Add --module-name argument to cython command

It can be useful to specify the module name for the output file
directly, rather than working it out from the enclosing file tree -
particularly for out of tree build systems, like Meson.

See: rgommers/scipy#31 (comment)
for background.

Cython/Compiler/CmdLine.py

@@ -145,6 +145,11 @@ def create_cython_argparser():
                       dest='compile_time_env', type=str,
                       action=ParseCompileTimeEnvAction,
                       help='Provides compile time env like DEF would do.')
+    parser.add_argument("--module-name",
+                      dest='module_name', type=str, action='store',
+                      help='Fully qualified module name. If not given, is '
+                           'deduced from the import path if source file is in '
+                           'a package, or equals the filename otherwise.')
     parser.add_argument('sources', nargs='*', default=[])
 
     # TODO: add help
@@ -222,5 +227,9 @@ def parse_command_line(args):
     if len(sources) == 0 and not options.show_version:
         parser.error("cython: Need at least one source file\n")
     if Options.embed and len(sources) > 1:
-        parser.error("cython: Only one source file allowed when using -embed\n")
+        parser.error(
+            "cython: Only one source file allowed when using --embed\n")
+    if options.module_name and len(sources) > 1:
+        parser.error(
+            "cython: Only one source file allowed when using --module-name\n")
     return options, sources

Cython/Compiler/Main.py

@@ -585,6 +585,9 @@ def compile_multiple(sources, options):
     a CompilationResultSet. Performs timestamp checking and/or recursion
     if these are specified in the options.
     """
+    if len(sources) > 1 and options.full_module_name:
+        raise RuntimeError('Full module name can only be set '
+                           'for single source compilation')
     # run_pipeline creates the context
     # context = Context.from_options(options)
     sources = [os.path.abspath(source) for source in sources]
@@ -603,8 +606,9 @@ def compile_multiple(sources, options):
             if (not timestamps) or out_of_date:
                 if verbose:
                     sys.stderr.write("Compiling %s\n" % source)
-
-                result = run_pipeline(source, options, context=context)
+                result = run_pipeline(source, options,
+                                      full_module_name=options.module_name,
+                                      context=context)
                 results.add(source, result)
                 # Compiling multiple sources in one context doesn't quite
                 # work properly yet.

Cython/Compiler/Options.py

@@ -735,6 +735,7 @@ def to_fingerprint(item):
     formal_grammar=False,
     gdb_debug=False,
     compile_time_env=None,
+    module_name=None,
     common_utility_include_dir=None,
     output_dir=None,
     build_dir=None,