Size behavior is not consistent for function arguments

Summary:

Size of a vector behaves differently from num_elements for function argument.

Description:

The variable used for size function is a function argument, declared as a vector.
Size of a vector returns error during compilation but num_elements does not.

Reproducible Steps:

The current calculation I am working with uses a function with vector type argument.
The size of this vector argument is used for further calculations.
num_elements seems to work fine but size fails.

If you have a reproducible example, please include it.

functions {

  real test(vector x){
    real N = size(x);
    return(N)
  }
}

Current Output:

The current output. Knowing what is the current behavior is useful.

SYNTAX ERROR, MESSAGE(S) FROM PARSER:
No matches for: 

  size(vector)

Available argument signatures for size:

  size(int[ ])
  size(real[ ])
  size(vector[ ])
  size(row_vector[ ])
  size(matrix[ ])
  size(int[ , ])
  size(real[ , ])
  size(vector[ , ])
  size(row_vector[ , ])
  size(matrix[ , ])
  size(int[ , , ])
  size(real[ , , ])
  size(vector[ , , ])
  size(row_vector[ , , ])
  size(matrix[ , , ])
  size(int[ , , , ])
  size(real[ , , , ])
  size(vector[ , , , ])
  size(row_vector[ , , , ])
  size(matrix[ , , , ])
  size(int[ , , , , ])
  size(real[ , , , , ])
  size(vector[ , , , , ])
  size(row_vector[ , , , , ])
  size(matrix[ , , , , ])
  size(int[ , , , , , ])
  size(real[ , , , , , ])
  size(vector[ , , , , , ])
  size(row_vector[ , , , , , ])
  size(matrix[ , , , , , ])
  size(int[ , , , , , , ])
  size(real[ , , , , , , ])
  size(vector[ , , , , , , ])
  size(row_vector[ , , , , , , ])
  size(matrix[ , , , , , , ])

 error in 'model42374ed5bbb7_model_code' at line 5, column 20
  -------------------------------------------------
     3: 
     4:   real test(vector x){
     5:     real N = size(x);
                           ^
     6:     return(N)
  -------------------------------------------------

Error in stanc(model_code = model_code) : 
  failed to parse Stan model 'model_code' due to the above error.
> 

Expected Output:

No error should be generated, could match to size(vector[ ])

Additional Information:

Provide any additional information here.

Current Version:

v2.22.0

Start with the supplied Stan function reproducer and compare how size(vector) is resolved with num_elements for function arguments. Trace the parser or signature-matching path responsible for the reported size(vector) error, then verify that the example compiles and returns the vector length without changing the existing array behavior.