TypeScript/src/compiler/program.ts

/// <reference path="sys.ts" />
/// <reference path="emitter.ts" />

namespace ts {
    /* @internal */ export let programTime = 0;
    /* @internal */ export let emitTime = 0;
    /* @internal */ export let ioReadTime = 0;
    /* @internal */ export let ioWriteTime = 0;

    /** The version of the TypeScript compiler release */
    export const version = "1.5.3";
    
    var emptyArray: any[] = [];
    
    export function findConfigFile(searchPath: string): string {
        var fileName = "tsconfig.json";
        while (true) {
            if (sys.fileExists(fileName)) {
                return fileName;
            }
            var parentPath = getDirectoryPath(searchPath);
            if (parentPath === searchPath) {
                break;
            }
            searchPath = parentPath;
            fileName = "../" + fileName;
        }
        return undefined;
    }

    export function createCompilerHost(options: CompilerOptions, setParentNodes?: boolean): CompilerHost {
        let currentDirectory: string;
        let existingDirectories: Map<boolean> = {};

        function getCanonicalFileName(fileName: string): string {
            // if underlying system can distinguish between two files whose names differs only in cases then file name already in canonical form.
            // otherwise use toLowerCase as a canonical form.
            return sys.useCaseSensitiveFileNames ? fileName : fileName.toLowerCase();
        }
        
        // returned by CScript sys environment
        let unsupportedFileEncodingErrorCode = -2147024809;

        function getSourceFile(fileName: string, languageVersion: ScriptTarget, onError?: (message: string) => void): SourceFile {
            let text: string;
            try {
                let start = new Date().getTime();
                text = sys.readFile(fileName, options.charset);
                ioReadTime += new Date().getTime() - start;
            }
            catch (e) {
                if (onError) {
                    onError(e.number === unsupportedFileEncodingErrorCode
                        ? createCompilerDiagnostic(Diagnostics.Unsupported_file_encoding).messageText
                        : e.message);
                }
                text = "";
            }

            return text !== undefined ? createSourceFile(fileName, text, languageVersion, setParentNodes) : undefined;
        }

        function directoryExists(directoryPath: string): boolean {
            if (hasProperty(existingDirectories, directoryPath)) {
                return true;
            }
            if (sys.directoryExists(directoryPath)) {
                existingDirectories[directoryPath] = true;
                return true;
            }
            return false;
        }

        function ensureDirectoriesExist(directoryPath: string) {
            if (directoryPath.length > getRootLength(directoryPath) && !directoryExists(directoryPath)) {
                let parentDirectory = getDirectoryPath(directoryPath);
                ensureDirectoriesExist(parentDirectory);
                sys.createDirectory(directoryPath);
            }
        }

        function writeFile(fileName: string, data: string, writeByteOrderMark: boolean, onError?: (message: string) => void) {
            try {
                var start = new Date().getTime();
                ensureDirectoriesExist(getDirectoryPath(normalizePath(fileName)));
                sys.writeFile(fileName, data, writeByteOrderMark);
                ioWriteTime += new Date().getTime() - start;
            }
            catch (e) {
                if (onError) {
                    onError(e.message);
                }
            }
        }

        const newLine = getNewLineCharacter(options);

        return {
            getSourceFile,
            getDefaultLibFileName: options => combinePaths(getDirectoryPath(normalizePath(sys.getExecutingFilePath())), getDefaultLibFileName(options)),
            writeFile,
            getCurrentDirectory: () => currentDirectory || (currentDirectory = sys.getCurrentDirectory()),
            useCaseSensitiveFileNames: () => sys.useCaseSensitiveFileNames,
            getCanonicalFileName,
            getNewLine: () => newLine
        };
    }

    export function getPreEmitDiagnostics(program: Program, sourceFile?: SourceFile): Diagnostic[] {
        let diagnostics = program.getOptionsDiagnostics().concat(
                          program.getSyntacticDiagnostics(sourceFile),
                          program.getGlobalDiagnostics(),
                          program.getSemanticDiagnostics(sourceFile));

        if (program.getCompilerOptions().declaration) {
            diagnostics.concat(program.getDeclarationDiagnostics(sourceFile));
        }

