🚀 Highlight merge diffs and conflict markers

[rygwdn]

When showing a patch for a merge with --cc or -c, git will generate patch prefixes that are two characters instead of just one, (e.g. ++ or -). Delta will highlight any lines that have a leading + or - but will not highlight lines with a leading space. I believe Delta should be highlighting the lines the same way git does (e.g. by ignoring the leading space so a - line is red and a + line is green).

Sample input from git show --cc 27d2427484c6efe283671300b48b5aadc7549c8a in this repo:

commit 27d2427484c6efe283671300b48b5aadc7549c8a
Merge: 55703ed 268887c
Author: Dan Davison <dandavison7@gmail.com>
Date:   Thu Apr 16 12:11:21 2020 -0400

    Merge branch 'master' into width-calc-fix

diff --cc Cargo.lock
index 9bd779d,5be85a6..cee10bb
--- a/Cargo.lock
+++ b/Cargo.lock
@@@ -293,11 -358,15 +358,16 @@@ dependencies =
   "regex 1.2.1 (registry+https://github.com/rust-lang/crates.io-index)",
   "shell-words 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
   "structopt 0.2.18 (registry+https://github.com/rust-lang/crates.io-index)",
-  "syntect 3.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
+  "syntect 4.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
   "unicode-segmentation 1.3.0 (registry+https://github.com/rust-lang/crates.io-index)",
 + "unicode-width 0.1.6 (registry+https://github.com/rust-lang/crates.io-index)",
  ]

+ [[package]]
+ name = "glob"
+ version = "0.3.0"
+ source = "registry+https://github.com/rust-lang/crates.io-index"
+
  [[package]]
  name = "heck"
  version = "0.3.1"
diff --cc Cargo.toml
index 914197f,cde6620..8e33592
--- a/Cargo.toml
+++ b/Cargo.toml
@@@ -27,9 -27,8 +27,9 @@@ lazy_static = "1.4
  regex = "1.2.1"
  shell-words = "0.1.0"
  structopt = "0.2.18"
- syntect = "3.2.0"
+ syntect = "4.1.0"
  unicode-segmentation = "1.3.0"
 +unicode-width = "0.1.6"

  [dependencies.error-chain]
  version = "0.12.1"

Git native highlighting:

Delta highlighting:

[dandavison]

Hi @rygwdn, thanks very much for this. Definitely on the list! There's a stub issue #25 for this but yours is much more helpful and better fleshed-out, so I'll close that one and retain this.

[rygwdn]

If it helps, the syntax for this "Combined diff format" indicates that the number of @ signs in the hunk header can be used to determine the number of files being compared, and thus the number of columns that should be considered for the +, -, and space characters. e.g. @@@ -27,9 -27,8 +27,9 @@@ lazy_static = "1.4 above indicates that 2 columns are being used vs 1 column if it were @@ -27,9 -27,8 +27,9 @@ lazy_static = "1.4 or 3 if it were @@@@ -27,9 -27,8 +27,9 @@@@ lazy_static = "1.4.

Seems to me that handle_hunk_meta_line could count the number of @ symbols and return it to be handed into handle_hunk_line which would then need to read more characters in the Some(' ') case to determine if it should be highlighted. It seems like any case where the first column has + or - is already being handled reasonably so the other cases probably don't need to change. I've never done any rust dev, so I'm not 100% sure how to do this, but I might take a stab at it if you don't think you'll get to it.

[dandavison]

Hi @rygwdn, that's very helpful, thanks a lot. You'd be really welcome to have a go at this -- there's plenty of work to go around at the moment! People have been very helpful opening issues and submitting PRs recently. The one thing I'd point out is that I think it would make sense to wait until @clnoll's work adding line number display in #190 is stable because they are also modifying handle_hunk_meta_line and parse_hunk_metadata. So, no pressure/obligation, but I'll ping this ticket again once those changes to handle_hunk_meta_line are ready.

[dandavison]

What I mean is: you're welcome to go ahead, I just wanted you to know that handle_hunk_meta_line will be changing. So perhaps it would make sense to not worry about that part, put in a stub implementation that returns what you would want regarding the number of @s, and focus on the highlighting, given that stub.

[phil-blain]

Very interested in this also. For bonus points, delta could color the conflict markers (>>>>>>>, <<<<<<<<, ======= and ||||||||||| for diff3-style conflicts ) in a different color.

EDIT it's not at all obvious when reading the git diff man page, but in presence of conflicted files, git diff uses the combined diff format. This can be seen in the vanilla diff header emitted by Git, which shows "diff --cc <file>". It can optionnally show the conflict in the more verbose -c mode ("diff --combined <file>"). The difference between these two modes is only detailed in the doc of the low-level git diff-tree command.