Adding upstream version 43.9.upstream/43.9upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

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+# Coding guide
+
+Our goal is to have all JavaScript code in GNOME follow a consistent style. In
+a dynamic language like JavaScript, it is essential to be rigorous about style
+(and unit tests), or you rapidly end up with a spaghetti-code mess.
+
+## A quick note
+
+Life isn't fun if you can't break the rules. If a rule seems unnecessarily
+restrictive while you're coding, ignore it, and let the patch reviewer decide
+what to do.
+
+## Indentation, braces and whitespace
+
+* Use four-space indents.
+* Braces are on the same line as their associated statements.
+* You should only omit braces if *both* sides of the statement are on one line.
+* One space after the `function` keyword.
+* No space between the function name in a declaration or a call.
+* One space before the parens in the `if` statements, or `while`, or `for` loops.
+
+```javascript
+    function foo(a, b) {
+        let bar;
+
+        if (a > b)
+            bar = do_thing(a);
+        else
+            bar = do_thing(b);
+
+        if (var == 5) {
+            for (let i = 0; i < 10; i++)
+                print(i);
+        } else {
+            print(20);
+        }
+    }
+```
+
+## Semicolons
+
+JavaScript allows omitting semicolons at the end of lines, but don't. Always
+end statements with a semicolon.
+
+## js2-mode
+
+If using Emacs, do not use js2-mode. It is outdated and hasn't worked for a
+while. emacs now has a built-in JavaScript mode, js-mode, based on
+espresso-mode. It is the de facto emacs mode for JavaScript.
+
+## File naming and creation
+
+For JavaScript files, use lowerCamelCase-style names, with a `.js` extension.
+
+We only use C where gjs/gobject-introspection is not available for the task, or
+where C would be cleaner. To work around limitations in
+gjs/gobject-introspection itself, add a new method in `shell-util.[ch]`.
+
+Like many other GNOME projects, we prefix our C source filenames with the
+library name followed by a dash, e.g. `shell-app-system.c`. Create a
+`-private.h` header when you want to share code internally in the
+library. These headers are not installed, distributed or introspected.
+
+## Imports
+
+Use UpperCamelCase when importing modules to distinguish them from ordinary
+variables, e.g.
+```javascript
+    const GLib = imports.gi.GLib;
+```
+Imports should be categorized into one of two places. The top-most import block
+should contain only "environment imports". These are either modules from
+gobject-introspection or modules added by gjs itself.
+
+The second block of imports should contain only "application imports". These
+are the JS code that is in the gnome-shell codebase,
+e.g. `imports.ui.popupMenu`.
+
+Each import block should be sorted alphabetically. Don't import modules you
+don't use.
+```javascript
+    const { GLib, Gio, St } = imports.gi;
+
+    const Main = imports.ui.main;
+    const Params = imports.misc.params;
+    const Util = imports.misc.util;
+```
+The alphabetical ordering should be done independently of the location of the
+location. Never reference `imports` in actual code.
+
+## Constants
+
+We use CONSTANTS_CASE to define constants. All constants should be directly
+under the imports:
+```javascript
+    const MY_DBUS_INTERFACE = 'org.my.Interface';
+```
+
+## Variable declaration
+
+Always use either `const` or `let` when defining a variable.
+```javascript
+    // Iterating over an array
+    for (let i = 0; i < arr.length; ++i)
+        let item = arr[i];
+
+    // Iterating over an object's properties
+    for (let prop in someobj) {
+        ...
+    }
+```
+
+If you use "var" then the variable is added to function scope, not block scope.
+See [What's new in JavaScript 1.7](https://developer.mozilla.org/en/JavaScript/New_in_JavaScript/1.7#Block_scope_with_let_%28Merge_into_let_Statement%29)
+
+## Classes
+
+There are many approaches to classes in JavaScript. We use standard ES6 classes
+whenever possible, that is when not inheriting from GObjects.
+```javascript
+    var IconLabelMenuItem = class extends PopupMenu.PopupMenuBaseItem {
+        constructor(icon, label) {
+            super({ reactive: false });
+            this.actor.add_child(icon);
+            this.actor.add_child(label);
+        }
+
+        open() {
+            log("menu opened!");
+        }
+    };
+```
+
+For GObject inheritance, we use the GObject.registerClass() function provided
+by gjs.
+```javascript
+    var MyActor = GObject.registerClass(
+    class MyActor extends Clutter.Actor {
+        _init(params) {
+            super._init(params);
+
+            this.name = 'MyCustomActor';
+        }
+    });
+```
+
+## GObject Introspection
+
+GObject Introspection is a powerful feature that allows us to have native
+bindings for almost any library built around GObject. If a library requires
+you to inherit from a type to use it, you can do so:
+```javascript
+    var MyClutterActor = GObject.registerClass(
+    class MyClutterActor extends Clutter.Actor {
+
+        vfunc_get_preferred_width(forHeight) {
+             return [100, 100];
+        }
+
+        vfunc_get_preferred_height(forWidth) {
+             return [100, 100];
+        }
+
+        vfunc_paint(paintContext) {
+             let framebuffer = paintContext.get_framebuffer();
+             let coglContext = framebuffer.get_context();
+             let alloc = this.get_allocation_box();
+
+             let pipeline = new Cogl.Pipeline(coglContext);
+             pipeline.set_color4ub(255, 0, 0, 255);
+
+             framebuffer.draw_rectangle(pipeline,
+		 alloc.x1, alloc.y1,
+		 alloc.x2, alloc.y2);
+        }
+    });
+```
+
+## Translatable strings, `environment.js`
+
+We use gettext to translate the GNOME Shell into all the languages that GNOME
+supports. The `gettext` function is aliased globally as `_`, you do not need to
+explicitly import it. This is done through some magic in the
+[environment.js](http://git.gnome.org/browse/gnome-shell/tree/js/ui/environment.js)
+file. If you can't find a method that's used, it's probably either in gjs itself
+or installed on the global object from the Environment.
