'Scale elements': may hang on scaling linked flowed text

[su_v]

Some examples of linked flowed text (linked for example to a frame with 'holes') in legacy files may cause Inkscape to "hang" (with high CPU usage) when the option to 'Scale elements' to 96dpi is chosen on open in Inkscape >= 0.92.

Steps to reproduce:
1) launch inkscape with default prefs
2) open attached SVG file
3) choose 'Scale elements' when prompted

Expected result:
The frame and the properties of the text using SVG lengths are scaled according to the DPI change. The layout of the flowed text is unchanged.

Actual result:
Inkscape appears to hang at processing the linked flowed text, using 100% CPU (one core).

Notes:
'Scale elements' of documents with problematic linked flowed text objects is affected by the preference setting:
'Behavior > Transforms > Store transformation'

The issue reproduces as reported with the default setting:
[x] Optimized

The reported issue does not reproduce after switching the setting to:
[x] Preserved

TODO:
Try to figure out a minimal test case / details which intentionally trigger the reported issue. So far this was encountered as side-effect of efforts to produce a reduced test case for bug #1655005.

Reproduced with Inkscape 0.92.0 r15299 and lp:inkscape/0.92.x r15309 on OS X 10.7.5.

[su_v (suv-lp)]

Backtrace after a (random) interrupt in the debugger while inkscape attempts to scale elements in the provided test case.
(tested with lp:inkscape/0.92.x r15309 on OS X 10.7.5)

[su_v (suv-lp)]

Not reproduced with Inkscape 0.92+devel r15407 (default prefs) on Ubuntu 14.04 with 'Scale test - all'.

<off-topic>The font-size of the linked flowed text is not scaled AFAICT.</off-topic>

[jazzynico (jazzynico)]

Also reproduced on Xubuntu 16.04, lp:inkscape/0.92.x rev. 15315.

[Hachmann (marenhachmann)]

Oh, I think this could be the same as https://bugs.launchpad.net/inkscape/+bug/1715442

[su_v (suv-lp)]

The file from mentioned bug #1715442 opens ok in 0.92.2 if inkscape is launched with the command line option '--no-convert-text-baseline-spacing' to prevent auto-fixing legacy (pre-0.92) files' text baseline spacing on opening ... i.e. not directly related to the issue tracked in this report (bug #1655053) which is triggered by one of the DPI change options the user has to explicitly select on opening.

I might have filed other reports at the time with issues related to the auto-fixing of baseline spaces, but I haven't checked atm.

[Hachmann (marenhachmann)]

Thank you, V!

[su_v (suv-lp)]

su_v wrote:
> I might have filed other reports at the time with issues related to
> the auto-fixing of baseline spaces, but I haven't checked atm.

@Hachmann - probably I had a vague recollection of bug #1655308, but that one is closed now, and the test case from your report (bug #1715442) still reproduces as described with 0.92.2 as well as with latest trunk (git master cdb439b8). Interestingly, in the description of bug #1655308 I had included a reference to this report (bug #1655053) as well.

[su_v (suv-lp)]

Copying my recent comment from bug #1715442:

<quote>
Hachmann wrote:
> Does this also fix the bugs you linked in the description, su_v?

AFAICT it might also fix bug #1655053:
test 1: latest trunk opens the test file "1655053-linked-flowed-text-hang-on-rescale-1.svg" ok, and scales the drawing for DPI change without hang.
test 2: with commit bfc701393 reverted, inkscape hangs when attempting to load the file, unless auto-fixing is disabled. If auto-fixing is disabled, the file opens ok, and then inkscape hangs when attempting to apply the scaling option for the DPI change.
I recommend further tests for bug #1655053.

The other report mentioned is already closed (as noted in the description).
</quote>