Add -parse-as-library to Swift library targets

2 files changed, 10 insertions, 0 deletions

diff --git a/mesonbuild/backend/ninjabackend.py b/mesonbuild/backend/ninjabackend.py
index ba75ce737..82411b0e6 100644
--- a/mesonbuild/backend/ninjabackend.py
+++ b/mesonbuild/backend/ninjabackend.py
@@ -2288,6 +2288,13 @@ class NinjaBackend(backends.Backend):
             compile_args += swiftc.get_cxx_interoperability_args(target.compilers)
         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)):
+            # swiftc treats modules with a single source file, and the main.swift file in multi-source file modules
+            # as top-level code. This is undesirable in library targets since it emits a main function. Add the
+            # -parse-as-library option as necessary to prevent emitting the main function while keeping files explicitly
+            # named main.swift treated as the entrypoint of the module in case this is desired.
+            if len(abssrc) == 1 and os.path.basename(abssrc[0]) != 'main.swift':
+                compile_args += swiftc.get_library_args()
         for i in reversed(target.get_include_dirs()):
             basedir = i.get_curdir()
             for d in i.get_incdirs():
diff --git a/mesonbuild/compilers/swift.py b/mesonbuild/compilers/swift.py
index 47d254be5..3fff7a1ff 100644
--- a/mesonbuild/compilers/swift.py
+++ b/mesonbuild/compilers/swift.py
@@ -159,6 +159,9 @@ class SwiftCompiler(Compiler):
         else:
             return ['-cxx-interoperability-mode=off']
 
+    def get_library_args(self) -> T.List[str]:
+        return ['-parse-as-library']
+
     def compute_parameters_with_absolute_paths(self, parameter_list: T.List[str],
                                                build_dir: str) -> T.List[str]:
         for idx, i in enumerate(parameter_list):