fix: transpile to es2017 as esnext may result in unsupported JS code

[Flarna]

Which problem is this PR solving?

Unsupported JS code is generated if e.g. optional chaining operator ?. is used.

Short description of the changes

Transpile to es2017 to ensure compatiblity with Node.Js 8. Otherwise use of
e.g. the optional chaining operator ?. supported since typescript 3.7 results
in js not running on nodejs 8. Es2017 is the minimum to get native await support.

[dyladan]

Is there a reason we even need to use es2017? On my machine es2015 produces a build that is nearly the same size, taking only a couple more seconds to build. Is there any real advantage to targeting such a late version of node?

esnext => ~45 seconds, 3988k for all packages
es2015 => ~50 seconds, 3996k for all packages (0.2% larger)

[vmarchaud]

@dyladan I believe that i may introduce polyfill in javascript code that may be slow and since we don't really have a benchmarking in place to mesure if we compile to slow code, i would prefer to use es2017 here

[dyladan]

Maybe in the future we could use a tagged release mechanism. Install with npm install @opentelemetry/node@0.2.0-es2015.

It is probably too much for alpha or even beta, but could be useful once we are 1.0

[OlivierAlbertini]

I'm agree with @vmarchaud

[Flarna]

I think it's not just performance. Polyfills tend to have hidden corners where they act different. I would assume that polyfills result in breaking the async stack trace feature introduced in nodejs 12. I could also imagine that async hooks show slightly different results.

if we ban use of await in @opentelemetry packages transpile to older standards would be easier but I see no reason to do so.

Maybe in the future we could use a tagged release mechanism. Install with npm install @opentelemetry/node@0.2.0-es2015.

I think this breaks semver range patterns (e.g. ^0.2.0).

Just to illustrate the difference some small typescript sample using await:

async function bar() { return Promise.resolve(15) }
async function foo() { return await bar() }

es2017:

async function bar() { return Promise.resolve(15); }
async function foo() { return await bar(); }

es2015:

var __awaiter = (this && this.__awaiter) || function (thisArg, _arguments, P, generator) {
    function adopt(value) { return value instanceof P ? value : new P(function (resolve) { resolve(value); }); }
    return new (P || (P = Promise))(function (resolve, reject) {
        function fulfilled(value) { try { step(generator.next(value)); } catch (e) { reject(e); } }
        function rejected(value) { try { step(generator["throw"](value)); } catch (e) { reject(e); } }
        function step(result) { result.done ? resolve(result.value) : adopt(result.value).then(fulfilled, rejected); }
        step((generator = generator.apply(thisArg, _arguments || [])).next());
    });
};
function bar() {
    return __awaiter(this, void 0, void 0, function* () { return Promise.resolve(15); });
}
function foo() {
    return __awaiter(this, void 0, void 0, function* () { return yield bar(); });
}

es5:

var __awaiter = (this && this.__awaiter) || function (thisArg, _arguments, P, generator) {
    function adopt(value) { return value instanceof P ? value : new P(function (resolve) { resolve(value); }); }
    return new (P || (P = Promise))(function (resolve, reject) {
        function fulfilled(value) { try { step(generator.next(value)); } catch (e) { reject(e); } }
        function rejected(value) { try { step(generator["throw"](value)); } catch (e) { reject(e); } }
        function step(result) { result.done ? resolve(result.value) : adopt(result.value).then(fulfilled, rejected); }
        step((generator = generator.apply(thisArg, _arguments || [])).next());
    });
};
var __generator = (this && this.__generator) || function (thisArg, body) {
    var _ = { label: 0, sent: function() { if (t[0] & 1) throw t[1]; return t[1]; }, trys: [], ops: [] }, f, y, t, g;
    return g = { next: verb(0), "throw": verb(1), "return": verb(2) }, typeof Symbol === "function" && (g[Symbol.iterator] = function() { return this; }), g;
    function verb(n) { return function (v) { return step([n, v]); }; }
    function step(op) {
        if (f) throw new TypeError("Generator is already executing.");
        while (_) try {
            if (f = 1, y && (t = op[0] & 2 ? y["return"] : op[0] ? y["throw"] || ((t = y["return"]) && t.call(y), 0) : y.next) && !(t = t.call(y, op[1])).done) return t;
            if (y = 0, t) op = [op[0] & 2, t.value];
            switch (op[0]) {
                case 0: case 1: t = op; break;
                case 4: _.label++; return { value: op[1], done: false };
                case 5: _.label++; y = op[1]; op = [0]; continue;
                case 7: op = _.ops.pop(); _.trys.pop(); continue;
                default:
                    if (!(t = _.trys, t = t.length > 0 && t[t.length - 1]) && (op[0] === 6 || op[0] === 2)) { _ = 0; continue; }
                    if (op[0] === 3 && (!t || (op[1] > t[0] && op[1] < t[3]))) { _.label = op[1]; break; }
                    if (op[0] === 6 && _.label < t[1]) { _.label = t[1]; t = op; break; }
                    if (t && _.label < t[2]) { _.label = t[2]; _.ops.push(op); break; }
                    if (t[2]) _.ops.pop();
                    _.trys.pop(); continue;
            }
            op = body.call(thisArg, _);
        } catch (e) { op = [6, e]; y = 0; } finally { f = t = 0; }
        if (op[0] & 5) throw op[1]; return { value: op[0] ? op[1] : void 0, done: true };
    }
};
function bar() {
    return __awaiter(this, void 0, void 0, function () { return __generator(this, function (_a) {
        return [2 /*return*/, Promise.resolve(15)];
    }); });
}
function foo() {
    return __awaiter(this, void 0, void 0, function () { return __generator(this, function (_a) {
        switch (_a.label) {
            case 0: return [4 /*yield*/, bar()];
            case 1: return [2 /*return*/, _a.sent()];
        }
    }); });
}

[obecny]

lgtm

[codecov-io]

Codecov Report

Merging #593 into master will decrease coverage by 0.14%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #593      +/-   ##
==========================================
- Coverage   92.31%   92.16%   -0.15%     
==========================================
  Files         177      182       +5     
  Lines        8728     9049     +321     
  Branches      758      797      +39     
==========================================
+ Hits         8057     8340     +283     
- Misses        671      709      +38

Impacted Files	Coverage Δ
...ges/opentelemetry-plugin-https/test/utils/utils.ts	33.33% <0%> (-26.67%)	⬇️
...ges/opentelemetry-exporter-zipkin/src/transform.ts	100% <0%> (ø)	⬆️
.../opentelemetry-exporter-zipkin/test/zipkin.test.ts	100% <0%> (ø)	⬆️
packages/opentelemetry-web/src/WebTracer.ts	100% <0%> (ø)	⬆️
packages/opentelemetry-plugin-https/src/utils.ts	100% <0%> (ø)	⬆️
...telemetry-scope-base/test/NoopScopeManager.test.ts	100% <0%> (ø)	⬆️
...entelemetry-exporter-zipkin/test/transform.test.ts	100% <0%> (ø)	⬆️
...ackages/opentelemetry-exporter-zipkin/src/utils.ts
...res/opentelemetry-plugin-pg/test/assertionUtils.ts	100% <0%> (ø)
...postgres/opentelemetry-plugin-pg/test/testUtils.ts	15% <0%> (ø)
... and 5 more