refactor: further decrease the number of extra targets to 496

Now the number of the extra targets that we need to have is about double
the number of the different dist types that we need to support - `496`.
Since this becomes `O(2n)`, this is probably the best we can do here.

Author: aignas

python/config_settings/BUILD.bazel

@@ -88,6 +88,33 @@ string_flag(
     visibility = ["//visibility:public"],
 )
 
+config_setting(
+    name = "is_pip_whl_auto",
+    flag_values = {
+        ":pip_whl": UseWhlFlag.AUTO,
+    },
+    # NOTE: Only public because it is used in pip hub repos.
+    visibility = ["//visibility:public"],
+)
+
+config_setting(
+    name = "is_pip_whl_no",
+    flag_values = {
+        ":pip_whl": UseWhlFlag.NO,
+    },
+    # NOTE: Only public because it is used in pip hub repos.
+    visibility = ["//visibility:public"],
+)
+
+config_setting(
+    name = "is_pip_whl_only",
+    flag_values = {
+        ":pip_whl": UseWhlFlag.ONLY,
+    },
+    # NOTE: Only public because it is used in pip hub repos.
+    visibility = ["//visibility:public"],
+)
+
 string_flag(
     name = "pip_whl_osx_arch",
     build_setting_default = UniversalWhlFlag.ARCH,

python/private/pip_config_settings.bzl

@@ -43,7 +43,6 @@ load(
     ":pip_flags.bzl",
     "INTERNAL_FLAGS",
     "UniversalWhlFlag",
-    "UseWhlFlag",
     "WhlLibcFlag",
 )
 
@@ -58,6 +57,9 @@ FLAGS = struct(
             "pip_whl_osx_arch",
             "pip_whl_osx_version",
             "py_linux_libc",
+            "is_pip_whl_no",
+            "is_pip_whl_only",
+            "is_pip_whl_auto",
         ]
     }
 )
@@ -289,31 +291,27 @@ def _whl_config_setting(*, name, flag_values, config_setting_rule = None, **kwar
     config_setting_rule = config_setting_rule or _config_setting_or
     config_setting_rule(
         name = "is_" + name,
-        flag_values = flag_values | {
-            FLAGS.pip_whl: UseWhlFlag.ONLY,
-        },
-        default = flag_values | {
-            FLAGS.pip_whl: UseWhlFlag.AUTO,
-        },
+        flag_values = flag_values,
+        use_whl_flag = FLAGS.is_pip_whl_only,
         **kwargs
     )
 
 def _sdist_config_setting(*, name, config_setting_rule = None, **kwargs):
     config_setting_rule = config_setting_rule or _config_setting_or
     config_setting_rule(
         name = "is_" + name,
-        flag_values = {FLAGS.pip_whl: UseWhlFlag.NO},
-        default = {FLAGS.pip_whl: UseWhlFlag.AUTO},
+        use_whl_flag = FLAGS.is_pip_whl_no,
         **kwargs
     )
 
-def _config_setting_or(*, name, flag_values, default, visibility, python_version = "", **kwargs):
+def _config_setting_or(*, name, use_whl_flag, python_version = "", **kwargs):
     if python_version:
         _name = name.replace("is_cp{}".format(python_version), "_is")
     else:
         _name = "_" + name
 
     is_python = ":is_python_" + (python_version or "default")
+    visibility = kwargs.get("visibility")
     native.alias(
         name = name,
         actual = select({
@@ -329,24 +327,19 @@ def _config_setting_or(*, name, flag_values, default, visibility, python_version
         return
 
     match_name = "_{}_1".format(name)
-    default_name = "_{}_2".format(name)
     native.config_setting(
         name = match_name,
-        flag_values = flag_values,
-        visibility = visibility,
-        **kwargs
-    )
-    native.config_setting(
-        name = default_name,
-        flag_values = default,
-        visibility = visibility,
+        flag_values = {
+            _flags.dist: "",
+        } | kwargs.pop("flag_values", {}),
         **kwargs
     )
     native.alias(
         name = _name,
         actual = select({
-            match_name: match_name,
-            "//conditions:default": default_name,
+            FLAGS.is_pip_whl_auto: match_name,
+            use_whl_flag: match_name,
+            "//conditions:default": use_whl_flag,
         }),
         visibility = visibility,
     )

python/private/pip_flags.bzl

@@ -54,6 +54,7 @@ WhlLibcFlag = enum(
 )
 
 INTERNAL_FLAGS = [
+    "dist",
     "whl_plat",
     "whl_plat_py3",
     "whl_plat_py3_abi3",