Add syntax highlight code for ignore files

[taconi]

Adding ignore file support by default so you don't need to install the language-ignore plugin.

[Andriamanitra]

I like the idea but I would reconsider the syntax groups. The current colors seem a bit weird because files are not statements, wildcards are not identifiers, and negated files are definitely not errors.

Screenshots

Using the default config:

Using my current config:

Maybe using diff-added and diff-deleted colors would make more sense?

[Andriamanitra]

Suggested change

	- identifier: '!|\*|\[.*]'
	- symbol.operator: '^!'
	- identifier: '\?|\*|\[.*?\]'
	- constant.specialChar: "\\\\."

• ! should only match when it's the first character on the line (exclamation mark in the middle of a file name has no special meaning)
• ? in .gitignore matches any single character except backslash
• The regex .* is greedy so it wouldn't work if you have something like dir[a-z]/file[a-z]. Changing it to .*? makes it non-greedy so it only matches until the next ].
• Add highlighting for escaped characters like \?

[taconi]

Based on your suggestions I thought of something like this, what do you think?

---
filetype: ignore

detect:
  filename: .*ignore$

rules:
  - statement: .*$           # files
  - constant.string: .*/$    # diretories
  - diff-deleted: '^!.*'    # negated

  - special: /
  - identifier: '^!|\?|\*|\[.*?]|\\.'

  - comment: '#.*$'

[taconi]

Are the colors strange?

[Andriamanitra]

The rules seem to work alright for common patterns but some of the weirder cases are not highlighted correctly.

[taconi]

[...] files are not statements, wildcards are not identifiers, and negated files are definitely not errors.
Maybe using diff-added and diff-deleted colors would make more sense?

The relationship was based on colors because of the existing identifiers I did not find any related to the ignore file patterns. diff-added and diff-deleted are also not nominally related.
I believe one thing that might bother you is that some color schemes add a background color to the error handler, so I don't see any problem with switching to diff-deleted.

[Andriamanitra]

If you commit the changes from #3104 (comment) it looks good to me

[taconi]

If you commit the changes from #3104 (comment) it looks good to me

@Andriamanitra Applied