This isn't a "complete" port of the standard library for embedded Swift, but
something that should serve as a starting point for further iterations on the
stdlib.
- General CMake logic for building a library as ".swiftmodule only" (ONLY_SWIFTMODULE).
- CMake logic in stdlib/public/core/CMakeLists.txt to start building the embedded stdlib for a handful of hardcoded target triples.
- Lots of annotations throughout the standard library to make types, functions, protocols unavailable in embedded Swift (@_unavailableInEmbedded).
- Mainly this is about stdlib functionality that relies on existentials, type erasure, metatypes, reflection, string interpolations.
- We rely on function body removal of unavailable functions to eliminate the actual problematic SIL code (existentials).
- Many .swift files are not included in the compilation of embedded stdlib at all, to simplify the scope of the annotations.
- EmbeddedStubs.swift is used to stub out (as unavailable and fatalError'd) the missing functionality.
Implemented as custom parsing logic instead of a proper attribute because we want it to be rewritten at parse time (into nothing in regular Swift mode, and into unconditional unavailable attr in embedded Swift mode), no serialization, printing, etc.
To enable MCCAS, the following driver options have been added
-cas-backend: Enable MCCAS backend in swift, the option
-cache-compile-job must also be used.
-cas-backend-mode=native: Set the CAS Backend mode to emit an object
file after materializing it from the CAS.
-cas-backend-mode=casid: Emit a file with the CASID for the CAS that was
created.
-cas-backend-mode=verify: Verify that the object file created is
identical to the object file materialized from the CAS.
-cas-emit-casid-file: Emit a .casid file next to the object file when
CAS Backend is enabled.
This enables one to use varying prefixes when checking diagnostics with the
DiagnosticVerifier. So for instance, I can make a test work both with and
without send-non-sendable enabled by adding additional prefixes. As an example:
```swift
// RUN: %target-swift-frontend ... -verify-additional-prefix no-sns-
// RUN: %target-swift-frontend ... -verify-additional-prefix sns-
let x = ... // expected-error {{This is always checked no matter what prefixes I added}}
let y = ... // expected-no-sns-error {{This is only checked if send non sendable is disabled}}
let z = ... // expected-sns-error {{This is only checked if send non sendable is enabled}}
let w = ... // expected-no-sns-error {{This is checked for a specific error when sns is disabled...}}
// expected-sns-error @-1 {{and for a different error when sns is enabled}}
```
rdar://114643840
Macro implementations can come from various locations associated with
different search paths. Add a frontend flag `-Rmacro-loading` to emit
a remark when each macro implementation module is resolved, providing
the kind of macro (shared library, executable, shared library loaded
via the plugin server) and appropriate paths. This allows one to tell
from the build load which macros are used.
Addresses rdar://110780311.
When `-warn-on-potentially-unavailable-enum-case` was introduced, the build
system was required to invoke `swift-frontend` at artificially low deployment
targets when emitting `.swiftinterface` files for legacy architectures. Because
the deployment target was low, some availability diagnostics needed to be
de-fanged in order to allow module interface emission to succeed. Today, the
build system is able to use the correct deployment target when emitting module
interfaces and the `-warn-on-potentially-unavailable-enum-case` is superfluous,
so deprecate it.
Resolves rdar://114092047
Clang dependency scanning produces scanner PCMs which we may want to live in a
different filesystem location than the main build module cache.
Resolves rdar://113222853
