bug: false positive of no-fallthrough for empty fallthrough in nested switch

[xubaiwang]

Lint Name

no-fallthrough

Code Snippet

function booleanAnd(b1: boolean, b2: boolean) {
  switch (b1) {
    case true:        // false positive lint here
      switch (b2) {
        case true:
        default:
          return true;
      }
    case false:
      switch (b2) {
        case true:
          return true;
        case false:
          return false;
      }
  }
}

Expected Result

No linting errors.

Actual Result

❯ deno lint foo.ts 
error[no-fallthrough]: Fallthrough is not allowed
 --> /home/xubaiw/foo.ts:3:5
  | 
3 |     case true:
  |     ^^^^^^^^^^
  | 
4 |       switch (b2) {
  | ^^^^^^^^^^^^^^^^^^^
  | 
5 |         case true:
  | ^^^^^^^^^^^^^^^^^^
  | 
6 |         default:
  | ^^^^^^^^^^^^^^^^
  | 
7 |           return true;
  | ^^^^^^^^^^^^^^^^^^^^^^
  | 
8 |       }
  | ^^^^^^^
  = hint: Add `break` or comment `/* falls through */` to your case statement

  docs: https://docs.deno.com/lint/rules/no-fallthrough


Found 1 problem
Checked 1 file

Additional Info

This issue is different from #1331 , which is involved with End::Break, while this issue is about End::Continue.

Also reported in denoland/deno#29805 (closed now).

This problem may arise from here:

deno_lint/src/control_flow/mod.rs

Lines 480 to 488 in 4a56a49

	.filter_map(|case| self.get_end_reason(case.start()))
	.try_fold(
	End::Forced {
	ret: false,
	throw: false,
	infinite_loop: false,
	},
	|acc, cur| acc.merge_forced(cur),
	);

The fallthrough case is considered End::Continue, and fail to merge in merge_forced.

Version

deno 2.3.5 (stable, release, x86_64-unknown-linux-gnu)
v8 13.7.152.6-rusty
typescript 5.8.3