Parser rejects structured (aggregate) initializers in `VAR` declarations — `Expected RParen, found :=`

[dreamclass]

Problem

Summary

STruC++ cannot parse an IEC 61131-3 structured initial value — the
( field := value, field := value, ... ) aggregate-initializer syntax used to
give a STRUCT-typed variable a default value in its declaration. The parser
reaches the first field := inside the parentheses, expects a closing ), and
aborts.

Environment

• STruC++ version: 0.6.2 (strucpp.exe, win64)

Impact

Compilation fails during parsing

Reproduction

Steps to reproduce

udt.st:

TYPE
    inner : STRUCT
        a : INT;
        b : INT;
    END_STRUCT;
    outer : STRUCT
        p : inner;
        q : INT;
    END_STRUCT;
END_TYPE

PROGRAM PLC_PRG
VAR
    s : outer := ( p := ( a := 1, b := 2 ), q := 3 );
END_VAR
    s.q := s.q + 1;
END_PROGRAM

strucpp udt.st -o udt.cpp --no-default-libs

Actual result

Compilation fails during parsing:

Compilation failed:

udt.st:14:22: error: Expected `RParen`, found `:=`.
  14 |     s : outer := ( p := ( a := 1, b := 2 ), q := 3 );
     |                      ^

Code Locations

No response

Fix

No response

Acceptance

STruC++ can parse an IEC 61131-3 structured initial value — the
( field := value, field := value, ... ) aggregate-initializer syntax used to
give a STRUCT-typed variable a default value in its declaration.