add optional 'getProjectVersion' method to perform fast up-to-date checks

src/services/services.ts

@@ -949,6 +949,7 @@ module ts {
     export interface LanguageServiceHost {
         getCompilationSettings(): CompilerOptions;
         getNewLine?(): string;
+        getProjectVersion?(): string;
         getScriptFileNames(): string[];
         getScriptVersion(fileName: string): string;
         getScriptSnapshot(fileName: string): IScriptSnapshot;
@@ -2353,6 +2354,7 @@ module ts {
         let syntaxTreeCache: SyntaxTreeCache = new SyntaxTreeCache(host);
         let ruleProvider: formatting.RulesProvider;
         let program: Program;
+        let lastProjectVersion: string;
 
         let useCaseSensitivefileNames = false;
         let cancellationToken = new CancellationTokenObject(host.getCancellationToken && host.getCancellationToken());
@@ -2392,6 +2394,18 @@ module ts {
         }
 
         function synchronizeHostData(): void {
+            // perform fast check if host supports it
+            if (host.getProjectVersion) {
+                let hostProjectVersion = host.getProjectVersion();
+                if (hostProjectVersion) {
+                    if (lastProjectVersion === hostProjectVersion) {
+                        return;
+                    }
+
+                    lastProjectVersion = hostProjectVersion;
+                }
+            }
+
             // Get a fresh cache of the host information
             let hostCache = new HostCache(host, getCanonicalFileName);
 

src/services/shims.ts

@@ -55,6 +55,7 @@ module ts {
         getCurrentDirectory(): string;
         getDefaultLibFileName(options: string): string;
         getNewLine?(): string;
+        getProjectVersion?(): string;
     }
 
     /** Public interface of the the of a config service shim instance.*/
@@ -260,6 +261,15 @@ module ts {
             this.shimHost.error(s);
         }
 
+        public getProjectVersion(): string {
+            if (!this.shimHost.getProjectVersion) {
+                // shimmed host does not support getProjectVersion
+                return undefined;
+            }
+
+            return this.shimHost.getProjectVersion();
+        }
+
         public getCompilationSettings(): CompilerOptions {
             var settingsJson = this.shimHost.getCompilationSettings();
             if (settingsJson == null || settingsJson == "") {