Bug 311707 – CredentialsContainer: performCommonChecks() should return RefPtr<Document> instead of bool

• Component: WebKit Misc.
• Status: RESOLVED FIXED

[Marcos Caceres]

In CredentialsContainer.cpp, `get()` and `isCreate()` both call `performCommonChecks()` which checks for a null document internally via RefPtr, then immediately re-acquire the document via `Ref document = *this->document()` — relying on an implicit contract that the document is still non-null.

```cpp
void CredentialsContainer::get(CredentialRequestOptions&& options, CredentialPromise&& promise)
{
    if (!performCommonChecks(options, promise))
        return;

    Ref document = *this->document(); // unsafe: re-acquires WeakPtr without null check
    ...
}
```

The fix is to change `performCommonChecks()` to return `RefPtr<Document>` (or null on failure), so callers receive the document directly without re-acquiring the WeakPtr:

```cpp
void CredentialsContainer::get(CredentialRequestOptions&& options, CredentialPromise&& promise)
{
    RefPtr document = performCommonChecks(options, promise);
    if (!document)
        return;
    ...
}
```

This makes the null-safety contract explicit and eliminates the implicit assumption.

Note: This is pre-existing code. In practice the implicit contract holds soundly under WebKit's single-threaded execution model, but it violates the spirit of WebKit's safer-cpp guidelines.

[Radar WebKit Bug Importer]

<rdar://problem/174293959>

[Marcos Caceres]

Pull request: https://github.com/WebKit/WebKit/pull/62256

[EWS]

Committed 310779@main (acecc70c2382): <https://commits.webkit.org/310779@main>

Reviewed commits have been landed. Closing PR #62256 and removing active labels.