Add support for emit-extension-block-symbols flag

This flag can be used when emitting a symbol graph to additionally include the symbols from the extension blocks.
This is useful when generating documentation with DocC so that the symbols from the extension blocks are included in the documentation.

swift/internal/compiling.bzl

@@ -54,6 +54,7 @@ load(
     "SWIFT_FEATURE_EMIT_SWIFTINTERFACE",
     "SWIFT_FEATURE_EMIT_SWIFTSOURCEINFO",
     "SWIFT_FEATURE_EMIT_SYMBOL_GRAPH",
+    "SWIFT_FEATURE_EMIT_SYMBOL_GRAPH_EXTENSION_BLOCKS",
     "SWIFT_FEATURE_ENABLE_BATCH_MODE",
     "SWIFT_FEATURE_ENABLE_LIBRARY_EVOLUTION",
     "SWIFT_FEATURE_ENABLE_SKIP_FUNCTION_BODIES",
@@ -859,6 +860,17 @@ def compile_action_configs(
             ],
             not_features = [SWIFT_FEATURE_SPLIT_DERIVED_FILES_GENERATION],
         ),
+        swift_toolchain_config.action_config(
+            actions = [
+                swift_action_names.COMPILE,
+            ],
+            configurators = [_emit_symbol_graph_extension_blocks_configurator],
+            features = [
+                SWIFT_FEATURE_EMIT_SYMBOL_GRAPH,
+                SWIFT_FEATURE_EMIT_SYMBOL_GRAPH_EXTENSION_BLOCKS,
+            ],
+            not_features = [SWIFT_FEATURE_SPLIT_DERIVED_FILES_GENERATION],
+        ),
         swift_toolchain_config.action_config(
             actions = [
                 swift_action_names.DERIVE_FILES,
@@ -2014,6 +2026,12 @@ def _emit_symbol_graph_configurator(prerequisites, args):
         prerequisites.symbol_graph_directory.path,
     )
 
+def _emit_symbol_graph_extension_blocks_configurator(_prerequisites, args):
+    args.add(
+        "-Xfrontend",
+        "-emit-extension-block-symbols",
+    )
+
 def _global_index_store_configurator(prerequisites, args):
     """Adds flags for index-store generation to the command line."""
     out_dir = prerequisites.indexstore_directory.dirname.split("/")[0]

swift/internal/feature_names.bzl

@@ -110,6 +110,9 @@ SWIFT_FEATURE_INDEX_WHILE_BUILDING = "swift.index_while_building"
 # If enabled, the compilation action for a target will produce a symbol graph.
 SWIFT_FEATURE_EMIT_SYMBOL_GRAPH = "swift.emit_symbol_graph"
 
+# If enabled when `SWIFT_FEATURE_EMIT_SYMBOL_GRAPH` is enabled, emits symbols for extension code blocks.
+SWIFT_FEATURE_EMIT_SYMBOL_GRAPH_EXTENSION_BLOCKS = "swift.emit_symbol_graph_extension_blocks"
+
 # If enabled the compilation action will not produce indexes for system modules.
 SWIFT_FEATURE_DISABLE_SYSTEM_INDEX = "swift.disable_system_index"
 

test/split_derived_files_tests.bzl

@@ -130,6 +130,14 @@ default_no_split_swiftmodule_symbol_graph_test = make_action_command_line_test_r
         ],
     },
 )
+default_no_split_swiftmodule_symbol_graph_extension_blocks_test = make_action_command_line_test_rule(
+    config_settings = {
+        "//command_line_option:features": [
+            "swift.emit_symbol_graph",
+            "swift.emit_symbol_graph_extension_blocks",
+        ],
+    },
+)
 
 def split_derived_files_test_suite(name):
     """Test suite for split derived files options.
@@ -320,6 +328,21 @@ def split_derived_files_test_suite(name):
             "-emit-symbol-graph",
             "-emit-symbol-graph-dir",
         ],
+        not_expected_argv = [
+            "-emit-extension-block-symbols",
+        ],
+        mnemonic = "SwiftCompile",
+        tags = [name],
+        target_under_test = "@build_bazel_rules_swift//test/fixtures/debug_settings:simple",
+    )
+
+    default_no_split_swiftmodule_symbol_graph_extension_blocks_test(
+        name = "{}_default_no_split_symbol_graph_extension_blocks_in_compile_action".format(name),
+        expected_argv = [
+            "-emit-symbol-graph",
+            "-emit-symbol-graph-dir",
+            "-emit-extension-block-symbols",
+        ],
         mnemonic = "SwiftCompile",
         tags = [name],
         target_under_test = "@build_bazel_rules_swift//test/fixtures/debug_settings:simple",