A few observations from looking at the attached testcases in Nightly and mozregression: OBSERVATION #1: - [reduced-testcase.html](https://bugzilla.mozilla.org/attachment.cgi?id=9060684) actually **works just fine in current Nightly** (and Nightly from the day that this bug was filed), *if* I turn off WebRender. - However, the original testcase is still broken regardless of whether WebRender is off. - So: reduced-testcase.html seems to have narrowed in on a different WebRender-specific bug. (Or perhaps it's a version of the same issue but it's possible to trigger it with a simpler testcase when WebRender is on.) OBSERVATION #2: Using the original testcase in mozregression, it looks like we actually render the testcase correctly as recently as August 2016, on my linux machine. Nightly 2016-08-25 produces EXPECTED RESULTS (vertical line extends all the way down), whereas Nightly 2016-08-26 produces an extra-severe broken result (completely blank SVG). This seems to have been a regression from https://hg.mozilla.org/mozilla-central/rev/d0910ce4cff8a1994e4d1d975ef7077f57f05668 which was a commit to switch us from Cairo to Skia as our backend on linux. (I confirmed that that was the culprit by trying the "broken" build with the pref reset to use cairo, like so: ``` mozregression --launch 2016-08-26 -a https://bugzilla.mozilla.org/attachment.cgi?id=9058252 --pref "gfx.content.azure.backends:'cairo'" ``` ...and this gave me EXPECTED RESULTS. I'm not sure yet what caused us to go from blank-SVG-area to line-partially-drawn-in-SVG-area, but I'm willing to bet it was another graphics backend change (perhaps a Skia upgrade). So, this leads me to believe this is a bug in our graphics backends (Skia and WebRender, at least), rather than a bug in our SVG-specific code.
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A few observations from looking at the attached testcases in Nightly and mozregression: OBSERVATION #1: - [reduced-testcase.html](https://bugzilla.mozilla.org/attachment.cgi?id=9060684) actually **works just fine in current Nightly** (and Nightly from the day that this bug was filed), *if* I turn off WebRender. - However, the [original testcase](https://bugzilla.mozilla.org/attachment.cgi?id=9058252) is still broken regardless of whether WebRender is off. - So: reduced-testcase.html seems to have narrowed in on a different WebRender-specific bug. (Or perhaps it's a version of the same issue but it's possible to trigger it with a simpler testcase when WebRender is on.) OBSERVATION #2: Using the original testcase in mozregression, it looks like we actually render the testcase correctly as recently as August 2016, on my linux machine. Nightly 2016-08-25 produces EXPECTED RESULTS (vertical line extends all the way down), whereas Nightly 2016-08-26 produces an extra-severe broken result (completely blank SVG). This seems to have been a regression from https://hg.mozilla.org/mozilla-central/rev/d0910ce4cff8a1994e4d1d975ef7077f57f05668 which was a commit to switch us from Cairo to Skia as our backend on linux. (I confirmed that that was the culprit by trying the "broken" build with the pref reset to use cairo, like so: ``` mozregression --launch 2016-08-26 -a https://bugzilla.mozilla.org/attachment.cgi?id=9058252 --pref "gfx.content.azure.backends:'cairo'" ``` ...and this gave me EXPECTED RESULTS. I'm not sure yet what caused us to go from blank-SVG-area to line-partially-drawn-in-SVG-area, but I'm willing to bet it was another graphics backend change (perhaps a Skia upgrade). So, this leads me to believe this is a bug in our graphics backends (Skia and WebRender, at least), rather than a bug in our SVG-specific code.