/**

* @fileoverview A TypeScript parser for the AssemblyScript subset.

*

* Takes the tokens produced by the `Tokenizer` and builds an abstract

* syntax tree composed of `Node`s wrapped in a `Source` out of it.

*

* @license Apache-2.0

*/

import {

CommonFlags,

LIBRARY_PREFIX,

PATH_DELIMITER

} from "./common";

import {

Tokenizer,

Token,

Range,

CommentHandler,

IdentifierHandling,

isIllegalVariableIdentifier

} from "./tokenizer";

import {

DiagnosticCode,

DiagnosticEmitter,

DiagnosticMessage

} from "./diagnostics";

import {

CharCode,

normalizePath

} from "./util";

import {

Node,

NodeKind,

Source,

SourceKind,

TypeNode,

TypeName,

NamedTypeNode,

FunctionTypeNode,

ArrowKind,

Expression,

AssertionKind,

CallExpression,

ClassExpression,

FunctionExpression,

IdentifierExpression,

StringLiteralExpression,

Statement,

BlockStatement,

BreakStatement,

ClassDeclaration,

ContinueStatement,

DeclarationStatement,

DecoratorNode,

DoStatement,

EnumDeclaration,

EnumValueDeclaration,

ExportImportStatement,

ExportMember,

ExportStatement,

ExpressionStatement,

ForOfStatement,

FunctionDeclaration,

IfStatement,

ImportDeclaration,

ImportStatement,

IndexSignatureNode,

NamespaceDeclaration,

ParameterNode,

ParameterKind,

ReturnStatement,

SwitchCase,

SwitchStatement,

ThrowStatement,

TryStatement,

TypeDeclaration,

TypeParameterNode,

VariableStatement,

VariableDeclaration,

VoidStatement,

WhileStatement,

ModuleDeclaration,

mangleInternalPath

} from "./ast";

/** Represents a dependee. */

class Dependee {

constructor(

public source: Source,

public reportNode: Node

) {}

}

/** Parser interface. */

export class Parser extends DiagnosticEmitter {

/** Source file names to be requested next. */

backlog: string[] = new Array();

/** Source file names already seen, that is processed or backlogged. */

seenlog: Set<string> = new Set();

/** Source file names already completely processed. */

donelog: Set<string> = new Set();

/** Optional handler to intercept comments while tokenizing. */

onComment: CommentHandler | null = null;

/** Current file being parsed. */

currentSource: Source | null = null;

/** Map of dependees being depended upon by a source, by path. */

dependees: Map<string, Dependee> = new Map();

/** An array of parsed sources. */

sources: Source[];

/** Current overridden module name. */

currentModuleName: string | null = null;

/** Constructs a new parser. */

constructor(

diagnostics: DiagnosticMessage[] | null = null,

sources: Source[] | null = null

) {

super(diagnostics);

this.sources = sources ? sources : new Array<Source>();

}

/** Parses a file and adds its definitions to the program. */

parseFile(

/** Source text of the file, or `null` to indicate not found. */

text: string | null,

/** Normalized path of the file. */

path: string,

/** Whether this is an entry file. */

isEntry: bool

): void {

// the frontend gives us paths with file extensions

var normalizedPath = normalizePath(path);

var internalPath = mangleInternalPath(normalizedPath);

// check if already processed

if (this.donelog.has(internalPath)) return;

this.donelog.add(internalPath); // do not parse again

this.seenlog.add(internalPath); // do not request again

// check if this is an error

if (text == null) {

let dependees = this.dependees;

let dependee: Dependee | null = null;

if (dependees.has(internalPath)) dependee = assert(dependees.get(internalPath));

this.error(

DiagnosticCode.File_0_not_found,

dependee

? dependee.reportNode.range

: null,

path

);

return;

}

// create the source element

var source = new Source(

isEntry

? SourceKind.USER_ENTRY

: path.startsWith(LIBRARY_PREFIX)

? path.indexOf(PATH_DELIMITER, LIBRARY_PREFIX.length) < 0

? SourceKind.LIBRARY_ENTRY

: SourceKind.LIBRARY

: SourceKind.USER,

normalizedPath,

text

);

this.sources.push(source);

this.currentSource = source;

this.currentModuleName = null;

// tokenize and parse

var tn = new Tokenizer(source, this.diagnostics);

tn.onComment = this.onComment;

var statements = source.statements;

while (!tn.skip(Token.ENDOFFILE)) {

let statement = this.parseTopLevelStatement(tn, null);

if (statement) {

statements.push(statement);

