[SR-12360] SwiftFormat uses a SwiftSyntax tag that can cause stack overflow in debug mode

[swift-ci]

Previous ID	SR-12360
Radar	rdar://problem/60832848
Original Reporter	cukier (JIRA User)
Type	Bug
Status	Resolved
Resolution	Done

Additional Detail from JIRA

| | | |------------------|-----------------| |Votes | 0 | |Component/s | swift-format | |Labels | Bug | |Assignee | @allevato | |Priority | Medium | md5: 4111fa0935f36cb69278ce6ab26c299c

Issue Description:

Stack overflow 2: revenge of the rdar://55929175

After implementing formatting in sourcekit-lsp I was investigating why it wasn't working for things that are nested four levels deep. After fighting with debugger, I had a hunch that it may be stack overflow. I found a comment in the function that was crashing:

    // The implementation of every generated case goes into its own function. This
    // circumvents an issue where the compiler allocates stack space for every
    // case statement next to each other in debug builds, causing it to allocate
    // ~50KB per call to this function. rdar://55929175

It crashes only in debug mode, on macos

To reproduce:

• clone https://github.com/Trzyipolkostkicukru/sourcekit-lsp/tree/format and checkout commit ed642036f4b9ce7696ad340523ed8e9b4bdb9761

• get toolchain swift-DEVELOPMENT-SNAPSHOT-2020-01-29-a and set it as your compiler

• compile and set up sourcekit-lsp

• try to format a file with 4+ levels of nesting, for example:

  do {
  do { do { do { print("Hello, world") } } } 
  }

[beccadax]

@swift-ci create

[akyrtzi]

@ahoppen fixed this in https://github.com/apple/swift-syntax/pull/205 but swift-format is using a snapshot tag that is prior to this improvement.

I think this is a case where swift-format needs to update the SwiftSyntax dependency.

\cc @allevato

[allevato]

I've just cut the swift-5.2-branch of swift-format which depends on swift-syntax 0.50200.0, which contains the above fix. The master branch is also using 0.50200.0 for the time being, so it will work there as well.