Rollup Version

4.16.2

Operating System (or Browser)

osx

Node Version (if applicable)

20

Link To Reproduction

https://rollupjs.org/repl/?version=4.16.2&shareable=JTd...

Expected Behaviour

acorn-walk simple visitor methods should be called after compilation.

function simple(node, visitors, baseVisitor) {
  if (!baseVisitor) baseVisitor = base
  ;(function c(node, override) {
    let type = override || node.type; // <--
    baseVisitor[type](node, c);
    if (visitors[type]) visitors[type](node);
  })(node);
}

In the provided repl, the node of type Identifier should trigger a recursive call to "c" with override = "Expression" and that should if (visitors[type]) visitors[type](node) -> console.log("node found")

If the override parameter is assumed undefined with treeshaking (even "safest" exhibits this issue), then the behavior is broken.

Actual Behaviour

acorn-walk simple visitor methods are not called because "override" is erroneously optimized out.

The simple visitors object is keyed on simpler override keys like Expression, not native es-tree node.type keys like ExpressionStatement, or FunctionExpression), the value of override is provided by the call through baseVisitor which then calls c again with the children of the node possibly classified by the override key for simple visitors[type] usage.

When rollup optimizes this out, then the simple visitor[type] callbacks are not run.

function simple(node, visitors, baseVisitor) {
  if (!baseVisitor) baseVisitor = base
  ;(function c(node, override) {
    let type = node.type; // <-- ⚠️ 
    baseVisitor[type](node, c);
    if (visitors[type]) visitors[type](node);
  })(node);
}