This is Richie Hindle's patch

[ 643835 ] Set Next Statement for Python debuggers

with a few tweaks by me: adding an unsigned or two, mentioning that
not all jumps are allowed in the doc for pdb, adding a NEWS item and
a note to whatsnew, and AuCTeX doing something cosmetic to libpdb.tex.

2 files changed, 315 insertions, 0 deletions

diff --git a/Lib/pdb.py b/Lib/pdb.py
index 94518ae..fffd0ad 100755
--- a/Lib/pdb.py
+++ b/Lib/pdb.py
@@ -506,6 +506,25 @@ class Pdb(bdb.Bdb, cmd.Cmd):
         return 1
     do_c = do_cont = do_continue
 
+    def do_jump(self, arg):
+        if self.curindex + 1 != len(self.stack):
+            print "*** You can only jump within the bottom frame"
+            return
+        try:
+            arg = int(arg)
+        except ValueError:
+            print "*** The 'jump' command requires a line number."
+        else:
+            try:
+                # Do the jump, fix up our copy of the stack, and display the
+                # new position
+                self.curframe.f_lineno = arg
+                self.stack[self.curindex] = self.stack[self.curindex][0], arg
+                self.print_stack_entry(self.stack[self.curindex])
+            except ValueError, e:
+                print '*** Jump failed:', e
+    do_j = do_jump
+
     def do_quit(self, arg):
         self.set_quit()
         return 1
@@ -805,6 +824,13 @@ Continue execution until the current function returns."""
         print """c(ont(inue))
 Continue execution, only stop when a breakpoint is encountered."""
 
+    def help_jump(self):
+        self.help_j()
+
+    def help_j(self):
+        print """j(ump) lineno
+Set the next line that will be executed."""
+
     def help_list(self):
         self.help_l()
 
diff --git a/Lib/test/test_trace.py b/Lib/test/test_trace.py
index faee713..f973a19 100644
--- a/Lib/test/test_trace.py
+++ b/Lib/test/test_trace.py
@@ -221,9 +221,298 @@ class RaisingTraceFuncTestCase(unittest.TestCase):
     def test_exception(self):
         self.run_test_for_event('exception')
 