} else {

this.skipStatement(tn);

}

}

}

/** Parses a top-level statement. */

parseTopLevelStatement(

tn: Tokenizer,

namespace: NamespaceDeclaration | null = null

): Statement | null {

var flags = namespace ? namespace.flags & CommonFlags.AMBIENT : CommonFlags.NONE;

var startPos = -1;

// check decorators

var decorators: DecoratorNode[] | null = null;

while (tn.skip(Token.AT)) {

if (startPos < 0) startPos = tn.tokenPos;

let decorator = this.parseDecorator(tn);

if (!decorator) {

this.skipStatement(tn);

continue;

}

if (!decorators) decorators = [decorator];

else decorators.push(decorator);

}

// check modifiers

var exportStart = 0;

var exportEnd = 0;

var defaultStart = 0;

var defaultEnd = 0;

if (tn.skip(Token.EXPORT)) {

if (startPos < 0) startPos = tn.tokenPos;

flags |= CommonFlags.EXPORT;

exportStart = tn.tokenPos;

exportEnd = tn.pos;

if (tn.skip(Token.DEFAULT)) {

defaultStart = tn.tokenPos;

defaultEnd = tn.pos;

}

}

var declareStart = 0;

var declareEnd = 0;

var contextIsAmbient = namespace != null && namespace.is(CommonFlags.AMBIENT);

if (tn.skip(Token.DECLARE)) {

if (contextIsAmbient) {

this.error(

DiagnosticCode.A_declare_modifier_cannot_be_used_in_an_already_ambient_context,

tn.range()

); // recoverable

} else {

if (startPos < 0) startPos = tn.tokenPos;

declareStart = startPos;

declareEnd = tn.pos;

flags |= CommonFlags.DECLARE | CommonFlags.AMBIENT;

}

} else if (contextIsAmbient) {

flags |= CommonFlags.AMBIENT;

}

// parse the statement

var statement: Statement | null = null;

// handle declarations

var first = tn.peek();

if (startPos < 0) startPos = tn.nextTokenPos;

switch (first) {

case Token.CONST: {

tn.next();

flags |= CommonFlags.CONST;

if (tn.skip(Token.ENUM)) {

statement = this.parseEnum(tn, flags, decorators, startPos);

} else {

statement = this.parseVariable(tn, flags, decorators, startPos);

}

decorators = null;

break;

}

case Token.LET: flags |= CommonFlags.LET;

case Token.VAR: {

tn.next();

statement = this.parseVariable(tn, flags, decorators, startPos);

decorators = null;

break;

}

case Token.ENUM: {

tn.next();

statement = this.parseEnum(tn, flags, decorators, startPos);

decorators = null;

break;

}

case Token.FUNCTION: {

tn.next();

statement = this.parseFunction(tn, flags, decorators, startPos);

decorators = null;

break;

}

case Token.ABSTRACT: {

let state = tn.mark();

tn.next();

let abstractStart = tn.tokenPos;

let abstractEnd = tn.pos;

let next = tn.peek(true);

if (tn.nextTokenOnNewLine) {

tn.reset(state);

statement = this.parseStatement(tn, true);

break;

}

if (next != Token.CLASS) {

if (next == Token.INTERFACE) {

this.error(

DiagnosticCode._abstract_modifier_can_only_appear_on_a_class_method_or_property_declaration,

tn.range(abstractStart, abstractEnd)

);

}

tn.reset(state);

statement = this.parseStatement(tn, true);

break;

} else {

tn.discard(state);

}

flags |= CommonFlags.ABSTRACT;

// fall through

}

case Token.CLASS:

case Token.INTERFACE: {

tn.next();

statement = this.parseClassOrInterface(tn, flags, decorators, startPos);

decorators = null;

break;

}

case Token.NAMESPACE: {

let state = tn.mark();

tn.next();

if (tn.peek(false, IdentifierHandling.PREFER) == Token.IDENTIFIER) {

tn.discard(state);

statement = this.parseNamespace(tn, flags, decorators, startPos);

decorators = null;

} else {

tn.reset(state);

statement = this.parseStatement(tn, true);

}

break;

}

case Token.IMPORT: {

tn.next();

flags |= CommonFlags.IMPORT;

if (flags & CommonFlags.EXPORT) {

statement = this.parseExportImport(tn, startPos);

} else {

statement = this.parseImport(tn);

