Add swift_interoperability_mode kwarg

Author: dblsaiko

docs/markdown/snippets/swift_cxx_interoperability.md

@@ -1,13 +1,23 @@
 ## Swift/C++ interoperability is now supported
 
 It is now possible to create Swift executables that can link to C++ or
-Objective-C++ libraries. Only specifying a bridging header for the Swift
-target is required.
+Objective-C++ libraries. To enable this feature, set the target kwarg
+_swift\_interoperability\_mode_ to 'cpp'.
+
+To import C++ code, specify a bridging header in the Swift target's
+sources, or use another way such as adding a directory containing a
+Clang module map to its include path.
+
+Note: Enabling C++ interoperability in a library target is a breaking
+change. Swift libraries that enable it need their consumers to enable
+it as well, as per [the Swift documentation][1].
 
 Swift 5.9 is required to use this feature. Xcode 15 is required if the
 Xcode backend is used.
 
 ```meson
 lib = static_library('mylib', 'mylib.cpp')
-exe = executable('prog', 'main.swift', 'mylib.h', link_with: lib)
+exe = executable('prog', 'main.swift', 'mylib.h', link_with: lib, swift_interoperability_mode: 'cpp')
 ```
+
+[1]: https://www.swift.org/documentation/cxx-interop/project-build-setup/#vending-packages-that-enable-c-interoperability

mesonbuild/backend/ninjabackend.py

@@ -2266,6 +2266,20 @@ def generate_swift_target(self, target) -> None:
         relsrc = []
         abs_headers = []
         header_imports = []
+
+        if not target.uses_swift_cpp_interop():
+            cpp_targets = [t for t in target.link_targets if t.uses_swift_cpp_interop()]
+            if cpp_targets != []:
+                target_word = 'targets' if len(cpp_targets) > 1 else 'target'
+                first = ', '.join(repr(t.name) for t in cpp_targets[:-1])
+                and_word = ' and ' if len(cpp_targets) > 1 else ''
+                last = repr(cpp_targets[-1].name)
+                enable_word = 'enable' if len(cpp_targets) > 1 else 'enables'
+                raise MesonException('Swift target {0} links against {1} {2}{3}{4} which {5} C++ interoperability. '
+                                     'This requires {0} to also have it enabled. '
+                                     'Add "swift_interoperability_mode: \'cpp\'" to the definition of {0}.'
+                                     .format(repr(target.name), target_word, first, and_word, last, enable_word))
+
         for i in target.get_sources():
             if swiftc.can_compile(i):
                 rels = i.rel_to_builddir(self.build_to_src)
@@ -2282,8 +2296,7 @@ def generate_swift_target(self, target) -> None:
         os.makedirs(self.get_target_private_dir_abs(target), exist_ok=True)
         compile_args = self.generate_basic_compiler_args(target, swiftc)
         compile_args += swiftc.get_module_args(module_name)
-        if mesonlib.version_compare(swiftc.version, '>=5.9'):
-            compile_args += swiftc.get_cxx_interoperability_args(target.compilers)
+        compile_args += swiftc.get_cxx_interoperability_args(target)
         compile_args += self.build.get_project_args(swiftc, target.subproject, target.for_machine)
         compile_args += self.build.get_global_args(swiftc, target.for_machine)
         if isinstance(target, (build.StaticLibrary, build.SharedLibrary)):

mesonbuild/backend/xcodebackend.py

@@ -1831,7 +1831,7 @@ def generate_single_build_target(self, objects_dict, target_name, target) -> Non
             settings_dict.add_item('SECTORDER_FLAGS', '')
             if is_swift and bridging_header:
                 settings_dict.add_item('SWIFT_OBJC_BRIDGING_HEADER', bridging_header)
-                if self.objversion >= 60 and 'cpp' in langs:
+                if self.objversion >= 60 and target.uses_swift_cpp_interop():
                     settings_dict.add_item('SWIFT_OBJC_INTEROP_MODE', 'objcxx')
             settings_dict.add_item('BUILD_DIR', symroot)
             settings_dict.add_item('OBJROOT', f'{symroot}/build')

mesonbuild/build.py

@@ -75,7 +75,7 @@ class DFeatures(TypedDict):
 vala_kwargs = {'vala_header', 'vala_gir', 'vala_vapi'}
 rust_kwargs = {'rust_crate_type', 'rust_dependency_map'}
 cs_kwargs = {'resources', 'cs_args'}
-swift_kwargs = {'swift_module_name'}
+swift_kwargs = {'swift_interoperability_mode', 'swift_module_name'}
 
 buildtarget_kwargs = {
     'build_by_default',
@@ -1275,6 +1275,8 @@ def process_kwargs(self, kwargs):
             raise InvalidArguments(f'Invalid rust_dependency_map "{rust_dependency_map}": must be a dictionary with string values.')
         self.rust_dependency_map = rust_dependency_map
 
