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.
Preamble macros introduce code at the beginning of a function body.
Allow them to introduce declarations as well, so long as the macro
declaration properly declares the names it introduces. This allows all
sorts of exciting macros that introduce (e.g.) new local variables
that one can use.
Implement type checking support for preamble macros, which expands the
preamble macros and introduces them at the beginning of the function
body prior to type checking. Ensure that the resulting function bodies
type-check properly, including when composing multiple preamble macros
and with a preamble macro applied to the body of a function that
itself came from a body macro.
Function body macros allow one to introduce a function body for a
particular function, either providing a body for a function that
doesn't have one, or wholesale replacing the body of a function that
was written with a new one.
