darwin: Also add the major version in the dylib

And symlink to the unversioned library for build-time linking.

https://developer.apple.com/library/content/documentation/DeveloperTools/Conceptual/DynamicLibraries/100-Articles/DynamicLibraryDesignGuidelines.html#//apple_ref/doc/uid/TP40002013-SW2

Unlike Autotools, we do not add the minor or micro version in the
filename because the Apple documentation says you must embed that inside
the library with -current_version.

mesonbuild/build.py

@@ -1114,10 +1114,13 @@ class SharedLibrary(BuildTarget):
         elif for_darwin(is_cross, env):
             prefix = 'lib'
             suffix = 'dylib'
-            # libfoo.dylib
-            self.filename_tpl = '{0.prefix}{0.name}.{0.suffix}'
-            # On OS X, the filename should never have the soversion
-            # See: https://github.com/mesonbuild/meson/pull/680
+            # On macOS, the filename can only contain the major version
+            if self.soversion:
+                # libfoo.X.dylib
+                self.filename_tpl = '{0.prefix}{0.name}.{0.soversion}.{0.suffix}'
+            else:
+                # libfoo.dylib
+                self.filename_tpl = '{0.prefix}{0.name}.{0.suffix}'
         else:
             prefix = 'lib'
             suffix = 'so'
@@ -1191,24 +1194,28 @@ class SharedLibrary(BuildTarget):
         If the versioned library name is libfoo.so.0.100.0, aliases are:
         * libfoo.so.0 (soversion) -> libfoo.so.0.100.0
         * libfoo.so (unversioned; for linking) -> libfoo.so.0
+        Same for dylib:
+        * libfoo.dylib (unversioned; for linking) -> libfoo.0.dylib
         """
         aliases = {}
-        # Aliases are only useful with .so libraries. Also if the .so library
-        # ends with .so (no versioning), we don't need aliases.
-        if self.suffix != 'so' or self.filename.endswith('.so'):
+        # Aliases are only useful with .so and .dylib libraries. Also if
+        # there's no self.soversion (no versioning), we don't need aliases.
+        if self.suffix not in ('so', 'dylib') or not self.soversion:
             return {}
-        # If ltversion != soversion we create an soversion alias:
+        # With .so libraries, the minor and micro versions are also in the
+        # filename. If ltversion != soversion we create an soversion alias:
         # libfoo.so.0 -> libfoo.so.0.100.0
-        if self.ltversion and self.ltversion != self.soversion:
-            if not self.soversion:
-                # This is done in self.process_kwargs()
-                raise AssertionError('BUG: If library version is defined, soversion must have been defined')
+        # Where libfoo.so.0.100.0 is the actual library
+        if self.suffix == 'so' and self.ltversion and self.ltversion != self.soversion:
             alias_tpl = self.filename_tpl.replace('ltversion', 'soversion')
             ltversion_filename = alias_tpl.format(self)
             aliases[ltversion_filename] = self.filename
+        # libfoo.so.0/libfoo.0.dylib is the actual library
         else:
             ltversion_filename = self.filename
-        # Unversioned alias: libfoo.so -> libfoo.so.0
+        # Unversioned alias:
+        #  libfoo.so -> libfoo.so.0
+        #  libfoo.dylib -> libfoo.0.dylib
         aliases[self.basic_filename_tpl.format(self)] = ltversion_filename
         return aliases
 

test cases/osx/2 library versions/installed_files.txt

@@ -1,4 +1,7 @@
 usr/lib/libsome.dylib
+usr/lib/libsome.0.dylib
 usr/lib/libnoversion.dylib
 usr/lib/libonlyversion.dylib
+usr/lib/libonlyversion.1.dylib
 usr/lib/libonlysoversion.dylib
+usr/lib/libonlysoversion.5.dylib