Migrate main workspace to bzlmod

All tests requiring an old Bazel version are located inside the integration
tests and examples which have their won sub workspaces.
Thus we can drop support for the legacy WORKSPACE setup in the main repo.
At the same time we simplify the main toolchain. It requires only a single
version.

MODULE.bazel

@@ -1,5 +1,6 @@
 module(
     name = "depend_on_what_you_use",
+    # Keep in sync with setup_step_2.bzl
     bazel_compatibility = [">=5.4.0"],
     compatibility_level = 0,
 )
@@ -30,37 +31,14 @@ use_repo(non_module_dependencies, "dwyu_pcpp")
 ### Development Dependencies
 ###
 
-# Update with each rules_python update for easy lookup until specifying the patch version for toolchain is possible again
-# Keep in syc with test/aspect/execute_tests.py
-# PATCH_MAPPING:
-#  "3.10": "3.10.13"
-#  "3.11": "3.11.6"
-#  "3.12": "3.12.0"
-#  "3.8": "3.8.18"
-#  "3.9": "3.9.18"
-# Choose different version via: --@rules_python//python/config_settings:python_version=Major.Minor.Patch mathing one of
-# the registered toolchains below.
 python = use_extension(
     "@rules_python//python/extensions:python.bzl",
     "python",
     dev_dependency = True,
 )
 python.toolchain(
-    is_default = True,
     python_version = "3.8",
 )
-python.toolchain(
-    python_version = "3.9",
-)
-python.toolchain(
-    python_version = "3.10",
-)
-python.toolchain(
-    python_version = "3.11",
-)
-python.toolchain(
-    python_version = "3.12",
-)
 
 pip_dev = use_extension(
     "@rules_python//python/extensions:pip.bzl",
@@ -74,22 +52,9 @@ pip_dev.parse(
 )
 use_repo(pip_dev, "dwyu_mypy_deps")
 
-non_module_dev_dependencies = use_extension(
-    "//third_party:extensions.bzl",
-    "non_module_dev_dependencies",
-    dev_dependency = True,
-)
-use_repo(non_module_dev_dependencies, "mypy_integration")
-
-###
-### The Migration phase using WORKSPACE.bzlmod and MODULE.bazel together does not support properly loading the implicit
-### Bazel dependencies. Thus, we need to load some basic things directly. This should become superfluous when we are
-### only using bzlmod eventually
-### Reference https://github.com/bazelbuild/bazel/blob/master/src/MODULE.tools
-###
-
-bazel_dep(
-    name = "platforms",
-    version = "0.0.7",
+mypy_dep = use_extension(
+    "//third_party:dev_extensions.bzl",
+    "mypy_dependency",
     dev_dependency = True,
 )
+use_repo(mypy_dep, "mypy_integration")

WORKSPACE

@@ -1,29 +1,2 @@
-workspace(name = "depend_on_what_you_use")
-
-#
-# Setup of public dependencies of this project
-#
-
-load("//:setup_step_1.bzl", "setup_step_1")
-
-setup_step_1()
-
-load("//:setup_step_2.bzl", "setup_step_2")
-
-setup_step_2()
-
-#
-# Setup of development dependencies of this project
-#
-
-load("//:dev_setup_step_1.bzl", "dev_setup_step_1")
-
-dev_setup_step_1()
-
-load("//:dev_setup_step_2.bzl", "dev_setup_step_2")
-
-dev_setup_step_2()
-
-load("//:dev_setup_step_3.bzl", "dev_setup_step_3")
-
-dev_setup_step_3()
+# For now we need a WORKSPACE file to mark the workspace root.
+# The projects has however migrated to the MODULE.bazel approach and thus the WORKSPACE file is empty.

setup_step_2.bzl

@@ -8,6 +8,7 @@ def setup_step_2():
 
     # Fail early for incompatible Bazel versions instead of printing obscure errors from within our implementation
     versions.check(
+        # Keep in sync with MODULE.bazel
         minimum_bazel_version = "5.4.0",
     )
 

third_party/dev_dependencies.bzl → third_party/dev_extensions.bzl

@@ -1,12 +1,14 @@
 load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
-load("@bazel_tools//tools/build_defs/repo:utils.bzl", "maybe")
 
-def dev_dependencies():
+def _mypy_extension_extension_impl(_ctx):
     version = "0a881be043e8eae72ad83610c6205e7972bcd5e1"
-    maybe(
-        http_archive,
+    http_archive(
         name = "mypy_integration",
         sha256 = "1b6c3b1d967ae87b83b7ec179a376a4ff501925488bb06960545e776a873aebd",
         strip_prefix = "bazel-mypy-integration-{v}".format(v = version),
         urls = ["https://github.com/martis42/bazel-mypy-integration/archive/{v}.tar.gz".format(v = version)],
     )
+
+mypy_dependency = module_extension(
+    implementation = _mypy_extension_extension_impl,
+)

third_party/extensions.bzl

@@ -1,13 +1,5 @@
-load("//third_party:dev_dependencies.bzl", "dev_dependencies")
 load("//third_party/pcpp:repository.bzl", "pcpp")
 
-def _non_module_dev_dependencies_impl(_ctx):
-    dev_dependencies()
-
-non_module_dev_dependencies = module_extension(
-    implementation = _non_module_dev_dependencies_impl,
-)
-
 def _non_module_dependencies_impl(_ctx):
     pcpp()