Inconsistency of allowing target+= #979
Description
Consider two stan programs:
prog1:
transformed parameters {
target += 1;
}prog2:
functions {
void foo_lp(real x){
target += x;
}
}
transformed parameters {
foo_lp(1);
}prog1. stan produces a type error:
Semantic error in 'prog1.stan', line 2, column 3 to column 15:
-------------------------------------------------
1: transformed parameters {
2: target += 1;
^
3: }
-------------------------------------------------
Target can only be accessed in the model block or in definitions of functions with the suffix _lp.
prog2.stan compiles just fine.
This is because we have this check for target+= statements:
stanc3/src/frontend/Semantic_check.ml
Lines 1112 to 1113 in 095b8ef
And this check for the calling of _lp functions:
stanc3/src/frontend/Semantic_check.ml
Lines 238 to 246 in 095b8ef