        return sortAndDeduplicateDiagnostics(diagnostics);
    }

    export function flattenDiagnosticMessageText(messageText: string | DiagnosticMessageChain, newLine: string): string {
        if (typeof messageText === "string") {
            return messageText;
        }
        else {
            let diagnosticChain = messageText;
            let result = "";

            let indent = 0;
            while (diagnosticChain) {
                if (indent) {
                    result += newLine;

                    for (let i = 0; i < indent; i++) {
                        result += "  ";
                    }
                }
                result += diagnosticChain.messageText;
                indent++;
                diagnosticChain = diagnosticChain.next;
            }

            return result;
        }
    }

    export function createProgram(rootNames: string[], options: CompilerOptions, host?: CompilerHost, oldProgram?: Program): Program {
        let program: Program;
        let files: SourceFile[] = [];
        let diagnostics = createDiagnosticCollection();

        let commonSourceDirectory: string;
        let diagnosticsProducingTypeChecker: TypeChecker;
        let noDiagnosticsTypeChecker: TypeChecker;
        let classifiableNames: Map<string>;

        let skipDefaultLib = options.noLib;

        let start = new Date().getTime();

        host = host || createCompilerHost(options);

        let filesByName = createFileMap<SourceFile>(fileName => host.getCanonicalFileName(fileName));
        
        // if old program was provided by has different target module kind - assume that it cannot be reused
        // different module kind can lead to different way of resolving modules
        if (oldProgram && oldProgram.getCompilerOptions().module !== options.module) {
            oldProgram = undefined;
        }
        
        if (!tryReuseStructureFromOldProgram()) {
            forEach(rootNames, name => processRootFile(name, false));
            // Do not process the default library if:
            //  - The '--noLib' flag is used.
            //  - A 'no-default-lib' reference comment is encountered in
            //      processing the root files.
            if (!skipDefaultLib) {
                processRootFile(host.getDefaultLibFileName(options), true);
            }
        }

        verifyCompilerOptions();

        programTime += new Date().getTime() - start;

        program = {
            getRootFileNames: () => rootNames,
            getSourceFile: getSourceFile,
            getSourceFiles: () => files,
            getCompilerOptions: () => options,
            getSyntacticDiagnostics,
            getOptionsDiagnostics,
            getGlobalDiagnostics,
            getSemanticDiagnostics,
            getDeclarationDiagnostics,
            getTypeChecker,
            getClassifiableNames,
            getDiagnosticsProducingTypeChecker,
            getCommonSourceDirectory: () => commonSourceDirectory,
            emit,
            getCurrentDirectory: () => host.getCurrentDirectory(),
            getNodeCount: () => getDiagnosticsProducingTypeChecker().getNodeCount(),
            getIdentifierCount: () => getDiagnosticsProducingTypeChecker().getIdentifierCount(),
            getSymbolCount: () => getDiagnosticsProducingTypeChecker().getSymbolCount(),
            getTypeCount: () => getDiagnosticsProducingTypeChecker().getTypeCount(),
        };
        return program;

        function getClassifiableNames() {
            if (!classifiableNames) {
                // Initialize a checker so that all our files are bound.
                getTypeChecker();
                classifiableNames = {};

                for (let sourceFile of files) {
                    copyMap(sourceFile.classifiableNames, classifiableNames);
                }
            }

            return classifiableNames;
        }

        function tryReuseStructureFromOldProgram(): boolean {
            if (!host.hasChanges) {
                // host does not support method 'hasChanges'
                return false;
            }
            if (!oldProgram) {
                return false;
            }
            
            Debug.assert(!oldProgram.structureIsReused);

            // there is an old program, check if we can reuse its structure
            let oldRootNames = oldProgram.getRootFileNames();
            if (rootNames.length !== oldRootNames.length) {
                // different amount of root names - structure cannot be reused
                return false;
            }
            
            for (let i = 0; i < rootNames.length; i++) {
                if (oldRootNames[i] !== rootNames[i]) {
                    // different order of root names - structure cannot be reused
                    return false;
                }
            }
            
            // check if program source files has changed in the way that can affect structure of the program
            let newSourceFiles: SourceFile[] = [];
            for (let oldSourceFile of oldProgram.getSourceFiles()) {
                let newSourceFile: SourceFile;
                if (host.hasChanges(oldSourceFile)) {
                    newSourceFile = host.getSourceFile(oldSourceFile.fileName, options.target);
                    if (!newSourceFile) {
                        return false;
                    }
                    
