Add support for void pointers in Opir JSON output

[tokyovigilante]

Futhark crashes when parsing C headers containing LLVM block pointer types, identified when attempting to wrap Apple's libdispatch library.

https://github.com/swiftlang/swift-corelibs-libdispatch/blob/main/src/BlocksRuntime/Block.h

// dispatch/object.h (simplified)
typedef void (^dispatch_block_t)(void);

Attempting to parse with Futhark:

import futhark

importc:
  compilerArg "-D__BLOCKS__"
  compilerArg "-fblocks"
  sysPath "/usr/include"
  "dispatch/dispatch.h"

gives the error:

Error: unhandled exception: Field 'base' not found in JsonNode [KeyError]

Opir output for the above:

{
  "kind": "pointer",
  "depth": 1
}

Absent base key (appropriately) but then later unconditionally accesses json["base"] cause crashes.

findAlias() (Line 265): Crashes extracting type aliases
addUsings() (Line 311): Crashes tracking dependencies
toNimType() (Lines 346, 370, 382, 408): Crashes generating type definitions

Patch adds hasKey("base") guards before accessing json["base"] in all relevant locations:

findAlias(): Return empty string (no alias to track)
addUsings(): Skip dependency tracking (bare pointers have no dependencies)
toNimType(): Generate opaque pointer type

Disclosure: patch partially generated by Claude Code, but thoroughly manually tested and reviewed.

[PMunch]

Hmm, this is very strange. Futhark definitely should support void pointers. Not quite sure what the caret notation in your snippet is though, is that even valid C?

[tokyovigilante]

Not quite sure what the caret notation in your snippet is though, is that even valid C?

Strictly speaking no, it's an LLVM C extension for blocks, which underpins Objective-C blocks as used in libdispatch. Sorry I've realised the description above isn't clear.

https://clang.llvm.org/docs/BlockLanguageSpec.html

Acknowledge this is not Futhark's issue, but hopefully the patch is additive only and doesn't break any other codegen. Haven't seen any issues with any of the other C libraries I'm using.

[tokyovigilante]

Just as an update, I'm no longer using libdispatch as the interoperability with non-Swift languages on Linux isn't great (can't guarantee main queue executes on main thread primarily) which is disappointing given that the performance was very good in non-UI tasks. So I'm happy if you want to close this.