Revised module resolution

Jakefile.js

@@ -141,7 +141,9 @@ var harnessSources = harnessCoreSources.concat([
     "session.ts",
     "versionCache.ts",
     "convertToBase64.ts",
-    "transpile.ts"
+    "transpile.ts",
+    "reuseProgramStructure.ts",
+    "cachingInServerLSHost.ts"
 ].map(function (f) {
     return path.join(unittestsDirectory, f);
 })).concat([

src/compiler/checker.ts

@@ -965,28 +965,19 @@ namespace ts {
             // Escape the name in the "require(...)" clause to ensure we find the right symbol.
             let moduleName = escapeIdentifier(moduleReferenceLiteral.text);
 
-            if (!moduleName) return;
+            if (!moduleName) {
+                return;
+            }
             let isRelative = isExternalModuleNameRelative(moduleName);
             if (!isRelative) {
                 let symbol = getSymbol(globals, "\"" + moduleName + "\"", SymbolFlags.ValueModule);
                 if (symbol) {
                     return symbol;
                 }
             }
-            let fileName: string;
-            let sourceFile: SourceFile;
-            while (true) {
-                fileName = normalizePath(combinePaths(searchPath, moduleName));
-                sourceFile = forEach(supportedExtensions, extension => host.getSourceFile(fileName + extension));
-                if (sourceFile || isRelative) {
-                    break;
-                }
-                let parentPath = getDirectoryPath(searchPath);
-                if (parentPath === searchPath) {
-                    break;
-                }
-                searchPath = parentPath;
-            }
+
+            let fileName = getResolvedModuleFileName(getSourceFile(location), moduleReferenceLiteral.text);
+            let sourceFile = fileName && host.getSourceFile(fileName);
             if (sourceFile) {
                 if (sourceFile.symbol) {
                     return sourceFile.symbol;

src/compiler/core.ts

@@ -24,6 +24,7 @@ namespace ts {
             set,
             contains,
             remove,
+            clear,
             forEachValue: forEachValueInMap
         };
 
@@ -51,6 +52,10 @@ namespace ts {
         function normalizeKey(key: string) {
             return getCanonicalFileName(normalizeSlashes(key));
         }
+
+        function clear() {
+            files = {};
+        }
     }
 
     export const enum Comparison {
@@ -716,7 +721,7 @@ namespace ts {
     /**
      *  List of supported extensions in order of file resolution precedence.
      */
-    export const supportedExtensions = [".tsx", ".ts", ".d.ts"];
+    export const supportedExtensions = [".ts", ".tsx", ".d.ts"];
 
     const extensionsToRemove = [".d.ts", ".ts", ".js", ".tsx", ".jsx"];
     export function removeFileExtension(path: string): string {