855850 - Use MOZ_STATIC_ASSERT and fix typo in "need to rearrange the mBits bitfield" compile-time error-check

Status: RESOLVED FIXED

(Core :: Layout, defect)

Description

[Daniel Holbert [:dholbert]]

nsLineBox.h currently has the following code:
149 #if NS_STYLE_CLEAR_LAST_VALUE > 15
150 need to rearrange the mBits bitfield;
151 #endif
https://mxr.mozilla.org/mozilla-central/source/layout/generic/nsLineBox.h#149

which apparently is intended to break the build if NS_STYLE_CLEAR_LAST_VALUE is larger than 15 (larger than what we can represent with 4 bits).

There is, however, no "mBits bitfield" (and never was).  We mean to say "mFlags", which is of type FlagBits (and which contains the 4 bits to store our "clear" value).  And while we're fixing that, we might as well make this a MOZ_STATIC_ASSERT.

Comment 1

[Daniel Holbert [:dholbert]]

(In reply to Daniel Holbert [:dholbert] from comment #0)
> There is, however, no "mBits bitfield" (and never was).

(for reference: the CVS commit that added this line was:
 http://bonsai.mozilla.org/cvsview2.cgi?diff_mode=context&whitespace_mode=show&root=/cvsroot&subdir=mozilla/layout/generic&command=DIFF_FRAMESET&file=nsLineBox.h&rev2=1.20&rev1=1.19
and even at that point, the bitfield in question was FlagBits mFlags -- there was no no mBits.)

Comment 2

[Daniel Holbert [:dholbert]]

Attachment: fix

This moves the check to be a static assert in the nsLineBox constructor. (This is a sensible location for the assertion, since we're asserting about a member-var of nsLineBox)

Comment 3

[Mats Palmgren (:mats)]

Comment on attachment 730901 [details] [diff] [review]
fix

r=mats

Comment 4

[Daniel Holbert [:dholbert]]

https://hg.mozilla.org/integration/mozilla-inbound/rev/ccf927340e8e

Comment 5

[Ryan VanderMeulen [:RyanVM]]

https://hg.mozilla.org/mozilla-central/rev/ccf927340e8e