                    // check tripleslash references
                    if (!arrayIsEqualTo(oldSourceFile.referencedFiles, newSourceFile.referencedFiles, fileReferenceIsEqualTo)) {
                        // tripleslash references has changed
                        return false;
                    }
                    
                    // check imports
                    collectExternalModuleReferences(newSourceFile);                    
                    if (!arrayIsEqualTo(oldSourceFile.imports, newSourceFile.imports, moduleNameIsEqualTo)) {
                        // imports has changed
                        return false;
                    }
                    // pass the cache of module resolutions from the old source file
                    newSourceFile.resolvedModules = oldSourceFile.resolvedModules;
                }
                else {
                    // file has no changes - use it as is
                    newSourceFile = oldSourceFile;
                }
                
                // if file has passed all checks it should be safe to reuse it
                newSourceFiles.push(newSourceFile);
            }
            
            // update fileName -> file mapping
            for (let file of newSourceFiles) {
                filesByName.set(file.fileName, file);
            }
            
            files = newSourceFiles;
            
            oldProgram.structureIsReused = true;
                
            return true;
        }

        function getEmitHost(writeFileCallback?: WriteFileCallback): EmitHost {
            return {
                getCanonicalFileName: fileName => host.getCanonicalFileName(fileName),
                getCommonSourceDirectory: program.getCommonSourceDirectory,
                getCompilerOptions: program.getCompilerOptions,
                getCurrentDirectory: () => host.getCurrentDirectory(),
                getNewLine: () => host.getNewLine(),
                getSourceFile: program.getSourceFile,
                getSourceFiles: program.getSourceFiles,
                writeFile: writeFileCallback || (
                    (fileName, data, writeByteOrderMark, onError) => host.writeFile(fileName, data, writeByteOrderMark, onError)),
            };
        }

        function getDiagnosticsProducingTypeChecker() {
            return diagnosticsProducingTypeChecker || (diagnosticsProducingTypeChecker = createTypeChecker(program, /*produceDiagnostics:*/ true));
        }

        function getTypeChecker() {
            return noDiagnosticsTypeChecker || (noDiagnosticsTypeChecker = createTypeChecker(program, /*produceDiagnostics:*/ false));
        }

        function emit(sourceFile?: SourceFile, writeFileCallback?: WriteFileCallback): EmitResult {
            // If the noEmitOnError flag is set, then check if we have any errors so far.  If so,
            // immediately bail out.
            if (options.noEmitOnError && getPreEmitDiagnostics(this).length > 0) {
                return { diagnostics: [], sourceMaps: undefined, emitSkipped: true };
            }

            // Create the emit resolver outside of the "emitTime" tracking code below.  That way
            // any cost associated with it (like type checking) are appropriate associated with
            // the type-checking counter.
            //
            // If the -out option is specified, we should not pass the source file to getEmitResolver.
            // This is because in the -out scenario all files need to be emitted, and therefore all
            // files need to be type checked. And the way to specify that all files need to be type
            // checked is to not pass the file to getEmitResolver.
            let emitResolver = getDiagnosticsProducingTypeChecker().getEmitResolver(options.out ? undefined : sourceFile);

            let start = new Date().getTime();

            let emitResult = emitFiles(
                emitResolver,
                getEmitHost(writeFileCallback),
                sourceFile);

            emitTime += new Date().getTime() - start;
            return emitResult;
        }

        function getSourceFile(fileName: string) {
            return filesByName.get(fileName);
        }

        function getDiagnosticsHelper(sourceFile: SourceFile, getDiagnostics: (sourceFile: SourceFile) => Diagnostic[]): Diagnostic[] {
            if (sourceFile) {
                return getDiagnostics(sourceFile);
            }

            let allDiagnostics: Diagnostic[] = [];
            forEach(program.getSourceFiles(), sourceFile => {
                addRange(allDiagnostics, getDiagnostics(sourceFile));
            });

            return sortAndDeduplicateDiagnostics(allDiagnostics);
        }

        function getSyntacticDiagnostics(sourceFile?: SourceFile): Diagnostic[] {
            return getDiagnosticsHelper(sourceFile, getSyntacticDiagnosticsForFile);
        }

        function getSemanticDiagnostics(sourceFile?: SourceFile): Diagnostic[] {
            return getDiagnosticsHelper(sourceFile, getSemanticDiagnosticsForFile);
        }

        function getDeclarationDiagnostics(sourceFile?: SourceFile): Diagnostic[] {
            return getDiagnosticsHelper(sourceFile, getDeclarationDiagnosticsForFile);
        }

        function getSyntacticDiagnosticsForFile(sourceFile: SourceFile): Diagnostic[] {
            return sourceFile.parseDiagnostics;
        }

        function getSemanticDiagnosticsForFile(sourceFile: SourceFile): Diagnostic[] {
            let typeChecker = getDiagnosticsProducingTypeChecker();

