I was looking through Swift's issues tab and found this issue (#57496), which points out the poor performance of `FlattenSequence/count`. The current `count` implementation calls `distance(from:to:)`, which iterates through the entire collection, so I thought I'd improve that method. The new version computes the distance as the sum of three parts, with a fast path when both indices belong to the same underlying collection. Note that it does this by calling either `count` or `distance(from:to:)` on each underlying collection, which makes `[repeatElement(0, count: Int.max)].joined().count` instant, for example.
`swift_willThrow` is called with an error right before it is thrown.
This existing entrypoint requires an already-boxed error existential;
with typed errors, we don't have the error existential on hand, so we
would need to allocate the box to throw a typed error. That's not okay.
Introduce a new `swift_willThrowTypedImpl` entry point into the runtime
that will first check for the presence of an error handler and, if one
is present, box the error to provide to the error handler. This
maintains the no-allocations path for typed errors while still
allowing existing error handlers to work.
This new entrypoint isn't available on older Swift runtimes, so create
a back-deployable shim called by the compiler. On new-enough platforms,
this will call through to `swift_willThrowTypedImpl`. On older
platforms, we drop the error and don't call the registered will-throw
handler at all. This is a compromise that avoids boxing when throwing
typed errors, at the cost of a slightly different experience for this
new feature on older runtimes.
Fixes rdar://119828459.
When the Swift module is not available, we'll synthesize the
Copyable/Escapable decls into the Builtin module.
In the future, it might be nice to just do this always, and define
typealiases for those types in the stdlib to refer to the ones in the
builtin module.
These functions were the odd ones out in not using `encoding` for this parameter label. Harmonizing this term will also make the documentation more consistent.
Allow the use of typed throws for the main functions of `@main` types,
and thread the thrown error through to a new entry point in the library,
`_errorInMainTyped`, which is generic in the thrown error type.
Fixes rdar://121603043.
This PR changes the deprecation annotation of `String.init(validatingUTF8: [CChar])` to match that of `String.init(validatingUTF8: UnsafePointer<CChar>)`. Both have been given new, undeprecated, renamed replacements (`validatingCString:`).
Resolves rdar://121674502.
