bpo-42609: Check recursion depth in the AST validator and optimizer

Include/compile.h

@@ -87,6 +87,9 @@ PyAPI_FUNC(int) PyCompile_OpcodeStackEffectWithJump(int opcode, int oparg, int j
 typedef struct {
     int optimize;
     int ff_features;
+
+    int recursion_depth;            /* current recursion depth */
+    int recursion_limit;            /* recursion limit */
 } _PyASTOptimizeState;
 
 PyAPI_FUNC(int) _PyAST_Optimize(struct _mod *, PyArena *arena, _PyASTOptimizeState *state);

Lib/test/test_compile.py

@@ -543,21 +543,24 @@ def test_compiler_recursion_limit(self):
         # XXX (ncoghlan): duplicating the scaling factor here is a little
         # ugly. Perhaps it should be exposed somewhere...
         fail_depth = sys.getrecursionlimit() * 3
+        crash_depth = sys.getrecursionlimit() * 300
         success_depth = int(fail_depth * 0.75)
 
-        def check_limit(prefix, repeated):
+        def check_limit(prefix, repeated, mode="single"):
             expect_ok = prefix + repeated * success_depth
-            self.compile_single(expect_ok)
-            broken = prefix + repeated * fail_depth
-            details = "Compiling ({!r} + {!r} * {})".format(
-                         prefix, repeated, fail_depth)
-            with self.assertRaises(RecursionError, msg=details):
-                self.compile_single(broken)
+            compile(expect_ok, '<test>', mode)
+            for depth in (fail_depth, crash_depth):
+                broken = prefix + repeated * depth
+                details = "Compiling ({!r} + {!r} * {})".format(
+                            prefix, repeated, depth)
+                with self.assertRaises(RecursionError, msg=details):
+                    compile(broken, '<test>', mode)
 
         check_limit("a", "()")
         check_limit("a", ".b")
         check_limit("a", "[0]")
         check_limit("a", "*a")
+        #check_limit("if a: pass", "\nelif a: pass", mode="exec")
 
     def test_null_terminated(self):
         # The source code is null-terminated internally, but bytes-like

Misc/NEWS.d/next/Core and Builtins/2020-12-12-14-28-31.bpo-42609.Qcd54b.rst

@@ -0,0 +1,3 @@
+Prevented crashes in the AST validator and optimizer when compile some
+absurdly long expressions like ``"+0"*1000000``. :exc:`RecursionError` is
+now raised instead.