            Debug.assert(!!sourceFile.bindDiagnostics);
            let bindDiagnostics = sourceFile.bindDiagnostics;
            let checkDiagnostics = typeChecker.getDiagnostics(sourceFile);
            let programDiagnostics = diagnostics.getDiagnostics(sourceFile.fileName);

            return bindDiagnostics.concat(checkDiagnostics).concat(programDiagnostics);
        }

        function getDeclarationDiagnosticsForFile(sourceFile: SourceFile): Diagnostic[] {
            if (!isDeclarationFile(sourceFile)) {
                let resolver = getDiagnosticsProducingTypeChecker().getEmitResolver(sourceFile);
                // Don't actually write any files since we're just getting diagnostics.
                var writeFile: WriteFileCallback = () => { };
                return ts.getDeclarationDiagnostics(getEmitHost(writeFile), resolver, sourceFile);
            }
        }

        function getOptionsDiagnostics(): Diagnostic[] {
            let allDiagnostics: Diagnostic[] = [];
            addRange(allDiagnostics, diagnostics.getGlobalDiagnostics());
            return sortAndDeduplicateDiagnostics(allDiagnostics);
        }

        function getGlobalDiagnostics(): Diagnostic[] {
            let allDiagnostics: Diagnostic[] = [];
            addRange(allDiagnostics, getDiagnosticsProducingTypeChecker().getGlobalDiagnostics());
            return sortAndDeduplicateDiagnostics(allDiagnostics);
        }

        function hasExtension(fileName: string): boolean {
            return getBaseFileName(fileName).indexOf(".") >= 0;
        }

        function processRootFile(fileName: string, isDefaultLib: boolean) {
            processSourceFile(normalizePath(fileName), isDefaultLib);
        }        
    
        function fileReferenceIsEqualTo(a: FileReference, b: FileReference): boolean {
            return a.fileName === b.fileName;
        }
        
        function moduleNameIsEqualTo(a: LiteralExpression, b: LiteralExpression): boolean {
            return a.text ===b.text;
        }
        
        function collectExternalModuleReferences(file: SourceFile): void {
            if (file.imports) {
                return;
            }
            
            let imports: LiteralExpression[];
            for (let node of file.statements) {
                switch (node.kind) {
                    case SyntaxKind.ImportDeclaration:
                    case SyntaxKind.ImportEqualsDeclaration:
                    case SyntaxKind.ExportDeclaration:
                        let moduleNameExpr = getExternalModuleName(node);
                        if (!moduleNameExpr || moduleNameExpr.kind !== SyntaxKind.StringLiteral) {
                            break;
                        }
                        if (!(<LiteralExpression>moduleNameExpr).text) {
                            break;
                        }

                        (imports || (imports = [])).push(<LiteralExpression>moduleNameExpr);
                        break;
                    case SyntaxKind.ModuleDeclaration:
                        if ((<ModuleDeclaration>node).name.kind === SyntaxKind.StringLiteral && (node.flags & NodeFlags.Ambient || isDeclarationFile(file))) {
                            // TypeScript 1.0 spec (April 2014): 12.1.6
                            // An AmbientExternalModuleDeclaration declares an external module. 
                            // This type of declaration is permitted only in the global module.
                            // The StringLiteral must specify a top - level external module name.
                            // Relative external module names are not permitted
                            forEachChild((<ModuleDeclaration>node).body, node => {
                                if (isExternalModuleImportEqualsDeclaration(node) &&
                                    getExternalModuleImportEqualsDeclarationExpression(node).kind === SyntaxKind.StringLiteral) {
                                    let moduleName = <LiteralExpression>getExternalModuleImportEqualsDeclarationExpression(node);
                                    // TypeScript 1.0 spec (April 2014): 12.1.6
                                    // An ExternalImportDeclaration in anAmbientExternalModuleDeclaration may reference other external modules 
                                    // only through top - level external module names. Relative external module names are not permitted.
                                    if (moduleName) {
                                        (imports || (imports = [])).push(moduleName);
                                    }
                                }
                            });
                        }
                        break;
                }
            }

