[php-src] Issue #14747: Why are constant expressions decided at compile time instead of in the grammar?

Issue: https://github.com/php/php-src/issues/14747 Author: chx ### Description I was looking at zend_language_parser.y and I was surprised to see attribute allows a full expr and there's no const_expr definition. When I look at zend_is_allowed_in_const_expr on the other hand, it only contains multiple comparisons to constants defined in the _zend_ast_kind enum. In turn, it seems to me these are created in zend_language_parser.y using calls like zend_ast_create(ZEND_AST_CLASS_CONST, $1, $4); That means it should be possible to simply take all the declarations which lead to such an zend_ast_create() calls for every constant in zend_is_allowed_in_const_expr and thus define a const_expr in the language parser instead of deciding whether an expression is constant at compile time. Mind you I never worked with yacc before so I might be totally wrong here, I am just reading the source code. But if my observation is correct... why there isn't a const_expr? Should I make an attempt in creating one :) ? Is there tooling which would help creating one such? ### PHP Version PHP 8.3.8 ### Operating System _No response_