}

break;

}

case Token.TYPE: { // also identifier

let state = tn.mark();

tn.next();

if (tn.peek(false, IdentifierHandling.PREFER) == Token.IDENTIFIER) {

tn.discard(state);

statement = this.parseTypeDeclaration(tn, flags, decorators, startPos);

decorators = null;

} else {

tn.reset(state);

statement = this.parseStatement(tn, true);

}

break;

}

case Token.MODULE: { // also identifier

let state = tn.mark();

tn.next();

if (tn.peek(true) == Token.STRINGLITERAL && !tn.nextTokenOnNewLine) {

tn.discard(state);

statement = this.parseModuleDeclaration(tn, flags);

} else {

tn.reset(state);

statement = this.parseStatement(tn, true);

}

break;

}

default: {

// handle plain exports

if (flags & CommonFlags.EXPORT) {

if (defaultEnd && tn.skipIdentifier(IdentifierHandling.PREFER)) {

if (declareEnd) {

this.error(

DiagnosticCode.An_export_assignment_cannot_have_modifiers,

tn.range(declareStart, declareEnd)

);

}

statement = this.parseExportDefaultAlias(tn, startPos, defaultStart, defaultEnd);

defaultStart = defaultEnd = 0; // consume

} else {

statement = this.parseExport(tn, startPos, (flags & CommonFlags.DECLARE) != 0);

}

// handle non-declaration statements

} else {

if (exportEnd) {

this.error(

DiagnosticCode._0_modifier_cannot_be_used_here,

tn.range(exportStart, exportEnd), "export"

); // recoverable

}

if (declareEnd) {

this.error(

DiagnosticCode._0_modifier_cannot_be_used_here,

tn.range(declareStart, declareEnd), "declare"

); // recoverable

}

if (!namespace) {

statement = this.parseStatement(tn, true);

} // TODO: else?

}

break;

}

}

// check for decorators that weren't consumed

if (decorators) {

for (let i = 0, k = decorators.length; i < k; ++i) {

this.error(

DiagnosticCode.Decorators_are_not_valid_here,

decorators[i].range

);

}

}

// check if this an `export default` declaration

if (defaultEnd && statement != null) {

switch (statement.kind) {

case NodeKind.ENUMDECLARATION:

case NodeKind.FUNCTIONDECLARATION:

case NodeKind.CLASSDECLARATION:

case NodeKind.INTERFACEDECLARATION:

case NodeKind.NAMESPACEDECLARATION: {

return Node.createExportDefaultStatement(<DeclarationStatement>statement, tn.range(startPos, tn.pos));

}

default: {

this.error(

DiagnosticCode._0_modifier_cannot_be_used_here,

tn.range(defaultStart, defaultEnd), "default"

);

}

}

}

return statement;

}

/** Obtains the next file to parse. */

nextFile(): string | null {

var backlog = this.backlog;

return backlog.length ? assert(backlog.shift()) : null;

}

/** Obtains the path of the dependee of the given imported file. */

getDependee(dependent: string): string | null {

var dependees = this.dependees;

if (dependees.has(dependent)) {

let dependee = assert(dependees.get(dependent));

return dependee.source.internalPath;

}

return null;

}

/** Finishes parsing. */

finish(): void {

if (this.backlog.length) throw new Error("backlog is not empty");

this.backlog = [];

this.seenlog.clear();

this.donelog.clear();

this.dependees.clear();

}

// types

/** Parses a type name. */

parseTypeName(

tn: Tokenizer

): TypeName | null {

// at: Identifier ('.' Identifier)*

var first = Node.createSimpleTypeName(tn.readIdentifier(), tn.range());

var current = first;

while (tn.skip(Token.DOT)) {

if (tn.skip(Token.IDENTIFIER)) {

let next = Node.createSimpleTypeName(tn.readIdentifier(), tn.range());

current.next = next;

current = next;

} else {

this.error(

DiagnosticCode.Identifier_expected,

tn.range(tn.pos)

);

return null;

}

}

return first;

}

/** Parses a type. */

parseType(

tn: Tokenizer,

acceptParenthesized: bool = true,

suppressErrors: bool = false

): TypeNode | null {

// before: Type

// NOTE: this parses our limited subset

var token = tn.next();

var startPos = tn.tokenPos;

var type: TypeNode;

// '(' ...

if (token == Token.OPENPAREN) {

// '(' FunctionSignature ')' '|' 'null'?

