feat(examples): make -cxx-interoperability-mode a feature

examples/xplatform/cxx_from_swift/BUILD

@@ -1,6 +1,8 @@
 load("@rules_cc//cc:cc_library.bzl", "cc_library")
 load("//swift:swift_binary.bzl", "swift_binary")
+load("//swift:swift_extract_symbol_graph.bzl", "swift_extract_symbol_graph")
 load("//swift:swift_interop_hint.bzl", "swift_interop_hint")
+load("//swift:swift_library.bzl", "swift_library")
 
 licenses(["notice"])
 
@@ -21,15 +23,31 @@ swift_interop_hint(
     module_name = "CxxCounter",
 )
 
-# 2. The Swift binary then depends on the `cc_library`. This causes a
+# 2. The Swift library then depends on the `cc_library`. This causes a
+# Swift-compatible module map to be created for the `cc_library` so that the
+# Swift code can import it.
+swift_library(
+    name = "swift_counter",
+    srcs = ["Counter.swift"],
+    features = ["swift.enable_cpp20_interop"],
+    module_name = "Counter",
+    deps = [":counter"],
+)
+
+# 3. The Swift binary then depends on the `cc_library`. This causes a
 # Swift-compatible module map to be created for the `cc_library` so that the
 # Swift code can import it. Be sure to enable C++ Interoperability in the Swift
 # compiler using the `-cxx-interoperability-mode` build flag.
 # https://www.swift.org/documentation/cxx-interop/project-build-setup/#mixing-swift-and-c-using-other-build-systems
 swift_binary(
     name = "cxx_from_swift",
     srcs = ["main.swift"],
-    copts = ["-cxx-interoperability-mode=default"],
+    features = ["swift.enable_cpp20_interop"],
     module_name = "main",
-    deps = [":counter"],
+    deps = [":swift_counter"],
+)
+
+swift_extract_symbol_graph(
+    name = "symbol_graph",
+    targets = [":swift_counter"],
 )

examples/xplatform/cxx_from_swift/Counter.swift

@@ -0,0 +1,11 @@
+// Import the C++ interface.
+@_exported import CxxCounter
+
+/// Wraps the C++ interface in a Swift interface.
+extension swiftexample.Counter {
+
+  mutating public func Decrement() {
+    count_ = count_ - 1
+  }
+
+}

examples/xplatform/cxx_from_swift/counter.h

@@ -18,8 +18,6 @@ class Counter {
  public:
   int Get() const;
   void Increment();
-
- private:
   int count_ = 0;
 };
 

examples/xplatform/cxx_from_swift/main.swift

@@ -13,7 +13,7 @@
 // limitations under the License.
 
 // Import the C++ interface.
-import CxxCounter
+import Counter
 
 var counter = swiftexample.Counter()
 for _ in 1...10 {

swift/internal/feature_names.bzl

@@ -399,3 +399,10 @@ SWIFT_FEATURE_THIN_LTO = "swift.thin_lto"
 
 # Enable full LTO and update output-file-map correctly
 SWIFT_FEATURE_FULL_LTO = "swift.full_lto"
+
+# Enables swift cpp interop. When enabled, this feature adds -cxx-interoperability-mode=default
+# along with the corresponding -std=c++<N> options. Use this when swift needs to imports a module
+# that has C++ headers.
+SWIFT_FEATURE_ENABLE_CPP17_INTEROP = "swift.enable_cpp17_interop"
+SWIFT_FEATURE_ENABLE_CPP20_INTEROP = "swift.enable_cpp20_interop"
+SWIFT_FEATURE_ENABLE_CPP23_INTEROP = "swift.enable_cpp23_interop"

