Enable swift.file_prefix_map by default if supported (#1014)

We already enable debug and coverage prefix maps, this one supersedes
those and potentially handles more cases in the future.

Author: keith

swift/internal/swift_autoconfiguration.bzl

@@ -30,6 +30,7 @@ load(
     "SWIFT_FEATURE_DEBUG_PREFIX_MAP",
     "SWIFT_FEATURE_ENABLE_BATCH_MODE",
     "SWIFT_FEATURE_ENABLE_SKIP_FUNCTION_BODIES",
+    "SWIFT_FEATURE_FILE_PREFIX_MAP",
     "SWIFT_FEATURE_LLD_GC_WORKAROUND",
     "SWIFT_FEATURE_MODULE_MAP_NO_PRIVATE_HEADERS",
     "SWIFT_FEATURE_NO_EMBED_DEBUG_MODULE",
@@ -91,6 +92,16 @@ def _check_skip_function_bodies(repository_ctx, swiftc_path, _temp_dir):
         "-experimental-skip-non-inlinable-function-bodies",
     )
 
+def _check_file_prefix_map(repository_ctx, swiftc_path, _temp_dir):
+    """Returns True if `swiftc` supports -file-prefix-map."""
+    return _swift_succeeds(
+        repository_ctx,
+        swiftc_path,
+        "-version",
+        "-file-prefix-map",
+        "foo=bar",
+    )
+
 def _check_enable_bare_slash_regex(repository_ctx, swiftc_path, _temp_dir):
     """Returns True if `swiftc` supports debug prefix mapping."""
     return _swift_succeeds(
@@ -209,6 +220,7 @@ def _compute_feature_values(repository_ctx, swiftc_path):
 _FEATURE_CHECKS = {
     SWIFT_FEATURE_ENABLE_BATCH_MODE: _check_enable_batch_mode,
     SWIFT_FEATURE_ENABLE_SKIP_FUNCTION_BODIES: _check_skip_function_bodies,
+    SWIFT_FEATURE_FILE_PREFIX_MAP: _check_file_prefix_map,
     SWIFT_FEATURE_LLD_GC_WORKAROUND: _check_supports_lld_gc_workaround,
     SWIFT_FEATURE_SUPPORTS_BARE_SLASH_REGEX: _check_enable_bare_slash_regex,
     SWIFT_FEATURE_SUPPORTS_PRIVATE_DEPS: _check_supports_private_deps,

swift/internal/xcode_swift_toolchain.bzl

@@ -635,6 +635,7 @@ def _xcode_swift_toolchain_impl(ctx):
 
     # Xcode 14 implies Swift 5.7.
     if _is_xcode_at_least_version(xcode_config, "14.0"):
+        requested_features.append(SWIFT_FEATURE_FILE_PREFIX_MAP)
         requested_features.append(SWIFT_FEATURE_SUPPORTS_BARE_SLASH_REGEX)
 
     env = _xcode_env(target_triple = target_triple, xcode_config = xcode_config)

test/features_tests.bzl

@@ -21,19 +21,10 @@ opt_no_wmo_test = make_action_command_line_test_rule(
     },
 )
 
-file_prefix_map_test = make_action_command_line_test_rule(
+disabled_file_prefix_map_test = make_action_command_line_test_rule(
     config_settings = {
         "//command_line_option:features": [
-            "swift.file_prefix_map",
-        ],
-    },
-)
-
-file_prefix_xcode_remap_test = make_action_command_line_test_rule(
-    config_settings = {
-        "//command_line_option:features": [
-            "swift.file_prefix_map",
-            "swift.remap_xcode_path",
+            "-swift.file_prefix_map",
         ],
     },
 )
@@ -83,26 +74,23 @@ def features_test_suite(name):
         expected_argv = [
             "-emit-object",
             "-I$(BIN_DIR)/test/fixtures/basic",
-        ],
-        not_expected_argv = [
-            "-file-prefix-map",
             "-Xwrapped-swift=-file-prefix-pwd-is-dot",
         ],
         mnemonic = "SwiftCompile",
         target_under_test = "@build_bazel_rules_swift//test/fixtures/basic:second",
     )
 
-    file_prefix_map_test(
+    disabled_file_prefix_map_test(
         name = "{}_file_prefix_map_test".format(name),
         tags = [name],
-        expected_argv = [
+        not_expected_argv = [
             "-Xwrapped-swift=-file-prefix-pwd-is-dot",
         ],
         mnemonic = "SwiftCompile",
         target_under_test = "@build_bazel_rules_swift//test/fixtures/debug_settings:simple",
     )
 
-    file_prefix_xcode_remap_test(
+    default_test(
         name = "{}_file_prefix_xcode_remap_test".format(name),
         tags = [name],
         expected_argv = [