0000842: Can't debug conditional statements without a block

(0002192)
rulatir (reporter)
2012-05-27 21:59

2) Just to eliminate one possibility: if callThis() returns true then callThat() is not called because the result of the logical OR expression is already known. That's an optimization done by PHP.

(0002193)
dinu (reporter)
2012-05-27 23:57

I know, it's pretty standard in any language :) I'm talking about that if the 2 calls are followed.

(0002208)
dinu (reporter)
2012-05-28 13:00

More details: cannot set a breakpoint on a conditional predicate without a block: try to set a breakpoint on doThis() or doThat() line

if($cond)
doThis();
else
doThat();

(0002226)
derick (administrator)
2012-06-01 23:40
edited on: 2012-06-01 23:41

For the first case, breakpoints are tricky. Sadly PHP itself doesn't generate the correct line numbers internally. See for example the code:

 22 function test2($random)
 23 {
 24     if ($random) 
 25         test2a();
 26     else 
 27         test2b();

Which in PHP turns into:

line     # *  op                           fetch          ext  return  operands
---------------------------------------------------------------------------------
  22     0  >   EXT_NOP
         1      RECV                                             !0
  25     2      EXT_STMT
         3    > JMPZ                                                     !0, ->8
         4  >   EXT_FCALL_BEGIN
         5      DO_FCALL                                      0          'test2a'
         6      EXT_FCALL_END
         7    > JMP                                                      ->11
  27     8  >   EXT_FCALL_BEGIN
         9      DO_FCALL                                      0          'test2b'
        10      EXT_FCALL_END
  28    11  >   EXT_STMT
        12    > RETURN                                                   null

as you can see, there is no line 24 or 26. One of the PHP folks is looking at fixing this, but this is currently not something I can address in Xdebug. Even more annoying, the case for "false" also hits line 25 due to PHP weirdness.

I will now have a look at the second case.

(0002227)
dinu (reporter)
2012-06-02 05:08
edited on: 2012-06-02 10:42

By your example, I should be able to set a breakpoint on 25 or 27. Which I am not; I try to ellaborate a litle on a test case:

1 <?php
2	function ret1(){
3		return 1;
4	}
5	function ret2(){
6		return 2;
7	}
8	function dummy1(){
9		echo 'dummy1';
10	}
11	function dummy2(){
12		echo 'dummy2';
13	}
14	if($x)
15		dummy1();
16	else
17		dummy2();
18	if(ret1()&&ret2())
19		dummy1();
20	else
21		dummy2();

TS1:
- set breakpoints on 15,17,19,21
- expected behavior: stop on 17,19
- actual behavior: breakpoints don't work, BUT debugger inadvertently stops on line 15, BUT on "step into" command goes into dummy2 at 6

TS2:
- set breakpoint on 14
- expected behavior: stop on 14
- actual behavior: doesn't work as per your explanations

TS3:
- Step over all the way to 18
- Step into 18; correctly goes into ret1 on 3
- Step out of ret1
- Expected behavior: execution should step into ret2 on 6 (most debuggers do it this way), or _at_least_ on 19 so I can debug dummy1
- Actual behavior: all if is skipped; seems to step out not of the function call but of the statement
- Consequence: the only way to step into a second conditional function or the predicate function is that I have the patience to step all the way through the first conditional function or add incognito breakpoints on function entries

(0002228)
dinu (reporter)
2012-06-02 05:25

More discussion over TS3 where I think a definite improvement can be made: most debuggers I'm familiar with interpret debugger commands on conditional statements the following way:

- Step over if statement
- Usual: breaks on first instruction of the branch taken
- XDEBUG: breaks on first instruction after if statement

- Step into if statement
- Usual&XDEBUG: step into first function in condition

- Step out of conditional function
- Usual: break into the next conditional function then at the first instruction of branch taken
- XDEBUG: break out of if statement

(0002299)
derick (administrator)
2012-06-27 22:11

Marking as "not fixable":

All cases really have the same cause.
In the first bit of TS1 (stop on 17):

It stops on line 15 because of this is where PHP places the if statement:

  15 8 EXT_STMT
         9 > JMPZ !0, ->1

This is something PHP *should* have put on line 14, but didn't. The step-into
goes correctly into dummy2 in line 12 (and not 6 like you wrote). This is
because that's what is the next executable line after the if-JMPZ has been
done.

The second case in TS1 (not stopping on line 19) is because PHP
doesn't generate an EXT_STMT, which is required for breakpoint insertions.

TS2 is indeed because PHP simply generates no code on line 14:

  11 6 EXT_STMT
         7 NOP
  15 8 EXT_STMT

TS3 is because PHP doesn't generate an EXT_STMT before the dummy1 call,
as it would do if you would have used braces. Hence it doesn't stop and
goes directly to the next breakable line in a scope higher than where
you were (the ret1 function online 3), wich is the EXT_STMT in line 23.

You fix all of this by just using braces.

