[webkit-dev] Watch out for std::optional's move constructor

[Geoffrey Garen]

> This expression WTFMove(*m_pendingWebsitePolicies) doesn't move std::optional<WebsitePoliciesData>, but moves the content of the std::optional, WebsitePoliciesData. I think your proposal doesn't work for this code.

The original code, which asserted, did this:

        if (auto pendingWebsitePolicies = WTFMove(m_pendingWebsitePolicies))
            WebsitePoliciesData::applyToDocumentLoader(WTFMove(*pendingWebsitePolicies), documentLoader);

The relevant expression was "WTFMove(m_pendingWebsitePolicies)”, which did move std::optional<WebsitePoliciesData>. The expectation in the code was that, after WTFMove(m_pendingWebsitePolicies), m_pendingWebsitePolicies would be empty.

Geoff
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