[Mangling] [NFC] Prepare for a new mangling prefix for Embedded Swift: $e

[kubamracek]

Given that Embedded Swift's ABI and layout of class metadata is (intentionally) different and incompatible with regular Swift, this PR is introducing a different mangling for all Embedded Swift. Concretely, it changes the mangling prefix from $s to $e.

For reviewing, I recommend looking at commits individually: The first commit is a mechanical change to pass an ASTContext to all instantiations of ASTMangler and its derivatives, which is a large diff but essentially an NFC.

This PR is a large diff, but it's an NFC, just preparing for an actual mangling change in a subsequent commit.

[slavapestov]

In ASTContext.cpp I see a handful of places where we call getASTContext() on a Type or Decl we have sitting nearby. Do you mind also changing those calls to directly use the new Context instance member that you added?

[benrimmington]

Should the new prefix be documented? docs/ABI/Mangling.rst

[kubamracek]

I'm missing a change to swift/docs/ABI/Mangling.rst?

Added.

[kubamracek]

Could you check if changing the mangling prefix changes the USRs used for indexing? Could you add a test to test/Index that builds with embedded mode and just has a FileCheck line for a simple declaration? (index_curry_thunk.swift seems to be a good starting point that you can simply further.

If it does change the USR prefix, I think that’s fine but we might need to do some downstream adjustments for that.

Added the test: test/Index/index_embedded.swift.

[kubamracek]

@swift-ci please test

[kubamracek]

Another place to update is in swift-demangle:

swift/tools/swift-demangle/swift-demangle.cpp

Line 341 in b073d3d

if (ch == 'S' || ch == 's') {

Fixed, added test.

[kubamracek]

@swift-ci please test

[augusto2112]

Can you make this a parameter in the constructor? It can be defaulted to true. Reason being that LLDB uses TypeRefBuilder to process types found in DWARF.

[augusto2112]

Can you add a function here that returns the Mangling Flavor of a string, and declare it on Demangle.h as well?

Something like:

std::optional<Mangle::ManglingFlavor> getManglingFlavor(llvm::StringRef mangledName) {
  if (!isSwiftSymbol(mangledName))
    return {};

  if (mangledName.starts_with("$e") || mangledName.starts_with("_$e"))
    return Mangle::ManglingFlavor::Embedded;
  return Mangle::ManglingFlavor::Default;
}

[kubamracek]

Given the size of this PR and the revlock with LLDB, I'm going to break this PR up, and stage the changes over a series of PRs. I have changed this PR to be a NFC, i.e. not actually changing the mangling just yet. Also added a legacy constructor on ASTMangler that does not require a ASTContext& passed in, to avoid this being a breaking API change.

Subsequent separate PRs will adapt LLDB, actually enable the $e prefix, and drop the legacy ASTMangler constructor.

[kubamracek]

@swift-ci please test

[kubamracek]

@swift-ci please test

[kubamracek]

@swift-ci please test

[kubamracek]

@swift-ci please test Linux platform

[kubamracek]

swiftlang/swift-driver#1744

@swift-ci please test