Build: ESLint: forbid unused function parameters

This commit requires all function parameters to be used, not just the last one.
In cases where that's not possible as we need to match an external API, there's
an escape hatch of prefixing an unused argument with `_`.

This change makes it easier to catch unused AMD dependencies and unused
parameters in internal functions the API of which we may change at will, among
other things.

Unused AMD dependencies have been removed as part of this commit.

Closes gh-4381

(cherry-picked from 438b1a3e8a)

build/tasks/build.js

@@ -372,7 +372,7 @@ module.exports = function( grunt ) {
 
 		// Ask for permission the first time
 		if ( insight.optOut === undefined ) {
-			insight.askPermission( null, function( error, result ) {
+			insight.askPermission( null, function( _error, result ) {
 				exec( result );
 			} );
 		} else {

dist/.eslintrc.json

@@ -7,9 +7,10 @@
 		// That is okay for the built version
 		"no-multiple-empty-lines": "off",
 
-		// Because sizzle is not compatible to jquery code style
+		// Sizzle is not compatible with jQuery code style
 		"no-nested-ternary": "off",
 		"no-unused-expressions": "off",
+		"no-unused-vars": "off",
 		"lines-around-comment": "off",
 		"space-in-parens": "off",
 		"camelcase": "off",

package.json

@@ -29,7 +29,7 @@
     "@babel/plugin-transform-for-of": "7.2.0",
     "commitplease": "3.2.0",
     "core-js": "2.6.5",
-    "eslint-config-jquery": "1.0.1",
+    "eslint-config-jquery": "2.0.0",
     "grunt": "1.0.3",
     "grunt-babel": "8.0.0",
     "grunt-cli": "1.3.2",

src/ajax.js

@@ -833,7 +833,7 @@ jQuery.extend( {
 	}
 } );
 
-jQuery.each( [ "get", "post" ], function( i, method ) {
+jQuery.each( [ "get", "post" ], function( _i, method ) {
 	jQuery[ method ] = function( url, data, callback, type ) {
 
 		// Shift arguments if data argument was omitted

src/attributes/attr.js

@@ -117,7 +117,7 @@ boolHook = {
 	}
 };
 
-jQuery.each( jQuery.expr.match.bool.source.match( /\w+/g ), function( i, name ) {
+jQuery.each( jQuery.expr.match.bool.source.match( /\w+/g ), function( _i, name ) {
 	var getter = attrHandle[ name ] || jQuery.find.attr;
 
 	attrHandle[ name ] = function( elem, name, isXML ) {

src/core.js

@@ -374,7 +374,7 @@ if ( typeof Symbol === "function" ) {
 
 // Populate the class2type map
 jQuery.each( "Boolean Number String Function Array Date RegExp Object Error Symbol".split( " " ),
-function( i, name ) {
+function( _i, name ) {
 	class2type[ "[object " + name + "]" ] = name.toLowerCase();
 } );
 

src/core/access.js

@@ -38,7 +38,7 @@ var access = function( elems, fn, key, value, chainable, emptyGet, raw ) {
 			// ...except when executing function values
 			} else {
 				bulk = fn;
-				fn = function( elem, key, value ) {
+				fn = function( elem, _key, value ) {
 					return bulk.call( jQuery( elem ), value );
 				};
 			}

src/core/camelCase.js

@@ -7,7 +7,7 @@ var rmsPrefix = /^-ms-/,
 	rdashAlpha = /-([a-z])/g;
 
 // Used by camelCase as callback to replace()
-function fcamelCase( all, letter ) {
+function fcamelCase( _all, letter ) {
 	return letter.toUpperCase();
 }
 

src/css.js

@@ -34,7 +34,7 @@ var
 		fontWeight: "400"
 	};
 
-function setPositiveNumber( elem, value, subtract ) {
+function setPositiveNumber( _elem, value, subtract ) {
 
 	// Any relative (+/-) values have already been
 	// normalized at this point
@@ -344,7 +344,7 @@ jQuery.extend( {
 	}
 } );
 
-jQuery.each( [ "height", "width" ], function( i, dimension ) {
+jQuery.each( [ "height", "width" ], function( _i, dimension ) {
 	jQuery.cssHooks[ dimension ] = {
 		get: function( elem, computed, extra ) {
 			if ( computed ) {

src/css/var/swap.js

@@ -3,7 +3,7 @@ define( function() {
 "use strict";
 
 // A method for quickly swapping in/out CSS properties to get correct calculations.
-return function( elem, options, callback, args ) {
+return function( elem, options, callback ) {
 	var ret, name,
 		old = {};
 
@@ -13,7 +13,7 @@ return function( elem, options, callback, args ) {
 		elem.style[ name ] = options[ name ];
 	}
 
-	ret = callback.apply( elem, args || [] );
+	ret = callback.call( elem );
 
