Wrong full-elimination on for stmt with var decl.

[7086cmd]

Given the code:

for (var { c, x: [d] } = {}; 0;);

In reality, our actual behavior is to eliminate the entire code, which is incorrect. We need to eliminate it to:

var { c: a, x: [c] } = {};

Also given:

for (var se = [1, 2]; false;);

need we handle it to:

var se=[1,2];

[7086cmd]

Related issue: rolldown/rolldown#2426 (comment).

I currently don't have much time to work on this since midterms are approaching. If anyone is interested in contributing, you're more than welcome!

Possible Solutions

We could hoist the initialization expression during the DCE AST pass. Since init is either a Variable Declaration or an Expression, this could be achieved by:

// variable declaration
ctx.ast.statement_declaration(SPAN, ctx.ast.declaration_from_variable(decl))
// expression
ctx.ast.statement_expression(SPAN, ctx.ast.move_expression(expr))

This code is just for reference; you’ll need to handle borrow and move semantics properly.

You can then join these statements with block statements. The DCE pass will handle eliminating any extra blocks, so you don't need to worry about that. Later, we can replace this with more complex statement handling, but for now, I've opted to use enter_statement instead of enter_statements.