math: Compilation error

Describe the bug

I got my first situation now where the initial syntax check or so that stan is doing passes, but the compilation fails. And I don’t really understand why or how I can start to debug this - I tried to change the code for an hour and it still fails. I cannot reproduce the compilation error when having the single function in a separate stan file.

To Reproduce

Apologies - I could not reproduce this bug so far in a minimum example. The problem comes down to a block of code like this:

matrix fun(matrix time) {
    matrix[rows(time), cols(time)] result;
    real val;
    val = time[1, 2];
    return result;
}

(note that this is simplified but it fails like this) It starts compiling but after few seconds gives a huge error message, that ends with:

stan/src/stan/model/indexing/rvalue.hpp:55:10: note:   template argument deduction/substitution failed:
/tmp/RtmpiGD5kC/model-4fe3695a40a9.hpp:436:17: note:   candidate expects 2 arguments, 4 provided
  436 |     val = rvalue(time, "time", index_uni(1), index_uni(2));
      |           ~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
make: *** [make/program:58: /tmp/RtmpiGD5kC/model-4fe3695a40a9] Fehler 1
Fehler: An error occured during compilation! See the message above for more information.

Expected behavior

I would have expected that the code compiles without error.

Operating system

Ubuntu 20.04.3 LTS

CmdStanR version number

CmdStan 2.28.2 via cmdstanr_0.4.0

Additional context

Compiler/Toolkit: g++ (Ubuntu 9.3.0-17ubuntu1~20.04) 9.3.0