feat: Add formatting support for C# and F# (#650)

purkhusid · alexeagle · web-flow · commit af01019b0ca2 · 2025-11-07T09:55:32.000-08:00
## What?
Adds formatting support for F# and C# using fantomas(F#) and
CSharpier(C#)

The formatters are not avilable as standalone executables and are
provided as NuGet packages via rules_dotnet by the end-user for
rules_lint

---

### Changes are visible to end-users: yes

&lt;!-- If no, please delete this section. --&gt;

- Searched for relevant documentation and updated as needed: yes
- Breaking change (forces users to change their own code or config): no
- Suggested release notes appear below: yes

### Test plan

- New test cases added

---------

Co-authored-by: Alex Eagle &lt;alex@aspect.dev&gt;
diff --git a/example/3rdparty/nuget/BUILD.bazel b/example/3rdparty/nuget/BUILD.bazel
diff --git a/example/3rdparty/nuget/paket.main.bzl b/example/3rdparty/nuget/paket.main.bzl
@@ -0,0 +1,14 @@
+"GENERATED"
+
+load("@rules_dotnet//dotnet:defs.bzl", "nuget_repo")
+
+def main():
+    "main"
+    nuget_repo(
+        name = "paket.main",
+        packages = [
+            {"name": "CSharpier", "id": "CSharpier", "version": "1.1.2", "sha512": "sha512-YG6asSE2fsk56QAqlPmuY8QHemWyJa+UDUh53PzynIONM9sC/u1hUjlZw/gsjx/AF+DOT3Q7Xm/U/BMhuoW/Hw==", "sources": ["https://api.nuget.org/v3/index.json"], "dependencies": {"net11": [], "net20": [], "net30": [], "net35": [], "net40": [], "net403": [], "net45": [], "net451": [], "net452": [], "net46": [], "net461": [], "net462": [], "net47": [], "net471": [], "net472": [], "net48": [], "net5.0": [], "net6.0": [], "net7.0": [], "net8.0": [], "net9.0": [], "netcoreapp1.0": [], "netcoreapp1.1": [], "netcoreapp2.0": [], "netcoreapp2.1": [], "netcoreapp2.2": [], "netcoreapp3.0": [], "netcoreapp3.1": [], "netstandard": [], "netstandard1.0": [], "netstandard1.1": [], "netstandard1.2": [], "netstandard1.3": [], "netstandard1.4": [], "netstandard1.5": [], "netstandard1.6": [], "netstandard2.0": [], "netstandard2.1": []}, "targeting_pack_overrides": [], "framework_list": [], "tools": {"net10.0": [{"name": "csharpier", "entrypoint": "CSharpier.dll", "runner": "dotnet"}], "net8.0": [{"name": "csharpier", "entrypoint": "CSharpier.dll", "runner": "dotnet"}], "net9.0": [{"name": "csharpier", "entrypoint": "CSharpier.dll", "runner": "dotnet"}]}},
+            {"name": "fantomas", "id": "fantomas", "version": "7.0.3", "sha512": "sha512-CCpCQzxLUh+r9sxTGYUKmtNoTBE/J/XDiVSwf+ge+4l9lnW7+R4pLuL7K4sOIbok8l95IvGA4XLFjS0B0ZEQdA==", "sources": ["https://api.nuget.org/v3/index.json"], "dependencies": {"net11": [], "net20": [], "net30": [], "net35": [], "net40": [], "net403": [], "net45": [], "net451": [], "net452": [], "net46": [], "net461": [], "net462": [], "net47": [], "net471": [], "net472": [], "net48": [], "net5.0": [], "net6.0": [], "net7.0": [], "net8.0": [], "net9.0": [], "netcoreapp1.0": [], "netcoreapp1.1": [], "netcoreapp2.0": [], "netcoreapp2.1": [], "netcoreapp2.2": [], "netcoreapp3.0": [], "netcoreapp3.1": [], "netstandard": [], "netstandard1.0": [], "netstandard1.1": [], "netstandard1.2": [], "netstandard1.3": [], "netstandard1.4": [], "netstandard1.5": [], "netstandard1.6": [], "netstandard2.0": [], "netstandard2.1": []}, "targeting_pack_overrides": [], "framework_list": [], "tools": {"net8.0": [{"name": "fantomas", "entrypoint": "fantomas.dll", "runner": "dotnet"}]}},
+            {"name": "Paket", "id": "Paket", "version": "9.0.2", "sha512": "sha512-VPMh+F1IvraKlKUJlVjI/nyr5eyKQMNLKbGcFo+pKpcvN2bAnrFl5WafGZ4A/ZTzLl0eyjb3AVcLx8Z/S8DF0g==", "sources": ["https://api.nuget.org/v3/index.json"], "dependencies": {"net11": [], "net20": [], "net30": [], "net35": [], "net40": [], "net403": [], "net45": [], "net451": [], "net452": [], "net46": [], "net461": [], "net462": [], "net47": [], "net471": [], "net472": [], "net48": [], "net5.0": [], "net6.0": [], "net7.0": [], "net8.0": [], "net9.0": [], "netcoreapp1.0": [], "netcoreapp1.1": [], "netcoreapp2.0": [], "netcoreapp2.1": [], "netcoreapp2.2": [], "netcoreapp3.0": [], "netcoreapp3.1": [], "netstandard": [], "netstandard1.0": [], "netstandard1.1": [], "netstandard1.2": [], "netstandard1.3": [], "netstandard1.4": [], "netstandard1.5": [], "netstandard1.6": [], "netstandard2.0": [], "netstandard2.1": []}, "targeting_pack_overrides": [], "framework_list": [], "tools": {"netcoreapp3.1": [{"name": "paket", "entrypoint": "paket.dll", "runner": "dotnet"}]}},
+        ],
+    )
diff --git a/example/3rdparty/nuget/paket.main_extension.bzl b/example/3rdparty/nuget/paket.main_extension.bzl
@@ -0,0 +1,11 @@
+"Generated"
+
+load(":paket.main.bzl", _main = "main")
+
+def _main_impl(module_ctx):
+    _main()
+    return module_ctx.extension_metadata(reproducible = True)
+
+main_extension = module_extension(
+    implementation = _main_impl,
+)
diff --git a/example/MODULE.bazel b/example/MODULE.bazel
@@ -9,6 +9,7 @@ bazel_dep(name = "aspect_rules_swc", version = "2.0.0")
 bazel_dep(name = "aspect_rules_ts", version = "3.0.0")
 bazel_dep(name = "bazel_lib", version = "3.0.0-rc.0")
 bazel_dep(name = "rules_buf", version = "0.5.2")
+bazel_dep(name = "rules_dotnet", version = "0.20.5")
 bazel_dep(name = "bazel_features", version = "1.29.0")
 bazel_dep(name = "bazel_skylib", version = "1.4.2")
 bazel_dep(name = "toolchains_llvm", version = "1.1.2")
@@ -130,6 +131,16 @@ rust.toolchain(
     versions = ["1.75.0"],
 )
 
