feat: support crystal tool format (#344)

README.md

@@ -201,6 +201,7 @@ You can view this list in vim with `:help conform-formatters`
 - [cljstyle](https://github.com/greglook/cljstyle) - Formatter for Clojure code.
 - [cmake_format](https://github.com/cheshirekow/cmake_format) - Parse cmake listfiles and format them nicely.
 - [codespell](https://github.com/codespell-project/codespell) - Check code for common misspellings.
+- [crystal](https://crystal-lang.org/) - Format Crystal code.
 - [csharpier](https://github.com/belav/csharpier) - The opinionated C# code formatter.
 - [cue_fmt](https://cuelang.org) - Format CUE files using `cue fmt` command.
 - [darker](https://github.com/akaihola/darker) - Run black only on changed lines.

doc/conform.txt

@@ -208,6 +208,7 @@ FORMATTERS                                                    *conform-formatter
 `cljstyle` - Formatter for Clojure code.
 `cmake_format` - Parse cmake listfiles and format them nicely.
 `codespell` - Check code for common misspellings.
+`crystal`- Format Crystal code.
 `csharpier` - The opinionated C# code formatter.
 `cue_fmt` - Format CUE files using `cue fmt` command.
 `darker` - Run black only on changed lines.

lua/conform/formatters/crystal.lua

@@ -0,0 +1,10 @@
+---@type conform.FileFormatterConfig
+return {
+  meta = {
+    url = "https://crystal-lang.org/",
+    description = "Format Crystal code.",
+  },
+  command = "crystal",
+  args = { "tool", "format", "-" },
+  stdin = true,
+}