537870 - VC7.1 confused by initialized declaration in for-statement conditional

Status: RESOLVED FIXED

(Core :: Widget, defect)

Description

[Karl Tomlinson (:karlt)]

Bug 518506 comment 43 pointed out that an initialized declaration in the
conditional of a for statement, added in that bug, confused VC7.1.
http://hg.mozilla.org/mozilla-central/annotate/5a63989cada8/widget/src/xpwidgets/nsBaseWidget.cpp#l1005

AFAIK this is valid ISO C++, since at least 1998, but
https://developer.mozilla.org/En/Developer_Guide/Build_Instructions/Windows_Prerequisites
says that mozilla-central and mozilla-1.9.2 (should) build with VC7.1.

(We don't support jemalloc with VC7.1, but that and VC8 may be the reason why
jemalloc is off by default with msvc.
http://hg.mozilla.org/mozilla-central/annotate/5a63989cada8//configure.in#l6713
)

Neil, do you know whether this is the only problem when compiling with VC7.1?
I'm assuming this caused a compiler error.
Do you know whether there is a good way to un-confuse VC7.1?
I guess the only option is to move the declaration outside the loop?
(Out of interest, I guess the same problem would happen with
if, while, and switch statements?)

Comment 1

[[e-mail]]

(In reply to comment #0)
> Neil, do you know whether this is the only problem when compiling with VC7.1?
Actually some of tracemonkey doesn't compile with VC7.1, although there is a pending review (for some time now, so probably bitrotted...) I can't remember any other problems offhand.

> Do you know whether there is a good way to un-confuse VC7.1?
> I guess the only option is to move the declaration outside the loop?
That's what I did to get it to compile locally.

> (Out of interest, I guess the same problem would happen with
> if, while, and switch statements?)
Probably.

Comment 2

[Karl Tomlinson (:karlt)]

Apparently VC7.1 understands initialized declarations in while-loop
conditionals
http://mxr.mozilla.org/mozilla-central/search?string=while+%28&find=&findi=&filter=while+\%28[*\w]%2B+\w%2B+%3D+&hitlimit=&tree=mozilla-central

and maybe in if-statements
http://mxr.mozilla.org/mozilla-central/search?string=if+%28&find=&findi=&filter=if+\%28[*\w]%2B+\w%2B+%3D+&hitlimit=&tree=mozilla-central
e.g. http://hg.mozilla.org/mozilla-central/annotate/106fa9dc5896/testing/mochitest/ssltunnel/ssltunnel.cpp#l730

(I don't see any in switch-statements.)

BTW, there is a similar initialized declaration in a for-loop conditional
introduced after Neil's patches in bug 513909
http://hg.mozilla.org/mozilla-central/rev/ca95f2397bc5#l1.15

Comment 3

[Karl Tomlinson (:karlt)]

Attachment: xpwidget patch

This is easy to fix, so let's fix.  Other options are declaring otherRect
(uninitialized) outside the for-loop, or declaring nextLink (initialized)
outside a while-loop.  But I like narrow variable scopes, so this dereferences
twice (when not optimized) to declare otherRect inside the for-loop.

Comment 4

[Karl Tomlinson (:karlt)]

http://hg.mozilla.org/mozilla-central/rev/29d0fadf3a20

Comment 5

[Benjamin Smedberg]

http://hg.mozilla.org/projects/firefox-lorentz/rev/bdb92894e4d1

Comment 6

[Mike Beltzner [:beltzner, not reading bugmail]]

Blanket approval for Lorentz merge to mozilla-1.9.2
a=beltzner for 1.9.2.4 - please make sure to mark status1.9.2:.4-fixed

Comment 7

[Benjamin Smedberg]

Merged into 1.9.2 at http://hg.mozilla.org/releases/mozilla-1.9.2/rev/84ba4d805430