Changes from stanc2

In the process of implementing stanc3, several bugs were found in stanc2 and were fixed in stanc3. We record these here. (A general theme is that error messages have changed a lot and should have improved.)

Target is a reserved variable name

Printing without a semi-colon is not allowed

Function arguments should not be allowed to shadow

ODE solver type checking was wrong

Non-returning function calls should be followed by a semi-colon

Parse error in if-else

Stanc gives run-time errors when using function names (e.g. add) corresponding to operators (e.g. +), for certain signatures

(This could either be a Stan Math error or a Stanc error.)

Variable declarations and statements can be mixed

see also this issue

Array constructors work with sampling statements

Added pretty printing functionality, exposing a pre-processed version of the Stan program from the compiler

Fixed parser warnings for semicolons in function arguments

Parser points to the name of non-existent functions rather than the end of the line

Correct error message when same identifier used for both fct name and var name

Parser flags use of _lxxf suffix on built-in functions in sampling statements

We disallow transpose operator on scalars

Throw informative error on non-ascii characters and other lexing errors

Better error message for program block names which contain typos

Improved line numbers in if/then errors

Fixed Windows/Unit line ending problems in error message locations

Parser promotes int to double when self-multiplying or self-dividing a vector

Better error message on non-existent higher-order function

Better error message when function already defined

Errors use Stan syntax (by leveraging pretty printer to render AST properly)