Introduce the concept of base language

Co-authored-by: Lea Verou <[email protected]>

Author: DmitrySharabin

src/core/registry.ts

@@ -1,7 +1,8 @@
 import { kebabToCamelCase } from '../shared/util';
-import { forEach } from '../util/iterables';
+import { cloneGrammar } from '../util/extend';
+import { forEach, toArray } from '../util/iterables';
 import { extend } from '../util/language-util';
-import type { ComponentProto, Grammar } from '../types';
+import type { ComponentProto, Grammar, LanguageProto } from '../types';
 import type { Prism } from './prism';
 
 interface Entry {
@@ -60,6 +61,13 @@ export class Registry {
 			// add aliases
 			forEach(proto.alias, alias => this.aliasMap.set(alias, id));
 
+			if ((proto as LanguageProto).base) {
+				proto.require = [
+					(proto as LanguageProto).base as ComponentProto,
+					...toArray(proto.require),
+				];
+			}
+
 			// dependencies
 			forEach(proto.require, register);
 
@@ -152,11 +160,6 @@ export class Registry {
 			return entry.evaluatedGrammar;
 		}
 
-		if (typeof grammar === 'object') {
-			// the grammar is a simple object, so we don't need to evaluate it
-			return (entry.evaluatedGrammar = grammar);
-		}
-
 		const required = (id: string): Grammar => {
 			const grammar = this.getLanguage(id);
 			if (!grammar) {
@@ -165,10 +168,24 @@ export class Registry {
 			return grammar;
 		};
 
-		return (entry.evaluatedGrammar = grammar({
-			getLanguage: required,
-			getOptionalLanguage: id => this.getLanguage(id),
-			extend: (id, ref) => extend(required(id), id, ref),
-		}));
+		const base = (entry?.proto as LanguageProto).base;
+		// We need this so that any code modifying the base grammar doesn't affect other instances
+		const baseGrammar = base && cloneGrammar(required(base.id), base.id);
+
+		let evaluatedGrammar =
+			typeof grammar === 'object'
+				? grammar
+				: grammar({
+						base: baseGrammar,
+						getLanguage: required,
+						getOptionalLanguage: id => this.getLanguage(id),
+						extend: (id, ref) => extend(required(id), id, ref),
+					});
+
+		if (base) {
+			evaluatedGrammar = extend(baseGrammar!, base.id, evaluatedGrammar);
+		}
+
+		return (entry.evaluatedGrammar = evaluatedGrammar);
 	}
 }

src/types.d.ts

@@ -1,8 +1,9 @@
-import type { Prism } from './core/prism';
 import type { TokenStream } from './core/classes/token';
+import type { Prism } from './core/prism';
 
 export interface GrammarOptions {
 	readonly getLanguage: (id: string) => Grammar;
+	readonly base?: Grammar;
 	readonly getOptionalLanguage: (id: string) => Grammar | undefined;
 	readonly extend: (id: string, ref: GrammarTokens) => Grammar;
 }
@@ -16,6 +17,7 @@ export interface ComponentProtoBase<Id extends string = string> {
 export interface LanguageProto<Id extends string = string> extends ComponentProtoBase<Id> {
 	grammar: Grammar | ((options: GrammarOptions) => Grammar);
 	plugin?: undefined;
+	base?: LanguageProto;
 }
 type PluginType<Name extends string> = unknown;
 export interface PluginProto<Id extends string = string> extends ComponentProtoBase<Id> {

src/util/extend.ts

@@ -38,7 +38,7 @@ export function extend (grammar: Grammar, id: string, reDef: Grammar): Grammar {
 	return lang;
 }
 
-function cloneGrammar (grammar: Grammar, id: string): Grammar {
+export function cloneGrammar (grammar: Grammar, id: string): Grammar {
 	const result: Grammar = {};
 
 	const visited = new Map<Grammar, Grammar>();