Merge branch 'master' into cacheParseConfigFile

Author: sheetalkamat

.github/pull_request_template.md

@@ -1,8 +1,8 @@
 <!--
 Thank you for submitting a pull request!
 
-Here's a checklist you might find useful.
-* [ ] There is an associated issue that is labeled 'Bug' or 'help wanted'
+Please verify that:
+* [ ] There is an associated issue in the `Backlog` milestone (**required**)
 * [ ] Code is up-to-date with the `master` branch
 * [ ] You've successfully run `gulp runtests` locally
 * [ ] There are new or updated unit tests validating the change
@@ -12,4 +12,3 @@ Refer to CONTRIBUTING.MD for more details.
 -->
 
 Fixes #
-

src/compiler/binder.ts

@@ -1625,15 +1625,8 @@ namespace ts {
         }
 
         function hasExportDeclarations(node: ModuleDeclaration | SourceFile): boolean {
-            const body = node.kind === SyntaxKind.SourceFile ? node : node.body;
-            if (body && (body.kind === SyntaxKind.SourceFile || body.kind === SyntaxKind.ModuleBlock)) {
-                for (const stat of (<BlockLike>body).statements) {
-                    if (stat.kind === SyntaxKind.ExportDeclaration || stat.kind === SyntaxKind.ExportAssignment) {
-                        return true;
-                    }
-                }
-            }
-            return false;
+            const body = isSourceFile(node) ? node : tryCast(node.body, isModuleBlock);
+            return !!body && body.statements.some(s => isExportDeclaration(s) || isExportAssignment(s));
         }
 
         function setExportContextFlag(node: ModuleDeclaration | SourceFile) {

src/compiler/checker.ts

@@ -94,8 +94,6 @@ namespace ts {
 
         const globalThisSymbol = createSymbol(SymbolFlags.Module, "globalThis" as __String, CheckFlags.Readonly);
         globalThisSymbol.exports = globals;
-        globalThisSymbol.valueDeclaration = createNode(SyntaxKind.Identifier) as Identifier;
-        (globalThisSymbol.valueDeclaration as Identifier).escapedText = "globalThis" as __String;
         globals.set(globalThisSymbol.escapedName, globalThisSymbol);
 
