interpreterbase: Add a helper method for typing positional arguments

We don't do a very good job of type checking in the interpreter,
sometimes we leave it to the mid layers of backends to do that (layering
violations) and sometimes we just don't check them at all. When we do
check them it's a ton of boilerplate and complicates the code. This
should help quite a bit.

1 files changed, 34 insertions, 0 deletions

diff --git a/run_unittests.py b/run_unittests.py
index 9cc36fb..06386c8 100755
--- a/run_unittests.py
+++ b/run_unittests.py
@@ -51,6 +51,7 @@ import mesonbuild.mesonlib
 import mesonbuild.coredata
 import mesonbuild.modules.gnome
 from mesonbuild.interpreter import Interpreter, ObjectHolder
+from mesonbuild.interpreterbase import typed_pos_args, InvalidArguments
 from mesonbuild.ast import AstInterpreter
 from mesonbuild.mesonlib import (
     BuildDirLock, LibType, MachineChoice, PerMachine, Version, is_windows,
@@ -1293,6 +1294,39 @@ class InternalTests(unittest.TestCase):
 
         self.assertFalse(errors)
 
+    def test_typed_pos_args_types(self) -> None:
+        @typed_pos_args('foo', str, int, bool)
+        def _(obj, node, args: T.Tuple[str, int, bool], kwargs) -> None:
+            self.assertIsInstance(args, tuple)
+            self.assertIsInstance(args[0], str)
+            self.assertIsInstance(args[1], int)
+            self.assertIsInstance(args[2], bool)
+
+        _(None, mock.Mock(), ['string', 1, False], None)
+
+    def test_typed_pos_args_types_invalid(self) -> None:
+        @typed_pos_args('foo', str, int, bool)
+        def _(obj, node, args: T.Tuple[str, int, bool], kwargs) -> None:
+            self.assertTrue(False)  # should not be reachable
+
+        with self.assertRaises(InvalidArguments) as cm:
+            _(None, mock.Mock(), ['string', 1.0, False], None)
+        self.assertEqual(str(cm.exception), 'foo argument 2 was of type "float" but should have been "int"')
+
+    def test_typed_pos_args_types_wrong_number(self) -> None:
+        @typed_pos_args('foo', str, int, bool)
+        def _(obj, node, args: T.Tuple[str, int, bool], kwargs) -> None:
+            self.assertTrue(False)  # should not be reachable
+
+        with self.assertRaises(InvalidArguments) as cm:
+            _(None, mock.Mock(), ['string', 1], None)
+        self.assertEqual(str(cm.exception), 'foo takes exactly 3 arguments, but got 2.')
+
+        with self.assertRaises(InvalidArguments) as cm:
+            _(None, mock.Mock(), ['string', 1, True, True], None)
+        self.assertEqual(str(cm.exception), 'foo takes exactly 3 arguments, but got 4.')
+
+
 @unittest.skipIf(is_tarball(), 'Skipping because this is a tarball release')
 class DataTests(unittest.TestCase):