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, 13 insertions, 5 deletions

diff --git a/mesonbuild/backend/ninjabackend.py b/mesonbuild/backend/ninjabackend.py
index a1d3e50..b6621c9 100644
--- a/mesonbuild/backend/ninjabackend.py
+++ b/mesonbuild/backend/ninjabackend.py
@@ -2785,7 +2785,7 @@ https://gcc.gnu.org/bugzilla/show_bug.cgi?id=47485'''))
                 commands += linker.get_std_shared_lib_link_args()
             # All shared libraries are PIC
             commands += linker.get_pic_args()
-            if not isinstance(target, build.SharedModule):
+            if not isinstance(target, build.SharedModule) or target.backwards_compat_want_soname:
                 # Add -Wl,-soname arguments on Linux, -install_name on OS X
                 commands += linker.get_soname_args(
                     self.environment, target.prefix, target.name, target.suffix,
diff --git a/mesonbuild/build.py b/mesonbuild/build.py
index 6036735..ad18a7f 100644
--- a/mesonbuild/build.py
+++ b/mesonbuild/build.py
@@ -1591,11 +1591,16 @@ You probably should put it in link_with instead.''')
             if isinstance(link_target, SharedModule):
                 if self.environment.machines[self.for_machine].is_darwin():
                     raise MesonException(
-                        'target links against shared modules. This is not permitted on OSX')
+                        f'target {self.name} links against shared module {link_target.name}. This is not permitted on OSX')
                 else:
-                    mlog.warning('target links against shared modules. This '
-                                 'is not recommended as it is not supported on some '
-                                 'platforms')
+                    mlog.deprecation(f'target {self.name} links against shared module {link_target.name}, which is incorrect.'
+                            '\n             '
+                            f'This will be an error in the future, so please use shared_library() for {link_target.name} instead.'
+                            '\n             '
+                            f'If shared_module() was used for {link_target.name} because it has references to undefined symbols,'
+                            '\n             '
+                            'use shared_libary() with `override_options: [\'b_lundef=false\']` instead.')
+                    link_target.backwards_compat_want_soname = True
                 return
 
 class Generator(HoldableObject):
@@ -2259,6 +2264,9 @@ class SharedModule(SharedLibrary):
             raise MesonException('Shared modules must not specify the soversion kwarg.')
         super().__init__(name, subdir, subproject, for_machine, sources, objects, environment, kwargs)
         self.typename = 'shared module'
+        # We need to set the soname in cases where build files link the module
+        # to build targets, see: https://github.com/mesonbuild/meson/issues/9492
+        self.backwards_compat_want_soname = False
 
     def get_default_install_dir(self, environment) -> T.Tuple[str, str]:
         return environment.get_shared_module_dir(), '{moduledir_shared}'