         const argumentsSymbol = createSymbol(SymbolFlags.Property, "arguments" as __String);
@@ -926,7 +924,12 @@ namespace ts {
                 recordMergedSymbol(target, source);
             }
             else if (target.flags & SymbolFlags.NamespaceModule) {
-                error(getNameOfDeclaration(source.declarations[0]), Diagnostics.Cannot_augment_module_0_with_value_exports_because_it_resolves_to_a_non_module_entity, symbolToString(target));
+                // Do not report an error when merging `var globalThis` with the built-in `globalThis`,
+                // as we will already report a "Declaration name conflicts..." error, and this error
+                // won't make much sense.
+                if (target !== globalThisSymbol) {
+                    error(getNameOfDeclaration(source.declarations[0]), Diagnostics.Cannot_augment_module_0_with_value_exports_because_it_resolves_to_a_non_module_entity, symbolToString(target));
+                }
             }
             else { // error
                 const isEitherEnum = !!(target.flags & SymbolFlags.Enum || source.flags & SymbolFlags.Enum);
@@ -1409,15 +1412,14 @@ namespace ts {
                         }
                         break;
                     case SyntaxKind.PropertyDeclaration:
-                    case SyntaxKind.PropertySignature:
                         // TypeScript 1.0 spec (April 2014): 8.4.1
                         // Initializer expressions for instance member variables are evaluated in the scope
                         // of the class constructor body but are not permitted to reference parameters or
                         // local variables of the constructor. This effectively means that entities from outer scopes
                         // by the same name as a constructor parameter or local variable are inaccessible
                         // in initializer expressions for instance member variables.
-                        if (isClassLike(location.parent) && !hasModifier(location, ModifierFlags.Static)) {
-                            const ctor = findConstructorDeclaration(location.parent);
+                        if (!hasModifier(location, ModifierFlags.Static)) {
+                            const ctor = findConstructorDeclaration(location.parent as ClassLikeDeclaration);
                             if (ctor && ctor.locals) {
                                 if (lookup(ctor.locals, name, meaning & SymbolFlags.Value)) {
                                     // Remember the property node, it will be used later to report appropriate error
@@ -9943,13 +9945,13 @@ namespace ts {
             return type.flags & TypeFlags.Union ? getIntersectionType(map((<IntersectionType>type).types, t => getIndexType(t, stringsOnly, noIndexSignatures))) :
                 type.flags & TypeFlags.Intersection ? getUnionType(map((<IntersectionType>type).types, t => getIndexType(t, stringsOnly, noIndexSignatures))) :
                 maybeTypeOfKind(type, TypeFlags.InstantiableNonPrimitive) ? getIndexTypeForGenericType(<InstantiableType | UnionOrIntersectionType>type, stringsOnly) :
-                getObjectFlags(type) & ObjectFlags.Mapped ? filterType(getConstraintTypeFromMappedType(<MappedType>type), t => !(noIndexSignatures && t.flags & (TypeFlags.Any | TypeFlags.String | TypeFlags.Number))) :
+                getObjectFlags(type) & ObjectFlags.Mapped ? filterType(getConstraintTypeFromMappedType(<MappedType>type), t => !(noIndexSignatures && t.flags & (TypeFlags.Any | TypeFlags.String))) :
                 type === wildcardType ? wildcardType :
                 type.flags & TypeFlags.Unknown ? neverType :
                 type.flags & (TypeFlags.Any | TypeFlags.Never) ? keyofConstraintType :
                 stringsOnly ? !noIndexSignatures && getIndexInfoOfType(type, IndexKind.String) ? stringType : getLiteralTypeFromProperties(type, TypeFlags.StringLiteral) :
                 !noIndexSignatures && getIndexInfoOfType(type, IndexKind.String) ? getUnionType([stringType, numberType, getLiteralTypeFromProperties(type, TypeFlags.UniqueESSymbol)]) :
-                !noIndexSignatures && getNonEnumNumberIndexInfo(type) ? getUnionType([numberType, getLiteralTypeFromProperties(type, TypeFlags.StringLiteral | TypeFlags.UniqueESSymbol)]) :
+                getNonEnumNumberIndexInfo(type) ? getUnionType([numberType, getLiteralTypeFromProperties(type, TypeFlags.StringLiteral | TypeFlags.UniqueESSymbol)]) :
                 getLiteralTypeFromProperties(type, TypeFlags.StringOrNumberLiteralOrUnique);
         }
 
@@ -10067,10 +10069,10 @@ namespace ts {
                 if (objectType.flags & (TypeFlags.Any | TypeFlags.Never)) {
                     return objectType;
                 }
-                const indexInfo = isTypeAssignableToKind(indexType, TypeFlags.NumberLike) && getIndexInfoOfType(objectType, IndexKind.Number) ||
-                    getIndexInfoOfType(objectType, IndexKind.String);
+                const stringIndexInfo = getIndexInfoOfType(objectType, IndexKind.String);
+                const indexInfo = isTypeAssignableToKind(indexType, TypeFlags.NumberLike) && getIndexInfoOfType(objectType, IndexKind.Number) || stringIndexInfo;
                 if (indexInfo) {
-                    if (accessFlags & AccessFlags.NoIndexSignatures) {
+                    if (accessFlags & AccessFlags.NoIndexSignatures && indexInfo === stringIndexInfo) {
                         if (accessExpression) {
                             error(accessExpression, Diagnostics.Type_0_cannot_be_used_to_index_type_1, typeToString(indexType), typeToString(originalObjectType));
                         }
@@ -14228,6 +14230,32 @@ namespace ts {
             return strictNullChecks ? getGlobalNonNullableTypeInstantiation(type) : type;
         }
 