swift/toolchains/config/compile_config.bzl

@@ -53,6 +53,9 @@ load(
     "SWIFT_FEATURE_EMIT_SWIFTINTERFACE",
     "SWIFT_FEATURE_ENABLE_BARE_SLASH_REGEX",
     "SWIFT_FEATURE_ENABLE_BATCH_MODE",
+    "SWIFT_FEATURE_ENABLE_CPP17_INTEROP",
+    "SWIFT_FEATURE_ENABLE_CPP20_INTEROP",
+    "SWIFT_FEATURE_ENABLE_CPP23_INTEROP",
     "SWIFT_FEATURE_ENABLE_LIBRARY_EVOLUTION",
     "SWIFT_FEATURE_ENABLE_SKIP_FUNCTION_BODIES",
     "SWIFT_FEATURE_ENABLE_TESTING",
@@ -1241,6 +1244,42 @@ def compile_action_configs(
                 SWIFT_FEATURE__SUPPORTS_V6,
             ],
         ),
+        ActionConfigInfo(
+            actions = [
+                SWIFT_ACTION_COMPILE,
+            ],
+            configurators = [
+                add_arg("-cxx-interoperability-mode=default"),
+                add_arg("-Xcc", "-std=c++17"),
+            ],
+            features = [
+                SWIFT_FEATURE_ENABLE_CPP17_INTEROP,
+            ],
+        ),
+        ActionConfigInfo(
+            actions = [
+                SWIFT_ACTION_COMPILE,
+            ],
+            configurators = [
+                add_arg("-cxx-interoperability-mode=default"),
+                add_arg("-Xcc", "-std=c++20"),
+            ],
+            features = [
+                SWIFT_FEATURE_ENABLE_CPP20_INTEROP,
+            ],
+        ),
+        ActionConfigInfo(
+            actions = [
+                SWIFT_ACTION_COMPILE,
+            ],
+            configurators = [
+                add_arg("-cxx-interoperability-mode=default"),
+                add_arg("-Xcc", "-std=c++23"),
+            ],
+            features = [
+                SWIFT_FEATURE_ENABLE_CPP23_INTEROP,
+            ],
+        ),
     ]
 
     # NOTE: The positions of these action configs in the list are important,

swift/toolchains/config/symbol_graph_config.bzl

@@ -18,7 +18,13 @@ load(
     "//swift/internal:action_names.bzl",
     "SWIFT_ACTION_SYMBOL_GRAPH_EXTRACT",
 )
-load(":action_config.bzl", "ActionConfigInfo")
+load(
+    "//swift/internal:feature_names.bzl",
+    "SWIFT_FEATURE_ENABLE_CPP17_INTEROP",
+    "SWIFT_FEATURE_ENABLE_CPP20_INTEROP",
+    "SWIFT_FEATURE_ENABLE_CPP23_INTEROP",
+)
+load(":action_config.bzl", "ActionConfigInfo", "add_arg")
 
 def symbol_graph_action_configs():
     """Returns the list of action configs needed to extract symbol graphs.
@@ -45,6 +51,36 @@ def symbol_graph_action_configs():
                 _symbol_graph_emit_extension_block_symbols_configurator,
             ],
         ),
+        ActionConfigInfo(
+            actions = [SWIFT_ACTION_SYMBOL_GRAPH_EXTRACT],
+            configurators = [
+                add_arg("-cxx-interoperability-mode=default"),
+                add_arg("-Xcc", "-std=c++17"),
+            ],
+            features = [
+                SWIFT_FEATURE_ENABLE_CPP17_INTEROP,
+            ],
+        ),
+        ActionConfigInfo(
+            actions = [SWIFT_ACTION_SYMBOL_GRAPH_EXTRACT],
+            configurators = [
+                add_arg("-cxx-interoperability-mode=default"),
+                add_arg("-Xcc", "-std=c++20"),
+            ],
+            features = [
+                SWIFT_FEATURE_ENABLE_CPP20_INTEROP,
+            ],
+        ),
+        ActionConfigInfo(
+            actions = [SWIFT_ACTION_SYMBOL_GRAPH_EXTRACT],
+            configurators = [
+                add_arg("-cxx-interoperability-mode=default"),
+                add_arg("-Xcc", "-std=c++23"),
+            ],
+            features = [
+                SWIFT_FEATURE_ENABLE_CPP23_INTEROP,
+            ],
+        ),
     ]
 
 def _symbol_graph_minimum_access_level_configurator(prerequisites, args):