Non-escapable struct definitions often have inicidental integer fields that are
unrelated to lifetime. Without an explicit initializer, the compiler would infer
these fields to be borrowed by the implicit intializer.
struct CountedSpan: ~Escapable {
let span: Span<Int>
let i: Int
/* infer: @lifetime(copy span, borrow i) init(...) */
}
This was done because
- we always want to infer lifetimes of synthesized code if possible
- inferring a borrow dependence is always conservative
But this was the wrong decision because it inevitabely results in lifetime
diagnostic errors elsewhere in the code that can't be tracked down at the use
site:
let span = CountedSpan(span: span, i: 3) // ERROR: span depends on the lifetime of this value
Instead, force the author of the data type to specify whether the type actually
depends on trivial fields or not. Such as:
struct CountedSpan: ~Escapable {
let span: Span<Int>
let i: Int
@lifetime(copy span) init(...) { ... }
}
This fix enables stricter diagnostics, so we need it in 6.2.
Fixes rdar://152130977 ([nonescapable] confusing diagnostic message when a
synthesized initializer generates dependence on an Int parameter)
Find all the usages of `--enable-experimental-feature` or
`--enable-upcoming-feature` in the tests and replace some of the
`REQUIRES: asserts` to use `REQUIRES: swift-feature-Foo` instead, which
should correctly apply to depending on the asserts/noasserts mode of the
toolchain for each feature.
Remove some comments that talked about enabling asserts since they don't
apply anymore (but I might had miss some).
All this was done with an automated script, so some formatting weirdness
might happen, but I hope I fixed most of those.
There might be some tests that were `REQUIRES: asserts` that might run
in `noasserts` toolchains now. This will normally be because their
feature went from experimental to upcoming/base and the tests were not
updated.
