1393235 - Fix improper usages of string functions

Status: RESOLVED FIXED

(Core :: XPCOM, enhancement)

Description

[Eric Rahm [:erahm]]

This fixes usages of `Find`, `RFind` and the equality operator that kind of
work right now but will break with the proper type checking of a templatized
version of the string classes.

For `Find` and `RFind` it appears that `nsCString::(R)Find("foo", 0)` calls
were being coerced to the `Find(char*, bool, int, int)` versions. The intent was
probably to just start searching from position zero.

For the equality operator, the type of nullptr is nullptr_t rather than
char(16_t)* so we'd need to add an operator overload that takes nullptr_t. In
this case just using `IsVoid` is probably more appropriate.

Comment 1

[Eric Rahm [:erahm]]

Attachment: Fix improper usages of string functions

Comment 2

[David Baron :dbaron: (⌚️UTC-4, no longer working on Mozilla)]

(In reply to Eric Rahm [:erahm] (please no mozreview requests) from comment #0)
> For the equality operator, the type of nullptr is nullptr_t rather than
> char(16_t)* so we'd need to add an operator overload that takes nullptr_t. In
> this case just using `IsVoid` is probably more appropriate.

I'm surprised those are equivalent.

Comment 3

[Eric Rahm [:erahm]]

(In reply to David Baron :dbaron: ⌚️UTC-7 from comment #2)
> (In reply to Eric Rahm [:erahm] (please no mozreview requests) from comment
> #0)
> > For the equality operator, the type of nullptr is nullptr_t rather than
> > char(16_t)* so we'd need to add an operator overload that takes nullptr_t. In
> > this case just using `IsVoid` is probably more appropriate.
> 
> I'm surprised those are equivalent.

Well I think the intent of |nsCString != nullptr| is the same as |!IsVoid()|, but you're right in practice [1] it's more of `!IsEmpty()`. Not sure if we should change it to do the "right" thing, or keep existing behavior.

[1] http://searchfox.org/mozilla-central/rev/48ea452803907f2575d81021e8678634e8067fc2/xpcom/string/nsTSubstring.cpp#794-807

Comment 4

[Nicholas Nethercote [inactive]]

Comment on attachment 8900477 [details] [diff] [review]
Fix improper usages of string functions

Review of attachment 8900477 [details] [diff] [review]:
-----------------------------------------------------------------

Those Find() functions are awful.

::: dom/media/gmp/ChromiumCDMChild.cpp
@@ +231,5 @@
>      // As laid out in the Chromium CDM API, if the CDM fails to load
>      // a session it calls OnResolveNewSessionPromise with nullptr as the sessionId.
>      // We can safely assume this means that we have failed to load a session
>      // as the other methods specify calling 'OnRejectPromise' when they fail.
> +    bool loadSuccessful = !aSessionId.IsVoid();

The incoming strings can be `nsCString(nullptr, 0)`, which I think becomes a non-void empty string, so this should probably be `!aSessionId.IsEmpty()` or equivalent.

Comment 5

[Eric Rahm [:erahm]]

https://hg.mozilla.org/integration/mozilla-inbound/rev/c5556637f69d48d84e51bfdb4c205a41ef2700e2
Bug 1393235 - Fix improper usages of string functions. r=njn

Comment 6

[Sebastian Hengst [:aryx] (needinfo me if it's about an intermittent or backout)]

https://hg.mozilla.org/mozilla-central/rev/c5556637f69d