code_richcompare() now uses the constants types

Issue #25843: When compiling code, don't merge constants if they are equal but
have a different types. For example, "f1, f2 = lambda: 1, lambda: 1.0" is now
correctly compiled to two different functions: f1() returns 1 (int) and f2()
returns 1.0 (int), even if 1 and 1.0 are equal.

Add a new _PyCode_ConstantKey() private function.

Lib/test/test_compile.py

@@ -572,6 +572,88 @@ if 1:
         exec(memoryview(b"ax = 123")[1:-1], namespace)
         self.assertEqual(namespace['x'], 12)
 
+    def check_constant(self, func, expected):
+        for const in func.__code__.co_consts:
+            if repr(const) == repr(expected):
+                break
+        else:
+            self.fail("unable to find constant %r in %r"
+                      % (expected, func.__code__.co_consts))
+
+    # Merging equal constants is not a strict requirement for the Python
+    # semantics, it's a more an implementation detail.
+    @support.cpython_only
+    def test_merge_constants(self):
+        # Issue #25843: compile() must merge constants which are equal
+        # and have the same type.
+
+        def check_same_constant(const):
+            ns = {}
+            code = "f1, f2 = lambda: %r, lambda: %r" % (const, const)
+            exec(code, ns)
+            f1 = ns['f1']
+            f2 = ns['f2']
+            self.assertIs(f1.__code__, f2.__code__)
+            self.check_constant(f1, const)
+            self.assertEqual(repr(f1()), repr(const))
+
+        check_same_constant(None)
+        check_same_constant(0)
+        check_same_constant(0.0)
+        check_same_constant(b'abc')
+        check_same_constant('abc')
+
+        # Note: "lambda: ..." emits "LOAD_CONST Ellipsis",
+        # whereas "lambda: Ellipsis" emits "LOAD_GLOBAL Ellipsis"
+        f1, f2 = lambda: ..., lambda: ...
+        self.assertIs(f1.__code__, f2.__code__)
+        self.check_constant(f1, Ellipsis)
+        self.assertEqual(repr(f1()), repr(Ellipsis))
+
+        # {0} is converted to a constant frozenset({0}) by the peephole
+        # optimizer
+        f1, f2 = lambda x: x in {0}, lambda x: x in {0}
+        self.assertIs(f1.__code__, f2.__code__)
+        self.check_constant(f1, frozenset({0}))
+        self.assertTrue(f1(0))
+
+    def test_dont_merge_constants(self):
+        # Issue #25843: compile() must not merge constants which are equal
+        # but have a different type.
+
+        def check_different_constants(const1, const2):
+            ns = {}
+            exec("f1, f2 = lambda: %r, lambda: %r" % (const1, const2), ns)
+            f1 = ns['f1']
+            f2 = ns['f2']
+            self.assertIsNot(f1.__code__, f2.__code__)
+            self.check_constant(f1, const1)
+            self.check_constant(f2, const2)
+            self.assertEqual(repr(f1()), repr(const1))
+            self.assertEqual(repr(f2()), repr(const2))
+
+        check_different_constants(0, 0.0)
+        check_different_constants(+0.0, -0.0)
+        check_different_constants((0,), (0.0,))
+
+        # check_different_constants() cannot be used because repr(-0j) is
+        # '(-0-0j)', but when '(-0-0j)' is evaluated to 0j: we loose the sign.
+        f1, f2 = lambda: +0.0j, lambda: -0.0j
+        self.assertIsNot(f1.__code__, f2.__code__)
+        self.check_constant(f1, +0.0j)
+        self.check_constant(f2, -0.0j)
+        self.assertEqual(repr(f1()), repr(+0.0j))
+        self.assertEqual(repr(f2()), repr(-0.0j))
+
+        # {0} is converted to a constant frozenset({0}) by the peephole
+        # optimizer
+        f1, f2 = lambda x: x in {0}, lambda x: x in {0.0}
+        self.assertIsNot(f1.__code__, f2.__code__)
+        self.check_constant(f1, frozenset({0}))
+        self.check_constant(f2, frozenset({0.0}))
+        self.assertTrue(f1(0))
+        self.assertTrue(f2(0.0))
+
 
 class TestStackSize(unittest.TestCase):
     # These tests check that the computed stack size for a code object