Contribute to vscode-xml with a custom language

Fixes #589

Signed-off-by: azerr <azerr@redhat.com>

Author: angelozerr

docs/Extensions.md

@@ -1,6 +1,36 @@
 # Extensions
 
-## Custom XML Extensions
+## Contribution in package.json
+
+### Custom language
+
+If your vscode extension defines a custom language `myxml` in package.json:
+
+ ```json
+"contributes": {
+    "languages": [
+        {
+            "id": "myxml",
+            "extensions": [
+                ".myxml"
+            ]
+        }
+    ]
+```
+
+and you want that `myxml` language uses [vscode-xml](https://github.com/redhat-developer/vscode-xml) language server, you need to declare it with `xmlLanguageParticipants`: 
+
+ ```json
+"contributes": {
+  "xmlLanguageParticipants": [
+    {
+      "languageId": "myxml"
+    }
+  ]
+}
+```
+   
+## Custom XML Extensions (written in Java)
 
 The [LemMinX - XML Language Server](https://github.com/eclipse/lemminx) can be extended to support custom completion, hover, validation, rename, etc by using the [Java Service Provider Interface (SPI)](https://www.baeldung.com/java-spi) mechanism.
 vscode-xml provides the ability to use your custom XML support provider, by adding external jars to the XML language server's classpath.

schemas/package.schema.json

@@ -1,20 +1,33 @@
 {
-	"$schema": "http://json-schema.org/draft-04/schema#",
-	"title": "XML Language server contributions to package.json",
-	"type": "object",
-	"properties": {
-		"contributes": {
-			"type": "object",
-			"properties": {
-				"xml.javaExtensions": {
-					"type": "array",
-					"markdownDescription": "XML language server extensions",
-					"items": {
-						"type": "string",
-						"description": "Relative path to a XML language server extension JAR file"
-					}
-				}
-			}
-		}
-	}
+    "$schema": "http://json-schema.org/draft-04/schema#",
+    "title": "XML Language server contributions to package.json",
+    "type": "object",
+    "properties": {
+        "contributes": {
+            "type": "object",
+            "properties": {
+                "xml.javaExtensions": {
+                    "type": "array",
+                    "markdownDescription": "XML language server extensions",
+                    "items": {
+                        "type": "string",
+                        "description": "Relative path to a XML language server extension JAR file"
+                    }
+                },
+                "xmlLanguageParticipants": {
+                    "type": "array",
+                    "description": "A list of languages that participate with the XML language server.",
+                    "items": {
+                        "type": "object",
+                        "properties": {
+                            "languageId": {
+                                "type": "string",
+                                "description": "The id of the language that participates with XML language server."
+                            }
+                        }
+                    }
+                }
+            }
+        }
+    }
 }

src/client/languageParticipants.ts

@@ -0,0 +1,78 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+import { DocumentSelector } from 'vscode-languageclient';
+import { Event, EventEmitter, extensions } from 'vscode';
+
+/**
+ * XML language participant contribution.
+ */
+interface LanguageParticipantContribution {
+  /**
+   * The id of the language which participates with the XML language server.
+   */
+  languageId: string;
+}
+
+export interface LanguageParticipants {
+  readonly onDidChange: Event<void>;
+  readonly documentSelector: DocumentSelector;
+  hasLanguage(languageId: string): boolean;
+  dispose(): void;
+}
+
+export function getLanguageParticipants(): LanguageParticipants {
+  const onDidChangeEmmiter = new EventEmitter<void>();
+  let languages = new Set<string>();
+
+  function update() {
+    const oldLanguages = languages;
+
+    languages = new Set();
+    languages.add('xml');
+    languages.add('xsl');
+    languages.add('dtd');
+    languages.add('svg');
+
+    for (const extension of extensions.all /*extensions.allAcrossExtensionHosts*/) {
+      const xmlLanguageParticipants = extension.packageJSON?.contributes?.xmlLanguageParticipants as LanguageParticipantContribution[];
+      if (Array.isArray(xmlLanguageParticipants)) {
+        for (const xmlLanguageParticipant of xmlLanguageParticipants) {
+          const languageId = xmlLanguageParticipant.languageId;
+          if (typeof languageId === 'string') {
+            languages.add(languageId);
+          }
+        }
+      }
+    }
+    return !isEqualSet(languages, oldLanguages);
+  }
+  update();
+
+  const changeListener = extensions.onDidChange(_ => {
+    if (update()) {
+      onDidChangeEmmiter.fire();
+    }
+  });
+
+  return {
+    onDidChange: onDidChangeEmmiter.event,
+    get documentSelector() { return Array.from(languages); },
+    hasLanguage(languageId: string) { return languages.has(languageId); },
+    dispose: () => changeListener.dispose()
+  };
+}
+
+function isEqualSet<T>(s1: Set<T>, s2: Set<T>) {
+  if (s1.size !== s2.size) {
+    return false;
+  }
+  for (const e of s1) {
+    if (!s2.has(e)) {
+      return false;
+    }
+  }
+  return true;
+}

src/client/xmlClient.ts

@@ -12,18 +12,11 @@ import { getXMLConfiguration, getXMLSettings, onConfigurationChange, subscribeJD
 import { containsVariableReferenceToCurrentFile } from '../settings/variableSubstitution';
 import * as Telemetry from '../telemetry';
 import { ClientErrorHandler } from './clientErrorHandler';
+import { getLanguageParticipants } from './languageParticipants';
 import { activateTagClosing, AutoCloseResult } from './tagClosing';
 
-export const XML_SUPPORTED_LANGUAGE_IDS = ['xml', 'xsl', 'dtd', 'svg'];
-
-const XML_DOCUMENT_SELECTOR: DocumentSelector =
-  XML_SUPPORTED_LANGUAGE_IDS
-    .map(langId => ({ scheme: 'file', language: langId }))
-    .concat(
-      XML_SUPPORTED_LANGUAGE_IDS
-        .map(langId => ({ scheme: 'untitled', language: langId }))
-    );
-
+const languageParticipants = getLanguageParticipants();
+export const XML_SUPPORTED_LANGUAGE_IDS = languageParticipants.documentSelector;
 
 const ExecuteClientCommandRequest: RequestType<ExecuteCommandParams, any, void> = new RequestType('xml/executeClientCommand');
 
@@ -136,7 +129,7 @@ function getLanguageClientOptions(
   context: ExtensionContext): LanguageClientOptions {
   return {
     // Register the server for xml, xsl, dtd, svg
-    documentSelector: XML_DOCUMENT_SELECTOR,
+    documentSelector: XML_SUPPORTED_LANGUAGE_IDS,
     revealOutputChannelOn: RevealOutputChannelOn.Never,
     //wrap with key 'settings' so it can be handled same a DidChangeConfiguration
     initializationOptions: {