Fixes #40905: Operating system specific args don't override args defined in the task

src/vs/workbench/parts/tasks/node/taskConfiguration.ts

@@ -858,7 +858,7 @@ namespace CommandConfiguration {
 			osConfig = fromBase(config.linux, context);
 		}
 		if (osConfig) {
-			result = assignProperties(result, osConfig);
+			result = assignProperties(result, osConfig, context.schemaVersion === Tasks.JsonSchemaVersion.V2_0_0);
 		}
 		return isEmpty(result) ? undefined : result;
 	}
@@ -929,7 +929,7 @@ namespace CommandConfiguration {
 		return _isEmpty(value, properties);
 	}
 
-	export function assignProperties(target: Tasks.CommandConfiguration, source: Tasks.CommandConfiguration): Tasks.CommandConfiguration {
+	export function assignProperties(target: Tasks.CommandConfiguration, source: Tasks.CommandConfiguration, overwriteArgs: boolean): Tasks.CommandConfiguration {
 		if (isEmpty(source)) {
 			return target;
 		}
@@ -941,7 +941,7 @@ namespace CommandConfiguration {
 		assignProperty(target, source, 'taskSelector');
 		assignProperty(target, source, 'suppressTaskName');
 		if (source.args !== void 0) {
-			if (target.args === void 0) {
+			if (target.args === void 0 || overwriteArgs) {
 				target.args = source.args;
 			} else {
 				target.args = target.args.concat(source.args);

src/vs/workbench/parts/tasks/test/electron-browser/configuration.test.ts

@@ -1585,6 +1585,56 @@ suite('Tasks version 2.0.0', () => {
 			presentation().echo(true);
 		testConfiguration(external, builder);
 	});
+	test('Arg overwrite', () => {
+		let external: ExternalTaskRunnerConfiguration = {
+			version: '2.0.0',
+			tasks: [
+				{
+					label: 'echo',
+					type: 'shell',
+					command: 'echo',
+					args: [
+						'global'
+					],
+					windows: {
+						args: [
+							'windows'
+						]
+					},
+					linux: {
+						args: [
+							'linux'
+						]
+					},
+					osx: {
+						args: [
+							'osx'
+						]
+					}
+				}
+			]
+		};
+		let builder = new ConfiguationBuilder();
+		if (Platform.isWindows) {
+			builder.task('echo', 'echo').
+				command().suppressTaskName(true).args(['windows']).
+				runtime(Tasks.RuntimeType.Shell).
+				presentation().echo(true);
+			testConfiguration(external, builder);
+		} else if (Platform.isLinux) {
+			builder.task('echo', 'echo').
+				command().suppressTaskName(true).args(['linux']).
+				runtime(Tasks.RuntimeType.Shell).
+				presentation().echo(true);
+			testConfiguration(external, builder);
+		} else if (Platform.isMacintosh) {
+			builder.task('echo', 'echo').
+				command().suppressTaskName(true).args(['osx']).
+				runtime(Tasks.RuntimeType.Shell).
+				presentation().echo(true);
+			testConfiguration(external, builder);
+		}
+	});
 });
 
 suite('Bugs / regression tests', () => {