From da6d525a11bf4e21bb69da8f1561fcbac2a72400 Mon Sep 17 00:00:00 2001
From: Matt Tracy <matt.r.tracy@gmail.com>
Date: Tue, 29 Sep 2015 14:44:34 -0400
Subject: [PATCH] Typescript: Make MithrilVirtualElement non-generic

`MithrilVirtualElement` was recently converted to be generic over `<T extends
MithrilController>`. The element's `children` may then contain other
`MithrilVirtualElement<T>` or `MithrilComponent<T>` elements.

Unfortunately, in common usage of 'm()' this can cause problems with Mithril's type
inference system. If a type is not explicitly provided to `m()`, the "T" of the
returned MithrilVirtualElement<T> will be inferred from its children. The
candidates for T will be the concrete types of the child MithrilComponent<T>; however, if no
candidate type is a subset of *every* candidate type, then TypeScript will be
unable to infer a valid type, and the call to `m()` will not compile.

To improve this behavior, this commit makes MithrilVirtualElement non-generic;
it's child collection can now contain MithrilComponent<MithrilController>, which
matches all valid MithrilComponent. This the same underlying issue as the
previous commit, which made MithrilRoutes non-generic.

The motivation for fixing this is threefold:

1. Because `m()` has so many overloads, in the case where a call to `m()` will
not compile due to the above issue, the syntax error provided by TypeScript is
not helpful.
2. In many cases, users will be calling `m<MithrilController>()` in their code
simply to get it to compile, which provides no additional utility over a
non-generic type and adds significant boilerplate.
3. Explicitly specifying subtypes to `m()` calls provides little utility; at
best, it can check that contained components implement some common interface.
However, type assertions like that can be provided in other places without
having to attach the information to the MithrilVirtualElement.
---
 mithril.d.ts | 36 ++++++++++++++++++------------------
 1 file changed, 18 insertions(+), 18 deletions(-)

diff --git a/mithril.d.ts b/mithril.d.ts
index 2952d92a..c7d2c6b6 100644
--- a/mithril.d.ts
+++ b/mithril.d.ts
@@ -20,13 +20,13 @@ declare module _mithril {
 		* @see m.mount
 		* @see m.component
 		*/
-		<T extends MithrilController>(
+		(
 			selector: string,
 			attributes: MithrilAttributes,
 			...children: Array<string |
-				MithrilVirtualElement<T> |
-				MithrilComponent<T>>
-		): MithrilVirtualElement<T>;
+				MithrilVirtualElement |
+				MithrilComponent<MithrilController>>
+		): MithrilVirtualElement;
 		
 		/**
 		* Creates a virtual element for use with m.render, m.mount, etc.
@@ -40,12 +40,12 @@ declare module _mithril {
 		* @see m.mount
 		* @see m.component
 		*/
-		<T extends MithrilController>(
+		(
 			selector: string,
 			...children: Array<string |
-				MithrilVirtualElement<T> |
-				MithrilComponent<T>>
-		): MithrilVirtualElement<T>;
+				MithrilVirtualElement |
+				MithrilComponent<MithrilController>>
+		): MithrilVirtualElement;
 
 		/**
 		* Initializes a component for use with m.render, m.mount, etc.
@@ -364,9 +364,9 @@ declare module _mithril {
 		* @param forceRecreation If true, overwrite the entire tree without
 		* diffing against it.
 		*/
-		render<T extends MithrilController>(
+		render(
 			rootElement: Element,
-			children: MithrilVirtualElement<T>|MithrilVirtualElement<T>[],
+			children: MithrilVirtualElement|MithrilVirtualElement[],
 			forceRecreation?: boolean
 		): void;
 
@@ -451,7 +451,7 @@ declare module _mithril {
 				element: Element,
 				isInitialized: boolean,
 				context?: MithrilContext,
-				vdom?: MithrilVirtualElement<T>
+				vdom?: MithrilVirtualElement
 			): void;
 
 			/**
@@ -615,7 +615,7 @@ declare module _mithril {
 	*
 	* @see m
 	*/
-	interface MithrilVirtualElement<T extends MithrilController> {
+	interface MithrilVirtualElement {
 		/**
 		* A key to optionally associate with this element.
 		*/
@@ -634,7 +634,7 @@ declare module _mithril {
 		/**
 		* The children of this element.
 		*/
-		children?: Array<string|MithrilVirtualElement<T>|MithrilComponent<T>>;
+		children?: Array<string|MithrilVirtualElement|MithrilComponent<MithrilController>>;
 	}
 
 	/**
@@ -686,11 +686,11 @@ declare module _mithril {
 		* @param context The associated context for this element.
 		* @param vdom The associated virtual element.
 		*/
-		<T extends MithrilController>(
+		(
 			element: Element,
 			isInitialized: boolean,
 			context: MithrilContext,
-			vdom: MithrilVirtualElement<T>
+			vdom: MithrilVirtualElement
 		): void;
 	}
 
@@ -758,7 +758,7 @@ declare module _mithril {
 		/**
 		* Creates a view out of virtual elements.
 		*/
-		(ctrl: T): MithrilVirtualElement<T>;
+		(ctrl: T): MithrilVirtualElement;
 	}
 
 	/**
@@ -781,7 +781,7 @@ declare module _mithril {
 		*
 		* @see m.component
 		*/
-		view(ctrl: T): MithrilVirtualElement<T>;
+		view(ctrl: T): MithrilVirtualElement;
 	}
 
 	/**
@@ -805,7 +805,7 @@ declare module _mithril {
 		*
 		* @see m.component
 		*/
-		view(ctrl: TController, arg1: T1, arg2: T2, arg3: T3, arg4: T4, ...args:any[]): MithrilVirtualElement<TController>;
+		view(ctrl: TController, arg1: T1, arg2: T2, arg3: T3, arg4: T4, ...args:any[]): MithrilVirtualElement;
 	}
 
 	/**