let isNullableSignature = tn.skip(Token.OPENPAREN);

// FunctionSignature?

let signature = this.tryParseFunctionType(tn);

if (signature) {

if (isNullableSignature) {

if (!tn.skip(Token.CLOSEPAREN)) {

this.error(

DiagnosticCode._0_expected,

tn.range(), ")"

);

return null;

}

if (!tn.skip(Token.BAR)) {

this.error(

DiagnosticCode._0_expected,

tn.range(), "|"

);

return null;

}

if (!tn.skip(Token.NULL)) {

this.error(

DiagnosticCode._0_expected,

tn.range(), "null"

);

}

signature.isNullable = true;

}

return signature;

} else if (isNullableSignature || this.tryParseSignatureIsSignature) {

this.error(

DiagnosticCode.Unexpected_token,

tn.range()

);

return null;

}

// Type (',' Type)* ')'

if (acceptParenthesized) {

let innerType = this.parseType(tn, false, suppressErrors);

if (!innerType) return null;

if (!tn.skip(Token.CLOSEPAREN)) {

if (!suppressErrors) {

this.error(

DiagnosticCode._0_expected,

tn.range(tn.pos), ")"

);

}

return null;

}

type = innerType;

type.range.start = startPos;

type.range.end = tn.pos;

} else {

this.error(

DiagnosticCode.Unexpected_token,

tn.range()

);

return null;

}

// 'void'

} else if (token == Token.VOID) {

type = Node.createNamedType(

Node.createSimpleTypeName("void", tn.range()), [], false, tn.range(startPos, tn.pos)

);

// 'this'

} else if (token == Token.THIS) {

type = Node.createNamedType(

Node.createSimpleTypeName("this", tn.range()), [], false, tn.range(startPos, tn.pos)

);

// 'true'

} else if (token == Token.TRUE || token == Token.FALSE) {

type = Node.createNamedType(

Node.createSimpleTypeName("bool", tn.range()), [], false, tn.range(startPos, tn.pos)

);

// 'null'

} else if (token == Token.NULL) {

type = Node.createNamedType(

Node.createSimpleTypeName("null", tn.range()), [], false, tn.range(startPos, tn.pos)

);

// StringLiteral

} else if (token == Token.STRINGLITERAL) {

tn.readString();

type = Node.createNamedType(

Node.createSimpleTypeName("string", tn.range()), [], false, tn.range(startPos, tn.pos)

);

// Identifier

} else if (token == Token.IDENTIFIER) {

let name = this.parseTypeName(tn);

if (!name) return null;

let parameters: TypeNode[] | null = null;

// Name<T>

if (tn.skip(Token.LESSTHAN)) {

do {

let parameter = this.parseType(tn, true, suppressErrors);

if (!parameter) return null;

if (!parameters) parameters = [ parameter ];

else parameters.push(parameter);

} while (tn.skip(Token.COMMA));

if (!tn.skip(Token.GREATERTHAN)) {

if (!suppressErrors) {

this.error(

DiagnosticCode._0_expected,

tn.range(tn.pos), ">"

);

}

return null;

}

}

if (!parameters) parameters = [];

type = Node.createNamedType(name, parameters, false, tn.range(startPos, tn.pos));

} else {

if (!suppressErrors) {

this.error(

DiagnosticCode.Type_expected,

tn.range()

);

}

return null;

}

// ... | null

while (tn.skip(Token.BAR)) {

if (tn.skip(Token.NULL)) {

type.isNullable = true;

} else {

let notNullStart = tn.pos;

let notNull = this.parseType(tn, false, true);

if (!suppressErrors) {

this.error(

DiagnosticCode._0_expected,

notNull ? notNull.range : tn.range(notNullStart), "null"

);

}

return null;

}

}

// ... [][]

while (tn.skip(Token.OPENBRACKET)) {

let bracketStart = tn.tokenPos;

if (!tn.skip(Token.CLOSEBRACKET)) {

if (!suppressErrors) {

this.error(

DiagnosticCode._0_expected,

tn.range(), "]"

);

}

return null;

}

let bracketRange = tn.range(bracketStart, tn.pos);

// ...[] | null

let nullable = false;

if (tn.skip(Token.BAR)) {

if (tn.skip(Token.NULL)) {

nullable = true;

} else {

if (!suppressErrors) {

this.error(

DiagnosticCode._0_expected,

tn.range(), "null"

);

}

return null;

