From 51ef99bff2fc32d9ad116fffe38706722c349a1a Mon Sep 17 00:00:00 2001
From: Fred Bricon <fbricon@gmail.com>
Date: Wed, 3 Apr 2024 13:50:46 +0200
Subject: [PATCH] WIP: enable javac-based compilation

Signed-off-by: Fred Bricon <fbricon@gmail.com>
---
 package.json             | 28 +++++++++++++++++++++++++++-
 src/javaServerStarter.ts | 33 ++++++++++++++++++++++++++++++++-
 src/requirements.ts      |  2 +-
 src/settings.ts          |  4 +++-
 4 files changed, 63 insertions(+), 4 deletions(-)

diff --git a/package.json b/package.json
index 4d90419517..3c00366c24 100644
--- a/package.json
+++ b/package.json
@@ -404,6 +404,17 @@
             "scope": "window",
             "order": 90
           },
+          "java.jdt.ls.javac.enabled": {
+            "type": "string",
+            "enum": [
+              "on",
+              "off"
+            ],
+            "default": "off",
+            "markdownDescription": "[Experimental] Specify whether to enable Javac-based compilation in the language server. Requires running this extension with Java 23",
+            "scope": "window",
+            "order": 95
+          },
           "java.trace.server": {
             "type": "string",
             "enum": [
@@ -1003,6 +1014,21 @@
             "scope": "window",
             "order": 10
           },
+          "java.completion.engine": {
+            "type": "string",
+            "default": "ecj",
+            "description": "[Experimental] Select code completion engine",
+            "scope": "window",
+            "enum": [
+              "ecj",
+              "dom"
+            ],
+            "markdownEnumDescriptions": [
+              "Use ECJ-based code completion engine (default)",
+              "Use (highly experimental) JDT DOM-based code completion engine (requires `java.jdt.ls.javac.enabled` to be `on`)"
+            ],
+            "order": 1000
+          },
           "java.completion.postfix.enabled": {
             "type": "boolean",
             "default": true,
@@ -1903,4 +1929,4 @@
   },
   "segmentWriteKey": "Y7Y5Xk8dKEhVZHTmAkFZkqgdN4d7c4lt",
   "segmentWriteKeyDebug": "BflPll7uuKOCm3y0g7JpfXLVBVFBivDE"
-}
+}
\ No newline at end of file
diff --git a/src/javaServerStarter.ts b/src/javaServerStarter.ts
index 6790973792..ed753bc704 100644
--- a/src/javaServerStarter.ts
+++ b/src/javaServerStarter.ts
@@ -104,7 +104,38 @@ function prepareParams(requirements: RequirementsData, workspacePath, context: E
 				// See https://github.com/redhat-developer/vscode-java/issues/2264
 				// It requires the internal API sun.nio.fs.WindowsFileAttributes.isDirectoryLink() to check if a Windows directory is symlink.
 				'--add-opens',
-				'java.base/sun.nio.fs=ALL-UNNAMED');
+				'java.base/sun.nio.fs=ALL-UNNAMED'
+				);
+
+	const javacEnabled = 'on' === getJavaConfiguration().get('jdt.ls.javac.enabled');
+	if (javacEnabled) {
+		// Javac flags
+		params.push(
+		'--add-opens',
+		'jdk.compiler/com.sun.tools.javac.main=ALL-UNNAMED',
+		'--add-opens',
+		'jdk.compiler/com.sun.tools.javac.util=ALL-UNNAMED',
+		'--add-opens',
+		'jdk.compiler/com.sun.tools.javac.tree=ALL-UNNAMED',
+		'--add-opens',
+		'jdk.compiler/com.sun.tools.javac.api=ALL-UNNAMED',
+		'--add-opens',
+		'jdk.compiler/com.sun.tools.javac.file=ALL-UNNAMED',
+		'--add-opens',
+		'jdk.compiler/com.sun.tools.javac.parser=ALL-UNNAMED',
+		'--add-opens',
+		'jdk.compiler/com.sun.tools.javac.comp=ALL-UNNAMED',
+		'--add-opens',
+		'jdk.compiler/com.sun.tools.javac.code=ALL-UNNAMED',
+		'-DICompilationUnitResolver=org.eclipse.jdt.core.dom.JavacCompilationUnitResolver',
+		'-DCompilationUnit.DOM_BASED_OPERATIONS=true',
+		'-DAbstractImageBuilder.compilerFactory=org.eclipse.jdt.internal.javac.JavacCompilerFactory'
+		);
+
+		if('dom' === getJavaConfiguration().get('java.completion.engine')){
+			params.push('-DCompilationUnit.codeComplete.DOM_BASED_OPERATIONS=true');
+		};
+	}
 
 	params.push('-Declipse.application=org.eclipse.jdt.ls.core.id1',
 				'-Dosgi.bundles.defaultStartLevel=4',
diff --git a/src/requirements.ts b/src/requirements.ts
index b753f2200f..51f441dbcc 100644
--- a/src/requirements.ts
+++ b/src/requirements.ts
@@ -10,7 +10,7 @@ import { logger } from './log';
 import { checkJavaPreferences } from './settings';
 import { listJdks, sortJdksBySource, sortJdksByVersion } from './jdkUtils';
 
-const REQUIRED_JDK_VERSION = 17;
+const REQUIRED_JDK_VERSION = 23;
 /* eslint-disable @typescript-eslint/naming-convention */
 export interface RequirementsData {
     tooling_jre: string;
diff --git a/src/settings.ts b/src/settings.ts
index e7b06c78fc..d187cc6109 100644
--- a/src/settings.ts
+++ b/src/settings.ts
@@ -136,7 +136,9 @@ function hasJavaConfigChanged(oldConfig: WorkspaceConfiguration, newConfig: Work
 		|| hasConfigKeyChanged('jdt.ls.vmargs', oldConfig, newConfig)
 		|| hasConfigKeyChanged('server.launchMode', oldConfig, newConfig)
 		|| hasConfigKeyChanged('sharedIndexes.location', oldConfig, newConfig)
-		|| hasConfigKeyChanged('transport', oldConfig, newConfig);
+		|| hasConfigKeyChanged('transport', oldConfig, newConfig)
+		|| hasConfigKeyChanged('jdt.ls.javac.enabled', oldConfig, newConfig)
+		|| hasConfigKeyChanged('java.completion.engine', oldConfig, newConfig);
 }
 
 function hasConfigKeyChanged(key, oldConfig, newConfig) {