[workspace] Factor glx and x11 to share a common implementation

tools/workspace/glx/repository.bzl

@@ -1,39 +1,13 @@
-load("//tools/workspace:os.bzl", "determine_os")
-
-def _impl(repository_ctx):
-    os_result = determine_os(repository_ctx)
-
-    if os_result.error != None:
-        fail(os_result.error)
-
-    if os_result.is_macos:
-        # On macOS, no targets should depend on @glx.
-        build_flavor = "macos"
-    elif os_result.is_ubuntu or os_result.is_manylinux:
-        build_flavor = "ubuntu"
-        hdrs = [
-            "GL/glx.h",
-            "GL/glxext.h",
-        ]
-        for hdr in hdrs:
-            repository_ctx.symlink(
-                "/usr/include/{}".format(hdr),
-                "include/{}".format(hdr),
-            )
-    else:
-        fail("Operating system is NOT supported {}".format(os_result))
-
-    repository_ctx.symlink(
-        Label(
-            "@drake//tools/workspace/glx:package-{}.BUILD.bazel".format(
-                build_flavor,
-            ),
-        ),
-        "BUILD.bazel",
+load("//tools/workspace:pkg_config.bzl", "pkg_config_repository")
+
+def glx_repository(name):
+    pkg_config_repository(
+        name = name,
+        licenses = ["notice"],  # SGI-B-2.0
+        modname = "glx",
+        extra_deps = [
+            "@opengl",
+            "@x11",
+        ],
+        defer_error_os_names = ["mac os x"],
     )
-
-glx_repository = repository_rule(
-    local = True,
-    configure = True,
-    implementation = _impl,
-)

tools/workspace/pkg_config.BUILD.tpl

@@ -2,6 +2,8 @@
 
 # %{topcomment}
 
+load("@drake//tools/skylark:cc.bzl", "cc_library")
+
 licenses(%{licenses})
 
 package(default_visibility = ["//visibility:public"])

tools/workspace/pkg_config.bzl

@@ -73,6 +73,26 @@ def setup_pkg_config_repository(repository_ctx):
     # Check if we can find the required *.pc file of any version.
     result = _run_pkg_config(repository_ctx, args, pkg_config_paths)
     if result.error != None:
+        defer_error_os_names = getattr(
+            repository_ctx.attr,
+            "defer_error_os_names",
+            [],
+        )
+        if repository_ctx.os.name in defer_error_os_names:
+            repository_ctx.file(
+                "BUILD.bazel",
+                """
+load("@drake//tools/skylark:cc.bzl", "cc_library")
+cc_library(
+    name = {name},
+    srcs = ["pkg_config_failed.cc"],
+    visibility = ["//visibility:public"],
+)
+                """.format(
+                    name = repr(repository_ctx.name),
+                ),
+            )
+            return struct(value = True, error = None)
         return result
 
     # If we have a minimum version, enforce that.
@@ -326,6 +346,7 @@ _do_pkg_config_repository = repository_rule(
         "pkg_config_paths": attr.string_list(),
         "homebrew_subdir": attr.string(),
         "extra_deprecation": attr.string(),
+        "defer_error_os_names": attr.string_list(),
     },
     local = True,
     configure = True,
@@ -389,6 +410,11 @@ def pkg_config_repository(**kwargs):
                          "/opt/homebrew/opt/libpng/lib/pkgconfig".
         extra_deprecation: (Optional) Add a deprecation message to the library
                            BUILD target.
+        defer_error_os_names: (Optional) On these operating systems (as named
+                              by repository_ctx.os.name), failure to find the
+                              *.pc file will yield a link-time error, not a
+                              fetch-time error. This is useful for externals
+                              that are guarded by select() statements.
     """
     if "deprecation" in kwargs:
         fail("When calling pkg_config_repository, don't use deprecation=str " +

tools/workspace/x11/repository.bzl

@@ -1,27 +1,9 @@
-load("//tools/workspace:os.bzl", "determine_os")
-load("//tools/workspace:pkg_config.bzl", "setup_pkg_config_repository")
+load("//tools/workspace:pkg_config.bzl", "pkg_config_repository")
 
-def _impl(repo_ctx):
-    # Only available on Ubuntu. On macOS, no targets should depend on @x11.
-    os_result = determine_os(repo_ctx)
-    if os_result.error != None:
-        fail(os_result.error)
-    if os_result.is_ubuntu or os_result.is_manylinux:
-        error = setup_pkg_config_repository(repo_ctx).error
-        if error != None:
-            fail(error)
-    else:
-        repo_ctx.symlink(
-            Label("@drake//tools/workspace/x11:package-macos.BUILD.bazel"),
-            "BUILD.bazel",
-        )
-
-x11_repository = repository_rule(
-    attrs = {
-        "modname": attr.string(default = "x11"),
-        "licenses": attr.string_list(default = ["notice"]),  # X11/MIT.
-    },
-    local = True,
-    configure = True,
-    implementation = _impl,
-)
+def x11_repository(name):
+    pkg_config_repository(
+        name = name,
+        licenses = ["notice"],  # X11/MIT
+        modname = "x11",
+        defer_error_os_names = ["mac os x"],
+    )