Issue History
Date Modified	Username	Field	Change
2012-05-25 04:57	dinu	New Issue
2012-05-27 21:59	rulatir	Note Added: 0002192
2012-05-27 23:57	dinu	Note Added: 0002193
2012-05-28 13:00	dinu	Note Added: 0002208
2012-06-01 23:40	derick	Note Added: 0002226
2012-06-01 23:40	derick	Note Edited: 0002226	View Revisions
2012-06-01 23:41	derick	Note Edited: 0002226	View Revisions
2012-06-02 05:08	dinu	Note Added: 0002227
2012-06-02 05:25	dinu	Note Added: 0002228
2012-06-02 10:42	derick	Note Edited: 0002227	View Revisions
2012-06-27 22:11	derick	Note Added: 0002299
2012-06-27 22:11	derick	Status	new => resolved
2012-06-27 22:11	derick	Resolution	open => not fixable
2012-06-27 22:11	derick	Assigned To	=> derick
2012-10-18 22:53	derick	Relationship added	has duplicate 0000895

Notes
(0002192) rulatir (reporter) 2012-05-27 21:59	2) Just to eliminate one possibility: if callThis() returns true then callThat() is not called because the result of the logical OR expression is already known. That's an optimization done by PHP.

(0002193) dinu (reporter) 2012-05-27 23:57	I know, it's pretty standard in any language :) I'm talking about that if the 2 calls are followed.

(0002208) dinu (reporter) 2012-05-28 13:00	More details: cannot set a breakpoint on a conditional predicate without a block: try to set a breakpoint on doThis() or doThat() line if($cond) doThis(); else doThat();

(0002226) derick (administrator) 2012-06-01 23:40 edited on: 2012-06-01 23:41	For the first case, breakpoints are tricky. Sadly PHP itself doesn't generate the correct line numbers internally. See for example the code: 22 function test2($random) 23 { 24 if ($random) 25 test2a(); 26 else 27 test2b(); Which in PHP turns into: line # * op fetch ext return operands --------------------------------------------------------------------------------- 22 0 > EXT_NOP 1 RECV !0 25 2 EXT_STMT 3 > JMPZ !0, ->8 4 > EXT_FCALL_BEGIN 5 DO_FCALL 0 'test2a' 6 EXT_FCALL_END 7 > JMP ->11 27 8 > EXT_FCALL_BEGIN 9 DO_FCALL 0 'test2b' 10 EXT_FCALL_END 28 11 > EXT_STMT 12 > RETURN null as you can see, there is no line 24 or 26. One of the PHP folks is looking at fixing this, but this is currently not something I can address in Xdebug. Even more annoying, the case for "false" also hits line 25 due to PHP weirdness. I will now have a look at the second case.

(0002227) dinu (reporter) 2012-06-02 05:08 edited on: 2012-06-02 10:42	By your example, I should be able to set a breakpoint on 25 or 27. Which I am not; I try to ellaborate a litle on a test case: 1 <?php 2 function ret1(){ 3 return 1; 4 } 5 function ret2(){ 6 return 2; 7 } 8 function dummy1(){ 9 echo 'dummy1'; 10 } 11 function dummy2(){ 12 echo 'dummy2'; 13 } 14 if($x) 15 dummy1(); 16 else 17 dummy2(); 18 if(ret1()&&ret2()) 19 dummy1(); 20 else 21 dummy2(); TS1: - set breakpoints on 15,17,19,21 - expected behavior: stop on 17,19 - actual behavior: breakpoints don't work, BUT debugger inadvertently stops on line 15, BUT on "step into" command goes into dummy2 at 6 TS2: - set breakpoint on 14 - expected behavior: stop on 14 - actual behavior: doesn't work as per your explanations TS3: - Step over all the way to 18 - Step into 18; correctly goes into ret1 on 3 - Step out of ret1 - Expected behavior: execution should step into ret2 on 6 (most debuggers do it this way), or _at_least_ on 19 so I can debug dummy1 - Actual behavior: all if is skipped; seems to step out not of the function call but of the statement - Consequence: the only way to step into a second conditional function or the predicate function is that I have the patience to step all the way through the first conditional function or add incognito breakpoints on function entries

(0002228) dinu (reporter) 2012-06-02 05:25	More discussion over TS3 where I think a definite improvement can be made: most debuggers I'm familiar with interpret debugger commands on conditional statements the following way: - Step over if statement - Usual: breaks on first instruction of the branch taken - XDEBUG: breaks on first instruction after if statement - Step into if statement - Usual&XDEBUG: step into first function in condition - Step out of conditional function - Usual: break into the next conditional function then at the first instruction of branch taken - XDEBUG: break out of if statement

(0002299) derick (administrator) 2012-06-27 22:11	Marking as "not fixable": All cases really have the same cause. In the first bit of TS1 (stop on 17): It stops on line 15 because of this is where PHP places the if statement: 15 8 EXT_STMT 9 > JMPZ !0, ->1 This is something PHP should have put on line 14, but didn't. The step-into goes correctly into dummy2 in line 12 (and not 6 like you wrote). This is because that's what is the next executable line after the if-JMPZ has been done. The second case in TS1 (not stopping on line 19) is because PHP doesn't generate an EXT_STMT, which is required for breakpoint insertions. TS2 is indeed because PHP simply generates no code on line 14: 11 6 EXT_STMT 7 NOP 15 8 EXT_STMT TS3 is because PHP doesn't generate an EXT_STMT before the dummy1 call, as it would do if you would have used braces. Hence it doesn't stop and goes directly to the next breakable line in a scope higher than where you were (the ret1 function online 3), wich is the EXT_STMT in line 23. You fix all of this by just using braces.