+
+# 'Jump' tests: assigning to frame.f_lineno within a trace function
+# moves the execution position - it's how debuggers implement a Jump
+# command (aka. "Set next statement").
+
+class JumpTracer:
+    """Defines a trace function that jumps from one place to another,
+    with the source and destination lines of the jump being defined by
+    the 'jump' property of the function under test."""
+
+    def __init__(self, function):
+        self.function = function
+        self.jumpFrom = function.jump[0]
+        self.jumpTo = function.jump[1]
+        self.done = False
+
+    def trace(self, frame, event, arg):
+        if not self.done and frame.f_code == self.function.func_code:
+            firstLine = frame.f_code.co_firstlineno
+            if frame.f_lineno == firstLine + self.jumpFrom:
+                # Cope with non-integer self.jumpTo (because of
+                # no_jump_to_non_integers below).
+                try:
+                    frame.f_lineno = firstLine + self.jumpTo
+                except TypeError:
+                    frame.f_lineno = self.jumpTo
+                self.done = True
+        return self.trace
+
+# The first set of 'jump' tests are for things that are allowed:
+
+def jump_simple_forwards(output):
+    output.append(1)
+    output.append(2)
+    output.append(3)
+
+jump_simple_forwards.jump = (1, 3)
+jump_simple_forwards.output = [3]
+
+def jump_simple_backwards(output):
+    output.append(1)
+    output.append(2)
+
+jump_simple_backwards.jump = (2, 1)
+jump_simple_backwards.output = [1, 1, 2]
+
+def jump_out_of_block_forwards(output):
+    for i in 1, 2:
+        output.append(2)
+        for j in [3]:  # Also tests jumping over a block
+            output.append(4)
+    output.append(5)
+
+jump_out_of_block_forwards.jump = (3, 5)
+jump_out_of_block_forwards.output = [2, 5]
+
+def jump_out_of_block_backwards(output):
+    output.append(1)
+    for i in [1]:
+        output.append(3)
+        for j in [2]:  # Also tests jumping over a block
+            output.append(5)
+        output.append(6)
+    output.append(7)
+
+jump_out_of_block_backwards.jump = (6, 1)
+jump_out_of_block_backwards.output = [1, 3, 5, 1, 3, 5, 6, 7]
+
+def jump_to_codeless_line(output):
+    output.append(1)
+    # Jumping to this line should skip to the next one.
+    output.append(3)
+
+jump_to_codeless_line.jump = (1, 2)
+jump_to_codeless_line.output = [3]
+
+def jump_to_same_line(output):
+    output.append(1)
+    output.append(2)
+    output.append(3)
+
+jump_to_same_line.jump = (2, 2)
+jump_to_same_line.output = [1, 2, 3]
+
+# Tests jumping within a finally block, and over one.
+def jump_in_nested_finally(output):
+    try:
+        output.append(2)
+    finally:
+        output.append(4)
+        try:
+            output.append(6)
+        finally:
+            output.append(8)
+        output.append(9)
+
+jump_in_nested_finally.jump = (4, 9)
+jump_in_nested_finally.output = [2, 9]
+
+# The second set of 'jump' tests are for things that are not allowed:
+
+def no_jump_too_far_forwards(output):
+    try:
+        output.append(2)
+        output.append(3)
+    except ValueError, e:
+        output.append('after' in str(e))
+
+no_jump_too_far_forwards.jump = (3, 6)
+no_jump_too_far_forwards.output = [2, True]
+
+def no_jump_too_far_backwards(output):
+    try:
+        output.append(2)
+        output.append(3)
+    except ValueError, e:
+        output.append('before' in str(e))
+
+no_jump_too_far_backwards.jump = (3, -1)
+no_jump_too_far_backwards.output = [2, True]
+
+# Test each kind of 'except' line.
+def no_jump_to_except_1(output):
+    try:
+        output.append(2)
+    except:
+        e = sys.exc_info()[1]
+        output.append('except' in str(e))
+
+no_jump_to_except_1.jump = (2, 3)
+no_jump_to_except_1.output = [True]
+
+def no_jump_to_except_2(output):
+    try:
+        output.append(2)
+    except ValueError:
+        e = sys.exc_info()[1]
+        output.append('except' in str(e))
+
+no_jump_to_except_2.jump = (2, 3)
+no_jump_to_except_2.output = [True]
+
+def no_jump_to_except_3(output):
+    try:
+        output.append(2)
+    except ValueError, e:
+        output.append('except' in str(e))
+
+no_jump_to_except_3.jump = (2, 3)
+no_jump_to_except_3.output = [True]
+
+def no_jump_to_except_4(output):
+    try:
+        output.append(2)
+    except (ValueError, RuntimeError), e:
+        output.append('except' in str(e))
+
+no_jump_to_except_4.jump = (2, 3)
+no_jump_to_except_4.output = [True]
+
+def no_jump_forwards_into_block(output):
+    try:
+        output.append(2)
+        for i in 1, 2:
+            output.append(4)
+    except ValueError, e:
+        output.append('into' in str(e))
+
+no_jump_forwards_into_block.jump = (2, 4)
+no_jump_forwards_into_block.output = [True]
+
+def no_jump_backwards_into_block(output):
+    try:
+        for i in 1, 2:
+            output.append(3)
+        output.append(4)
+    except ValueError, e:
+        output.append('into' in str(e))
+
+no_jump_backwards_into_block.jump = (4, 3)
+no_jump_backwards_into_block.output = [3, 3, True]
+
+def no_jump_into_finally_block(output):
+    try:
+        try:
+            output.append(3)
+            x = 1
+        finally:
+            output.append(6)
+    except ValueError, e:
+        output.append('finally' in str(e))
+
+no_jump_into_finally_block.jump = (4, 6)
+no_jump_into_finally_block.output = [3, 6, True]  # The 'finally' still runs
+
+def no_jump_out_of_finally_block(output):
+    try:
+        try:
+            output.append(3)
+        finally:
+            output.append(5)
+            output.append(6)
+    except ValueError, e:
+        output.append('finally' in str(e))
+
+no_jump_out_of_finally_block.jump = (5, 1)
+no_jump_out_of_finally_block.output = [3, True]
+
+# This verifies the line-numbers-must-be-integers rule.
+def no_jump_to_non_integers(output):
+    try:
+        output.append(2)
+    except ValueError, e:
+        output.append('integer' in str(e))
+
+no_jump_to_non_integers.jump = (2, "Spam")
+no_jump_to_non_integers.output = [True]
+
+# This verifies that you can't set f_lineno via _getframe or similar
+# trickery.
+def no_jump_without_trace_function():
+    try:
+        previous_frame = sys._getframe().f_back
+        previous_frame.f_lineno = previous_frame.f_lineno
+    except ValueError, e:
+        # This is the exception we wanted; make sure the error message
+        # talks about trace functions.
+        if 'trace' not in str(e):
+            raise
+    else:
+        # Something's wrong - the expected exception wasn't raised.
+        raise RuntimeError, "Trace-function-less jump failed to fail"
+
+
+class JumpTestCase(unittest.TestCase):
+    def compare_jump_output(self, expected, received):
+        if received != expected:
+            self.fail( "Outputs don't match:\n" +
+                       "Expected: " + repr(expected) + "\n" +
+                       "Received: " + repr(received))
+
+    def run_test(self, func):
+        tracer = JumpTracer(func)
+        sys.settrace(tracer.trace)
+        output = []
+        func(output)
+        sys.settrace(None)
+        self.compare_jump_output(func.output, output)
+
+    def test_01_jump_simple_forwards(self):
+        self.run_test(jump_simple_forwards)
+    def test_02_jump_simple_backwards(self):
+        self.run_test(jump_simple_backwards)
+    def test_03_jump_out_of_block_forwards(self):
+        self.run_test(jump_out_of_block_forwards)
+    def test_04_jump_out_of_block_backwards(self):
+        self.run_test(jump_out_of_block_backwards)
+    def test_05_jump_to_codeless_line(self):
+        self.run_test(jump_to_codeless_line)
+    def test_06_jump_to_same_line(self):
+        self.run_test(jump_to_same_line)
+    def test_07_jump_in_nested_finally(self):
+        self.run_test(jump_in_nested_finally)
+    def test_08_no_jump_too_far_forwards(self):
+        self.run_test(no_jump_too_far_forwards)
+    def test_09_no_jump_too_far_backwards(self):
+        self.run_test(no_jump_too_far_backwards)
+    def test_10_no_jump_to_except_1(self):
+        self.run_test(no_jump_to_except_1)
+    def test_11_no_jump_to_except_2(self):
+        self.run_test(no_jump_to_except_2)
+    def test_12_no_jump_to_except_3(self):
+        self.run_test(no_jump_to_except_3)
+    def test_13_no_jump_to_except_4(self):
+        self.run_test(no_jump_to_except_4)
+    def test_14_no_jump_forwards_into_block(self):
+        self.run_test(no_jump_forwards_into_block)
+    def test_15_no_jump_backwards_into_block(self):
+        self.run_test(no_jump_backwards_into_block)
+    def test_16_no_jump_into_finally_block(self):
+        self.run_test(no_jump_into_finally_block)
+    def test_17_no_jump_out_of_finally_block(self):
+        self.run_test(no_jump_out_of_finally_block)
+    def test_18_no_jump_to_non_integers(self):
+        self.run_test(no_jump_to_non_integers)
+    def test_19_no_jump_without_trace_function(self):
+        no_jump_without_trace_function()
+
 def test_main():
     test_support.run_unittest(TraceTestCase)
     test_support.run_unittest(RaisingTraceFuncTestCase)
+    test_support.run_unittest(JumpTestCase)
 
 if __name__ == "__main__":
     test_main()