            file.imports = imports || emptyArray;
        }

        function processSourceFile(fileName: string, isDefaultLib: boolean, refFile?: SourceFile, refPos?: number, refEnd?: number) {
            let start: number;
            let length: number;
            let extensions: string;
            let diagnosticArgument: string[];
            if (refEnd !== undefined && refPos !== undefined) {
                start = refPos;
                length = refEnd - refPos;
            }
            let diagnostic: DiagnosticMessage;
            if (hasExtension(fileName)) {
                if (!options.allowNonTsExtensions && !forEach(supportedExtensions, extension => fileExtensionIs(host.getCanonicalFileName(fileName), extension))) {
                    diagnostic = Diagnostics.File_0_has_unsupported_extension_The_only_supported_extensions_are_1;
                    diagnosticArgument = [fileName, "'" + supportedExtensions.join("', '") + "'"];
                }
                else if (!findSourceFile(fileName, isDefaultLib, refFile, refPos, refEnd)) {
                    diagnostic = Diagnostics.File_0_not_found;
                    diagnosticArgument = [fileName];
                }
                else if (refFile && host.getCanonicalFileName(fileName) === host.getCanonicalFileName(refFile.fileName)) {
                    diagnostic = Diagnostics.A_file_cannot_have_a_reference_to_itself;
                    diagnosticArgument = [fileName];
                }
            }
            else {
                var nonTsFile: SourceFile = options.allowNonTsExtensions && findSourceFile(fileName, isDefaultLib, refFile, refPos, refEnd);
                if (!nonTsFile) {
                    if (options.allowNonTsExtensions) {
                        diagnostic = Diagnostics.File_0_not_found;
                        diagnosticArgument = [fileName];
                    }
                    else if (!forEach(supportedExtensions, extension => findSourceFile(fileName + extension, isDefaultLib, refFile, refPos, refEnd))) {
                        diagnostic = Diagnostics.File_0_not_found;
                        fileName += ".ts";
                        diagnosticArgument = [fileName];
                    }
                }
            }

            if (diagnostic) {
                if (refFile) {
                    diagnostics.add(createFileDiagnostic(refFile, start, length, diagnostic, ...diagnosticArgument));
                }
                else {
                    diagnostics.add(createCompilerDiagnostic(diagnostic, ...diagnosticArgument));
                }
            }
        }

        // Get source file from normalized fileName
        function findSourceFile(fileName: string, isDefaultLib: boolean, refFile?: SourceFile, refStart?: number, refLength?: number): SourceFile {
            let canonicalName = host.getCanonicalFileName(normalizeSlashes(fileName));
            if (filesByName.contains(canonicalName)) {
                // We've already looked for this file, use cached result
                return getSourceFileFromCache(fileName, canonicalName, /*useAbsolutePath*/ false);
            }
            else {
                let normalizedAbsolutePath = getNormalizedAbsolutePath(fileName, host.getCurrentDirectory());
                let canonicalAbsolutePath = host.getCanonicalFileName(normalizedAbsolutePath);
                if (filesByName.contains(canonicalAbsolutePath)) {
                    return getSourceFileFromCache(normalizedAbsolutePath, canonicalAbsolutePath, /*useAbsolutePath*/ true);
                }

                // We haven't looked for this file, do so now and cache result
                let file = host.getSourceFile(fileName, options.target, hostErrorMessage => {
                    if (refFile) {
                        diagnostics.add(createFileDiagnostic(refFile, refStart, refLength,
                            Diagnostics.Cannot_read_file_0_Colon_1, fileName, hostErrorMessage));
                    }
                    else {
                        diagnostics.add(createCompilerDiagnostic(Diagnostics.Cannot_read_file_0_Colon_1, fileName, hostErrorMessage));
                    }
                });
                filesByName.set(canonicalName, file);
                if (file) {
                    skipDefaultLib = skipDefaultLib || file.hasNoDefaultLib;

