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Never force legacy layout on NG objects. #27792

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merged 1 commit into from Feb 26, 2021

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@chromium-wpt-export-bot chromium-wpt-export-bot commented Feb 26, 2021

Remove dangerous legacy fallback code from LayoutObject(), and do this
safely in the child insertion code instead.

Calling a virtual method in a base class constructor doesn't work.
IsLayoutNGObject() would always return false, since that's how it's
implemented in LayoutObject. This code could cause us to mark an NG
object as requiring legacy fallback, which would make the NG engine
delegate the job to the legacy engine. But the legacy engine would
refuse to do anything, since it's an NG object, so it would delegate to
NG, and so on... Infinite recursion.

The !IsLayoutNGObject() check in LayoutObject() was a mistake added in
CL:2414289, which basically had no effect at all. But we can just remove
the entire thing now, and rely on the new hook in the child insertion
code instead.

Note that the new test doesn't fail without this fix when run normally
by the test runner, because the test needs LayoutNGTextControl to be
disabled in order to fail (so that we attempt legacy fallback), but this
feature is currently set to "test". Unlike the fuzzer, it seems...

Bug: 1181687
Change-Id: I2f174824e4b86d9ae2e5b3b319df7f6036b4f13d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2720104
Reviewed-by: Ian Kilpatrick <ikilpatrick@chromium.org>
Commit-Queue: Morten Stenshorne <mstensho@chromium.org>
Cr-Commit-Position: refs/heads/master@{#858052}

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The review process for this patch is being conducted in the Chromium project.

Remove dangerous legacy fallback code from LayoutObject(), and do this
safely in the child insertion code instead.

Calling a virtual method in a base class constructor doesn't work.
IsLayoutNGObject() would always return false, since that's how it's
implemented in LayoutObject. This code could cause us to mark an NG
object as requiring legacy fallback, which would make the NG engine
delegate the job to the legacy engine. But the legacy engine would
refuse to do anything, since it's an NG object, so it would delegate to
NG, and so on... Infinite recursion.

The !IsLayoutNGObject() check in LayoutObject() was a mistake added in
CL:2414289, which basically had no effect at all. But we can just remove
the entire thing now, and rely on the new hook in the child insertion
code instead.

Note that the new test doesn't fail without this fix when run normally
by the test runner, because the test needs LayoutNGTextControl to be
disabled in order to fail (so that we attempt legacy fallback), but this
feature is currently set to "test". Unlike the fuzzer, it seems...

Bug: 1181687
Change-Id: I2f174824e4b86d9ae2e5b3b319df7f6036b4f13d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2720104
Reviewed-by: Ian Kilpatrick <ikilpatrick@chromium.org>
Commit-Queue: Morten Stenshorne <mstensho@chromium.org>
Cr-Commit-Position: refs/heads/master@{#858052}
@chromium-wpt-export-bot chromium-wpt-export-bot force-pushed the chromium-export-cl-2720104 branch from 0132407 to 9f1dec8 Feb 26, 2021
@chromium-wpt-export-bot chromium-wpt-export-bot merged commit b71ded0 into master Feb 26, 2021
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@chromium-wpt-export-bot chromium-wpt-export-bot deleted the chromium-export-cl-2720104 branch Feb 26, 2021
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