1362403 - step in for...in loop jumps out of loop instead of next iteration

Status: VERIFIED FIXED

(DevTools :: Debugger, defect)

Description

[Daniel Lehmann]

Attachment: Example of bug

User Agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:53.0) Gecko/20100101 Firefox/53.0
Build ID: 20170418123106

Steps to reproduce:

1. Open attached example.html in Firefox 53.0 or Firefox Developer Edition 54.0a2 (both affected).
2. Open Developer Tools, go to Debugger.
3. Set breakpoints in lines 10, 15, and 20.
4. Reload to hit first breakpoint.
5. Click "Step In" once


Actual results:

- Debugger pauses at line 14 (after for...in loop!)
- Console shows output of three iterations ("for ... in 1", "for ... in 2", and "for ... in 3")


Expected results:

- Debugger should pause at line 10 again for next iteration
- Console should show output only of first iteration after one step ("for ... in 1")

Comment 1

[Daniel Lehmann]

Attachment: Video capture of bug in Firefox Developer Edition 54.0a2

Comment 2

[Daniel Lehmann]

Note that the stepIn behavior in for...in loop is inconsistent with:

1. Breakpoints in for...in loop: A breakpoint on line 15 is hit 3 times when resuming execution, once per loop iteration. This is expected and correct.
2. Stepping and Breakpoints in for...of loop: stepIn on line 20 correctly executes only one iteration. We need to step multiple times to execute all iterations.

This can also be seen in the video capture (see attachment 2 [details] [diff] [review]).

Comment 3

[Jason Laster [:jlast]]

Thanks for the helpful videos. This helps explain the issue really well.

Comment 4

[Tom Tromey :tromey]

For me there is no difference between the first and second loops; only the third one works.

Comment 5

[Tom Tromey :tromey]

The problem with the for-in is that the loopentry is not marked as being in the "for" line.

The loop looks like:

00017:  goto 58 (+41)                   # ITER undefined

# from ifeq @ 00063
00022:  loophead                        # ITER MOREITER
00023:  setlocal 1                      # ITER MOREITER
00027:  getgname "console"              # ITER MOREITER console
00032:  dup                             # ITER MOREITER console console
00033:  callprop "log"                  # ITER MOREITER console console.log
00038:  swap                            # ITER MOREITER console.log console
00039:  string "for ... in "            # ITER MOREITER console.log console "for ... in "
00044:  getlocal 0                      # ITER MOREITER console.log console "for ... in " array
00048:  getlocal 1                      # ITER MOREITER console.log console "for ... in " array prop1
00052:  getelem                         # ITER MOREITER console.log console "for ... in " array[prop1]
00053:  add                             # ITER MOREITER console.log console ("for ... in " + array[prop1])
00054:  call-ignores-rv 1               # ITER MOREITER console.log(...)
00057:  pop                             # ITER MOREITER

# from goto @ 00017
00058:  loopentry 129                   # ITER undefined


And the line table says:

 ofs line    pc  delta desc     args
[...]
  6:    4    17 [   7] for-in   closingjump 46
  8:    4    23 [   6] colspan 7
 10:    4    27 [   4] newline 
 11:    5    27 [   0] colspan 4
 13:    5    71 [  44] xdelta  

That is, PC=58 is still marked as line 5 (which in my copy of the test is the console.log).

Comment 6

[Tom Tromey :tromey]

Testing a patch.

Comment 7

[Tom Tromey :tromey]

Attachment: Bug 1362403 - update source coordinates after emitting loop bodies;

Review commit: https://reviewboard.mozilla.org/r/136594/diff/#index_header
See other reviews: https://reviewboard.mozilla.org/r/136594/

Comment 8

[Jim Blandy :jimb]

Comment on attachment 8864948 [details]
Bug 1362403 - update source coordinates after emitting loop bodies;

https://reviewboard.mozilla.org/r/136594/#review139700

Gorgeous! And a great test.

Comment 9

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/3e44cbaec84b
update source coordinates after emitting loop bodies; r=jimb

Comment 10

[Iris Hsiao [:ihsiao]]

https://hg.mozilla.org/mozilla-central/rev/3e44cbaec84b

Comment 11

[Md. Rahimul Islam]

I have successfully reproduced the bug in firefox Nightly 55.0a1 (2017-05-05) (32-bit) with windows 10 (32 bit) 

Verified as fixed with latest nightly 55.0a1 (2017-05-17) (32-bit)

Build ID:   20170517030204
Mozilla/5.0 (Windows NT 10.0; rv:55.0) Gecko/20100101 Firefox/55.0

Comment 12

[Mohammad Maruf Rahman]

I have reproduced this bug with Nightly 55.0a1 (2017-04-18) (64-bit) in Ubuntu 16.04!

This bug's fix is now verified with latest Nightly!

Build ID   : 20170518100156
User Agent : Mozilla/5.0 (X11; Linux x86_64; rv:55.0) Gecko/20100101 Firefox/55.0

Comment 13

[Mohammad Maruf Rahman]

 As per Comment 11 & Comment 12, I am marking this bug as verified fixed.