Add tree-sitter-git-diff (#1373)

* add submodule on tree-sitter-git-diff

* add git-diff highlights

* inject git-diff into git-commit

* update tree-sitter-git-commit with fix for bad diff case

* add git-diff to language support docs

* include-children in diff injections

This ensures that children nodes of $.message are included in the
injection, such as $.user or issue/pr numbers. Without this change,
diffs containing '#' or '@' characters can trip up the injection and
be parsed separately.

See #1373 (comment)

* set diff language's scope as source.diff

.gitmodules

@@ -174,3 +174,7 @@
 	path = helix-syntax/languages/tree-sitter-git-commit
 	url = https://github.com/the-mikedavis/tree-sitter-git-commit.git
 	shallow = true
+[submodule "helix-syntax/languages/tree-sitter-git-diff"]
+	path = helix-syntax/languages/tree-sitter-git-diff
+	url = https://github.com/the-mikedavis/tree-sitter-git-diff.git
+	shallow = true

book/src/generated/lang-support.md

@@ -12,6 +12,7 @@
 | elixir | ✓ |  |  | `elixir-ls` |
 | fish | ✓ | ✓ | ✓ |  |
 | git-commit | ✓ |  |  |  |
+| git-diff | ✓ |  |  |  |
 | glsl | ✓ |  | ✓ |  |
 | go | ✓ | ✓ | ✓ | `gopls` |
 | html | ✓ |  |  |  |

languages.toml

@@ -481,3 +481,12 @@ roots = []
 file-types = ["COMMIT_EDITMSG"]
 comment-token = "#"
 indent = { tab-width = 2, unit = "  " }
+
+[[language]]
+name = "git-diff"
+scope = "source.diff"
+roots = []
+file-types = ["diff"]
+injection-regex = "diff"
+comment-token = "#"
+indent = { tab-width = 2, unit = "  " }

runtime/queries/git-commit/highlights.scm

@@ -13,7 +13,3 @@
 
 [":" "->"] @punctuation.delimeter
 (comment) @comment
-
-; once we have diff injections, @comment should become @none
-((comment (scissors))
- (message)+ @comment)

runtime/queries/git-commit/injections.scm

@@ -1,12 +1,7 @@
-; once a diff grammar is available, we can inject diff highlighting into the
-; trailer after scissors (git commit --verbose)
-; see https://github.com/helix-editor/helix/pull/1338#issuecomment-1000013539
-;
-; ((comment (scissors))
-;  (message) @injection.content
-;  (#set! injection.language "diff"))
-
-; ---
+((comment (scissors))
+ (message) @injection.content
+ (#set! injection.include-children)
+ (#set! injection.language "diff"))
 
 ; once a rebase grammar is available, we can inject rebase highlighting into
 ; interactive rebase summary sections like so:

runtime/queries/git-diff/highlights.scm

@@ -0,0 +1,6 @@
+[(addition) (new_file)] @diff.plus
+[(deletion) (old_file)] @diff.minus
+
+(commit) @constant
+(location) @attribute
+(command) @markup.bold