chore(rules): use bzlmod (#320)

Requires fixing up the brittle runfiles logic in one example, since
bzlmod changes the repository names and requires a proper runfiles
helper library.
/cc @fmeum

rules/.bazelrc

@@ -0,0 +1 @@
+common --enable_bzlmod

rules/.bazelversion

@@ -0,0 +1 @@
+6.3.2

rules/MODULE.bazel

@@ -0,0 +1,4 @@
+"Bazel dependencies, see https://registry.bazel.build"
+
+bazel_dep(name = "bazel_skylib", version = "1.4.2")
+bazel_dep(name = "rules_python", version = "0.25.0")

rules/WORKSPACE

@@ -1,34 +1 @@
-workspace(name = "examples")
-
-load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
-
-http_archive(
-    name = "rules_python",
-    sha256 = "aa96a691d3a8177f3215b14b0edc9641787abaaa30363a080165d06ab65e1161",
-    url = "https://github.com/bazelbuild/rules_python/releases/download/0.0.1/rules_python-0.0.1.tar.gz",
-)
-
-load("@rules_python//python:repositories.bzl", "py_repositories")
-
-py_repositories()
-
-# Only needed if using the packaging rules.
-load("@rules_python//python:pip.bzl", "pip_repositories")
-
-pip_repositories()
-
-# Load Skylib 0.9.0 as instructed at
-# https://github.com/bazelbuild/bazel-skylib/releases/tag/1.0.2
-
-http_archive(
-    name = "bazel_skylib",
-    sha256 = "f7be3474d42aae265405a592bb7da8e171919d74c16f082a5457840f06054728",
-    urls = [
-        "https://mirror.bazel.build/github.com/bazelbuild/bazel-skylib/releases/download/1.2.1/bazel-skylib-1.2.1.tar.gz",
-        "https://github.com/bazelbuild/bazel-skylib/releases/download/1.2.1/bazel-skylib-1.2.1.tar.gz",
-    ],
-)
-
-load("@bazel_skylib//:workspace.bzl", "bazel_skylib_workspace")
-
-bazel_skylib_workspace()
+# Marker that this folder is the root of the Bazel workspace

rules/runfiles/complex_tool.bzl

@@ -3,17 +3,27 @@
 A tool (executable used for action registration) may depend on another
 tool with its own runfiles. This example demonstrates this scenario."""
 
+# Bash helper function for looking up runfiles.
+# Vendored from
+# https://github.com/bazelbuild/bazel/blob/master/tools/bash/runfiles/runfiles.bash
+BASH_RLOCATION_FUNCTION = r"""\
+# --- begin runfiles.bash initialization v3 ---
+set -uo pipefail; set +e; f=bazel_tools/tools/bash/runfiles/runfiles.bash
+source "${RUNFILES_DIR:-/dev/null}/$f" 2>/dev/null || \
+  source "$(grep -sm1 "^$f " "${RUNFILES_MANIFEST_FILE:-/dev/null}" | cut -f2- -d' ')" 2>/dev/null || \
+  source "$0.runfiles/$f" 2>/dev/null || \
+  source "$(grep -sm1 "^$f " "$0.runfiles_manifest" | cut -f2- -d' ')" 2>/dev/null || \
+  source "$(grep -sm1 "^$f " "$0.exe.runfiles_manifest" | cut -f2- -d' ')" 2>/dev/null || \
+  { echo>&2 "ERROR: cannot find $f"; exit 1; }; f=; set -e
+# --- end runfiles.bash initialization v3 ---
+"""
+
 def _sub_tool_impl(ctx):
     # Since this tool may be used by another tool, it must support accepting
-    # a different runfiles directory root. The runfiles directory is always
-    # adjacent to the *root* tool being run, which may not be this tool.
-    # (In this case, this is done by environment variable RUNFILES_DIR.)
-    command = """
-if [[ -z "${RUNFILES_DIR}" ]]; then
-  RUNFILES_DIR=${0}.runfiles
-fi
+    # a different runfiles directory root. The runfiles helper library does this correctly.
+    command = BASH_RLOCATION_FUNCTION + """
 
-cat ${RUNFILES_DIR}/examples/runfiles/data.txt > $1"""
+cat $(rlocation examples/runfiles/data.txt) > $1"""
 
     # Using root_symlinks or symlinks for a tool is very brittle if the
     # tool may be used by another tool; there will be a collision when merging
@@ -43,7 +53,7 @@ sub_tool = rule(
 )
 
 def _complex_tool_impl(ctx):
-    my_runfiles = ctx.runfiles(files = [ctx.files._data[0]])
+    my_runfiles = ctx.runfiles(files = [ctx.files._data[0], ctx.files._runfiles_lib[0]])
 
     # Use runfiles.merge to merge the runfiles of both tools. All runfiles will
     # be rooted under the runfiles directory owned by this rule, however.
@@ -60,11 +70,10 @@ def _complex_tool_impl(ctx):
 
     runfiles_relative_tool_path = ctx.workspace_name + "/" + ctx.attr._subtool[DefaultInfo].files_to_run.executable.short_path
 
-    # This tool forwards its runfiles directory via the RUNFILES_DIR to the
-    # subtool, otherwise the subtool would be looking to $0.runfiles, which does
-    # not exist.
-    command = ("#!/bin/bash\nexport RUNFILES_DIR=\"$0.runfiles\" && " +
-               "${RUNFILES_DIR}/%s $1 && cat ${RUNFILES_DIR}/examples/%s >> $1") % (
+    # This tool expects that the subtool will correctly resolve its runfiles.
+    command = ("#!/bin/bash\n{}" +
+               "$(rlocation {}) $1 && cat $(rlocation examples/{}) >> $1").format(
+        BASH_RLOCATION_FUNCTION,
         runfiles_relative_tool_path,
         ctx.files._data[0].short_path,
     )
@@ -92,5 +101,9 @@ complex_tool = rule(
             allow_files = True,
             default = ":complex_tool_data.txt",
         ),
+        "_runfiles_lib": attr.label(
+            allow_single_file = True,
+            default = "@bazel_tools//tools/bash/runfiles",
+        ),
     },
 )