Incorrect coverage reporting with throw in a block

[Trott]

• Version: 11.9.0
• Platform: Darwin LIB-0F7FVH8-LT 18.2.0 Darwin Kernel Version 18.2.0: Mon Nov 12 20:24:46 PST 2018; root:xnu-4903.231.4~2/RELEASE_X86_64 x86_64

In file foo.js:

if (true) {
  throw new Error('foo');
}

I run this:

c8 node foo.js 

I get this output:

/Users/trott/io.js/foo.js:2
  throw new Error('foo');
  ^

Error: foo
    at Object.<anonymous> (/Users/trott/io.js/foo.js:2:9)
    at Module._compile (internal/modules/cjs/loader.js:734:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:745:10)
    at Module.load (internal/modules/cjs/loader.js:626:32)
    at tryModuleLoad (internal/modules/cjs/loader.js:566:12)
    at Function.Module._load (internal/modules/cjs/loader.js:558:3)
    at Function.Module.runMain (internal/modules/cjs/loader.js:797:12)
    at executeUserCode (internal/bootstrap/node.js:526:15)
    at startMainThreadExecution (internal/bootstrap/node.js:439:3)
----------|----------|----------|----------|----------|-------------------|
File      |  % Stmts | % Branch |  % Funcs |  % Lines | Uncovered Line #s |
----------|----------|----------|----------|----------|-------------------|
All files |       50 |    66.67 |      100 |       50 |                   |
 foo.js   |       50 |    66.67 |      100 |       50 |               3,4 |
----------|----------|----------|----------|----------|-------------------|

What I expected:

I would not expect there to be a line 4 mentioned in the coverage report because the script is three lines long.
I would not expect line 3 to be mentioned as uncovered because there is nothing executable on it.
I would expect Lines to be covered 100% (but not Branch).

[thealjey]

@Trott if you don't handle errors, how do you expect accurate results? the script terminates after that throw

[Trott]

@Trott if you don't handle errors, how do you expect accurate results?

Failing to catch the error is not the problem. I did that for simplicity. Here:

$ cat foo.js
function doSomething(foo) {
  if (foo === 'throw') {
    throw new Error('foo');
  }
  console.log('Your foo is OK.');
}

try {
  doSomething('foo');
  doSomething('throw');
} catch (e) {
  console.log(`caught ${e}`);
}
$ c8 node foo.js
Your foo is OK.
caught Error: foo
----------|----------|----------|----------|----------|-------------------|
File      |  % Stmts | % Branch |  % Funcs |  % Lines | Uncovered Line #s |
----------|----------|----------|----------|----------|-------------------|
All files |    92.86 |       80 |      100 |    92.86 |                   |
 foo.js   |    92.86 |       80 |      100 |    92.86 |                 4 |
----------|----------|----------|----------|----------|-------------------|
$ 

It is still incorrectly telling me that there is an uncovered branch when there is not. It is also still incorrectly reporting that line 4 is uncovered. Line 4 does not contain any executable code. Both branches of the if statement are being exercised. All errors are being caught.

[Trott]

Incidentally, the throw isn't the problem per se. It appears that anything that returns control from the block will result in mis-reporting that the brace on a line by itself is uncovered.

$ cat foo.js
function doSomething(foo) {
  if (foo === 'return') {
    return foo;
  }
  console.log('Your foo is OK.');
}

doSomething('foo');
doSomething('return');
$ c8 node foo.js
Your foo is OK.
----------|----------|----------|----------|----------|-------------------|
File      |  % Stmts | % Branch |  % Funcs |  % Lines | Uncovered Line #s |
----------|----------|----------|----------|----------|-------------------|
All files |       90 |       80 |      100 |       90 |                   |
 foo.js   |       90 |       80 |      100 |       90 |                 4 |
----------|----------|----------|----------|----------|-------------------|
$ 

[thealjey]

I think this is a duplicate of #54

[bcoe]

see: https://bugs.chromium.org/p/v8/issues/detail?id=8691&q=coverage%20throw&colspec=ID%20Type%20Status%20Priority%20Owner%20Summary%20HW%20OS%20Component%20Stars

[shinnn]

Though the V8 bug referenced in #62 (comment) still seems unresolved, with Node.js v11.13.0 the code and command in #62 (comment) works as expected now.

$ node -v
v11.13.0

$ npx c8 node foo.js
/Users/Shinnosuke/foo.js:2
  throw new Error('foo');
  ^

Error: foo
    at Object.<anonymous> (/Users/Shinnosuke/foo.js:2:9)
    at Module._compile (internal/modules/cjs/loader.js:805:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:816:10)
    at Module.load (internal/modules/cjs/loader.js:672:32)
    at tryModuleLoad (internal/modules/cjs/loader.js:612:12)
    at Function.Module._load (internal/modules/cjs/loader.js:604:3)
    at Function.Module.runMain (internal/modules/cjs/loader.js:868:12)
    at internal/main/run_main_module.js:21:11
----------|----------|----------|----------|----------|-------------------|
File      |  % Stmts | % Branch |  % Funcs |  % Lines | Uncovered Line #s |
----------|----------|----------|----------|----------|-------------------|
All files |      100 |      100 |      100 |      100 |                   |
 foo.js   |      100 |      100 |      100 |      100 |                   |
----------|----------|----------|----------|----------|-------------------|

[Trott]

Though the V8 bug referenced in #62 (comment) still seems unresolved, with Node.js v11.13.0 the code and command in #62 (comment) works as expected now.

I believe @bcoe floated a fix in Node.js itself for the V8 that ships with Node.js.

[bcoe]

this issue is corrected as of Node 13.