Hotfix alloc crash, when no read data avail.

[furby-tm]

Note

This fixes a Swift memory allocation crash, when attempting to allocate an internally managed buffer with a capacity of 0 (zero), if there's no read data available for the data copy we early out and return nil.

Backtrace

Thread 1 Crashed::  Dispatch queue: CosmoEditor.TreeSitter.EditQueue
0   libswiftCore.dylib                       0x1ad1eeb74 swift_slowAlloc.cold.1 + 16
1   libswiftCore.dylib                       0x1ad12d500 swift_slowAlloc + 88
2   libswiftCore.dylib                       0x1ad06da1c static UnsafeMutableBufferPointer.allocate(capacity:) + 124
3   Kraken                                   0x109a4d098 readFunction(payload:byteIndex:position:bytesRead:) + 596 (Input.swift:60)
4   Kraken                                   0x109a4cd74 @objc readFunction(payload:byteIndex:position:bytesRead:) + 40
5   Kraken                                   0x10af42f64 ts_lexer__get_chunk + 76 (lexer.c:59)
6   Kraken                                   0x10af5cf18 ts_lexer__do_advance + 548 (lexer.c:195)
7   Kraken                                   0x10af42518 ts_lexer__advance + 508 (lexer.c:217)
8   Kraken                                   0x10b201e24 ts_lex + 60
9   Kraken                                   0x10af5e3bc ts_parser__lex + 1224 (parser.c:485)
10  Kraken                                   0x10af4823c ts_parser__advance + 340 (parser.c:1441)
11  Kraken                                   0x10af477bc ts_parser_parse + 1384 (parser.c:1933)
12  Kraken                                   0x109a58028 Parser.parse(tree:encoding:readBlock:) + 368 (Parser.swift:116)
13  Kraken                                   0x100939ebc TreeSitterState.parseDocument(readCallback:readBlock:) + 484 (TreeSitterState.swift:94)
14  Kraken                                   0x100939504 TreeSitterState.init(codeLanguage:readCallback:readBlock:) + 296 (TreeSitterState.swift:52)
15  Kraken                                   0x1009393cc TreeSitterState.__allocating_init(codeLanguage:readCallback:readBlock:) + 88
16  Kraken                                   0x100935c3c closure #1 in TreeSitterClient.setState(language:readCallback:readBlock:) + 364 (TreeSitterClient.swift:145)
17  Kraken                                   0x100936430 closure #1 in TreeSitterClient.performAsync(_:) + 996 

LLDB Breakpoint

Process 88310 stopped
* thread #3, queue = 'CosmoEditor.TreeSitter.EditQueue', stop reason = EXC_BREAKPOINT (code=1, subcode=0x1ad1eeb74)
    frame #0: 0x00000001ad1eeb74 libswiftCore.dylib`swift_slowAlloc.cold.1 + 16
libswiftCore.dylib`swift_slowAlloc.cold.1:
->  0x1ad1eeb74 <+16>: brk    #0x1

libswiftCore.dylib`swift_allocBox.cold.1:
    0x1ad1eeb78 <+0>:  adrp   x8, 186
    0x1ad1eeb7c <+4>:  add    x8, x8, #0x8f0            ; "Could not allocate memory."
    0x1ad1eeb80 <+8>:  adrp   x9, 359303

[mattmassicotte]

Wow! Thank you!

Do you have a situation that can easily reproduce this? I’d love to capture it in a test.

[furby-tm]

Wow! Thank you!

Do you have a situation that can easily reproduce this? I’d love to capture it in a test.

It's a weird one for sure! I was able to reproduce it from this project here, simply adjust the following line, by shifting branch: "hotfix-read-empty-noalloc" to revision: "b0e00f8", and it should summon the error immediately upon launching the application (or at least upon opening any file within that program that enables syntax highlighting; such as opening a *.swift file from the File > Open dialog) -- after building and running the app via swift run.

However; I'm also building all of Pixar's Universal Scene Description with that Swift package 😅; so I would advise a much smaller reproducible project than having to deal with all of that.

If I find some time I may be able to create you a small SwiftPM test project repo, copying over my same TreeSitters over to that project repo along with a super basic little "hello world" executable app to spool it up if that's something that may be of use to you.

[mattmassicotte]

It turned out to be easy to make a test that goes down this code path: f46c79e

However, bizarrely, it does not crash! I wonder if this is something that is ok in debug mode? Anyways, I think that's suficeint for now. We tried. Thanks again for your help here.