Add disable system index feature (#563)

Author: keith

swift/internal/compiling.bzl

@@ -36,6 +36,7 @@ load(
     "SWIFT_FEATURE_COVERAGE_PREFIX_MAP",
     "SWIFT_FEATURE_DBG",
     "SWIFT_FEATURE_DEBUG_PREFIX_MAP",
+    "SWIFT_FEATURE_DISABLE_SYSTEM_INDEX",
     "SWIFT_FEATURE_EMIT_C_MODULE",
     "SWIFT_FEATURE_EMIT_SWIFTINTERFACE",
     "SWIFT_FEATURE_ENABLE_BATCH_MODE",
@@ -717,6 +718,18 @@ def compile_action_configs():
             configurators = [_index_while_building_configurator],
             features = [SWIFT_FEATURE_INDEX_WHILE_BUILDING],
         ),
+        swift_toolchain_config.action_config(
+            actions = [swift_action_names.COMPILE],
+            configurators = [
+                swift_toolchain_config.add_arg(
+                    "-index-ignore-system-modules",
+                ),
+            ],
+            features = [
+                SWIFT_FEATURE_INDEX_WHILE_BUILDING,
+                SWIFT_FEATURE_DISABLE_SYSTEM_INDEX,
+            ],
+        ),
 
         # User-defined conditional compilation flags (defined for Swift; those
         # passed directly to ClangImporter are handled above).

swift/internal/feature_names.bzl

@@ -102,6 +102,9 @@ SWIFT_FEATURE_FULL_DEBUG_INFO = "swift.full_debug_info"
 # If enabled, the compilation action for a target will produce an index store.
 SWIFT_FEATURE_INDEX_WHILE_BUILDING = "swift.index_while_building"
 
+# If enabled the compilation action will not produce indexes for system modules.
+SWIFT_FEATURE_DISABLE_SYSTEM_INDEX = "swift.disable_system_index"
+
 # If enabled, Swift libraries, binaries, and tests will only have automatic
 # dependencies on the targets provided by the toolchain's
 # `required_implicit_deps` field but not those in the `optional_implicit_deps`