+        self.swift_interoperability_mode = kwargs.get('swift_interoperability_mode')
+
         self.swift_module_name = kwargs.get('swift_module_name')
         if self.swift_module_name == '':
             self.swift_module_name = self.name
@@ -1702,6 +1704,9 @@ def uses_rust_abi(self) -> bool:
     def uses_fortran(self) -> bool:
         return 'fortran' in self.compilers
 
+    def uses_swift_cpp_interop(self) -> bool:
+        return self.swift_interoperability_mode == 'cpp' and 'swift' in self.compilers
+
     def get_using_msvc(self) -> bool:
         '''
         Check if the dynamic linker is MSVC. Used by Executable, StaticLibrary,

mesonbuild/compilers/compilers.py

@@ -1121,9 +1121,6 @@ def get_crt_link_args(self, crt_val: str, buildtype: str) -> T.List[str]:
     def get_compile_only_args(self) -> T.List[str]:
         return []
 
-    def get_cxx_interoperability_args(self, lang: T.Dict[str, Compiler]) -> T.List[str]:
-        raise EnvironmentException('This compiler does not support CXX interoperability')
-
     def get_preprocess_only_args(self) -> T.List[str]:
         raise EnvironmentException('This compiler does not have a preprocessor')
 

mesonbuild/compilers/swift.py

@@ -153,11 +153,14 @@ def get_working_directory_args(self, path: str) -> T.Optional[T.List[str]]:
 
         return ['-working-directory', path]
 
-    def get_cxx_interoperability_args(self, lang: T.Dict[str, Compiler]) -> T.List[str]:
-        if 'cpp' in lang or 'objcpp' in lang:
-            return ['-cxx-interoperability-mode=default']
-        else:
-            return ['-cxx-interoperability-mode=off']
+    def get_cxx_interoperability_args(self, target: T.Optional[build.BuildTarget] = None) -> T.List[str]:
+        if target is not None and not target.uses_swift_cpp_interop():
+            return []
+
+        if version_compare(self.version, '<5.9'):
+            raise MesonException(f'Compiler {self} does not support C++ interoperability')
+
+        return ['-cxx-interoperability-mode=default']
 
     def get_library_args(self) -> T.List[str]:
         return ['-parse-as-library']

mesonbuild/interpreter/kwargs.py

@@ -363,6 +363,7 @@ class _BuildTarget(_BaseBuildTarget):
     d_module_versions: T.List[T.Union[str, int]]
     d_unittest: bool
     rust_dependency_map: T.Dict[str, str]
+    swift_interoperability_mode: Literal['c', 'cpp']
     swift_module_name: str
     sources: SourcesVarargsType
     c_args: T.List[str]

mesonbuild/interpreter/type_checking.py

@@ -633,6 +633,7 @@ def _name_suffix_validator(arg: T.Optional[T.Union[str, T.List]]) -> T.Optional[
         default={},
         since='1.2.0',
     ),
+    KwargInfo('swift_interoperability_mode', str, default='c', validator=in_set_validator({'c', 'cpp'}), since='1.9.0'),
     KwargInfo('swift_module_name', str, default='', since='1.9.0'),
     KwargInfo('build_rpath', str, default='', since='0.42.0'),
     KwargInfo(

test cases/swift/11 mixed cpp/meson.build

@@ -8,5 +8,5 @@ if not swiftc.version().version_compare('>= 5.9')
 endif
 
 lib = static_library('mylib', 'mylib.cpp')
-exe = executable('prog', 'main.swift', 'mylib.h', link_with: lib)
+exe = executable('prog', 'main.swift', 'mylib.h', link_with: lib, swift_interoperability_mode: 'cpp')
 test('cpp interface', exe)

test cases/swift/13 mixed objcpp/meson.build

@@ -8,5 +8,5 @@ if not swiftc.version().version_compare('>= 5.9')
 endif
 
 lib = static_library('mylib', 'mylib.mm')
-exe = executable('prog', 'main.swift', 'mylib.h', link_with: lib)
+exe = executable('prog', 'main.swift', 'mylib.h', link_with: lib, swift_interoperability_mode: 'cpp')
 test('objcpp interface', exe)