See: #8398

fixes #8398

The problem: you currently can't use hooks to determine whether a compilation has failed. This makes it hard to wrap compilers with custom error handling. In master, the only time hooks.failed is called is when compilation fails during watch-mode. This PR calls the hook for normal compilations also.

What kind of change does this PR introduce?

This PR ensures the failed-hooked is called whenever compilation fails.

The finalCallback (from compiler.run(finalCallback) fame) is called as a bail-out whenever there's an error. So adding the call to the failed-hook here makes sense because it minimizes the code changes.

Did you add tests for your changes?

Yes, added a test. To ensure this PR does the trick, either run the tests or the code below:

const webpack = require("webpack");

const compiler = webpack({
	bail: true,
	context: __dirname,
	mode: "production",
	entry: "./missing",
	output: {
		path: "/",
		filename: "bundle.js"
	}
});

compiler.hooks.failed.tap("CompilerTest", err => {
	console.log("I made it to Flavortown:\n", err);
});

compiler.run((err, stats) => {
	if (err || stats.hasError()) {
		console.log("Compilation failed.");
	}
});

Does this PR introduce a breaking change?

As far as I can tell, it should not break anything. That is, unless folks have existing code for the failed-hook that they never expect to be called, which seems unlikely.

What needs to be documented once your changes are merged?

The docs actually already state the failed-hook is called on failure, so nothing should need to be updated. This PR just makes the behavior match the docs.