Add support for extensionless documents to the parametric language server

.vscode/settings.json

@@ -0,0 +1,6 @@
+{
+  "files.exclude": {
+    "rascal-lsp": true,
+    "rascal-vscode-extension": true
+  }
+}

rascal-language-servers.code-workspace

@@ -5,6 +5,10 @@
 		},
 		{
 			"path": "rascal-vscode-extension"
+		},
+		{
+			"name": "root",
+			"path": "."
 		}
 	],
 	"extensions": {

rascal-lsp/src/main/java/org/rascalmpl/vscode/lsp/parametric/ParametricTextDocumentService.java

@@ -644,7 +644,17 @@ private static <T> T last(List<T> l) {
     }
 
     private Optional<String> safeLanguage(ISourceLocation loc) {
-        return Optional.ofNullable(registeredExtensions.get(extension(loc)));
+        var ext = extension(loc);
+        if ("".equals(ext)) {
+            if (contributions.size() == 1) {
+                logger.trace("file was opened without an extension; falling back to the single registered language for: {}", loc);
+                return contributions.keySet().stream().findFirst();
+            } else {
+                logger.error("file was opened without an extension and there are multiple languages registered, so we cannot pick a fallback for: {}", loc);
+                return Optional.empty();
+            }
+        }
+        return Optional.ofNullable(registeredExtensions.get(ext));
     }
 
     private String language(ISourceLocation loc) {

rascal-vscode-extension/src/test/vscode-suite/dsl.test.ts

@@ -25,7 +25,7 @@
  * POSSIBILITY OF SUCH DAMAGE.
  */
 
-import { SideBarView, VSBrowser, WebDriver, Workbench } from 'vscode-extension-tester';
+import { InputBox, TextEditor, SideBarView, VSBrowser, WebDriver, Workbench } from 'vscode-extension-tester';
 import { Delays, IDEOperations, ignoreFails, printRascalOutputOnFailure, RascalREPL, sleep, TestWorkspace } from './utils';
 
 import { expect } from 'chai';
@@ -75,7 +75,6 @@ parameterizedDescribe(function (errorRecovery: boolean) {
         await repl.terminate();
     }
 
-
     before(async () => {
         browser = VSBrowser.instance;
         driver = browser.driver;
@@ -103,7 +102,7 @@ parameterizedDescribe(function (errorRecovery: boolean) {
         await fs.writeFile(TestWorkspace.picoFile, picoFileBackup);
     });
 
-    it("have highlighting and parse errors", async function () {
+    it("has highlighting and parse errors", async function () {
         await ignoreFails(new Workbench().getEditorView().closeAllEditors());
         const editor = await ide.openModule(TestWorkspace.picoFile);
         const isPicoLoading = ide.statusContains("Pico");
@@ -126,7 +125,7 @@ parameterizedDescribe(function (errorRecovery: boolean) {
         }
     }).retries(2);
 
-    it("have highlighting and parse errors for second extension", async function () {
+    it("has highlighting and parse errors for second extension", async function () {
         const editor = await ide.openModule(TestWorkspace.picoNewFile);
         await ide.hasSyntaxHighlighting(editor);
         try {
@@ -137,6 +136,40 @@ parameterizedDescribe(function (errorRecovery: boolean) {
         }
     });
 
+    it("has syntax highlighting in documents without extension", async function () {
+        await bench.executeCommand("workbench.action.files.newUntitledFile");
+        await bench.executeCommand("workbench.action.editor.changeLanguageMode");
+
+        const inputBox = new InputBox();
+        await inputBox.setText("parametric-rascalmpl");
+        await inputBox.confirm();
+
+        const file = "Untitled-1";
+        const editor = await driver.wait(async () => {
+            const result = await ignoreFails(new Workbench().getEditorView().openEditor(file)) as TextEditor;
+            if (result && await ignoreFails(result.getTitle()) === file) {
+                return result;
+            }
+            return undefined! as TextEditor;
+        }, Delays.normal, "Could not open file");
+        expect(editor).to.not.be.undefined;
+
+        await editor.setText(`begin
+  declare
+     a : natural;
+  a := 2
+end
+`);
+        await ide.hasSyntaxHighlighting(editor, Delays.slow);
+
+        try {
+            await editor.setTextAtLine(4, "  a := ");
+            await ide.hasErrorSquiggly(editor, Delays.slow);
+        } finally {
+            await ide.revertOpenChanges();
+        }
+    }).retries(2);
+
     it("error recovery works", async function () {
         if (!errorRecovery) { this.skip(); }
         const editor = await ide.openModule(TestWorkspace.picoNewFile);