1254247 - MOZ_MUST_USE treats expressions evaluating to lvalue references as MUST_USE

Status: RESOLVED FIXED

(Developer Infrastructure :: Source Code Analysis, defect)

Description

[Timothy Nikkel (:tnikkel)]

Bug 1214037 didn't seem to fix this problem for making DrawResult a must use type.

Here is one of many try pushes
https://treeherder.mozilla.org/#/jobs?repo=try&revision=d89631512db0

The code

  DrawResult result = SUCCESS;
  result &= FunctionReturnDrawResult();

always seems to get flagged as not using the value (in many places). Trivially changing it to

  DrawResult result = SUCCESS;
  DrawResult resul2 = FunctionReturnDrawResult();
  result = result & result2;

makes the error go away. However this code still triggers the error

  DrawResult result = SUCCESS;
  result = result & FunctionReturnDrawResult();

Comment 1

[Seth Fowler [:seth] [:s2h]]

Just chiming in: I too would really like to see this fixed. It let us prevent some important classes of errors that are definitely visible to our users as rendering issues.

Comment 2

[Nika Layzell [:nika] (ni? for response)]

Attachment: Ignore implicit Expr wrappers due to temporary cleanup in MUST_USE analysis

Turns out that these expressions contained temporaries, which meant that the expression was wrapped. With this patch those wrappers are now ignored.

Sorry for the delay, I'm in my last 3 weeks of class, and have remarkably little time to do this sort of stuff.

try: https://treeherder.mozilla.org/#/jobs?repo=try&revision=83f03890f8fd

Comment 3

[Pulsebot]

https://hg.mozilla.org/integration/mozilla-inbound/rev/79af3a479ce9

Comment 4

[Ryan VanderMeulen [:RyanVM]]

https://hg.mozilla.org/mozilla-central/rev/79af3a479ce9

Comment 5

[Timothy Nikkel (:tnikkel)]

Thanks!