Relax import/export elision rules for separate compilation

src/compiler/checker.ts

@@ -713,8 +713,14 @@ module ts {
         function markExportAsReferenced(node: ImportEqualsDeclaration | ExportAssignment | ExportSpecifier) {
             let symbol = getSymbolOfNode(node);
             let target = resolveAlias(symbol);
-            if (target && target !== unknownSymbol && target.flags & SymbolFlags.Value && !isConstEnumOrConstEnumOnlyModule(target)) {
-                markAliasSymbolAsReferenced(symbol);
+            if (target) {
+                let markAlias =
+                    (target === unknownSymbol && compilerOptions.separateCompilation) ||
+                    (target !== unknownSymbol && target.flags & SymbolFlags.Value && !isConstEnumOrConstEnumOnlyModule(target));
+
+                if (markAlias) {
+                    markAliasSymbolAsReferenced(symbol);
+                }
             }
         }
 
@@ -9747,7 +9753,9 @@ module ts {
 
                     checkKindsOfPropertyMemberOverrides(type, baseType);
                 }
+            }
 
+            if (type.baseTypes.length || (baseTypeNode && compilerOptions.separateCompilation)) {
                 // Check that base type can be evaluated as expression
                 checkExpressionOrQualifiedName(baseTypeNode.typeName);
             }
@@ -11266,11 +11274,16 @@ module ts {
                 // parent is not source file or it is not reference to internal module
                 return false;
             }
-            return isAliasResolvedToValue(getSymbolOfNode(node));
+
+            var isValue = isAliasResolvedToValue(getSymbolOfNode(node));
+            return isValue && node.moduleReference && !nodeIsMissing(node.moduleReference);
         }
 
         function isAliasResolvedToValue(symbol: Symbol): boolean {
             let target = resolveAlias(symbol);
+            if (target === unknownSymbol && compilerOptions.separateCompilation) {
+                return true;
+            }
             // const enums and modules that contain only const enums are not considered values from the emit perespective
             return target !== unknownSymbol && target.flags & SymbolFlags.Value && !isConstEnumOrConstEnumOnlyModule(target);
         }

src/compiler/types.ts

@@ -1587,6 +1587,7 @@ module ts {
         target?: ScriptTarget;
         version?: boolean;
         watch?: boolean;
+        separateCompilation?: boolean;
         /* @internal */ stripInternal?: boolean;
         [option: string]: string | number | boolean;
     }

src/services/services.ts

@@ -1635,6 +1635,77 @@ module ts {
         sourceFile.scriptSnapshot = scriptSnapshot;
     }
 
+    export function transpile(input: string, compilerOptions?: CompilerOptions, fileName?: string, syntaxErrors?: Diagnostic[]): string {
+        let options = compilerOptions ? ts.clone(compilerOptions) : getDefaultCompilerOptions();
+
+        // Single file transformation is only guaranteed to be correct inside an external module.
+        // External modules have their own scope and cannot contribute to internal modules outside their
+        // scope. 
+        if (options.target !== ScriptTarget.ES6 && (!options.module || options.module === ModuleKind.None)) {
+            // TODO: add errors
+        }
+
+        // In single file transformation the compiler does not have access to declaration sites.
+        // Const enum property accesses will not be detected if they are not in the same file as the enum.
+        // thus they are going to be emitted as normal propety access. To ensure correct behaviour at runtime,
+        // we need to generate the actual enum object so that the property accesses do not fail.
+        options.preserveConstEnums = true;
+
+        // No reason to get declarations, we are only returning javascript
+        options.declaration = false;
+
+        // Filename can be non-ts file.
+        options.allowNonTsExtensions = true;
+
+        // enable relaxed emit rules
+        options.separateCompilation = true;
+
+        // We are not resolving references or modules, or even including the default library. Disabling 
+        // emit on error will block generating the output and has no meaningful use here.
+        options.noEmitOnError = false;
+
+        // No resolution requests will be honored anyways. So do not do it
+        options.noResolve = true;
+
+        // TODO (vladima): this should be enabled after adding support to inlinable source maps
+        options.sourceMap = false;
+
+        // Parse
+        var inputFileName = fileName || "module.ts";
+        var sourceFile = ts.createSourceFile(inputFileName, input, options.target);
+
+        // Store syntactic diagnostics
+        if (syntaxErrors && sourceFile.parseDiagnostics) {
+            syntaxErrors.push(...sourceFile.parseDiagnostics);
+        }
+
+        // Output
+        let outputText: string;
+
+        // Create a compilerHost object to allow the compiler to read and write files
+        var compilerHost: CompilerHost = {
+            getSourceFile: (fileName, target) => fileName === inputFileName ? sourceFile : undefined,
+            writeFile: (name, text, writeByteOrderMark) => {
+                Debug.assert(outputText === undefined, "Unexpected multiple outputs for the file: " + name);
+                outputText = text;
+            },
+            getDefaultLibFileName: () => "lib.d.ts",
+            useCaseSensitiveFileNames: () => false,
+            getCanonicalFileName: fileName => fileName,
+            getCurrentDirectory: () => "",
+            getNewLine: () => "\r\n"
+        };
+
+        var program = ts.createProgram([inputFileName], options, compilerHost);
+
+        // Emit
+        program.emit();
+
+        Debug.assert(outputText !== undefined, "Output generation failed");
+
+        return outputText;
+    }
+
     export function createLanguageServiceSourceFile(fileName: string, scriptSnapshot: IScriptSnapshot, scriptTarget: ScriptTarget, version: string, setNodeParents: boolean): SourceFile {
         let sourceFile = createSourceFile(fileName, scriptSnapshot.getText(0, scriptSnapshot.getLength()), scriptTarget, setNodeParents);
         setSourceFileFields(sourceFile, scriptSnapshot, version);