Core: Warn when setting hooks for a different module

This will become an error in QUnit 3.

Ref #1576.
Closes #1586.

src/module.js

@@ -1,3 +1,5 @@
+import Logger from "./logger";
+
 import config from "./core/config";
 
 import SuiteReport from "./reports/suite";
@@ -94,6 +96,11 @@ function processModule( name, options, executeNow, modifiers = {} ) {
 
 	function setHookFunction( module, hookName ) {
 		return function setHook( callback ) {
+			if ( config.currentModule !== module ) {
+				Logger.warn( "The `" + hookName + "` hook was called inside the wrong module. " +
+					"Instead, use hooks provided by the callback to the containing module." +
+					"This will become an error in QUnit 3.0." );
+			}
 			module.hooks[ hookName ].push( callback );
 		};
 	}

test/cli/fixtures/expected/tap-outputs.js

@@ -331,5 +331,14 @@ ok 3 module B > test D
 # pass 2
 # skip 1
 # todo 1
+# fail 0`,
+
+	"qunit incorrect-hooks-warning/test.js":
+`TAP version 13
+ok 1 module providing hooks > module not providing hooks > has a test
+1..1
+# pass 1
+# skip 0
+# todo 0
 # fail 0`
 };

test/cli/fixtures/incorrect-hooks-warning/test.js

@@ -0,0 +1,9 @@
+QUnit.module( "module providing hooks", function( hooks ) {
+	QUnit.module( "module not providing hooks", function() {
+		// eslint-disable-next-line qunit/no-hooks-from-ancestor-modules
+		hooks.beforeEach( function() {} );
+		QUnit.test( "has a test", function( assert ) {
+			assert.true( true );
+		} );
+	} );
+} );

test/cli/main.js

@@ -311,4 +311,13 @@ QUnit.module( "CLI Main", () => {
 			assert.equal( execution.stdout, expectedOutput[ command ] );
 		} );
 	} );
+
+	QUnit.test( "warns about incorrect hook usage", async assert => {
+		const command = "qunit incorrect-hooks-warning/test.js";
+		const execution = await execute( command );
+
+		assert.equal( execution.code, 0 );
+		assert.equal( execution.stderr, "The `beforeEach` hook was called inside the wrong module. Instead, use hooks provided by the callback to the containing module.This will become an error in QUnit 3.0.", "The warning shows" );
+		assert.equal( execution.stdout, expectedOutput[ command ] );
+	} );
 } );