vscode-dotty: Auto-indentation support for brace-less syntax

By default, vscode knows how to auto-indent code with braces, e.g.
given:

    if (foo) {

pressing "Enter" will add one level of indentation. Similarly, entering
a closing brace can unindent a line.

Ideally, we'd like to do something similar with the brace-less syntax.
This commit is a first attempt at doing so by using the built-in support
in vscode for defining indentation patterns. Proper automatic
unindentation seems much harder to achieve.

Author: smarter

vscode-dotty/src/extension.ts

@@ -50,6 +50,18 @@ function isConfiguredProject() {
 }
 
 export function activate(context: ExtensionContext) {
+  // Override the language configuration from vscode-scala (doing this from
+  // package.json does not work)
+  vscode.languages.setLanguageConfiguration("scala", {
+    "indentationRules": {
+      // Auto-indent when pressing enter on a line matching this regexp
+      "increaseIndentPattern": /(((\b(then|else|do|catch|finally|yield|match|while|try|for|if|case)\b)|\bif\s*\(.*\)|=|=>|<-|=>>)\s*$)/,
+      // Auto-unindent disabled, because it doesn't work well with all
+      // indentation styles
+      "decreaseIndentPattern": /^.$/
+    }
+  })
+
   extensionContext = context
   outputChannel = vscode.window.createOutputChannel("Dotty")
   tracer = new Tracer({