false positive: no-unreachable inside catch block when throwing value created outside scope of try

[jsejcksn]

Lint Name

no-unreachable

Code Snippet

lint_fail_test.ts:

import { assert } from "jsr:@std/assert@^1.0.1/assert";
import { assertThrows } from "jsr:@std/assert@^1.0.1/throws";

Deno.test("lint", () => {
  const error = assertThrows(
    () => {
      const fooError = new Error("foo");
      try {
        throw fooError;
      } catch (cause) {
        assert(cause instanceof Error && cause.message === "foo");
     // ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
        throw new Error("bar", { cause }); /*                    │
        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~                       │
        │                                                        │
        └─ error[no-unreachable]: This statement is unreachable ─┘ */
      }
    },
    Error,
    "bar",
  );

  assert(error.cause instanceof Error && error.cause.message === "foo");
});

Expected Result

Running deno lint lint_fail_test.ts exits with status code 0

Actual Result

Exits with status code 1 (see additional info below)

Additional Info

For comparison, here's the same test module except that the declaration of fooError is inside the try block:

lint_pass_test.ts:

import { assert } from "jsr:@std/assert@^1.0.1/assert";
import { assertThrows } from "jsr:@std/assert@^1.0.1/throws";

Deno.test("lint", () => {
  const error = assertThrows(
    () => {
      try {
        const fooError = new Error("foo");
        throw fooError;
      } catch (cause) {
        assert(cause instanceof Error && cause.message === "foo");
        throw new Error("bar", { cause });
      }
    },
    Error,
    "bar",
  );

  assert(error.cause instanceof Error && error.cause.message === "foo");
});

The module lint_pass_test.ts passes linting, and both test modules complete successfully using Deno's test runner. Here is terminal output for both modules:

% deno lint lint_pass_test.ts
Checked 1 file

% deno lint lint_fail_test.ts
error[no-unreachable]: This statement is unreachable
  --> /Users/deno/lint_fail_test.ts:11:9
   | 
11 |         assert(cause instanceof Error && cause.message === "foo");
   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

  docs: https://lint.deno.land/rules/no-unreachable


error[no-unreachable]: This statement is unreachable
  --> /Users/deno/lint_fail_test.ts:13:9
   | 
13 |         throw new Error("bar", { cause }); /*                    │
   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

  docs: https://lint.deno.land/rules/no-unreachable


Found 2 problems
Checked 1 file

% deno test *_test.ts
Check file:///Users/deno/lint_fail_test.ts
Check file:///Users/deno/lint_pass_test.ts
running 1 test from ./lint_fail_test.ts
lint ... ok (0ms)
running 1 test from ./lint_pass_test.ts
lint ... ok (0ms)

ok | 2 passed | 0 failed (10ms)

This was discovered in a CI failure here:

• https://github.com/denoland/std/actions/runs/10131143544/job/28013460563?pr=5561

…and might be a regression. Ref:

• False positive: no-unreachable unexpectedly flags statements inside catch clause #716

Version

deno 1.45.4 (release, aarch64-apple-darwin)
v8 12.7.224.13
typescript 5.5.2