Implement Bazel Clang toolchain

bazel/clang_toolchain/config_detection.bzl

@@ -0,0 +1,113 @@
+# Copyright 2025 Steven Le Rouzic
+#
+# SPDX-License-Identifier: BSD-3-Clause
+
+def _copy_file(ctx, from_path, to_path):
+    content = ctx.read(from_path)
+    ctx.file(to_path, content = content)
+
+def _get_clang_info(ctx, clang_path, line_prefix):
+    result = ctx.execute([clang_path, "--version"])
+    if result.return_code != 0:
+        return None
+
+    for l in result.stdout.splitlines():
+        if l.startswith(line_prefix):
+            l = l[len(line_prefix):]
+            return l.split(" ")[0]
+
+    return None
+
+def _get_clang_version(ctx, clang_path):
+    return _get_clang_info(ctx, clang_path, "clang version ")
+
+def _get_clang_lib_dir(ctx, clang_path):
+    result = ctx.execute([clang_path, "-no-canonical-prefixes", "--print-resource-dir"])
+    if result.return_code != 0:
+        return None
+
+    return result.stdout
+
+def _get_include_dirs(ctx, clang_path):
+    ctx.file("detect.cpp", content = "")
+    detect_path = ctx.path("detect.cpp")
+    res = ctx.execute([
+        clang_path,
+        "-v",
+        "-no-canonical-prefixes",
+        "-fsyntax-only",
+        "-x", "c++",
+        detect_path,
+    ])
+
+    lines = res.stderr.splitlines()
+    listing_include_dirs = False
+    include_dirs = []
+
+    for l in lines:
+        if l.startswith("#include <...> search starts here:"):
+            listing_include_dirs = True
+        elif l.startswith("End of search list."):
+            listing_include_dirs = False
+        elif listing_include_dirs:
+            include_dirs.append(l.strip())
+
+    return include_dirs
+
+def _impl(ctx):
+    _copy_file(ctx, ctx.attr._build_bazel, "BUILD.bazel")
+    _copy_file(ctx, ctx.attr._toolchain_config_bzl, "toolchain_config.bzl")
+
+    clang_path = ctx.which("clang")
+    if not clang_path:
+        fail("Could not find clang")
+
+    clang_version = _get_clang_version(ctx, clang_path)
+    if not clang_version:
+        fail("Could not detect clang version")
+
+    clang_lib_dir = _get_clang_lib_dir(ctx, clang_path)
+    if not clang_lib_dir:
+        fail("Could not detect clang lib dir")
+
+    include_dirs = _get_include_dirs(ctx, clang_path)
+    if not include_dirs:
+        fail("Could not detect include dirs")
+
+    ctx.template(
+        "clang_config.bzl",
+        ctx.attr._clang_config_bzl_tpl,
+        executable = False,
+        substitutions = {
+            "{CLANG_BINDIR}": str(clang_path.dirname),
+            "{CLANG_LIBDIR}": str(clang_lib_dir).strip().replace("\\", "/"),
+            "{CLANG_INCLUDE_DIRS}": str(include_dirs),
+        },
+    )
+
+
+_config_detection = repository_rule(
+    implementation = _impl,
+    local = True,
+    configure = True,
+    attrs = {
+        "_build_bazel": attr.label(
+            default = Label("//bazel/clang_toolchain:clang_toolchain.BUILD.bazel"),
+            allow_single_file = True,
+        ),
+        "_toolchain_config_bzl": attr.label(
+            default = Label("//bazel/clang_toolchain:toolchain_config.bzl"),
+            allow_single_file = True,
+        ),
+        "_clang_config_bzl_tpl": attr.label(
+            default = Label("//bazel/clang_toolchain:clang_config.bzl.tpl"),
+            allow_single_file = True,
+        ),
+    },
+)
+
+clang_toolchain = module_extension(
+    implementation = lambda ctx: _config_detection(
+        name = "clang_toolchain",
+    ),
+)