async function "branch not covered"

[spudly]

Almost every time I write a function with async/await syntax, I have this problem:

The tooltop indicates that there is a "branch not covered," but I've made sure to cover every branch.

The same statistics are given when nyc generates the coverage results in the terminal, which leads me to believe the problem is in nyc and not in istanbul.

That number should be 100%, but it thinks there's an extra code branch that's not covered.

If I've missed something obvious, or if there's a workaround for this, please let me know.

[bcoe]

@spudly unfortunately our ability to cover ES6 syntax is slightly spotty, would love help debugging; I know that @novemberborn has dug into this a bit, and has gone so far as writing a pure-ES6 proof of concept.

[spudly]

I'd like to help debug but honestly I have no idea where to begin or what to look for. Is there some documentation somewhere that can point me in the right direction?

[novemberborn]

The same statistics are given when nyc generates the coverage results in the terminal, which leads me to believe the problem is in nyc and not in istanbul.

nyc just wraps istanbul. I assume you're transpiling your async usage to generators? Most likely when we get the coverage for the transpiled code we're unable to map it back to your original source. When that happens nyc has no choice but drop that coverage.

[bcoe]

@spudly we have some similar bugs logged here:

https://github.com/gotwarlost/istanbul/issues/626

In lieu of us swapping out the guts of nyc with a more ES6 aware library (something that @novemberborn is working on) it might be worthwhile to start digging into Istanbul a bit more, to see if some of these mapping issues can be patched. Ultimately, this will most likely require a better understanding of esprima as well (more so than I currently have).

[bcoe]

@spudly I tried to recreate this issue (see #266) and have actually been unable to:

I'm closing this issue in favor of #266, could you submit a failing example against that branch and we can use that as a jumping off point.

[bcoe]

@spudly give this a spin:

https://github.com/bcoe/nyc#use-babel-plugin__coverage__-for-better-es6es7-support

we've released better support for ES6/ES7 coverage using the coverage instrumentation library.

[spudly]

Sorry for the long delay. Tried the new solution, but I can't get past this:

Error: /Users/ssorense/workspace/cms-packages/packages/cms-cli/src/utils/login.js: Expected type "Statement" with option {}
    at Object.t.(anonymous function) [as assertStatement] (/Users/ssorense/workspace/cms-packages/packages/cms-cli/node_modules/babel-types/lib/index.js:361:13)
    at Emitter.Ep.explodeStatement (/Users/ssorense/workspace/cms-packages/packages/cms-cli/node_modules/babel-plugin-transform-regenerator/lib/emit.js:338:5)
    at /Users/ssorense/workspace/cms-packages/packages/cms-cli/node_modules/babel-plugin-transform-regenerator/lib/emit.js:544:18
    at Array.forEach (native)
    at /Users/ssorense/workspace/cms-packages/packages/cms-cli/node_modules/babel-plugin-transform-regenerator/lib/emit.js:543:38
    at Array.forEach (native)
    at Emitter.<anonymous> (/Users/ssorense/workspace/cms-packages/packages/cms-cli/node_modules/babel-plugin-transform-regenerator/lib/emit.js:539:27)
Error: non-zero error code
    at Error (native)
    at ChildProcess.<anonymous> (/Users/ssorense/workspace/cms-packages/packages/cms-cli/node_modules/pify-process/build/pifyProcess.js:12:19)
    at emitTwo (events.js:106:13)
    at ChildProcess.emit (events.js:191:7)
    at Process.ChildProcess._handle.onexit (internal/child_process.js:204:12)

[Ewocker]

Hi, This is still happening to the latest nyc version, is there a change ? Using "babel-plugin-istanbul": "^4.1.6" "nyc": "^11.8.0" "istanbul": "^1.1.0-alpha.1" or "0.4.5"

This has been really annoying to me.

[egrivel]

Hi,

We're still getting this issue with current versions of nyc, istanbul, etc. It looks like the transpiler is adding an unreachable case statement. The following source code:

_testAsync: async (caseId, context) => {
  let response;
  try {
    response = await ajax.get('this/is/my/API/call', {context});
    return response.body;
  } catch (error) {
    response.message = 'Failure getting API response';
  }
  return response;
}

gets transpiled into:

_testAsync: function () {
  var _testAsync2 = _asyncToGenerator(
  /*#__PURE__*/
  regeneratorRuntime.mark(function _callee2(caseId, context) {
    var response;
    return regeneratorRuntime.wrap(function _callee2$(_context2) {
      while (1) {
        switch (_context2.prev = _context2.next) {
          case 0:
            _context2.prev = 0;
            _context2.next = 3;
            return dcps_ui_ajax__WEBPACK_IMPORTED_MODULE_1___default.a.get('this/is/my/API/call', 
              context: context
            });

          case 3:
            response = _context2.sent;
            return _context2.abrupt("return", response.body);

          case 7:
            _context2.prev = 7;
            _context2.t0 = _context2["catch"](0);
            response.message = 'Failure getting API response';

          case 10:
            return _context2.abrupt("return", response);

          case 11:
          case "end":
            return _context2.stop();
        }
      }
    }, _callee2, this, [[0, 7]]);
  }));

  function _testAsync(_x5, _x6) {
    return _testAsync2.apply(this, arguments);
  }

  return _testAsync;
}(),

and then it seems that case 11: is unreachable.

The same problem happens when the return response is inside the catch block, or when we throw an exception while handling the error.

[elbertcastaneda]

I have this problem with the last version of nyc (14.1.1):

async init() {
    super._emit('beforeInit');

    await this.setForeignKeys(async () => {      // <<-- This async statement is the problem (My coverage report showed "Branch not covered" in this line)  
      const foreignKeys = await this._getForeignKeys();
      return foreignKeys;
    });
}

I'm going to add my devDependencies in case they would be helpful for something:

{
"...": "...",
"devDependencies": {
    "@babel/core": "^7.4.5",
    "@babel/plugin-proposal-class-properties": "^7.4.4",
    "@babel/plugin-proposal-export-default-from": "^7.2.0",
    "@babel/plugin-transform-runtime": "^7.4.4",
    "@babel/polyfill": "^7.4.4",
    "@babel/preset-env": "^7.4.5",
    "@babel/register": "^7.4.4",
    "@babel/runtime": "^7.4.5",
    "@types/knex": "^0.16.1",
    "babel-eslint": "^10.0.2",
    "chai": "^4.2.0",
    "eslint": "^6.0.1",
    "eslint-config-airbnb-base": "^13.2.0",
    "mocha": "^6.1.4",
    "nodemon": "^1.19.1",
    "nyc": "^14.1.1",
    "sinon": "^7.3.2",
    "source-map-support": "^0.5.12"
  },
"...": "..."
}

[coreyfarrell]

Please open a new ticket including all required information (especially a minimal demonstration repository). No action will be taken on this ticket.

[shonubijerry]

I noticed that when I declare a method inside a class namespace using async/await, nyc will cover all its branches but, if I declare the same method with async/await outside a class namespace, nyc will report branch not covered in its coverage.

[edmooliveira29]

I solved only updating version of the node to 15.12.0