vala: Use 'vala_header' and 'vala_vapi' directly

Move the fallback logic into 'BuildTarget.process_kwargs' to use the
target name instead.

mesonbuild/backend/ninjabackend.py

@@ -992,15 +992,14 @@ int dummy;
             # Library name
             args += ['--library=' + target.name]
             # Outputted header
-            hname = os.path.join(self.get_target_dir(target), target.vala_header if isinstance(target.vala_header, str) else (target.name + '.h'))
+            hname = os.path.join(self.get_target_dir(target), target.vala_header)
             args += ['-H', hname]
             valac_outputs.append(hname)
             # Outputted vapi file
-            base_vapi = target.vala_vapi if isinstance(target.vala_vapi, str) else (target.name + '.vapi')
-            vapiname = os.path.join(self.get_target_dir(target), base_vapi)
+            vapiname = os.path.join(self.get_target_dir(target), target.vala_vapi)
             # Force valac to write the vapi file in the target build dir.
             # Without this, it will write it inside c_out_dir
-            args += ['--vapi=../' + base_vapi]
+            args += ['--vapi=../' + target.vala_vapi]
             valac_outputs.append(vapiname)
         if self.environment.coredata.get_builtin_option('werror'):
             args += valac.get_werror_args()

mesonbuild/build.py

@@ -452,8 +452,8 @@ class BuildTarget():
             valalist = [valalist]
         self.add_compiler_args('vala', valalist)
         if not isinstance(self, Executable):
-            self.vala_header = kwargs.get('vala_header', None)
-            self.vala_vapi = kwargs.get('vala_vapi', None)
+            self.vala_header = kwargs.get('vala_header', self.name + '.h')
+            self.vala_vapi = kwargs.get('vala_vapi', self.name + '.vapi')
         dlist = stringlistify(kwargs.get('d_args', []))
         self.add_compiler_args('d', dlist)
         self.link_args = kwargs.get('link_args', [])