shared_module: Add soname when used as a link target

Emit a detailed deprecation warning that explains what to do instead.
Also add a unittest.

```
DEPRECATION: target prog links against shared module mymod, which is incorrect.
             This will be an error in the future, so please use shared_library() for mymod instead.
             If shared_module() was used for mymod because it has references to undefined symbols,
             use shared_libary() with `override_options: ['b_lundef=false']` instead.
```

Fixes https://github.com/mesonbuild/meson/issues/9492

2 files changed, 22 insertions, 2 deletions

diff --git a/unittests/allplatformstests.py b/unittests/allplatformstests.py
index 03992bd..30c0572 100644
--- a/unittests/allplatformstests.py
+++ b/unittests/allplatformstests.py
@@ -1946,8 +1946,10 @@ class AllPlatformTests(BasePlatformTests):
         """
         tdir = os.path.join(self.unit_test_dir, '30 shared_mod linking')
         out = self.init(tdir)
-        msg = ('WARNING: target links against shared modules. This is not '
-               'recommended as it is not supported on some platforms')
+        msg = ('''DEPRECATION: target prog links against shared module mymod, which is incorrect.
+             This will be an error in the future, so please use shared_library() for mymod instead.
+             If shared_module() was used for mymod because it has references to undefined symbols,
+             use shared_libary() with `override_options: ['b_lundef=false']` instead.''')
         self.assertIn(msg, out)
 
     def test_mixed_language_linker_check(self):
diff --git a/unittests/linuxliketests.py b/unittests/linuxliketests.py
index 0f99f01..8ff0f8e 100644
--- a/unittests/linuxliketests.py
+++ b/unittests/linuxliketests.py
@@ -438,6 +438,24 @@ class LinuxlikeTests(BasePlatformTests):
         self.assertEqual(get_soname(bothset), 'libbothset.so.1.2.3')
         self.assertEqual(len(self.glob_sofiles_without_privdir(bothset[:-3] + '*')), 3)
 
+        # A shared_module that is not linked to anything
+        module = os.path.join(libpath, 'libsome_module.so')
+        self.assertPathExists(module)
+        self.assertFalse(os.path.islink(module))
+        self.assertEqual(get_soname(module), None)
+
+        # A shared_module that is not linked to an executable with link_with:
+        module = os.path.join(libpath, 'liblinked_module1.so')
+        self.assertPathExists(module)
+        self.assertFalse(os.path.islink(module))
+        self.assertEqual(get_soname(module), 'liblinked_module1.so')
+
+        # A shared_module that is not linked to an executable with dependencies:
+        module = os.path.join(libpath, 'liblinked_module2.so')
+        self.assertPathExists(module)
+        self.assertFalse(os.path.islink(module))
+        self.assertEqual(get_soname(module), 'liblinked_module2.so')
+
     def test_soname(self):
         self._test_soname_impl(self.builddir, False)