}

}

type = Node.createNamedType(

Node.createSimpleTypeName("Array", bracketRange),

[ type ],

nullable,

tn.range(startPos, tn.pos)

);

if (nullable) break;

}

return type;

}

// Indicates whether tryParseSignature determined that it is handling a Signature

private tryParseSignatureIsSignature: bool = false;

/** Parses a function type, as used in type declarations. */

tryParseFunctionType(

tn: Tokenizer

): FunctionTypeNode | null {

// at '(': ('...'? Identifier '?'? ':' Type (',' '...'? Identifier '?'? ':' Type)* )? ')' '=>' Type

var state = tn.mark();

var startPos = tn.tokenPos;

var parameters: ParameterNode[] | null = null;

var thisType: NamedTypeNode | null = null;

var isSignature: bool = false;

var firstParamNameNoType: IdentifierExpression | null = null;

var firstParamKind: ParameterKind = ParameterKind.DEFAULT;

if (tn.skip(Token.CLOSEPAREN)) {

isSignature = true;

tn.discard(state);

parameters = [];

} else {

isSignature = false; // not yet known

do {

let paramStart = -1;

let kind = ParameterKind.DEFAULT;

if (tn.skip(Token.DOT_DOT_DOT)) {

paramStart = tn.tokenPos;

isSignature = true;

tn.discard(state);

kind = ParameterKind.REST;

}

if (tn.skip(Token.THIS)) {

if (paramStart < 0) paramStart = tn.tokenPos;

if (tn.skip(Token.COLON)) {

isSignature = true;

tn.discard(state);

let type = this.parseType(tn, false);

if (!type) return null;

if (type.kind != NodeKind.NAMEDTYPE) {

this.error(

DiagnosticCode.Identifier_expected,

type.range

);

this.tryParseSignatureIsSignature = true;

return null;

}

thisType = <NamedTypeNode>type;

} else {

tn.reset(state);

this.tryParseSignatureIsSignature = false;

return null;

}

} else if (tn.skipIdentifier()) {

if (paramStart < 0) paramStart = tn.tokenPos;

let name = Node.createIdentifierExpression(tn.readIdentifier(), tn.range(tn.tokenPos, tn.pos));

if (tn.skip(Token.QUESTION)) {

isSignature = true;

tn.discard(state);

if (kind == ParameterKind.REST) {

this.error(

DiagnosticCode.A_rest_parameter_cannot_be_optional,

tn.range()

); // recoverable

} else {

kind = ParameterKind.OPTIONAL;

}

}

if (tn.skip(Token.COLON)) {

isSignature = true;

tn.discard(state);

let type = this.parseType(tn); // not suppressing errors because known

if (!type) {

this.tryParseSignatureIsSignature = isSignature;

return null;

}

let param = Node.createParameter(kind, name, type, null, tn.range(paramStart, tn.pos));

if (!parameters) parameters = [ param ];

else parameters.push(param);

} else {

if (!isSignature) {

if (tn.peek() == Token.COMMA) {

isSignature = true;

tn.discard(state);

}

}

if (isSignature) {

let param = Node.createParameter(kind, name, Node.createOmittedType(tn.range(tn.pos)), null, tn.range(paramStart, tn.pos));

if (!parameters) parameters = [ param ];

else parameters.push(param);

this.error(

DiagnosticCode.Type_expected,

param.type.range

); // recoverable

} else if (!parameters) {

// on '(' Identifier ^',' we don't yet know whether this is a

// parenthesized or a function type, hence we have to delay the

// respective diagnostic until we know for sure.

firstParamNameNoType = name;

firstParamKind = kind;

}

}

} else {

if (isSignature) {

this.error(

DiagnosticCode.Identifier_expected,

tn.range()

);

} else {

tn.reset(state);

}

this.tryParseSignatureIsSignature = isSignature;

return null;

}

} while (tn.skip(Token.COMMA));

if (!tn.skip(Token.CLOSEPAREN)) {

if (isSignature) {

this.error(

DiagnosticCode._0_expected,

tn.range(), ")"

);

} else {

tn.reset(state);

}

this.tryParseSignatureIsSignature = isSignature;

return null;

