[BUG] Mojo crashes on autoparameterized function parameter

[soraros]

Bug description

As title. __type_of also doesn't work. only the explicit from compiles.

Steps to reproduce

Either of the following crashes the compiler:

fn reduce[f: fn (x: Scalar) -> Scalar[x.type]]():
  ...

fn reduce[f: fn [dt: DType](x: Scalar[dt]) -> __type_of(x)]():
  ...

System information

Mojo 24.1.1 on Docker, Intel Mac

[ematejska]

I don't see this failing with 24.2.

Here is the code I have:
fn reducef: fn [dt: DType](x: Scalar[dt]) -> __type_of(x):
pass

fn main():
print("hello")

@soraros Does this work for you with 24.2 and if not could you provide a fully formed example?

[soraros]

@ematejska I think now it only crashes the LSP, on both 24.2 and nightly. Notice that it is a full example.

[soraros]

Actually, it's not crashing the LSP. Or at least the LSP itself isn't crashing. When you open a test.mojo with the above code snippet, the LSP is producing the following:

["INFO" - 6:09:45 PM] Activating language client for URI 'file:///workspaces/nightly/mojo-dev/stdlib/test.mojo'
I[18:09:45.429] --> textDocument/didOpen
D[18:09:45.429] --> textDocument/didOpen: uri='file:///workspaces/nightly/mojo-dev/stdlib/test.mojo', version=99
I[18:09:45.429] --> textDocument/documentSymbol(909)
I[18:09:45.429] --> textDocument/semanticTokens/full(910)
I[18:09:45.429] --> textDocument/codeAction(911)
E[18:09:45.439] Crash recovered: CrashRecoveryContext::RetCode (on POSIX: signal number + 128) = 139
E[18:09:45.439] A crash happened in the mojo parser when processing the file file:///workspaces/nightly/mojo-dev/stdlib/test.mojo.
Please report this issue in https://github.com/modularml/mojo/issues along with all the relevant source codes with the contents they had at crash time.
I[18:09:45.439] --> textDocument/publishDiagnostics
D[18:09:45.439] >>> {"jsonrpc":"2.0","method":"textDocument/publishDiagnostics","params":{"diagnostics":[{"message":"A crash happened in the mojo parser with the current version of this file. Please report this issue in https://github.com/modularml/mojo/issues along with all the relevant source codes with their current contents.","range":{"end":{"character":0,"line":0},"start":{"character":0,"line":0}},"severity":1,"source":"mojo"}],"uri":"file:///workspaces/nightly/mojo-dev/stdlib/test.mojo","version":99}}

[River707]

Hmm, oof, we'll take a look! Thanks for the easy repro, makes it really easy to dig into this stuff

[River707]

This should be fixed in the next release!