+
+        /**
+         * Is source potentially coercible to target type under `==`.
+         * Assumes that `source` is a constituent of a union, hence
+         * the boolean literal flag on the LHS, but not on the RHS.
+         *
+         * This does not fully replicate the semantics of `==`. The
+         * intention is to catch cases that are clearly not right.
+         *
+         * Comparing (string | number) to number should not remove the
+         * string element.
+         *
+         * Comparing (string | number) to 1 will remove the string
+         * element, though this is not sound. This is a pragmatic
+         * choice.
+         *
+         * @see narrowTypeByEquality
+         *
+         * @param source
+         * @param target
+         */
+        function isCoercibleUnderDoubleEquals(source: Type, target: Type): boolean {
+            return ((source.flags & (TypeFlags.Number | TypeFlags.String | TypeFlags.BooleanLiteral)) !== 0)
+                && ((target.flags & (TypeFlags.Number | TypeFlags.String | TypeFlags.Boolean)) !== 0);
+        }
+
         /**
          * Return true if type was inferred from an object literal, written as an object type literal, or is the shape of a module
          * with no call or construct signatures.
@@ -16571,7 +16599,10 @@ namespace ts {
                     return type;
                 }
                 if (assumeTrue) {
-                    const narrowedType = filterType(type, t => areTypesComparable(t, valueType));
+                    const filterFn: (t: Type) => boolean = operator === SyntaxKind.EqualsEqualsToken ?
+                        (t => areTypesComparable(t, valueType) || isCoercibleUnderDoubleEquals(t, valueType)) :
+                        t => areTypesComparable(t, valueType);
+                    const narrowedType = filterType(type, filterFn);
                     return narrowedType.flags & TypeFlags.Never ? type : replacePrimitivesWithLiterals(narrowedType, valueType);
                 }
                 if (isUnitType(valueType)) {
@@ -21973,6 +22004,13 @@ namespace ts {
                     const arg = (<PrefixUnaryExpression>node).operand;
                     return op === SyntaxKind.MinusToken && (arg.kind === SyntaxKind.NumericLiteral || arg.kind === SyntaxKind.BigIntLiteral) ||
                         op === SyntaxKind.PlusToken && arg.kind === SyntaxKind.NumericLiteral;
+                case SyntaxKind.PropertyAccessExpression:
+                case SyntaxKind.ElementAccessExpression:
+                    const expr = (<PropertyAccessExpression | ElementAccessExpression>node).expression;
+                    if (isIdentifier(expr)) {
+                        const symbol = getSymbolAtLocation(expr);
+                        return !!(symbol && (symbol.flags & SymbolFlags.Enum) && getEnumKind(symbol) === EnumKind.Literal);
+                    }
             }
             return false;
         }
@@ -21981,7 +22019,7 @@ namespace ts {
             let exprType = checkExpression(expression, checkMode);
             if (isConstTypeReference(type)) {
                 if (!isValidConstAssertionArgument(expression)) {
-                    error(expression, Diagnostics.A_const_assertion_can_only_be_applied_to_a_string_number_boolean_array_or_object_literal);
+                    error(expression, Diagnostics.A_const_assertions_can_only_be_applied_to_references_to_enum_members_or_string_number_boolean_array_or_object_literals);
                 }
                 return getRegularTypeOfLiteralType(exprType);
             }
@@ -25629,7 +25667,7 @@ namespace ts {
             }
 
             if (!compilerOptions.experimentalDecorators) {
-                error(node, Diagnostics.Experimental_support_for_decorators_is_a_feature_that_is_subject_to_change_in_a_future_release_Set_the_experimentalDecorators_option_to_remove_this_warning);
+                error(node, Diagnostics.Experimental_support_for_decorators_is_a_feature_that_is_subject_to_change_in_a_future_release_Set_the_experimentalDecorators_option_in_your_tsconfig_or_jsconfig_to_remove_this_warning);
             }
 