+
+Use 'single quotes' for programming strings that should not be translated
+and "double quotes" for strings that the user may see. This allows us to
+quickly find untranslated or mistranslated strings by grepping through the
+sources for double quotes without a gettext call around them.
+
+## `actor` (deprecated) and `_delegate`
+
+gjs allows us to set so-called "expando properties" on introspected objects,
+allowing us to treat them like any other. Because the Shell was built before
+you could inherit from GTypes natively in JS, in some cases we have a wrapper
+class that has a property called `actor` (now deprecated). We call this
+wrapper class the "delegate".
+
+We sometimes use expando properties to set a property called `_delegate` on
+the actor itself:
+```javascript
+    var MyActor = GObject.registerClass(
+    class MyActor extends Clutter.Actor {
+        _init(params) {
+            super._init(params);
+            this._delegate = this;
+        }
+    });
+```
+
+Or using the deprecated `actor`:
+```javascript
+    var MyClass = class {
+        constructor() {
+            this.actor = new St.Button({ text: "This is a button" });
+            this.actor._delegate = this;
+
+            this.actor.connect('clicked', this._onClicked.bind(this));
+        }
+
+        _onClicked(actor) {
+            actor.set_label("You clicked the button!");
+        }
+    };
+```
+
+The 'delegate' property is important for anything which trying to get the
+delegate object from an associated actor. For instance, the drag and drop
+system calls the `handleDragOver` function on the delegate of a "drop target"
+when the user drags an item over it. If you do not set the `_delegate`
+property, your actor will not be able to be dropped onto.
+In case the class is an actor itself, the `_delegate` can be just set to `this`.
+
+## Functional style
+
+JavaScript Array objects offer a lot of common functional programming
+capabilities such as forEach, map, filter and so on. You can use these when
+they make sense, but please don't have a spaghetti mess of function programming
+messed in a procedural style. Use your best judgment.
+
+## Closures
+
+`this` will not be captured in a closure, it is relative to how the closure is
+invoked, not to the value of this where the closure is created, because "this"
+is a keyword with a value passed in at function invocation time, it is not a
+variable that can be captured in closures.
+
+All closures should be wrapped with Function.prototype.bind or use arrow
+notation.
+```javascript
+    let closure1 = () => this._fnorbate();
+    let closure2 = this._fnorbate.bind(this);
+```
+
+A more realistic example would be connecting to a signal on a method of a
+prototype:
+```javascript
+    const FnorbLib = imports.fborbLib;
+
+    var MyClass = class {
+        _init() {
+            let fnorb = new FnorbLib.Fnorb();
+            fnorb.connect('frobate', this._onFnorbFrobate.bind(this));
+        }
+
+        _onFnorbFrobate(fnorb) {
+            this._updateFnorb();
+        }
+    };
+```
+
+## Object literal syntax
+
+In JavaScript, these are equivalent:
+```javascript
+    foo = { 'bar': 42 };
+    foo = { bar: 42 };
+```
+
+and so are these:
+```javascript
+    var b = foo['bar'];
+    var b = foo.bar;
+```
+
+If your usage of an object is like an object, then you're defining "member
+variables." For member variables, use the no-quotes no-brackets syntax: `{ bar:
+42 }` `foo.bar`.
+
+If your usage of an object is like a hash table (and thus conceptually the keys
+can have special chars in them), don't use quotes, but use brackets: `{ bar: 42
+}`, `foo['bar']`.
+
+## Animations
+
+Most objects that are animated are actors, and most properties used in animations
+are animatable, which means they can use implicit animations:
+
+```javascript
+    moveActor(actor, x, y) {
+        actor.ease({
+            x,
+            y,
+            duration: 500, // ms
+            mode: Clutter.AnimationMode.EASE_OUT_QUAD
+        });
+    }
+```
+
+The above is a convenience wrapper around the actual Clutter API, and should generally
+be preferred over the more verbose:
+
+```javascript
+    moveActor(actor, x, y) {
+        actor.save_easing_state();
+
+        actor.set_easing_duration(500);
+        actor.set_easing_mode(Clutter.AnimationMode.EASE_OUT_QUAD);
+        actor.set({
+            x,
+            y
+        });
+
+        actor.restore_easing_state();
+    }
+```
+
+There is a similar convenience API around Clutter.PropertyTransition to animate
+actor (or actor meta) properties that cannot use implicit animations:
+
+```javascript
+    desaturateActor(actor, desaturate) {
+        let factor = desaturate ? 1.0 : 0.0;
+        actor.ease_property('@effects.desaturate.factor', factor, {
+            duration: 500, // ms
+            mode: Clutter.AnimationMode.EASE_OUT_QUAD
+        });
+    }
+```