Incorrect branch coverage for async methods

• v12.22.5:
• macOS 11.5.2:

I’ve noticed some inexplicable uncovered branch reports after switching from nyc to c8. The uncovered branches were the closing braces of async methods. The issue can be reproduced with the following code:

class Test {
  constructor(msg) {
    this.msg = msg;
  }

  async say() {
    return this.msg;
  } // uncovered branch?
}

const main = async () => {
  const t = new Test('hello');
  console.log(await t.say());
};

main().catch(console.error);

Running c8:

npx c8 node src/test.js
hello
----------|---------|----------|---------|---------|-------------------
File      | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s 
----------|---------|----------|---------|---------|-------------------
All files |     100 |       80 |     100 |     100 |                   
 test.js  |     100 |       80 |     100 |     100 | 8                
----------|---------|----------|---------|---------|-------------------

Line 8 is the closing } of the async test() method.

[bcoe]

@stefan-guggisberg perhaps keep this issue open, so other folks understand this category of issue.

[bcoe]

@stefan-guggisberg this was likely a bug in v8 itself, which appears to have been fixed in newer versions of Node.js (I couldn’t reproduce in v14/v16)

Unfortunately these updates to v8 can’t always be back-ported to older Node.js versions (so I won’t be able to fix in c8).

Can you potentially run coverage on a newer version of Node.js? while still testing on Node 12, i.e., run coverage on the latest and greatest Node.js, test on all versions you support.