                    // Set the source file for normalized absolute path
                    filesByName.set(canonicalAbsolutePath, file);

                    if (!options.noResolve) {
                        let basePath = getDirectoryPath(fileName);
                        processReferencedFiles(file, basePath);
                        processImportedModules(file, basePath);
                    }
                    if (isDefaultLib) {
                        file.isDefaultLib = true;
                        files.unshift(file);
                    }
                    else {
                        files.push(file);
                    }
                }

                return file;
            }

            function getSourceFileFromCache(fileName: string, canonicalName: string, useAbsolutePath: boolean): SourceFile {
                let file = filesByName.get(canonicalName);
                if (file && host.useCaseSensitiveFileNames()) {
                    let sourceFileName = useAbsolutePath ? getNormalizedAbsolutePath(file.fileName, host.getCurrentDirectory()) : file.fileName;
                    if (canonicalName !== sourceFileName) {
                        diagnostics.add(createFileDiagnostic(refFile, refStart, refLength,
                            Diagnostics.File_name_0_differs_from_already_included_file_name_1_only_in_casing, fileName, sourceFileName));
                    }
                }
                return file;
            }
        }

        function processReferencedFiles(file: SourceFile, basePath: string) {
            forEach(file.referencedFiles, ref => {
                let referencedFileName = isRootedDiskPath(ref.fileName) ? ref.fileName : combinePaths(basePath, ref.fileName);
                processSourceFile(normalizePath(referencedFileName), /* isDefaultLib */ false, file, ref.pos, ref.end);
            });
        }
        
        function processImportedModules(file: SourceFile, basePath: string) {            
            collectExternalModuleReferences(file);            
            if (file.imports.length) {               
                let allImportsInTheCache = false;

                // try to grab existing module resolutions from the old source file
                let oldSourceFile: SourceFile = oldProgram && oldProgram.getSourceFile(file.fileName);
                if (oldSourceFile) {
                    file.resolvedModules = oldSourceFile.resolvedModules;
                
                    // check that all imports are contained in resolved modules cache
                    // if at least one of imports in not in the cache - cache needs to be reinitialized
                    checkImports: {
                        if (file.resolvedModules) {
                            for (let moduleName of file.imports) {
                                if (!hasResolvedModuleName(file, moduleName)) {
                                    break checkImports;
                                }
                            }

                            allImportsInTheCache = true;
                        }
                    }
                }
                
                if (!allImportsInTheCache) {
                    // initialize resolvedModules with empty map
                    // old module resolutions still can be used to avoid actual file system probing
                    let resolvedModules = file.resolvedModules;
                    file.resolvedModules = {};
                    for (let moduleName of file.imports) {
                        resolveModule(moduleName, resolvedModules);
                    }
                }
            }
            else {
                // no imports - drop cached module resolutions
                file.resolvedModules = undefined;
            }
            return;

            function findModuleSourceFile(fileName: string, nameLiteral: Expression) {
                return findSourceFile(fileName, /* isDefaultLib */ false, file, nameLiteral.pos, nameLiteral.end - nameLiteral.pos);
            }

            function resolveModule(moduleNameExpr: LiteralExpression, existingResolutions: Map<string>): void {
                let searchPath = basePath;
                let searchName: string;

                if (existingResolutions && hasProperty(existingResolutions, moduleNameExpr.text)) {
                    let fileName = existingResolutions[moduleNameExpr.text];
                    // use existing resolution
                    setResolvedModuleName(file, moduleNameExpr, fileName);
                    if (fileName) {
                        findModuleSourceFile(fileName, moduleNameExpr);
                    }
                    return;
                }

                while (true) {
                    searchName = normalizePath(combinePaths(searchPath, moduleNameExpr.text));
                    let referencedSourceFile = forEach(supportedExtensions, extension => findModuleSourceFile(searchName + extension, moduleNameExpr));
                    if (referencedSourceFile) {
                        setResolvedModuleName(file, moduleNameExpr, referencedSourceFile.fileName);
                        return;
                    }

                    let parentPath = getDirectoryPath(searchPath);
                    if (parentPath === searchPath) {
                        break;
                    }
                    searchPath = parentPath;
                }
                // mark reference as non-resolved
                setResolvedModuleName(file, moduleNameExpr, undefined);
            }
        }

