improve error msg when delcaration is made after assignment

[yizhang-yiz]

Summary:

When declare after assignment the msg is not informative.

Description:

When declare after assignment the error msg is
variable xxx does not exitst
where xxx is the type name of the declared variable. This is not informative to beginners.

Reproducible Steps:

make a model with the following transformed data

transformed data {
  real x;
  x = 3.0;
  real z;
  z = 3.0
}

Current Output:

SYNTAX ERROR, MESSAGE(S) FROM PARSER:

variable "real" does not exist.

Expected Output:

More informative information on the order of declaration & assignment.

Current Version:

v2.17.1

[bob-carpenter]

Thanks---the message should definitely be improved. The plan is to relax the language to allow that to be legal, but until then, there needs to be a better message.

[VMatthijs]

Mixing var decls and statements in any order is now allowed in stanc3, in case that addresses the issue.

[mcol]

Fixed in stanc3.