[build] Use clang-format from bzlmod

Remove clang-format prereqs from the OS.

This makes it easier to use an identical version number across all of
our supported development OS's, without relying on their various
package managers to remain consistent.

MODULE.bazel

@@ -73,6 +73,14 @@ spdlog_repository = use_repo_rule(
 
 spdlog_repository(name = "pkgconfig_spdlog")
 
+# Add additional modules we use as tools (not runtime dependencies).
+
+bazel_dep(name = "toolchains_llvm", version = "1.2.0")
+
+llvm = use_extension("@toolchains_llvm//toolchain/extensions:llvm.bzl", "llvm")
+llvm.toolchain(llvm_version = "15.0.5")
+use_repo(llvm, "llvm_toolchain")
+
 # Load dependencies which are "public", i.e., made available to downstream
 # projects.
 #

doc/_pages/clion.md

@@ -176,18 +176,15 @@ CLion such that the modification may not be immediately apparent. When in doubt,
 select away from the target file and back; this will cause the file to refresh
 and you can confirm that the file has been modified as expected.
 
-First, make sure you have installed ``clang-format-15``
-(see [Tools for Code Style Compliance](/code_style_tools.html)).
-
 ### Clang format selected file
 
 Open the ``Edit Tool`` for external tools as outlined above and enter the
 following values for the fields:
 
 * **Name:** ``Clang Format Full File``
 * **Description:** ``Apply clang-format to the active file``
-* **Program:** ``clang-format-15``
-* **Arguments:** ``-i $FileName$``
+* **Program:** ``bazel``
+* **Arguments:** ``run //tools/lint:clang-format -- -i $FileName$``
 * **Working directory:** ``$FileDir$``
 * **Advanced Options:** Uncheck ``Open console for tool output``
 
@@ -200,8 +197,8 @@ following values for the fields:
 
 * **Name:** ``Clang Format Selected Lines``
 * **Description:** ``Apply clang-format to the selected lines``
-* **Program:** ``clang-format-15``
-* **Arguments:** ``-lines $SelectionStartLine$:$SelectionEndLine$ -i $FileName$``
+* **Program:** ``bazel``
+* **Arguments:** ``run //tools/lint:clang-format -- -lines $SelectionStartLine$:$SelectionEndLine$ -i $FileName$``
 * **Working directory:** ``$FileDir$``
 * **Advanced Options:** Uncheck ``Open console for tool output``
 

doc/_pages/code_style_tools.md

@@ -41,14 +41,11 @@ User manuals for the style-checking tools are as follows:
 
 ## C/C++: Clang-Format
 
-The [Mandatory platform-specific instructions](/from_source.html#mandatory-platform-specific-instructions)
-install Drake's required version of ``clang-format``, depending on the platform
-(macOS or Ubuntu).
-
 To run ``clang-format``:
 
 ```
-clang-format-15 -i -style=file [file name]
+cd drake
+bazel run /tools/lint:clang-format -- -i -style=file [file name]
 ```
 
 Using ``clang-format`` will modify the entire file that is specified. As an
@@ -57,17 +54,12 @@ portions of a file that you have modified. To run ``git clang-format``:
 
 ```
 # For development on Ubuntu: format a file that has been staged in git
-git clang-format-15 --binary=/usr/bin/clang-format-15 -- [file name]
+git clang-format --binary=/path/to/drake/bazel-bin/tools/lint/clang-format -- [file name]
 
 # For development on Ubuntu: format a file that has been modified but not staged
-git clang-format-15 --binary=/usr/bin/clang-format-15 -f -- [file name]
+git clang-format --binary=/path/to/drake/bazel-bin/tools/lint/clang-format -f -- [file name]
 ```
 
-On macOS, the command to use is
-``/opt/homebrew/opt/llvm@15/bin/clang-format``.
-Note in particular that ``15`` is part of the directory name, not a suffix on
-the program name.
-
 ### IDE integration
 
 Most IDEs can run ``clang-format`` automatically.

doc/_pages/emacs.md

@@ -26,6 +26,7 @@ On Ubuntu ``sudo apt install elpa-magit``.
 
 Use ``(require 'clang-format)`` to enable the ``M-x clang-format-...`` family of
 functions. Also check that the customize variable ``clang-format-executable`` is
-set to Drake's preferred value ``clang-format-15``.
+set to Drake's preferred value
+``/path/to/drake/bazel-bin/tools/lint/clang-format``.
 
