#1750076: Debugger did not step on every iteration of a while statement.

The mapping between bytecode offsets and source lines (lnotab) did not contain
an entry for the beginning of the loop.

Now it does, and the lnotab can be a bit larger:
in particular, several statements on the same line generate several entries.
However, this does not bother the settrace function, which will trigger only
one 'line' event.

The lnotab seems to be exactly the same as with python2.4.

diff --git a/Lib/test/test_trace.py b/Lib/test/test_trace.py
index 144fc66dcea79b8dde33ae1c8385514945924ad0..7f7db334ed06370dcd575e29b289c32b75823bb3 100644 (file)
--- a/Lib/test/test_trace.py
+++ b/Lib/test/test_trace.py
@@ -252,14 +252,16 @@ class TraceTestCase(unittest.TestCase):
                 "\n".join(difflib.ndiff([str(x) for x in expected_events],
                                         [str(x) for x in events])))
 
-
-    def run_test(self, func):
+    def run_and_compare(self, func, events):
         tracer = Tracer()
         sys.settrace(tracer.trace)
         func()
         sys.settrace(None)
         self.compare_events(func.func_code.co_firstlineno,
-                            tracer.events, func.events)
+                            tracer.events, events)
+
+    def run_test(self, func):
+        self.run_and_compare(func, func.events)
 
     def run_test2(self, func):
         tracer = Tracer()
@@ -321,6 +323,49 @@ class TraceTestCase(unittest.TestCase):
         self.compare_events(generator_example.__code__.co_firstlineno,
                             tracer.events, generator_example.events)
 
+    def test_14_onliner_if(self):
+        def onliners():
+            if True: False
+            else: True
+            return 0
+        self.run_and_compare(
+            onliners,
+            [(0, 'call'),
+             (1, 'line'),
+             (3, 'line'),
+             (3, 'return')])
+
+    def test_15_loops(self):
+        # issue1750076: "while" expression is skipped by debugger
+        def for_example():
+            for x in range(2):
+                pass
+        self.run_and_compare(
+            for_example,
+            [(0, 'call'),
+             (1, 'line'),
+             (2, 'line'),
+             (1, 'line'),
+             (2, 'line'),
+             (1, 'line'),
+             (1, 'return')])
+
+        def while_example():
+            # While expression should be traced on every loop
+            x = 2
+            while x > 0:
+                x -= 1
+        self.run_and_compare(
+            while_example,
+            [(0, 'call'),
+             (2, 'line'),
+             (3, 'line'),
+             (4, 'line'),
+             (3, 'line'),
+             (4, 'line'),
+             (3, 'line'),
+             (3, 'return')])
+
 class RaisingTraceFuncTestCase(unittest.TestCase):
     def trace(self, frame, event, arg):
         """A trace function that raises an exception in response to a

diff --git a/Misc/NEWS b/Misc/NEWS
index 38dc8edcb2087db3b1cbe872a85208bc0b990d0c..8a4b4492a27db44fa1f6079dea6262ea90e313b7 100644 (file)
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -388,6 +388,10 @@ Core and builtins
 Library
 -------
 
+- #175006: The debugger used to skip the condition of a "while" statement
+  after the first iteration. Now it correctly steps on the expression, and
+  breakpoints on the "while" statement are honored on each loop.
+
 - #1765140: add an optional delay argument to FileHandler and its
   subclasses. Defaults to false (existing behaviour), but if true,
   defers opening the file until the first call to emit().

diff --git a/Python/compile.c b/Python/compile.c
index 0dd1082151e7c6ffc37f22afd19341df19684050..f9b5ac4a523c03b642bc6344b74db2b9f44726af 100644 (file)
--- a/Python/compile.c
+++ b/Python/compile.c
@@ -638,11 +638,16 @@ compiler_next_instr(struct compiler *c, basicblock *b)
        return b->b_iused++;
 }
 
-/* Set the i_lineno member of the instruction at offse off if the
-   line number for the current expression/statement (?) has not
+/* Set the i_lineno member of the instruction at offset off if the
+   line number for the current expression/statement has not
    already been set.  If it has been set, the call has no effect.
 
-   Every time a new node is b
+   The line number is reset in the following cases:
+   - when entering a new scope
+   - on each statement
+   - on each expression that start a new line
+   - before the "except" clause
+   - before the "for" and "while" expressions
 */
 
 static void
@@ -1611,9 +1616,8 @@ compiler_for(struct compiler *c, stmt_ty s)
        VISIT(c, expr, s->v.For.iter);
        ADDOP(c, GET_ITER);
        compiler_use_next_block(c, start);
-       /* XXX(nnorwitz): is there a better way to handle this?
-          for loops are special, we want to be able to trace them
-          each time around, so we need to set an extra line number. */
+       /* for expressions must be traced on each iteration,
+          so we need to set an extra line number. */
        c->u->u_lineno_set = false;
        ADDOP_JREL(c, FOR_ITER, cleanup);
        VISIT(c, expr, s->v.For.target);
@@ -1660,6 +1664,9 @@ compiler_while(struct compiler *c, stmt_ty s)
        if (!compiler_push_fblock(c, LOOP, loop))
                return 0;
        if (constant == -1) {
+               /* while expressions must be traced on each iteration,
+                  so we need to set an extra line number. */
+               c->u->u_lineno_set = false;
                VISIT(c, expr, s->v.While.test);
                ADDOP_JREL(c, JUMP_IF_FALSE, anchor);
                ADDOP(c, POP_TOP);
@@ -1840,8 +1847,8 @@ compiler_try_except(struct compiler *c, stmt_ty s)
                                                s->v.TryExcept.handlers, i);
                if (!handler->type && i < n-1)
                    return compiler_error(c, "default 'except:' must be last");
-       c->u->u_lineno_set = false;
-       c->u->u_lineno = handler->lineno;
+               c->u->u_lineno_set = false;
+               c->u->u_lineno = handler->lineno;
                except = compiler_new_block(c);
                if (except == NULL)
                        return 0;
@@ -3553,12 +3560,6 @@ assemble_lnotab(struct assembler *a, struct instr *i)
        assert(d_bytecode >= 0);
        assert(d_lineno >= 0);
 
-       /* XXX(nnorwitz): is there a better way to handle this?
-          for loops are special, we want to be able to trace them
-          each time around, so we need to set an extra line number. */
-       if (d_lineno == 0 && i->i_opcode != FOR_ITER)
-               return 1;
-
        if (d_bytecode > 255) {
                int j, nbytes, ncodes = d_bytecode / 255;
                nbytes = a->a_lnotab_off + 2 * ncodes;