did not think of it on Friday, but delta would be even more excellent if the similarity index (in percent) was indicated in parenthesis on the header line, for both renamed and copied files, something like this:

$ GIT_PAGER=../delta/target/release/delta git diff --cached -C -C

copied: first_file ⟶   copied_file (100%)
─────────────────────────────────────────────────────────────────

[WhyNotHugo]

This currently gets swallowed for files that have been moved, making them very hard to miss from diffs.

For example, here, at a glance, it seems that there's only a single change on-screen:

The raw output does include a reference though:

> git --no-pager log -p 49352587a29cb1130d963ade600e64810d596544 | less
commit 49352587a29cb1130d963ade600e64810d596544
Author: somini <[email protected]>
Date:   Mon Dec 27 12:19:58 2021 +0000

    Move icon to the app_id location
    
    This is so that the desktop files picks it up correctly.

diff --git a/resources/meson.build b/resources/meson.build
index 3e5c97a..7c99454 100644
--- a/resources/meson.build
+++ b/resources/meson.build
@@ -15,7 +15,7 @@ resources = gnome.compile_resources(
 
 scour = find_program('scour', required: false)
 
-icon = 'wdisplays.svg'
+icon = 'network.cycles.wdisplays.svg'
 icondir = get_option('datadir') / 'icons' / 'hicolor' / 'scalable' / 'apps'
 
 if scour.found()
diff --git a/resources/wdisplays.svg b/resources/network.cycles.wdisplays.svg
similarity index 100%
rename from resources/wdisplays.svg
rename to resources/network.cycles.wdisplays.svg

commit a9aa7472e37a44b1aaa962d3794f68553e9f81fe
Merge: 5c6568a cfc8339
Author: Arti Zirk <[email protected]>
Date:   Mon Mar 29 11:33:43 2021 +0300

    Merge remote-tracking branch 'IntinteDAO/patch-1'

commit 5c6568a5b066e86d79a55f1d5334b2096a42715c
Merge: dd7e1e2 5198a9c
Author: Arti Zirk <[email protected]>
Date:   Mon Mar 29 11:30:31 2021 +0300

    Merge remote-tracking branch 'emersion/fix-global-version'

commit 5198a9c94b40ff157c284df413be5402f1b75118
Author: Simon Ser <[email protected]>
Date:   Wed Jul 8 11:57:35 2020 +0200

    Use correct versions when binding globals
    
    Changes to protocols aren't forward-compatible. It's not possible to use

Passing similarity index 100% in regular text colour would stand out enough, IMHO.

[dandavison]

I have to admit I'm not quite seeing the value -- but I'm sure it's me being dense/lazy since someone has gone to the trouble of adding the feature to git! If it's 100% then there's no diff to show, so I'm not sure what value there is in showing the 100% here: copied: first_file ⟶ copied_file (100%).

And if it's <100% then there's a diff, so that will be highly visible.

Would someone mind explaining how this feature is used?

[WhyNotHugo]

The file change location in these cases, but the change does not stand out. All the orange content is (as seen in the screenshot) metadata about changes. So while skimming trying to see changes in a log, file moves don't stand out and are easy to omit.

[mentalisttraceur]

It's nice for false positives: delete one file, write another file, have Git show it as a rename+diff, get confused ("why does git think this is a move?! did I do something wrong? ..."), notice "51% similar" ("on that's why. well, okay then I guess").

[mentalisttraceur]

Note that git allows us to change the similarity threshold when looking at logs/diffs, so knowing the degree of similarity of existing matches can help us know what to set that parameter to if we want to adjust what it dispays as a rename, etc.

[mentalisttraceur]

Oh, big reason! We don't always see the diff with a rename.

Sometimes people use git diff/git log format options which shows the file summaries (modified, added, renamed, etc) but not the hunks.

I personally have done this with git log several times in my life (I can't remember exactly why anymore, probably to get a birds eye view of how a code base evolved, but I do remember going out of my way to look up how to do it at least twice over the years).