+# Configure .Net toolchains
+dotnet = use_extension("@rules_dotnet//dotnet:extensions.bzl", "dotnet")
+dotnet.toolchain(dotnet_version = "9.0.306")
+use_repo(dotnet, "dotnet_toolchains")
+
+register_toolchains("@dotnet_toolchains//:all")
+
+main_extension = use_extension("//3rdparty/nuget:paket.main_extension.bzl", "main_extension")
+use_repo(main_extension, "paket.main")
+
 ruby = use_extension("@rules_ruby//ruby:extensions.bzl", "ruby")
 ruby.toolchain(
     name = "ruby",
diff --git a/example/paket.dependencies b/example/paket.dependencies
@@ -0,0 +1,7 @@
+framework: net9.0
+source https://api.nuget.org/v3/index.json
+storage: none
+
+nuget Paket 9.0.2
+nuget fantomas 7.0.3
+nuget CSharpier 1.1.2
diff --git a/example/paket.lock b/example/paket.lock
@@ -0,0 +1,7 @@
+STORAGE: NONE
+RESTRICTION: == net9.0
+NUGET
+  remote: https://api.nuget.org/v3/index.json
+    CSharpier (1.1.2)
+    fantomas (7.0.3)
+    Paket (9.0.2)
diff --git a/example/src/hello.cs b/example/src/hello.cs
@@ -0,0 +1,11 @@
+using System; 
+
+namespace HelloWorldApp { 
+    
+    class Geeks { 
+        
+        static void Main(string[] args) { 
+            Console.WriteLine("Hello World!");Console.ReadKey(); 
+        } 
+    } 
+}
diff --git a/example/src/hello.fs b/example/src/hello.fs
@@ -0,0 +1,6 @@
+open System
+
+[<EntryPoint>]
+let main argv =
+    printfn "Hello World";Console.ReadLine() |> ignore
+    0
diff --git a/example/tools/BUILD.bazel b/example/tools/BUILD.bazel
diff --git a/example/tools/bzlmod.bzl b/example/tools/bzlmod.bzl
@@ -0,0 +1,5 @@
+"""Utility functions for Bzlmod-related checks."""
+
+def bzlmod_is_enabled():
+    """Returns True if Bzlmod is enabled, False otherwise."""
+    str(Label("//:invalid")).startswith("@@")
diff --git a/example/tools/format/BUILD.bazel b/example/tools/format/BUILD.bazel
@@ -9,6 +9,7 @@ load("@aspect_rules_lint//format:defs.bzl", "format_multirun", "format_test")
 load("@npm//:prettier/package_json.bzl", prettier = "bin")
 load("@rules_java//java:defs.bzl", "java_binary")
 load("@rules_python//python/entry_points:py_console_script_binary.bzl", "py_console_script_binary")
+load("//tools:bzlmod.bzl", "bzlmod_is_enabled")
 