        function computeCommonSourceDirectory(sourceFiles: SourceFile[]): string {
            let commonPathComponents: string[];
            let currentDirectory = host.getCurrentDirectory();
            forEach(files, sourceFile => {
                // Each file contributes into common source file path
                if (isDeclarationFile(sourceFile)) {
                    return;
                }

                let sourcePathComponents = getNormalizedPathComponents(sourceFile.fileName, currentDirectory);
                sourcePathComponents.pop(); // The base file name is not part of the common directory path

                if (!commonPathComponents) {
                    // first file
                    commonPathComponents = sourcePathComponents;
                    return;
                }

                for (let i = 0, n = Math.min(commonPathComponents.length, sourcePathComponents.length); i < n; i++) {
                    if (commonPathComponents[i] !== sourcePathComponents[i]) {
                        if (i === 0) {
                            diagnostics.add(createCompilerDiagnostic(Diagnostics.Cannot_find_the_common_subdirectory_path_for_the_input_files));
                            return;
                        }

                        // New common path found that is 0 -> i-1
                        commonPathComponents.length = i;
                        break;
                    }
                }

                // If the sourcePathComponents was shorter than the commonPathComponents, truncate to the sourcePathComponents
                if (sourcePathComponents.length < commonPathComponents.length) {
                    commonPathComponents.length = sourcePathComponents.length;
                }
            });

            return getNormalizedPathFromPathComponents(commonPathComponents);
        }

        function checkSourceFilesBelongToPath(sourceFiles: SourceFile[], rootDirectory: string): boolean {
            let allFilesBelongToPath = true;
            if (sourceFiles) {
                let currentDirectory = host.getCurrentDirectory();
                let absoluteRootDirectoryPath = host.getCanonicalFileName(getNormalizedAbsolutePath(rootDirectory, currentDirectory));

                for (var sourceFile of sourceFiles) {
                    if (!isDeclarationFile(sourceFile)) {
                        let absoluteSourceFilePath = host.getCanonicalFileName(getNormalizedAbsolutePath(sourceFile.fileName, currentDirectory));
                        if (absoluteSourceFilePath.indexOf(absoluteRootDirectoryPath) !== 0) {
                            diagnostics.add(createCompilerDiagnostic(Diagnostics.File_0_is_not_under_rootDir_1_rootDir_is_expected_to_contain_all_source_files, sourceFile.fileName, options.rootDir));
                            allFilesBelongToPath = false;
                        }
                    }
                }
            }

            return allFilesBelongToPath;
        }

        function verifyCompilerOptions() {
            if (options.isolatedModules) {
                if (options.sourceMap) {
                    diagnostics.add(createCompilerDiagnostic(Diagnostics.Option_sourceMap_cannot_be_specified_with_option_isolatedModules));
                }

                if (options.declaration) {
                    diagnostics.add(createCompilerDiagnostic(Diagnostics.Option_declaration_cannot_be_specified_with_option_isolatedModules));
                }

                if (options.noEmitOnError) {
                    diagnostics.add(createCompilerDiagnostic(Diagnostics.Option_noEmitOnError_cannot_be_specified_with_option_isolatedModules));
                }

                if (options.out) {
                    diagnostics.add(createCompilerDiagnostic(Diagnostics.Option_out_cannot_be_specified_with_option_isolatedModules));
                }
            }

            if (options.inlineSourceMap) {
                if (options.sourceMap) {
                    diagnostics.add(createCompilerDiagnostic(Diagnostics.Option_sourceMap_cannot_be_specified_with_option_inlineSourceMap));
                }
                if (options.mapRoot) {
                    diagnostics.add(createCompilerDiagnostic(Diagnostics.Option_mapRoot_cannot_be_specified_with_option_inlineSourceMap));
                }
                if (options.sourceRoot) {
                    diagnostics.add(createCompilerDiagnostic(Diagnostics.Option_sourceRoot_cannot_be_specified_with_option_inlineSourceMap));
                }
            }


            if (options.inlineSources) {
                if (!options.sourceMap && !options.inlineSourceMap) {
                    diagnostics.add(createCompilerDiagnostic(Diagnostics.Option_inlineSources_can_only_be_used_when_either_option_inlineSourceMap_or_option_sourceMap_is_provided));
                }
            }

