Make format_checker languages configurable and add C++ support

format_checker/README.md

@@ -32,7 +32,7 @@
 Defines the main macro to use in projects:
 
 ```python
-def use_format_targets(fix_name = "format.fix", check_name = "format.check"):
+def use_format_targets(fix_name = "format.fix", check_name = "format.check", languages = None):
     ...
 ```
 
@@ -41,6 +41,19 @@ This sets up:
 - `format.fix` — a multi-run rule that applies formatting tools
 - `format.check` — a test rule that checks formatting
 
+The `languages` parameter selects which formatters are wired up. Supported values:
+
+| Language   | Formatter                                              |
+| ---------- | ------------------------------------------------------ |
+| `python`   | `@aspect_rules_lint//format:ruff`                      |
+| `rust`     | `@score_tooling//format_checker:rustfmt_with_policies` |
+| `starlark` | `@buildifier_prebuilt//:buildifier`                    |
+| `yaml`     | `@aspect_rules_lint//format:yamlfmt`                   |
+| `cpp`      | `@llvm_toolchain//:clang-format`                       |
+
+When `languages` is omitted, every language except `cpp` is enabled. C++ is
+opt-in so that projects without C++ code do not depend on the LLVM toolchain.
+
 ### `MODULE.bazel`
 
 Declares this module and includes required dependencies:
@@ -87,6 +100,13 @@ This will register two Bazel targets:
 - `bazel run //:format.fix` — fixes format issues
 - `bazel test //:format.check` — fails on unformatted files
 
+To control which formatters run, pass an explicit `languages` list:
+
+```python
+# Only check Python and Starlark.
+use_format_targets(languages = ["python", "starlark"])
+```
+
 ### 3️⃣ In VS Code settings:
 
 ⚠️ First formatting run can be slow!
@@ -116,6 +136,23 @@ bazel run @score_tooling//format_checker:rustfmt_with_policies
 
 ---
 
+## C++ support
+
+C++ formatting is opt-in. Enable it by adding `cpp` to the `languages` list:
+
+```python
+use_format_targets(languages = ["python", "rust", "starlark", "yaml", "cpp"])
+```
+
+- Formatter label: `@llvm_toolchain//:clang-format`, which requires the LLVM
+  toolchain (`toolchains_llvm`) to be available in the consuming module.
+- clang-format runs with `--style=file`, so a `.clang-format` configuration file
+  is expected in the repository tree.
+- Because enabling `cpp` introduces the LLVM dependency, it is excluded from the
+  default language set.
+
+---
+
 ## Benefits
 
 ✅ Centralized formatting config with local file scope

format_checker/macros.bzl

@@ -12,23 +12,54 @@
 # *******************************************************************************
 load("@aspect_rules_lint//format:defs.bzl", "format_multirun", "format_test")
 
-def use_format_targets(fix_name = "format.fix", check_name = "format.check"):
+# Maps a user-facing language name to the (attribute, formatter label) pair that
+# is forwarded to aspect_rules_lint's format_multirun / format_test rules.
+_FORMATTERS = {
+    "python": ("python", "@aspect_rules_lint//format:ruff"),
+    "rust": ("rust", "@score_tooling//format_checker:rustfmt_with_policies"),
+    "starlark": ("starlark", "@buildifier_prebuilt//:buildifier"),
+    "yaml": ("yaml", "@aspect_rules_lint//format:yamlfmt"),
+    "cpp": ("cc", "@llvm_toolchain//:clang-format"),
+}
+
+# Languages enabled when the caller does not specify a selection. C++ is left
+# out so that projects without C++ code do not depend on the LLVM toolchain.
+_DEFAULT_LANGUAGES = ["python", "rust", "starlark", "yaml"]
+
+def use_format_targets(fix_name = "format.fix", check_name = "format.check", languages = None):
+    """Registers format.fix and format.check targets for the selected languages.
+
+    Args:
+        fix_name: Name of the format_multirun target that applies formatting.
+        check_name: Name of the format_test target that checks formatting.
+        languages: List of language names to enable. Supported values are the
+            keys of _FORMATTERS.
+    """
+    if languages == None:
+        languages = _DEFAULT_LANGUAGES
+
+    formatters = {}
+    for language in languages:
+        if language not in _FORMATTERS:
+            fail("Unsupported format language '{}'. Supported languages are: {}.".format(
+                language,
+                ", ".join(sorted(_FORMATTERS.keys())),
+            ))
+        attribute, label = _FORMATTERS[language]
+        formatters[attribute] = label
+
     format_multirun(
         name = fix_name,
-        python = "@aspect_rules_lint//format:ruff",
-        rust = "@score_tooling//format_checker:rustfmt_with_policies",
-        starlark = "@buildifier_prebuilt//:buildifier",
-        yaml = "@aspect_rules_lint//format:yamlfmt",
         visibility = ["//visibility:public"],
+        tags = ["manual"],
+        **formatters
     )
 
     format_test(
         name = check_name,
         no_sandbox = True,
-        python = "@aspect_rules_lint//format:ruff",
-        rust = "@score_tooling//format_checker:rustfmt_with_policies",
-        starlark = "@buildifier_prebuilt//:buildifier",
-        yaml = "@aspect_rules_lint//format:yamlfmt",
         workspace = "//:MODULE.bazel",
+        tags = ["manual"],
         visibility = ["//visibility:public"],
+        **formatters
     )