Overhaul versioning and naming of libraries

This commit contains several changes to the naming and versioning of
shared and static libraries. The details are documented at:
https://github.com/mesonbuild/meson/pull/417

Here's a brief summary:

* The results of binary and compiler detection via environment functions
  are now cached so that they can be called repeatedly without
  performance penalty. This is necessary because every
  build.SharedLibrary object has to know whether the compiler is MSVC or
  not (output filenames depend on that), and so the compiler detection
  has to be called for each object instantiation.

* Linux shared libraries don't always have a library version. Sometimes
  only soversions are specified (and vice-versa), so support both.

* Don't use versioned filenames when generating DLLs, DLLs are never
  versioned using the suffix in the way that .so libraries are. Hence,
  they don't use "aliases". Only Linux shared libraries use those.

* OS X dylibs do not use filename aliases at all. They only use the
  soversion in the dylib name (libfoo.X.dylib), and that's it. If
  there's no soversion specified, the dylib is called libfoo.dylib.
  Further versioning in dylibs is supposed to be done with the
  -current_version argument to clang, but this is TBD.

  https://developer.apple.com/library/mac/documentation/DeveloperTools/Conceptual/DynamicLibraries/100-Articles/DynamicLibraryDesignGuidelines.html#//apple_ref/doc/uid/TP40002013-SW23

* Install DLLs into bindir and import libraries into libdir

* Static libraries are now always called libfoo.a, even with MSVC

* .lib import libraries are always generated when building with MSVC

* .dll.a import libraries are always generated when building with
  MinGW/GCC or MinGW/clang

* TODO: Use dlltool if available to generate .dll.a when .lib is
  generated and vice-versa.

* Library and executable suffix/prefixes are now always correctly
  overriden by the values of the 'name_prefix' and 'name_suffix' keyword
  arguments.

1 files changed, 7 insertions, 3 deletions

diff --git a/mesonbuild/backend/backends.py b/mesonbuild/backend/backends.py
index bc49966..37503ba 100644
--- a/mesonbuild/backend/backends.py
+++ b/mesonbuild/backend/backends.py
@@ -105,9 +105,13 @@ class Backend():
         # On some platforms (msvc for instance), the file that is used for
         # dynamic linking is not the same as the dynamic library itself. This
         # file is called an import library, and we want to link against that.
-        # On platforms where this distinction is not important, the import
-        # library is the same as the dynamic library itself.
-        return os.path.join(self.get_target_dir(target), target.get_import_filename())
+        # On all other platforms, we link to the library directly.
+        if isinstance(target, build.SharedLibrary):
+            link_lib = target.get_import_filename() or target.get_filename()
+            return os.path.join(self.get_target_dir(target), link_lib)
+        elif isinstance(target, build.StaticLibrary):
+            return os.path.join(self.get_target_dir(target), target.get_filename())
+        raise AssertionError('BUG: Tried to link to something that\'s not a library')
 
     def get_target_dir(self, target):
         if self.environment.coredata.get_builtin_option('layout') == 'mirror':