1717526 - String's implicit conversion operator causes COW relocations

Status: RESOLVED FIXED

(Core :: XPCOM, defect, P2)

Description

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

The operator Span<char_type> operator defined on nsTSubstring in bug 1295611 implicitly invokes BeginWriting() which can relocate the string's backing buffer to make it writable. This means that any code which casts a non-const nsTSubstring to a Span<char_type> will make the string owned.

We shouldn't do this kind of relocation implicitly, as it can be done accidentally very easily, such as when a user is intending to use operator Span<const char_type>. This patch tracks changing uses of the non-const operator to be explicit calls instead.

Comment 1

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

Attachment: Bug 1717526 - String's implicit conversion operator causes COW relocations,

Comment 2

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/3beb01f5d643
String's implicit conversion operator causes COW relocations, r=xpcom-reviewers,mccr8

Comment 3

[Alexandru Michis [:malexandru]]

Backed out changeset 3beb01f5d643 (Bug 1717526) for causing gtest failures in SpanTest.from_xpcom_collections
Backout link: https://hg.mozilla.org/integration/autoland/rev/15b20f4cd02f9497f40e3dfe06adbc9dab1eb050
Push with failures, failure log.

Comment 4

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/3afce3166219
String's implicit conversion operator causes COW relocations, r=xpcom-reviewers,mccr8

Comment 5

[Marian-Vasile Laza]

https://hg.mozilla.org/mozilla-central/rev/3afce3166219