no-fallthrough warns when infinite loop with no break precludes fallthrough

[peetklecha]

Lint Name

no-fallthrough

Code Snippet

function* sequence(type: "even" | "odd" | "prime") {
  let num = 0;
  switch (type) {
    case "even":
      while (true) {
        if (isEven(num)) yield num;
        num += 1;
      }
      // break;
    case "odd":
      ...
  }
}

Expected Result

There should be no warning.

Actual Result

Fallthrough is not allowed
Add `break` or comment `/* falls through */` to your case statementdeno-lint(no-fallthrough)

Uncommenting the break causes that to receive an unreachable code warning, which shows that the linter already identifies the loop as never breaking.

Additional Info

Same basic issue as #1042 but this should be even more straightforward to fix.

Version

deno 1.33.2 (release, x86_64-apple-darwin)
v8 11.4.183.1
typescript 5.0.3

[magurotuna]

I think the core of the issue can be seen in the following snippet:

switch (someValue) {
  case 0:
    while (true) {}
  default:
    console.log(42);
}

The control flow analyzer does know while (true) {} is an infinite loop. However, this information is not utilized well by no-fallthrough rule - maybe the straightforward way to solve this would be that we let no-fallthrough skip the fallthrough check if the final point of a case (i.e. in the above example, the point right after while (true) {} but before going into the next branch, default:) is unreachable. This may require some fix in control flow analyzer.