}

}

var returnType: TypeNode | null;

if (tn.skip(Token.EQUALS_GREATERTHAN)) {

if (!isSignature) {

isSignature = true;

tn.discard(state);

if (firstParamNameNoType) { // now we know

let param = Node.createParameter(

firstParamKind,

firstParamNameNoType,

Node.createOmittedType(firstParamNameNoType.range.atEnd),

null,

firstParamNameNoType.range

);

if (!parameters) parameters = [ param ];

else parameters.push(param);

this.error(

DiagnosticCode.Type_expected,

param.type.range

); // recoverable

}

}

returnType = this.parseType(tn);

if (!returnType) {

this.tryParseSignatureIsSignature = isSignature;

return null;

}

} else {

if (isSignature) {

this.error(

DiagnosticCode._0_expected,

tn.range(), "=>"

);

} else {

tn.reset(state);

}

this.tryParseSignatureIsSignature = isSignature;

return null;

}

this.tryParseSignatureIsSignature = true;

if (!parameters) parameters = [];

return Node.createFunctionType(

parameters,

returnType,

thisType,

false,

tn.range(startPos, tn.pos)

);

}

// statements

parseDecorator(

tn: Tokenizer

): DecoratorNode | null {

// at '@': Identifier ('.' Identifier)* '(' Arguments

var startPos = tn.tokenPos;

if (tn.skipIdentifier()) {

let name = tn.readIdentifier();

let expression: Expression = Node.createIdentifierExpression(name, tn.range(startPos, tn.pos));

while (tn.skip(Token.DOT)) {

if (tn.skipIdentifier(IdentifierHandling.PREFER)) {

name = tn.readIdentifier();

expression = Node.createPropertyAccessExpression(

expression,

Node.createIdentifierExpression(name, tn.range()),

tn.range(startPos, tn.pos)

);

} else {

this.error(

DiagnosticCode.Identifier_expected,

tn.range()

);

return null;

}

}

let args: Expression[] | null;

if (tn.skip(Token.OPENPAREN)) {

args = this.parseArguments(tn);

if (args) {

return Node.createDecorator(expression, args, tn.range(startPos, tn.pos));

}

} else {

return Node.createDecorator(expression, null, tn.range(startPos, tn.pos));

}

} else {

this.error(

DiagnosticCode.Identifier_expected,

tn.range()

);

}

return null;

}

parseVariable(

tn: Tokenizer,

flags: CommonFlags,

decorators: DecoratorNode[] | null,

startPos: i32,

isFor: bool = false

): VariableStatement | null {

// at ('const' | 'let' | 'var'): VariableDeclaration (',' VariableDeclaration)* ';'?

var declarations = new Array<VariableDeclaration>();

do {

let declaration = this.parseVariableDeclaration(tn, flags, decorators, isFor);

if (!declaration) return null;

declaration.overriddenModuleName = this.currentModuleName;

declarations.push(declaration);

} while (tn.skip(Token.COMMA));

var ret = Node.createVariableStatement(decorators, declarations, tn.range(startPos, tn.pos));

tn.skip(Token.SEMICOLON);

return ret;

}

parseVariableDeclaration(

tn: Tokenizer,

parentFlags: CommonFlags,

parentDecorators: DecoratorNode[] | null,

isFor: bool = false

): VariableDeclaration | null {

// before: Identifier (':' Type)? ('=' Expression)?

if (!tn.skipIdentifier()) {

this.error(

DiagnosticCode.Identifier_expected,

tn.range()

);

return null;

}

var identifier = Node.createIdentifierExpression(tn.readIdentifier(), tn.range());

if (isIllegalVariableIdentifier(identifier.text)) {

this.error(

DiagnosticCode.Identifier_expected,

identifier.range

);

}

var flags = parentFlags;

if (tn.skip(Token.EXCLAMATION)) {

flags |= CommonFlags.DEFINITELY_ASSIGNED;

}

var type: TypeNode | null = null;

if (tn.skip(Token.COLON)) {

type = this.parseType(tn, true);

}

var initializer: Expression | null = null;

if (tn.skip(Token.EQUALS)) {

if (flags & CommonFlags.AMBIENT) {

this.error(

DiagnosticCode.Initializers_are_not_allowed_in_ambient_contexts,

tn.range()

); // recoverable

}

initializer = this.parseExpression(tn, Precedence.COMMA + 1);

if (!initializer) return null;

} else if (!isFor) {

if (flags & CommonFlags.CONST) {

if (!(flags & CommonFlags.AMBIENT)) {

this.error(

DiagnosticCode._const_declarations_must_be_initialized,

identifier.range

); // recoverable

}

} else if (!type) { // neither type nor initializer

this.error(

DiagnosticCode.Type_expected,

tn.range(tn.pos)

); // recoverable