1203314 - Make operator<< a method on unused_t

Status: RESOLVED FIXED

(Core :: MFBT, defect)

Description

[Andrew McCreight [:mccr8]]

If you include mozilla/unused.h in a file that also includes Chromium IPC logging, then operator overload resolution somehow decides that the << from unused is the right one. Making operator<< a method on unused_t rather than a free-floating function fixes this problem.

Comment 1

[Andrew McCreight [:mccr8]]

Attachment: Make operator<< a method on unused_t.

This prevents operator overload resolution from failing when this file
is included in a file that uses Chromium IPC logging.

Comment 2

[Pulsebot]

https://hg.mozilla.org/integration/mozilla-inbound/rev/f04c038de236

Comment 3

[Carsten Book [:Tomcat]]

https://hg.mozilla.org/mozilla-central/rev/f04c038de236

Comment 4

[Jed Davis [:jld] ⟨⏰|UTC-7⟩ ⟦he/him⟧]

(In reply to Andrew McCreight [:mccr8] from comment #0)
> If you include mozilla/unused.h in a file that also includes Chromium IPC
> logging, then operator overload resolution somehow decides that the << from
> unused is the right one.

Before this patch, mfbt/unused.h defined ::mozilla::operator<< and ipc/chromium/src/base/logging.h defined ::operator<<.  So, when you << to a ::mozilla::Logger&, the compiler looks in namespace ::mozilla (argument-dependent lookup), sees only definitions that don't match the provided types, and complains.

Arguably it's the IPC header that's wrong, but it's a moot point now (until the next time someone defines ::mozilla::operator<< and it comes into contact with IPC).