bpo-30953: Improve error messages and add tests for jumping (GH-6196)

into/out of an except block.

Lib/test/test_sys_settrace.py

@@ -1201,8 +1201,16 @@ class JumpTestCase(unittest.TestCase):
             output.append(7)
         output.append(8)
 
-    @jump_test(3, 6, [2, 5, 6], (ValueError, 'finally'))
+    @jump_test(1, 5, [], (ValueError, "into a 'finally'"))
     def test_no_jump_into_finally_block(output):
+        output.append(1)
+        try:
+            output.append(3)
+        finally:
+            output.append(5)
+
+    @jump_test(3, 6, [2, 5, 6], (ValueError, "into a 'finally'"))
+    def test_no_jump_into_finally_block_from_try_block(output):
         try:
             output.append(2)
             output.append(3)
@@ -1211,21 +1219,71 @@ class JumpTestCase(unittest.TestCase):
             output.append(6)
         output.append(7)
 
-    @jump_test(1, 5, [], (ValueError, 'finally'))
-    def test_no_jump_into_finally_block_2(output):
+    @jump_test(5, 1, [1, 3], (ValueError, "out of a 'finally'"))
+    def test_no_jump_out_of_finally_block(output):
         output.append(1)
         try:
             output.append(3)
         finally:
             output.append(5)
 
-    @jump_test(5, 1, [1, 3], (ValueError, 'finally'))
-    def test_no_jump_out_of_finally_block(output):
+    @jump_test(1, 5, [], (ValueError, "into an 'except'"))
+    def test_no_jump_into_bare_except_block(output):
         output.append(1)
         try:
             output.append(3)
-        finally:
+        except:
+            output.append(5)
+
+    @jump_test(1, 5, [], (ValueError, "into an 'except'"))
+    def test_no_jump_into_qualified_except_block(output):
+        output.append(1)
+        try:
+            output.append(3)
+        except Exception:
+            output.append(5)
+
+    @jump_test(3, 6, [2, 5, 6], (ValueError, "into an 'except'"))
+    def test_no_jump_into_bare_except_block_from_try_block(output):
+        try:
+            output.append(2)
+            output.append(3)
+        except:  # executed if the jump is failed
             output.append(5)
+            output.append(6)
+            raise
+        output.append(8)
+
+    @jump_test(3, 6, [2], (ValueError, "into an 'except'"))
+    def test_no_jump_into_qualified_except_block_from_try_block(output):
+        try:
+            output.append(2)
+            output.append(3)
+        except ZeroDivisionError:
+            output.append(5)
+            output.append(6)
+            raise
+        output.append(8)
+
+    @jump_test(7, 1, [1, 3, 6], (ValueError, "out of an 'except'"))
+    def test_no_jump_out_of_bare_except_block(output):
+        output.append(1)
+        try:
+            output.append(3)
+            1/0
+        except:
+            output.append(6)
+            output.append(7)
+
+    @jump_test(7, 1, [1, 3, 6], (ValueError, "out of an 'except'"))
+    def test_no_jump_out_of_qualified_except_block(output):
+        output.append(1)
+        try:
+            output.append(3)
+            1/0
+        except Exception:
+            output.append(6)
+            output.append(7)
 
     @jump_test(3, 5, [1, 2, -2], (ValueError, 'into'))
     def test_no_jump_between_with_blocks(output):

Objects/frameobject.c

@@ -277,8 +277,12 @@ frame_setlineno(PyFrameObject *f, PyObject* p_new_lineno)
             int first_in = target_addr <= f->f_lasti && f->f_lasti <= addr;
             int second_in = target_addr <= new_lasti && new_lasti <= addr;
             if (first_in != second_in) {
-                PyErr_SetString(PyExc_ValueError,
-                                "can't jump into or out of a 'finally' block");
+                op = code[target_addr];
+                PyErr_Format(PyExc_ValueError,
+                             "can't jump %s %s block",
+                             second_in ? "into" : "out of",
+                             (op == DUP_TOP || op == POP_TOP) ?
+                                "an 'except'" : "a 'finally'");
                 return -1;
             }
             break;