Allow variadic arguments to m.fragment (#2328)

* Implement support for variadic arguments to `m.fragment`

While I was at it, I refactored the common logic out of `hyperscript`.

* Add a missed change from #2326

* Update docs + changelog [skip ci]

* Explain rationale for `hyperscriptVnode`'s calling convention

This way, it doesn't get erroneously "cleaned up" into something worse,
and so it's clearer how it'd be potentially optimized once ES5 support
is dropped.

docs/change-log.md

@@ -54,6 +54,7 @@
     - All of the `m.*` properties from `mithril` are re-exported as named exports in addition to being attached to `m`.
     - `m()` itself from `mithril` is exported as the default export.
     - `mithril/stream`'s primary export is exported as the default export.
+- fragments: allow same attrs/children overloading logic as hyperscript ([#2328](https://github.com/MithrilJS/mithril.js/pull/2328))
 
 #### Bug fixes
 

docs/fragment.md

@@ -37,9 +37,9 @@ Generates a fragment [vnode](vnodes.md)
 
 Argument    | Type                                                | Required | Description
 ----------- | --------------------------------------------------- | -------- | ---
-`attrs`     | `Object`                                            | Yes      | A map of attributes
-`children`  | `Array<Vnode|String|Number|Boolean|null|undefined>` | Yes      | A list of vnodes
-**returns** | `Vnode`                                             |          | A fragment [vnode](vnodes.md)
+`attrs`     | `Object`                                            | No       | HTML attributes or element properties
+`children`  | `Array<Vnode>|String|Number|Boolean`                | No       | Child [vnodes](vnodes.md#structure). Can be written as [splat arguments](signatures.md#splats)
+**returns** | `Vnode`                                             |          | A fragment [vnode](vnodes.md#structure)
 
 [How to read signatures](signatures.md)
 
@@ -49,14 +49,14 @@ Argument    | Type                                                | Required | D
 
 `m.fragment()` creates a [fragment vnode](vnodes.md) with attributes. It is meant for advanced use cases involving [keys](keys.md) or [lifecyle methods](lifecycle-methods.md).
 
-A fragment vnode represents a list of DOM elements. If you want a regular element vnode that represents only one DOM element, you should use [`m()`](hyperscript.md) instead.
+A fragment vnode represents a list of DOM elements. If you want a regular element vnode that represents only one DOM element and don't require keyed logic, you should use [`m()`](hyperscript.md) instead.
 
-Normally you can use simple arrays instead to denote a list of nodes:
+Normally you can use simple arrays or splats instead to denote a list of nodes:
 
 ```javascript
 var groupVisible = true
 
-m("ul", [
+m("ul",
 	m("li", "child 1"),
 	m("li", "child 2"),
 	groupVisible ? [
@@ -64,7 +64,7 @@ m("ul", [
 		m("li", "child 3"),
 		m("li", "child 4"),
 	] : null
-])
+)
 ```
 
 However, Javascript arrays cannot be keyed or hold lifecycle methods. One option would be to create a wrapper element to host the key or lifecycle method, but sometimes it is not desirable to have an extra element (for example in complex table structures). In those cases, a fragment vnode can be used instead.

docs/hyperscript.md

@@ -40,12 +40,12 @@ You can also [use HTML syntax](https://babeljs.io/repl/#?code=%2F**%20%40jsx%20m
 
 ### Signature
 
-`vnode = m(selector, attributes, children)`
+`vnode = m(selector, attrs, children)`
 
 Argument     | Type                                       | Required | Description
 ------------ | ------------------------------------------ | -------- | ---
 `selector`   | `String|Object`                            | Yes      | A CSS selector or a [component](components.md)
-`attributes` | `Object`                                   | No       | HTML attributes or element properties
+`attrs`      | `Object`                                   | No       | HTML attributes or element properties
 `children`   | `Array<Vnode>|String|Number|Boolean`       | No       | Child [vnodes](vnodes.md#structure). Can be written as [splat arguments](signatures.md#splats)
 **returns**  | `Vnode`                                    |          | A [vnode](vnodes.md#structure)
 
@@ -55,7 +55,7 @@ Argument     | Type                                       | Required | Descripti
 
 ### How it works
 
-Mithril provides a hyperscript function `m()`, which allows expressing any HTML structure using javascript syntax. It accepts a `selector` string (required), an `attributes` object (optional) and a `children` array (optional).
+Mithril provides a hyperscript function `m()`, which allows expressing any HTML structure using javascript syntax. It accepts a `selector` string (required), an `attrs` object (optional) and a `children` array (optional).
 
 ```javascript
 m("div", {id: "box"}, "hello")