1607952 - Construction of ComputedGridTrackInfo uses a method and std::move on the same variable

Status: RESOLVED FIXED

(Core :: CSS Parsing and Computation, defect)

Description

[Emily McDonough [:alaskanemily]]

This can be seen at https://searchfox.org/mozilla-central/rev/be7d1f2d52dd9474ca2df145190a817614c924e4/layout/generic/nsGridContainerFrame.cpp#7624

The order of argument evaluation is implementation-defined, so we can't trust whether the .Length() or the std::move() will get executed first.

Comment 1

[Emily McDonough [:alaskanemily]]

Attachment: Bug 1607952 - Avoid using both std::move and a method on the same variable for getting the number of explicit tracks for ComputedGridTrackInfo

The order of argument evaluation is implementation-defined, so we can't trust
whether the .Length() or the std::move() will get executed first.

Comment 2

[Emily McDonough [:alaskanemily]]

I was originally wrong, since the constructor takes this argument by rvalue and so the result will be correct.

This is still a little scary because a change to the types in the constructor's argument list could make this still compile, but then depend on compiler-dependent argument evaluation order to get the correct result.

Comment 3

[Emily McDonough [:alaskanemily]]

Attachment: Bug 1607952 - Avoid using both std::move and a method on the same variable for getting the number of explicit tracks for ComputedGridTrackInfo

The order of argument evaluation is implementation-defined, so we can't trust
whether the .Length() or the std::move() will get executed first. This is OK
right now since the constructor takes the argument by rvalue and so it can't be
emptied out before the .Length() call. However, a change to the types in the
constructor's argument list could make this still compile, but then depend on
compiler-dependent argument evaluation order to get the correct result.

Comment 4

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/92cfc3ecc1f6
Avoid using both std::move and a method on the same variable for getting the number of explicit tracks for ComputedGridTrackInfo r=emilio

Comment 5

[Arthur Iakab [arthur_iakab]]

https://hg.mozilla.org/mozilla-central/rev/92cfc3ecc1f6