🍒[6.1] Add a flag to dump the AST as JSON.

[allevato]

• Explanation: Support dumping the AST in JSON format.
• Scope: This primarily only affects ASTDumper and the frontend interface (a new flag). It does not impact how code is compiled.
• Issues: N/A
• Original PRs: Add a flag to dump the AST as JSON. (Second version) #78463, as well as [AST] Dump decl attributes #77937 (@rintaro) to include attribute dumping.
• Risk: Low. This only affects ASTDumper.
• Testing: Lit tests from the original PR exercise the new feature.
• Reviewers: @hamishknight

[allevato]

@swift-ci please smoke test

[DougGregor]

@swift-ci please test

[DougGregor]

We need full (non-smoke) tests for the 6.1 branch, so I just kicked those off

[DougGregor]

I'm okay with us taking this, but it does look like the Windows issue is a legitimate bug?

[allevato]

I'm okay with us taking this, but it does look like the Windows issue is a legitimate bug?

That test uses @DebugDescription as a convenience since it's a macro that's defined in the standard library, but all it cares about is whether some expansion occurred. When I compare the JSON dump in the log to one that I generate locally, there are no macro-expanded decls at all. This makes sense after tracking down #71685, which wraps all the generated decls in #if !os(Windows). What doesn't make sense is why the same test didn't fail on main—I don't see any changes since the 6.1 branch cut that would re-enable the macro there.

[allevato]

While I wait for my Windows build of the 6.1 branch to make progress, I'll work on updating the test to use its own macro instead of depending on one from stdlib. If that passes on all platforms, I can update main afterwards to use the same test going forward.

[allevato]

@swift-ci please test