 	// Revert the old values
 	for ( name in options ) {

src/deferred.js

@@ -79,7 +79,7 @@ jQuery.extend( {
 					var fns = arguments;
 
 					return jQuery.Deferred( function( newDefer ) {
-						jQuery.each( tuples, function( i, tuple ) {
+						jQuery.each( tuples, function( _i, tuple ) {
 
 							// Map tuples (progress, done, fail) to arguments (done, fail, progress)
 							var fn = isFunction( fns[ tuple[ 4 ] ] ) && fns[ tuple[ 4 ] ];

src/effects.js

@@ -7,7 +7,6 @@ define( [
 	"./var/rnothtmlwhite",
 	"./css/var/cssExpand",
 	"./css/var/isHiddenWithinTree",
-	"./css/var/swap",
 	"./css/adjustCSS",
 	"./data/var/dataPriv",
 	"./css/showHide",
@@ -20,7 +19,7 @@ define( [
 	"./css",
 	"./effects/Tween"
 ], function( jQuery, camelCase, document, isFunction, rcssNum, rnothtmlwhite, cssExpand,
-	isHiddenWithinTree, swap, adjustCSS, dataPriv, showHide ) {
+	isHiddenWithinTree, adjustCSS, dataPriv, showHide ) {
 
 "use strict";
 
@@ -625,7 +624,7 @@ jQuery.fn.extend( {
 	}
 } );
 
-jQuery.each( [ "toggle", "show", "hide" ], function( i, name ) {
+jQuery.each( [ "toggle", "show", "hide" ], function( _i, name ) {
 	var cssFn = jQuery.fn[ name ];
 	jQuery.fn[ name ] = function( speed, easing, callback ) {
 		return speed == null || typeof speed === "boolean" ?

src/event/ajax.js

@@ -13,7 +13,7 @@ jQuery.each( [
 	"ajaxError",
 	"ajaxSuccess",
 	"ajaxSend"
-], function( i, type ) {
+], function( _i, type ) {
 	jQuery.fn[ type ] = function( fn ) {
 		return this.on( type, fn );
 	};

src/event/alias.js

@@ -10,7 +10,7 @@ define( [
 jQuery.each( ( "blur focus focusin focusout resize scroll click dblclick " +
 	"mousedown mouseup mousemove mouseover mouseout mouseenter mouseleave " +
 	"change select submit keydown keypress keyup contextmenu" ).split( " " ),
-	function( i, name ) {
+	function( _i, name ) {
 
 	// Handle event binding
 	jQuery.fn[ name ] = function( data, fn ) {

src/offset.js

@@ -1,7 +1,6 @@
 define( [
 	"./core",
 	"./core/access",
-	"./var/document",
 	"./var/documentElement",
 	"./var/isFunction",
 	"./css/var/rnumnonpx",
@@ -12,8 +11,8 @@ define( [
 	"./core/init",
 	"./css",
 	"./selector" // contains
-], function( jQuery, access, document, documentElement, isFunction, rnumnonpx,
-             curCSS, addGetHookIf, support, isWindow ) {
+], function( jQuery, access, documentElement, isFunction, rnumnonpx,
+	curCSS, addGetHookIf, support, isWindow ) {
 
 "use strict";
 
@@ -214,7 +213,7 @@ jQuery.each( { scrollLeft: "pageXOffset", scrollTop: "pageYOffset" }, function(
 // Blink bug: https://bugs.chromium.org/p/chromium/issues/detail?id=589347
 // getComputedStyle returns percent when specified for top/left/bottom/right;
 // rather than make the css module depend on the offset module, just check for it here
-jQuery.each( [ "top", "left" ], function( i, prop ) {
+jQuery.each( [ "top", "left" ], function( _i, prop ) {
 	jQuery.cssHooks[ prop ] = addGetHookIf( support.pixelPosition,
 		function( elem, computed ) {
 			if ( computed ) {

src/serialize.js

@@ -114,7 +114,7 @@ jQuery.fn.extend( {
 				rsubmittable.test( this.nodeName ) && !rsubmitterTypes.test( type ) &&
 				( this.checked || !rcheckableType.test( type ) );
 		} )
-		.map( function( i, elem ) {
+		.map( function( _i, elem ) {
 			var val = jQuery( this ).val();
 
 			if ( val == null ) {

src/traversing.js

@@ -118,7 +118,7 @@ jQuery.each( {
 	parents: function( elem ) {
 		return dir( elem, "parentNode" );
 	},
-	parentsUntil: function( elem, i, until ) {
+	parentsUntil: function( elem, _i, until ) {
 		return dir( elem, "parentNode", until );
 	},
 	next: function( elem ) {
@@ -133,10 +133,10 @@ jQuery.each( {
 	prevAll: function( elem ) {
 		return dir( elem, "previousSibling" );
 	},
-	nextUntil: function( elem, i, until ) {
+	nextUntil: function( elem, _i, until ) {
 		return dir( elem, "nextSibling", until );
 	},
-	prevUntil: function( elem, i, until ) {
+	prevUntil: function( elem, _i, until ) {
 		return dir( elem, "previousSibling", until );
 	},
 	siblings: function( elem ) {