             const firstDecorator = node.decorators[0];
@@ -26427,14 +26465,28 @@ namespace ts {
             }
             // For a binding pattern, validate the initializer and exit
             if (isBindingPattern(node.name)) {
-                // Don't validate for-in initializer as it is already an error
-                if (node.initializer && node.parent.parent.kind !== SyntaxKind.ForInStatement) {
-                    const initializerType = checkExpressionCached(node.initializer);
-                    if (strictNullChecks && node.name.elements.length === 0) {
-                        checkNonNullNonVoidType(initializerType, node);
+                const needCheckInitializer = node.initializer && node.parent.parent.kind !== SyntaxKind.ForInStatement;
+                const needCheckWidenedType = node.name.elements.length === 0;
+                if (needCheckInitializer || needCheckWidenedType) {
+                    // Don't validate for-in initializer as it is already an error
+                    const widenedType = getWidenedTypeForVariableLikeDeclaration(node);
+                    if (needCheckInitializer) {
+                        const initializerType = checkExpressionCached(node.initializer!);
+                        if (strictNullChecks && needCheckWidenedType) {
+                            checkNonNullNonVoidType(initializerType, node);
+                        }
+                        else {
+                            checkTypeAssignableToAndOptionallyElaborate(initializerType, getWidenedTypeForVariableLikeDeclaration(node), node, node.initializer);
+                        }
                     }
-                    else {
-                        checkTypeAssignableToAndOptionallyElaborate(initializerType, getWidenedTypeForVariableLikeDeclaration(node), node, node.initializer);
+                    // check the binding pattern with empty elements
+                    if (needCheckWidenedType) {
+                        if (isArrayBindingPattern(node.name)) {
+                            checkIteratedTypeOrElementType(widenedType, node, /* allowStringInput */ false, /* allowAsyncIterables */ false);
+                        }
+                        else if (strictNullChecks) {
+                            checkNonNullNonVoidType(widenedType, node);
+                        }
                     }
                 }
                 return;
@@ -30407,6 +30459,14 @@ namespace ts {
                     continue;
                 }
                 if (!isExternalOrCommonJsModule(file)) {
+                    // It is an error for a non-external-module (i.e. script) to declare its own `globalThis`.
+                    // We can't use `builtinGlobals` for this due to synthetic expando-namespace generation in JS files.
+                    const fileGlobalThisSymbol = file.locals!.get("globalThis" as __String);
+                    if (fileGlobalThisSymbol) {
+                        for (const declaration of fileGlobalThisSymbol.declarations) {
+                            diagnostics.add(createDiagnosticForNode(declaration, Diagnostics.Declaration_name_conflicts_with_built_in_global_identifier_0, "globalThis"));
+                        }
+                    }
                     mergeSymbolTable(globals, file.locals!);
                 }
                 if (file.jsGlobalAugmentations) {
@@ -30452,6 +30512,7 @@ namespace ts {
             getSymbolLinks(undefinedSymbol).type = undefinedWideningType;
             getSymbolLinks(argumentsSymbol).type = getGlobalType("IArguments" as __String, /*arity*/ 0, /*reportErrors*/ true);
             getSymbolLinks(unknownSymbol).type = errorType;
+            getSymbolLinks(globalThisSymbol).type = createObjectType(ObjectFlags.Anonymous, globalThisSymbol);
 