 <!--- TODO(jwnimmer-tri) Explain 'google-c-style from the styleguide. -->

doc/_pages/vscode.md

@@ -29,4 +29,4 @@ on code formatting work well. Take note of "Format Document",
 
 In the VS Code Options configuration, check that the option for
 ``C_Cpp: Clang_format_path`` is set to Drake's preferred value
-``clang-format-15``.
+``/path/to/drake/bazel-bin/tools/lint/clang-format``.

setup/mac/source_distribution/install_prereqs.sh

@@ -7,15 +7,10 @@
 
 set -euxo pipefail
 
-with_test_only=1
-
 while [ "${1:-}" != "" ]; do
   case "$1" in
-    # Do NOT install prerequisites that are only needed to build and/or run
-    # unit tests, i.e., those prerequisites that are not dependencies of
-    # bazel { build, run } //:install.
     --without-test-only)
-      with_test_only=0
+      # Ignored for backwards compatibility.
       ;;
     *)
       echo 'Invalid command line argument' >&2
@@ -35,7 +30,3 @@ if ! command -v brew &>/dev/null; then
 fi
 
 brew bundle --file="${BASH_SOURCE%/*}/Brewfile" --no-lock
-
-if [[ "${with_test_only}" -eq 1 ]]; then
-  brew bundle --file="${BASH_SOURCE%/*}/Brewfile-test-only" --no-lock
-fi

setup/ubuntu/source_distribution/packages-jammy-test-only.txt

@@ -1,4 +1,3 @@
-clang-format-15
 curl
 kcov
 libstdc++6-10-dbg

setup/ubuntu/source_distribution/packages-noble-test-only.txt

@@ -1,4 +1,3 @@
-clang-format-15
 curl
 libstdc++6-10-dbg
 python3-dateutil

tools/lint/BUILD.bazel

@@ -48,9 +48,22 @@ drake_py_library(
     name = "clang_format",
     testonly = 1,
     srcs = ["clang_format.py"],
-    data = ["//:.clang-format"],
+    data = [
+        "//:.clang-format",
+        "@llvm_toolchain//:clang-format",
+    ],
     deps = [
         ":module_py",
+        "@rules_python//python/runfiles",
+    ],
+)
+
+drake_py_binary(
+    name = "clang-format",
+    testonly = 1,
+    srcs = ["clang_format.py"],
+    deps = [
+        ":clang_format",
     ],
 )
 

tools/lint/clang_format.py

@@ -2,23 +2,24 @@
 """
 
 import os
-import platform
-
-
-def get_clang_format_path(version=None):
-    """Call with version=None to use Drake's default version.
-    Otherwise, pass the desired major version as an int.
-    """
-    if version is None:
-        version = 15
-    if platform.system() == "Darwin":
-        if platform.machine() == "arm64":
-            homebrew = "/opt/homebrew"
-        else:
-            homebrew = "/usr/local"
-        path = f"{homebrew}/opt/llvm@{version}/bin/clang-format"
-    else:
-        path = f"/usr/bin/clang-format-{version}"
-    if os.path.isfile(path):
-        return path
-    raise RuntimeError("Could not find required clang-format at " + path)
+from pathlib import Path
+import sys
+
+from python import runfiles
+
+
+def get_clang_format_path():
+    manifest = runfiles.Create()
+    path = Path(manifest.Rlocation("llvm_toolchain/clang-format"))
+    if not path.is_file():
+        raise RuntimeError(f"Could not find required clang-format at {path}")
+    return path
+
+
+def _main():
+    exe = get_clang_format_path()
+    os.execvp(exe, [exe] + sys.argv[1:])
+
+
+if __name__ == "__main__":
+    _main()

tools/lint/clang_format_lint.py

@@ -31,7 +31,8 @@ def _check_clang_format_idempotence(filename):
     if not changes:
         return 0
     print("ERROR: {} needs clang-format".format(filename))
-    print("note: fix via {} -style=file -i {}".format(clang_format, filename))
+    print("note: fix via {} -style=file -i {}".format(
+        "bazel-bin/tools/lint/clang-format", filename))
     return 1
 
 

tools/workspace/default.bzl

@@ -415,6 +415,7 @@ REPOS_ALREADY_PROVIDED_BY_BAZEL_MODULES = [
     "rules_rust",
     "rules_shell",
     "spdlog",
+    "toolchains_llvm",
 ]
 
 # This is the list of repositories that Drake provides as a module extension

tools/workspace/workspace_bzlmod_sync_test.py

@@ -68,6 +68,7 @@ def test_version_sync(self):
 
         # Don't check modules that are known to be module-only.
         del modules["bazel_features"]
+        del modules["toolchains_llvm"]
 
         # Don't check modules whose repository rule twin is pkgconfig (and thus
         # doesn't have a github pinned version that we need to keep in sync).