Enable Python toolchains by default

    (This is a roll-forward of bazelbuild/bazel@bf66dc7.)

    This flips --incompatible_use_python_toolchains, which deprecates --python_top (and for the most part, --python_path). See #7899 for more on the change and migration procedure.

    Known downstream breakages are summarized [here](bazelbuild/bazel#7899 (comment)).

    Fixes #7899, fixes #7375, significant progress on #4815.

    RELNOTES[INC]: Python rules now determine the Python runtime using toolchains rather than `--python_top` and `--python_path`, which are deprecated. See [#7899](bazelbuild/bazel#7899) for information on declaring Python toolchains and migrating your code. As a side-benefit, this addresses [#4815](bazelbuild/bazel#4815) (incorrect interpreter version used) on non-Windows platforms. Note however that some builds break due to getting the version they asked for -- consider setting `python_version = "PY2"` on Python 2 targets and `--host_force_python=PY2` if any Python 2 targets are used in the host configuration. You can temporarily opt out of this change with `--incompatible_use_python_toolchains=false`.

    PiperOrigin-RevId: 250918912

dataset/GitHub_Java/bazelbuild.bazel/src/main/java/com/google/devtools/build/lib/rules/python/PythonOptions.java

@@ -244,21 +244,6 @@ public String getTypeDescription() {
               + "--python_top.")
   public boolean incompatibleUsePythonToolchains;
 
-  @Option(
-      name = "incompatible_load_python_rules_from_bzl",
-      defaultValue = "false",
-      documentationCategory = OptionDocumentationCategory.UNDOCUMENTED,
-      effectTags = {OptionEffectTag.LOADING_AND_ANALYSIS},
-      metadataTags = {
-        OptionMetadataTag.INCOMPATIBLE_CHANGE,
-        OptionMetadataTag.TRIGGERED_BY_ALL_INCOMPATIBLE_CHANGES,
-      },
-      help =
-          "If enabled, direct use of the native Python rules is disabled. Please use the Starlark "
-              + "rules instead: https://github.com/bazelbuild/rules_python. See also "
-              + "https://github.com/bazelbuild/bazel/issues/9006.")
-  public boolean loadPythonRulesFromBzl;
-
   @Option(
       name = "experimental_build_transitive_python_runfiles",
       defaultValue = "true",
@@ -270,21 +255,24 @@ public String getTypeDescription() {
   public boolean buildTransitiveRunfilesTrees;
 
   @Option(
-      name = "incompatible_default_to_explicit_init_py",
-      defaultValue = "false",
-      documentationCategory = OptionDocumentationCategory.GENERIC_INPUTS,
-      effectTags = {OptionEffectTag.AFFECTS_OUTPUTS},
+      name = "incompatible_windows_escape_python_args",
+      defaultValue = "true",
+      documentationCategory = OptionDocumentationCategory.OUTPUT_PARAMETERS,
+      effectTags = {
+        OptionEffectTag.ACTION_COMMAND_LINES,
+        OptionEffectTag.AFFECTS_OUTPUTS,
+      },
       metadataTags = {
         OptionMetadataTag.INCOMPATIBLE_CHANGE,
         OptionMetadataTag.TRIGGERED_BY_ALL_INCOMPATIBLE_CHANGES
       },
       help =
-          "This flag changes the default behavior so that __init__.py files are no longer "
-              + "automatically created in the runfiles of Python targets. Precisely, when a "
-              + "py_binary or py_test target has legacy_create_init set to \"auto\" (the default), "
-              + "it is treated as false if and only if this flag is set. See "
-              + "https://github.com/bazelbuild/bazel/issues/10076.")
-  public boolean incompatibleDefaultToExplicitInitPy;
+          "On Linux/macOS/non-Windows: no-op. On Windows: this flag affects how py_binary and"
+              + " py_test targets are built: how their launcher escapes command line flags. When"
+              + " this flag is true, the launcher escapes command line flags using Windows-style"
+              + " escaping (correct behavior). When the flag is false, the launcher uses Bash-style"
+              + " escaping (buggy behavior). See https://github.com/bazelbuild/bazel/issues/7958")
+  public boolean windowsEscapePythonArgs;
 
   @Override
   public Map<OptionDefinition, SelectRestriction> getSelectRestrictions() {
@@ -404,7 +392,7 @@ public FragmentOptions getHost() {
     hostPythonOptions.buildPythonZip = buildPythonZip;
     hostPythonOptions.incompatibleDisallowLegacyPyProvider = incompatibleDisallowLegacyPyProvider;
     hostPythonOptions.incompatibleUsePythonToolchains = incompatibleUsePythonToolchains;
-    hostPythonOptions.loadPythonRulesFromBzl = loadPythonRulesFromBzl;
+    hostPythonOptions.windowsEscapePythonArgs = windowsEscapePythonArgs;
 
     // Save host options in case of a further exec->host transition.
     hostPythonOptions.hostForcePython = hostForcePython;