Make htmlBuilder and mathmlBuilder params type-safe. (#1312)

* Make htmlBuilder and mathmlBuilder params type-safe.

Also correct and refine some of the ParseNode types.

src/defineEnvironment.js

@@ -7,6 +7,7 @@ import ParseNode from "./ParseNode";
 
 import type Parser from "./Parser";
 import type {ArgType, Mode} from "./types";
+import type {NodeType} from "./ParseNode";
 
 /**
  * The context contains the following properties:
@@ -25,11 +26,11 @@ type EnvContext = {|
  *  - args: an array of arguments passed to \begin{name}
  *  - optArgs: an array of optional arguments passed to \begin{name}
  */
-type EnvHandler = (
+type EnvHandler<NODETYPE: NodeType> = (
     context: EnvContext,
     args: ParseNode<*>[],
     optArgs: (?ParseNode<*>)[],
-) => ParseNode<*>;
+) => ParseNode<NODETYPE>;
 
 /**
  *  - numArgs: (default 0) The number of arguments after the \begin{name} function.
@@ -49,13 +50,16 @@ type EnvProps = {
  * 2. requires all arguments except argType
  * It is generated by `defineEnvironment()` below.
  */
-export type EnvSpec = {|
+export type EnvSpec<NODETYPE: NodeType> = {|
+    type: NODETYPE, // Need to use the type to avoid error. See NOTES below.
     numArgs: number,
     argTypes?: ArgType[],
     greediness: number,
     allowedInText: boolean,
     numOptionalArgs: number,
-    handler: EnvHandler,
+    // FLOW TYPE NOTES: Same issue as the notes on the handler of FunctionSpec
+    // in defineFunction.
+    handler: EnvHandler<*>,
 |};
 
 /**
@@ -63,11 +67,11 @@ export type EnvSpec = {|
  * `environments.js` exports this same dictionary again and makes it public.
  * `Parser.js` requires this dictionary via `environments.js`.
  */
-export const _environments: {[string]: EnvSpec} = {};
+export const _environments: {[string]: EnvSpec<*>} = {};
 
-type EnvDefSpec = {|
+type EnvDefSpec<NODETYPE: NodeType> = {|
     // Unique string to differentiate parse nodes.
-    type: string,
+    type: NODETYPE,
 
     // List of functions which use the give handler, htmlBuilder,
     // and mathmlBuilder.
@@ -76,34 +80,35 @@ type EnvDefSpec = {|
     // Properties that control how the environments are parsed.
     props: EnvProps,
 
-    handler: EnvHandler,
+    handler: EnvHandler<NODETYPE>,
 
     // This function returns an object representing the DOM structure to be
     // created when rendering the defined LaTeX function.
-    // TODO: Port buildHTML to flow and make the group and return types explicit.
-    htmlBuilder: (group: *, options: Options) => *,
+    // TODO: Port buildHTML to flow and make the return type explicit.
+    htmlBuilder: (group: ParseNode<NODETYPE>, options: Options) => *,
 
     // This function returns an object representing the MathML structure to be
     // created when rendering the defined LaTeX function.
-    // TODO: Port buildMathML to flow and make the group and return types explicit.
-    mathmlBuilder: (group: *, options: Options) => *,
+    // TODO: Port buildMathML to flow and make the return type explicit.
+    mathmlBuilder: (group: ParseNode<NODETYPE>, options: Options) => *,
 |};
 
-export default function defineEnvironment({
+export default function defineEnvironment<NODETYPE: NodeType>({
     type,
     names,
     props,
     handler,
     htmlBuilder,
     mathmlBuilder,
-}: EnvDefSpec) {
-    // Set default values of environments
+}: EnvDefSpec<NODETYPE>) {
+    // Set default values of environments.
     const data = {
+        type,
         numArgs: props.numArgs || 0,
         greediness: 1,
         allowedInText: false,
         numOptionalArgs: 0,
-        handler: handler,
+        handler,
     };
     for (let i = 0; i < names.length; ++i) {
         _environments[names[i]] = data;