             // Initialize special types
             globalArrayType = getGlobalType("Array" as __String, /*arity*/ 1, /*reportErrors*/ true);
@@ -31179,6 +31240,13 @@ namespace ts {
 
             for (const prop of node.properties) {
                 if (prop.kind === SyntaxKind.SpreadAssignment) {
+                    if (inDestructuring) {
+                        // a rest property cannot be destructured any further
+                        const expression = skipParentheses(prop.expression);
+                        if (isArrayLiteralExpression(expression) || isObjectLiteralExpression(expression)) {
+                            return grammarErrorOnNode(prop.expression, Diagnostics.A_rest_element_cannot_contain_a_binding_pattern);
+                        }
+                    }
                     continue;
                 }
                 const name = prop.name;
@@ -31841,7 +31909,7 @@ namespace ts {
                     return false;
             }
 
-            return grammarErrorOnFirstToken(node, Diagnostics.A_declare_modifier_is_required_for_a_top_level_declaration_in_a_d_ts_file);
+            return grammarErrorOnFirstToken(node, Diagnostics.Top_level_declarations_in_d_ts_files_must_start_with_either_a_declare_or_export_modifier);
         }
 
         function checkGrammarTopLevelElementsForRequiredDeclareModifier(file: SourceFile): boolean {

src/compiler/commandLineParser.ts

@@ -16,6 +16,7 @@ namespace ts {
         ["es2017", "lib.es2017.d.ts"],
         ["es2018", "lib.es2018.d.ts"],
         ["es2019", "lib.es2019.d.ts"],
+        ["es2020", "lib.es2020.d.ts"],
         ["esnext", "lib.esnext.d.ts"],
         // Host only
         ["dom", "lib.dom.d.ts"],
@@ -46,6 +47,8 @@ namespace ts {
         ["es2019.array", "lib.es2019.array.d.ts"],
         ["es2019.string", "lib.es2019.string.d.ts"],
         ["es2019.symbol", "lib.es2019.symbol.d.ts"],
+        ["es2020.string", "lib.es2020.string.d.ts"],
+        ["es2020.symbol.wellknown", "lib.es2020.symbol.wellknown.d.ts"],
         ["esnext.array", "lib.es2019.array.d.ts"],
         ["esnext.symbol", "lib.es2019.symbol.d.ts"],
         ["esnext.asynciterable", "lib.es2018.asynciterable.d.ts"],
@@ -210,6 +213,7 @@ namespace ts {
                 es2017: ScriptTarget.ES2017,
                 es2018: ScriptTarget.ES2018,
                 es2019: ScriptTarget.ES2019,
+                es2020: ScriptTarget.ES2020,
                 esnext: ScriptTarget.ESNext,
             }),
             affectsSourceFile: true,

src/compiler/core.ts

@@ -1639,39 +1639,6 @@ namespace ts {
         };
     }
 
-    /**
-     * High-order function, creates a function that executes a function composition.
-     * For example, `chain(a, b)` is the equivalent of `x => ((a', b') => y => b'(a'(y)))(a(x), b(x))`
-     *
-     * @param args The functions to chain.
-     */
-    export function chain<T, U>(...args: ((t: T) => (u: U) => U)[]): (t: T) => (u: U) => U;
-    export function chain<T, U>(a: (t: T) => (u: U) => U, b: (t: T) => (u: U) => U, c: (t: T) => (u: U) => U, d: (t: T) => (u: U) => U, e: (t: T) => (u: U) => U): (t: T) => (u: U) => U {
-        if (e) {
-            const args: ((t: T) => (u: U) => U)[] = [];
-            for (let i = 0; i < arguments.length; i++) {
-                args[i] = arguments[i];
-            }
-
-            return t => compose(...map(args, f => f(t)));
-        }
-        else if (d) {
-            return t => compose(a(t), b(t), c(t), d(t));
-        }
-        else if (c) {
-            return t => compose(a(t), b(t), c(t));
-        }
-        else if (b) {
-            return t => compose(a(t), b(t));
-        }
-        else if (a) {
-            return t => compose(a(t));
-        }
-        else {
-            return _ => u => u;
-        }
-    }
-
     /**
      * High-order function, composes functions. Note that functions are composed inside-out;
      * for example, `compose(a, b)` is the equivalent of `x => b(a(x))`.