            if (!options.sourceMap && (options.mapRoot || options.sourceRoot)) {
                // Error to specify --mapRoot or --sourceRoot without mapSourceFiles
                if (options.mapRoot) {
                    diagnostics.add(createCompilerDiagnostic(Diagnostics.Option_mapRoot_cannot_be_specified_without_specifying_sourceMap_option));
                }
                if (options.sourceRoot) {
                    diagnostics.add(createCompilerDiagnostic(Diagnostics.Option_sourceRoot_cannot_be_specified_without_specifying_sourceMap_option));
                }
                return;
            }

            let languageVersion = options.target || ScriptTarget.ES3;

            let firstExternalModuleSourceFile = forEach(files, f => isExternalModule(f) ? f : undefined);
            if (options.isolatedModules) {
                if (!options.module && languageVersion < ScriptTarget.ES6) {
                    diagnostics.add(createCompilerDiagnostic(Diagnostics.Option_isolatedModules_can_only_be_used_when_either_option_module_is_provided_or_option_target_is_ES6_or_higher));
                }

                let firstNonExternalModuleSourceFile = forEach(files, f => !isExternalModule(f) && !isDeclarationFile(f) ? f : undefined);
                if (firstNonExternalModuleSourceFile) {
                    let span = getErrorSpanForNode(firstNonExternalModuleSourceFile, firstNonExternalModuleSourceFile);
                    diagnostics.add(createFileDiagnostic(firstNonExternalModuleSourceFile, span.start, span.length, Diagnostics.Cannot_compile_namespaces_when_the_isolatedModules_flag_is_provided));
                }
            }
            else if (firstExternalModuleSourceFile && languageVersion < ScriptTarget.ES6 && !options.module) {
                // We cannot use createDiagnosticFromNode because nodes do not have parents yet 
                let span = getErrorSpanForNode(firstExternalModuleSourceFile, firstExternalModuleSourceFile.externalModuleIndicator);
                diagnostics.add(createFileDiagnostic(firstExternalModuleSourceFile, span.start, span.length, Diagnostics.Cannot_compile_modules_unless_the_module_flag_is_provided));
            }

            // Cannot specify module gen target when in es6 or above
            if (options.module && languageVersion >= ScriptTarget.ES6) {
                diagnostics.add(createCompilerDiagnostic(Diagnostics.Cannot_compile_modules_into_commonjs_amd_system_or_umd_when_targeting_ES6_or_higher));
            }

            // there has to be common source directory if user specified --outdir || --sourceRoot
            // if user specified --mapRoot, there needs to be common source directory if there would be multiple files being emitted
            if (options.outDir || // there is --outDir specified
                options.sourceRoot || // there is --sourceRoot specified
                (options.mapRoot &&  // there is --mapRoot specified and there would be multiple js files generated
                    (!options.out || firstExternalModuleSourceFile !== undefined))) {

                if (options.rootDir && checkSourceFilesBelongToPath(files, options.rootDir)) {
                    // If a rootDir is specified and is valid use it as the commonSourceDirectory
                    commonSourceDirectory = getNormalizedAbsolutePath(options.rootDir, host.getCurrentDirectory());
                }
                else {
                    // Compute the commonSourceDirectory from the input files
                    commonSourceDirectory = computeCommonSourceDirectory(files);
                }

                if (commonSourceDirectory && commonSourceDirectory[commonSourceDirectory.length - 1] !== directorySeparator) {
                    // Make sure directory path ends with directory separator so this string can directly 
                    // used to replace with "" to get the relative path of the source file and the relative path doesn't
                    // start with / making it rooted path
                    commonSourceDirectory += directorySeparator;
                }
            }

            if (options.noEmit) {
                if (options.out || options.outDir) {
                    diagnostics.add(createCompilerDiagnostic(Diagnostics.Option_noEmit_cannot_be_specified_with_option_out_or_outDir));
                }

                if (options.declaration) {
                    diagnostics.add(createCompilerDiagnostic(Diagnostics.Option_noEmit_cannot_be_specified_with_option_declaration));
                }
            }
            
            if (options.emitDecoratorMetadata &&
                !options.experimentalDecorators) {
                diagnostics.add(createCompilerDiagnostic(Diagnostics.Option_experimentalDecorators_must_also_be_specified_when_option_emitDecoratorMetadata_is_specified));
            }
        }
    }
}