 package(default_visibility = ["//:__subpackages__"])
 
@@ -94,8 +95,12 @@ format_multirun(
     name = "format",
     c = "@llvm_toolchain_llvm//:bin/clang-format",
     cc = "@llvm_toolchain_llvm//:bin/clang-format",
+    # Disable when using WORKSPACE due to rules_dotnet only supporting Bzlmod
+    csharp = "@paket.main//csharpier/tools:csharpier" if bzlmod_is_enabled() else None,
     css = ":prettier",
     cuda = "@llvm_toolchain_llvm//:bin/clang-format",
+    # Disable when using WORKSPACE due to rules_dotnet only supporting Bzlmod
+    fsharp = "@paket.main//fantomas/tools:fantomas" if bzlmod_is_enabled() else None,
     gherkin = ":prettier",
     # You can use standard gofmt instead of stricter gofumpt:
     # go = "@go_sdk//:bin/gofmt",
diff --git a/example/update-dotnet-deps.sh b/example/update-dotnet-deps.sh
@@ -0,0 +1,8 @@
+#!/usr/bin/env bash
+
+set -eou pipefail
+
+SCRIPT_DIR=$(cd -- "$(dirname -- "${BASH_SOURCE[0]}")" &>/dev/null && pwd)
+
+(cd "${SCRIPT_DIR}" && bazel run @paket.main//paket/tools:paket -- install)
+bazel run @rules_dotnet//tools/paket2bazel -- --dependencies-file "${SCRIPT_DIR}/paket.dependencies" --output-folder "${SCRIPT_DIR}/3rdparty/nuget"
diff --git a/format/defs.bzl b/format/defs.bzl
@@ -211,6 +211,11 @@ def _tools_loop(name, kwargs):
         lang_attribute = to_attribute_name(lang)
         if lang_attribute not in kwargs.keys():
             continue
+        elif kwargs[lang_attribute] == None:  # If the attribute is explicitly set to None, skip this language
+            kwargs.pop(lang_attribute, None)
+            kwargs.pop(lang_attribute + "_fix_args", None)
+            kwargs.pop(lang_attribute + "_check_args", None)
+            continue
 
