Internal error with extern linked-list-like data structure relying on a type alias

[bmcdonald3]

Summary of Problem

While working to get the Apache Arrow header files working with c2chapel, I was hitting an internal error with the below snippet of code. I explored the error a bit with @bradcray, and we observed that it seemed to be happening due to a AST node being replaced, but we were unable to figure out if that should be happening/what was causing the error.

Steps to Reproduce

Source Code:

use SysCTypes;
use CPtr;

extern record _GHook {
  var next : c_ptr(GHook);
}

extern type GHook = _GHook;

Compiling this program (using CHPL_LLVM=none) with chpl ghook.chpl ghook.chpl:8: internal error: assertion error [resolution/postFold.cpp:105]`

[edit: to someone compiling in non-developer mode, this error shows up as: internal error: RES-POS-OLD-0105 chpl version 1.25.0 pre-release (3df047aa28)

Commenting out line 5 resolves the error.

Configuration Information

• Output of $CHPL_HOME/util/printchplenv --anonymize:

  CHPL_TARGET_PLATFORM: darwin
  CHPL_TARGET_COMPILER: clang
  CHPL_TARGET_ARCH: x86_64
  CHPL_TARGET_CPU: native
  CHPL_LOCALE_MODEL: flat
  CHPL_COMM: none
  CHPL_TASKS: qthreads
  CHPL_LAUNCHER: none
  CHPL_TIMERS: generic
  CHPL_UNWIND: none
  CHPL_MEM: jemalloc
  CHPL_ATOMICS: cstdlib
  CHPL_GMP: bundled
  CHPL_HWLOC: bundled
  CHPL_RE2: bundled
  CHPL_LLVM: none *
  CHPL_AUX_FILESYS: none

• Back-end compiler and version, e.g. gcc --version or clang --version:

  Apple clang version 12.0.5 (clang-1205.0.22.9)
  Target: x86_64-apple-darwin20.3.0
  Thread model: posix

[bradcray]

Interesting note: If I add --ignore-errors to the chpl command-line, I get all the way through to the C compilation step. Given the nature of the assertion ("Is this thing still in the AST?"), I was not expecting this.

[bradcray]

Some other interesting observations:

• if I change the type of next from c_ptr(GHook) to c_ptr(_GHook), I get no errors and make it to C compilation
• if I remove both extern labels, I get a GHook used before defined error on the declaration of the next field
• if GHook is extern, but _GHook is not, I get the assertion error
• if _GHook is extern, but GHook is not, I get the "used before defined" error again

@bmcdonald3 : Based on this, I'd try using the workaround in the first bullet for your 20,000 line file and see if that gets you through compilation as a workaround. We should still understand/fix this issue (internal errors are bad), but if that gets you unblocked, I'd run with it.

[edit: I renamed the issue to be a bit more precise as a result of these observations]

[bmcdonald3]

@bradcray Great, thanks for digging into this, glad to have the Arrow headers (hopefully) working fully now!

edit: there are quite a few instances of this in the generated code, so while I was eventually able to sort through all of them, there are a bunch of these in the arrow code.