options: use an OptionKey for `get_default_for_b_option`

We have the OptionKey in the one caller that exists already, and this
allows us to do a hash lookup instead of a linear walk.

2 files changed, 7 insertions, 7 deletions

diff --git a/mesonbuild/interpreter/interpreter.py b/mesonbuild/interpreter/interpreter.py
index b0bda8556..c8c05f0bd 100644
--- a/mesonbuild/interpreter/interpreter.py
+++ b/mesonbuild/interpreter/interpreter.py
@@ -1087,7 +1087,7 @@ class Interpreter(InterpreterBase, HoldableObject):
             if self.coredata.optstore.is_base_option(optkey):
                 # Due to backwards compatibility return the default
                 # option for base options instead of erroring out.
-                return self.coredata.optstore.get_default_for_b_option(optname)
+                return self.coredata.optstore.get_default_for_b_option(optkey)
             else:
                 if self.subproject:
                     raise MesonException(f'Option {optname} does not exist for subproject {self.subproject}.')
diff --git a/mesonbuild/options.py b/mesonbuild/options.py
index 25e2a9f43..ab4fcbe0c 100644
--- a/mesonbuild/options.py
+++ b/mesonbuild/options.py
@@ -1140,13 +1140,13 @@ class OptionStore:
         (value_object, value) = self.get_value_object_and_value_for(key)
         return (value_object, value)
 
-    def get_default_for_b_option(self, keyname: str) -> ElementaryOptionValues:
-        assert keyname.startswith('b_')
+    def get_default_for_b_option(self, key: OptionKey) -> ElementaryOptionValues:
+        assert self.is_base_option(key)
         from .compilers.compilers import BASE_OPTIONS
-        for bkey, bvalue in BASE_OPTIONS.items():
-            if bkey.name == keyname:
-                return T.cast('ElementaryOptionValues', bvalue.default)
-        raise MesonBugException(f'Requested base option {keyname} which does not exist.')
+        try:
+            return T.cast('ElementaryOptionValues', BASE_OPTIONS[key.evolve(subproject=None)].default)
+        except KeyError:
+            raise MesonBugException(f'Requested base option {key} which does not exist.')
 
     def remove(self, key: OptionKey) -> None:
         del self.options[key]