Pass default_shell_env through actions

Through the investigation of
bazelbuild/bazel#12049 one of the things I
discovered was that when using `actions.run` there are 2 options for
environment variables. `use_default_shell_env = True` is recommended,
but cannot be used if you want to also pass `env` to the actions. To
support Xcode version selection we have to pass `env` with those
variables. Without the default shell env, we only get the environment
variables defined in the crosstool, but not those passed with
`--action_env`. This now adds variables passed as
`--action_env=FOO=BAR`, but not those passed as `--action_env=FOO`
(where the value is supposed to pass through).

This is useful to ensure a few things:

1. The default PATH things are executed with includes /usr/local/bin.
   This can result in pollution of binaries from homebrew. Previously
   there was no way to limit this
2. This should be a good replacement for using custom Swift toolchains.
   Currently those environment variables only apply to some actions
   (excluding those from bazel) using `--action_env=TOOLCHAINS=foo`
   should work better than the current solution (this change can be made
   as a followup)

swift/internal/linking.bzl

@@ -15,6 +15,7 @@
 """Implementation of linking logic for Swift."""
 
 load("@bazel_skylib//lib:collections.bzl", "collections")
+load("@bazel_skylib//lib:dicts.bzl", "dicts")
 load("@bazel_skylib//lib:partial.bzl", "partial")
 load(
     "@bazel_tools//tools/build_defs/cc:action_names.bzl",
@@ -27,13 +28,15 @@ def _register_static_library_link_action(
         cc_feature_configuration,
         objects,
         output,
+        env,
         swift_toolchain):
     """Registers an action that creates a static library.
 
     Args:
         actions: The object used to register actions.
         cc_feature_configuration: The C++ feature configuration to use when
             constructing the action.
+        env: Extra environment to run archive command with.
         objects: A list of `File`s denoting object (`.o`) files that will be
             linked.
         output: A `File` to which the output library will be written.
@@ -68,10 +71,13 @@ def _register_static_library_link_action(
     else:
         args.add_all(objects)
 
-    env = cc_common.get_environment_variables(
-        action_name = CPP_LINK_STATIC_LIBRARY_ACTION_NAME,
-        feature_configuration = cc_feature_configuration,
-        variables = archiver_variables,
+    env = dicts.add(
+        env,
+        cc_common.get_environment_variables(
+            action_name = CPP_LINK_STATIC_LIBRARY_ACTION_NAME,
+            feature_configuration = cc_feature_configuration,
+            variables = archiver_variables,
+        ),
     )
 
     execution_requirements_list = cc_common.get_execution_requirements(
@@ -105,6 +111,7 @@ def create_linker_input(
         library_name,
         objects,
         owner,
+        env,
         swift_toolchain,
         additional_inputs = [],
         user_link_flags = []):
@@ -126,6 +133,7 @@ def create_linker_input(
         objects: A list of `File`s denoting object (`.o`) files that will be
             linked.
         owner: The `Label` of the target that owns this linker input.
+        env: Extra environment to launch the link command with.
         swift_toolchain: The Swift toolchain provider to use when constructing
             the action.
         additional_inputs: A list of extra `File` inputs passed to the linking
@@ -154,6 +162,7 @@ def create_linker_input(
             cc_feature_configuration = cc_feature_configuration,
             objects = objects,
             output = static_library,
+            env = env,
             swift_toolchain = swift_toolchain,
         )
     else:

swift/internal/swift_grpc_library.bzl

@@ -300,6 +300,7 @@ def _swift_grpc_library_impl(ctx):
             feature_configuration = feature_configuration,
         ),
         compilation_outputs = compilation_outputs,
+        env = ctx.configuration.default_shell_env,
         is_dynamic = False,
         is_static = True,
         library_name = ctx.label.name,

swift/internal/swift_library.bzl

@@ -211,6 +211,7 @@ def _swift_library_impl(ctx):
             feature_configuration = feature_configuration,
         ),
         compilation_outputs = compilation_outputs,
+        env = ctx.configuration.default_shell_env,
         is_dynamic = False,
         is_static = True,
         library_name = ctx.label.name,

swift/internal/swift_module_alias.bzl

@@ -80,6 +80,7 @@ def _swift_module_alias_impl(ctx):
             feature_configuration = feature_configuration,
         ),
         compilation_outputs = compilation_outputs,
+        env = ctx.configuration.default_shell_env,
         is_dynamic = False,
         is_static = True,
         library_name = ctx.label.name,

swift/internal/swift_protoc_gen_aspect.bzl

@@ -433,6 +433,7 @@ def _swift_protoc_gen_aspect_impl(target, aspect_ctx):
                 feature_configuration = feature_configuration,
             ),
             compilation_outputs = compilation_outputs,
+            env = aspect_ctx.configuration.default_shell_env,
             is_dynamic = False,
             is_static = True,
             # Prevent conflicts with C++ protos in the same output directory,

swift/internal/xcode_swift_toolchain.bzl

@@ -742,7 +742,10 @@ def _xcode_swift_toolchain_impl(ctx):
     if _is_xcode_at_least_version(xcode_config, "12.5"):
         requested_features.append(SWIFT_FEATURE_SUPPORTS_SYSTEM_MODULE_FLAG)
 
-    env = _xcode_env(platform = platform, xcode_config = xcode_config)
+    env = dicts.add(
+        ctx.configuration.default_shell_env,
+        _xcode_env(platform = platform, xcode_config = xcode_config),
+    )
     execution_requirements = xcode_config.execution_info()
     generated_header_rewriter = ctx.executable.generated_header_rewriter