Newlines after a return statement considered to be uncovered code

[Avaq]

System information

$ uname -a
Linux thinkpad-avaq 4.19.75 #1-NixOS SMP Sat Sep 21 05:17:15 UTC 2019 x86_64 GNU/Linux
$ node -v
v12.11.1

(also tested on Node 12.5.0)

Description

In some cases (see below), c8 considers the newlines after a return statement to be "uncovered code".

Steps to reproduce

1. Install c8:

   $ npm install c8

2. Write the following content to src/index.mjs:

   const f = ({}) => {
     const b = {};
     return;
   }
   
   f ({});

3. Write the following content to test/index.mjs:

   import '../src/index.mjs'

4. Run c8:

   $ c8 node --experimental-modules test/index.mjs 
   (node:4857) ExperimentalWarning: The ESM module loader is experimental.
   -----------|----------|----------|----------|----------|-------------------|
   File       |  % Stmts | % Branch |  % Funcs |  % Lines | Uncovered Line #s |
   -----------|----------|----------|----------|----------|-------------------|
   All files  |      100 |    66.67 |      100 |      100 |                   |
    index.mjs |      100 |    66.67 |      100 |      100 |                 3 |
   -----------|----------|----------|----------|----------|-------------------|

Expected result

I expect to see no uncovered lines.

Actual result

Line 3 ( return;) is considered "partially covered". If I add additional newlines after the return statement, they come up as fully uncovered lines. If I remove the statement prior to the return statement, the problem goes away. If I stop using destructuring in the function arguments, the problem also goes away.

Possible related issues

• Incorrect coverage reported for ternaries in some situations #61
• Function definition after the return statement #66
• bug: coverage reported incorrectly with source-maps on Node 12 #90 (comment)

[bcoe]

this is likely an issue with the upstream v8 engine.

[bcoe]

I've confirmed that this is the same issue as #66, fix incoming.