This replaces usages of `llvm::fs` and string manipulation with
`std::filesystem`, also replacing `std::string` with
`std::filesystem::path` where it made sense.
Moreover MD5 hashing used in macOS file remapping was replaced by
SHA256 hashing using a small header-only SHA256 C++ library with an
MIT license, https://github.com/okdshin/PicoSHA2.
File contents hashing was relocated to the newly created `file` library
for later planned reuse.
This should cover `-merge-modules` mode.
Dumping of the configuration to the target files was moved to a
separate pair of header/source files, as now it is also done in
`SwiftOutputRewrite.cpp`.
Previously we were not extracting any `swiftmodule` file that was not
a system or a built-in one. This was done to avoid re-extracting
`swiftmodule` files that were built previously in the same build, but it
turned out to be too eager, as there are legitimate cases where a
non-system, non-built-in precompiled swift module can be used. An
example of that is the `PackageDescription` module used in Swift
Package Manager manifest files (`Package.swift`).
We now relax the test and trigger module extraction on all loaded
modules that do not have source files (we trigger source file extraction
for those). The catch, is that we also create empty trap files for
current output `swiftmodule` files (including possible alias locations
set up by XCode).
This means that if a following extractor run loads a previously built
`swiftmodule` file, although it will trigger module extraction, this
will however be skipped as it will find its target file already present
(this is done via the `TargetFile` semantics).
Currently, we have a number of assertions in the codebase and certain
assumptions about the AST. These don't always hold, sometimes leading to
a crash in the extractor.
The crashes leave incomplete TRAP files that cannot be imported into the
database.
With this change, we still get those incomplete TRAP files, but we also
get a database in the end (even thoough it is also incomplete as we
cannot import everything).
