dependencies/detect: rewrite get_dep_indentifier around DEPENDENCY_KWS

This gives us one source of truth, as well as ensure that an empty value
and a default value are treated the same.

mesonbuild/dependencies/detect.py

@@ -41,32 +41,34 @@ def __contains__(self, key: object) -> bool:
 def get_dep_identifier(name: str, kwargs: T.Dict[str, T.Any]) -> 'TV_DepID':
     identifier: 'TV_DepID' = (('name', name), )
     from ..interpreter.type_checking import DEPENDENCY_KWS
-    nkwargs = {k.name: k.default for k in DEPENDENCY_KWS}
-    nkwargs.update(kwargs)
 
     assert len(DEPENDENCY_KWS) == 20, \
            'Extra kwargs have been added to dependency(), please review if it makes sense to handle it here'
-    for key, value in nkwargs.items():
-        # 'version' is irrelevant for caching; the caller must check version matches
-        # 'native' is handled above with `for_machine`
-        # 'required' is irrelevant for caching; the caller handles it separately
-        # 'fallback' and 'allow_fallback' is not part of the cache because,
-        #     once a dependency has been found through a fallback, it should
-        #     be used for the rest of the Meson run.
-        # 'default_options' is only used in fallback case
-        # 'not_found_message' has no impact on the dependency lookup
-        # 'include_type' is handled after the dependency lookup
-        if key in {'version', 'native', 'required', 'fallback', 'allow_fallback', 'default_options',
-                   'not_found_message', 'include_type'}:
-            continue
+    # 'version' is irrelevant for caching; the caller must check version matches
+    # 'native' is handled above with `for_machine`
+    # 'required' is irrelevant for caching; the caller handles it separately
+    # 'fallback' and 'allow_fallback' is not part of the cache because,
+    #     once a dependency has been found through a fallback, it should
+    #     be used for the rest of the Meson run.
+    # 'default_options' is only used in fallback case
+    # 'not_found_message' has no impact on the dependency lookup
+    # 'include_type' is handled after the dependency lookup
+    # 'method' does not matter, we really only want one kind of a dependency
+    invalid_keys = {
+        'version', 'native', 'required', 'fallback', 'allow_fallback',
+        'default_options', 'not_found_message', 'include_type'}
+    valid_keys = [n for n in DEPENDENCY_KWS
+                  if n.name not in invalid_keys]
+    for dep in valid_keys:
+        value = kwargs.get(dep.name, dep.default)
         # All keyword arguments are strings, ints, or lists (or lists of lists)
         if isinstance(value, list):
             for i in value:
                 assert isinstance(i, str), i
             value = tuple(frozenset(listify(value)))
         else:
             assert value is None or isinstance(value, (str, bool, int)), value
-        identifier = (*identifier, (key, value),)
+        identifier = (*identifier, (dep.name, value),)
     return identifier
 
 display_name_map = {