Don't allow non-equality comparisons across types.

mesonbuild/interpreterbase.py

@@ -221,6 +221,11 @@ class InterpreterBase:
             return val1 == val2
         elif node.ctype == '!=':
             return val1 != val2
+        elif not isinstance(val1, type(val2)):
+            raise InterpreterException(
+                'Values of different types ({}, {}) cannot be compared using {}.'.format(type(val1).__name__,
+                                                                                         type(val2).__name__,
+                                                                                         node.ctype))
         elif not self.is_elementary_type(val1):
             raise InterpreterException('{} can only be compared for equality.'.format(node.left.value))
         elif not self.is_elementary_type(val2):

test cases/failing/52 inconsistent comparison/meson.build

@@ -0,0 +1,7 @@
+project('kwarg before arg', 'c')
+
+# All of these should fail, though only the first one will error out if
+# everything's working correctly.
+assert([] < 'st', 'should fail')
+assert([] < 1, 'should fail')
+assert(2 < 'st', 'should fail')