Prune empty `case` blocks before a `default`

[dgp1130]

I think there's an opportunity to further optimize switch statements by removing empty case blocks before a default.

Input:

switch (globalThis.foo) {
  case 'first': {
    console.log('first');
  }
  case 'second':
  default: {
    console.log('default');
  }
}

Expected output:

switch (globalThis.foo) {
  case 'first': console.log('first');
  default: console.log('default');
}

Actual output (0.27.1):

switch (globalThis.foo) {
  case 'first': console.log('first');
  case 'second': // Unnecessary!
  default: console.log('default');
}

Playground link

I think you do need to keep case statements which contain expressions (case getSecond(): ...) as that's probably important for execution order and potential side effects. But I think any literal values should be safe to remove, and that's likely the most common case with switch statements.

[evanw]

Thank you for the suggestion. I agree.

Another note (for myself): if after minification the switch body contains a single case, then it can potentially be reduced further. Terser turns the input into this:

"first"===globalThis.foo&&console.log("first"),console.log("default");

If there's a break before the second case, Terser turns the input into this instead:

if("first"===globalThis.foo)console.log("first");else console.log("default");

Which should of course then become this (not sure why Terser doesn't do that):

"first"===globalThis.foo?console.log("first"):console.log("default");