         tool_label = kwargs.pop(lang_attribute)
         target_name = "_".join([name, lang.replace(" ", "_"), "with", toolname])
diff --git a/format/private/filter.jq b/format/private/filter.jq
@@ -1,9 +1,11 @@
 # Filter languages we understand
 with_entries(select(.key | IN(
     "C++",
+    "C#",
     "CSS",
     "Cuda",
     "Markdown",
+    "F#",
     "Go",
     "Gherkin",
     "GraphQL",
diff --git a/format/private/format.sh b/format/private/format.sh
@@ -118,7 +118,9 @@ function ls-files {
       'C') patterns=('*.c' '*.cats' '*.h' '*.idc') ;;
       'C++') patterns=('*.cpp' '*.c++' '*.cc' '*.cp' '*.cppm' '*.cxx' '*.h' '*.h++' '*.hh' '*.hpp' '*.hxx' '*.inc' '*.inl' '*.ino' '*.ipp' '*.ixx' '*.re' '*.tcc' '*.tpp' '*.txx') ;;
       'Cuda') patterns=('*.cu' '*.cuh') ;;
+      'C#') patterns=('*.cs' '*.cshtml') ;;
       'CSS') patterns=('*.css') ;;
+      'F#') patterns=('*.fs') ;;
       'Go') patterns=('*.go') ;;
       'GraphQL') patterns=('*.graphql' '*.gql' '*.graphqls') ;;
       'HTML') patterns=('*.html' '*.hta' '*.htm' '*.html.hl' '*.inc' '*.xht' '*.xhtml') ;;
diff --git a/format/private/formatter_binary.bzl b/format/private/formatter_binary.bzl
@@ -31,6 +31,8 @@ TOOLS = {
     "Rust": "rustfmt",
     "XML": "prettier",
     "Gherkin": "prettier",
+    "F#": "fantomas",
+    "C#": "csharpier",
 }
 
 # Provided to make install more convenient
@@ -62,6 +64,8 @@ CHECK_FLAGS = {
     "clang-format": "--style=file --fallback-style=none --dry-run -Werror",
     "yamlfmt": "-lint",
     "rustfmt": "--check",
+    "fantomas": "--check",
+    "csharpier": "check",
 }
 
 # Flags to pass each tool when running in default mode
@@ -90,9 +94,15 @@ FIX_FLAGS = {
     "clang-format": "-style=file --fallback-style=none -i",
     "yamlfmt": "",
     "rustfmt": "",
+    "fantomas": "",
+    "csharpier": "format",
 }
 
 def to_attribute_name(lang):
     if lang == "C++":
         return "cc"
+    if lang == "C#":
+        return "csharp"
+    if lang == "F#":
+        return "fsharp"
     return lang.lower().replace(" ", "_")
diff --git a/format/test/BUILD.bazel b/format/test/BUILD.bazel
@@ -39,8 +39,10 @@ UNIQUE_TOOLS = sets.to_list(sets.make(TOOLS.values()))
 format_multirun(
     name = "format",
     cc = ":mock_clang-format.sh",
+    csharp = ":mock_csharpier.sh",
     css = ":mock_prettier.sh",
     cuda = ":mock_clang-format.sh",
+    fsharp = ":mock_fantomas.sh",
     gherkin = ":mock_prettier.sh",
     go = ":mock_gofmt.sh",
     graphql = ":mock_prettier.sh",
diff --git a/format/test/format_test.bats b/format/test/format_test.bats
@@ -201,3 +201,17 @@ bats_load_library "bats-assert"
 
     assert_output --partial "+ prettier --write example/src/hello.feature"
 }
+
+@test "should run fantomas on F#" {
+    run bazel run //format/test:format_F#_with_fantomas
+    assert_success
+
+    assert_output --partial "+ fantomas example/src/hello.fs"
+}
+
+@test "should run csharpier on C#" {
+    run bazel run //format/test:format_C#_with_csharpier
+    assert_success
+
+    assert_output --partial "+ csharpier format example/src/hello.cs"
+}
