Linked flowed text: inkscape hangs when setting outer line-height to zero

[su_v]

The new feature in Inkscape >= 0.92 to adjust the font-size and line-height of the outer text style may fail with linked flowed text when attempting to set outer line-height to '0' to not override the inner line-heights relative to the inner font-size: inkscape appears to hang while processing the new layout (with high CPU usage).

Steps to reproduce:
1) launch inkscape (default prefs)
2) open attached test case
3) switch to the text tool, select the flowed text
4) activate outer text style
5) set line-height to '0', press <Return>

Expected result:
The outer line-height is reset, and the baseline spacing will be adjusted to 125% of the font-size used as inner style (on <flowDiv/>).

Actual result:
Inkscape ponders the change ...

Notes:
The reduced test case is based on 'share/examples/flow-go.svg', and was encountered when attempting to "fix" the baseline spacing of this legacy text file to match the text layout as rendered with older Inkscape versions.

The same issue reproduces when attempting to "fix" the baseline spacing with the extension discussed in bug #1652340: in this case Inkscape hangs when reloading the modified SVG content returned by the script.

The underlying issue is possibly related to / also exposed in bug #1655053.

Reproduced with Inkscape 0.92.0 r15299 and lp:inkscape/0.92.x r15315 on OS X 10.7.5.

[su_v (suv-lp)]

Reproduced (not fixed) with Inkscape 0.92+devel r15407 (default prefs) on Ubuntu 14.04 with 'Scale test - all'.

[jazzynico (jazzynico)]

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

[Tavmjong Bah (tavmjong-free)]

Should be fixed in trunk (r15460).

If text does not fit on a line, the text algorithm tries again at a position line-height farther down. But if the line-height is zero this leads to an infinite loop. Now Inkscape will give up if this situation is detected.

[jazzynico (jazzynico)]

Fix confirmed on Xubuntu 16.04, lp:inkscape rev. 15467.

[jazzynico (jazzynico)]

Proposing to backport to 0.92.2.

[jazzynico (jazzynico)]

Patch for 0.92.x attached.

[jazzynico (jazzynico)]

Fixed in lp:inkscape/0.92.x rev. 15386.

[jazzynico (jazzynico)]

Correction, fixed rev. 15387.