Merge branch 'master' into any-constraint-as-upper-bound

.mailmap

@@ -121,6 +121,7 @@ Ken Howard <[email protected]>
 Kevin Lang  <[email protected]>
 kimamula <[email protected]> # Kenji Imamula
 Kitson Kelly  <[email protected]>
+Krishnadas Babu <[email protected]>
 Klaus Meinhardt  <[email protected]>
 Kyle Kelley <[email protected]>
 Lorant Pinter <[email protected]>

CONTRIBUTING.md

@@ -47,6 +47,16 @@ In general, things we find useful when reviewing suggestions are:
 
 # Instructions for Contributing Code
 
+## Tips
+
+### Faster clones
+
+The TypeScript repository is relatively large. To save some time, you might want to clone it without the repo's full history using `git clone --depth=1`.
+
+### Using local builds
+
+Run `gulp build` to build a version of the compiler/language service that reflects changes you've made. You can then run `node <repo-root>/built/local/tsc.js` in place of `tsc` in your project. For example, to run `tsc --watch` from within the root of the repository on a file called `test.ts`, you can run `node ./built/local/tsc.js --watch test.ts`.
+
 ## Contributing bug fixes
 
 TypeScript is currently accepting contributions in the form of bug fixes. A bug must have an issue tracking it in the issue tracker that has been approved ("Milestone == Community") by the TypeScript team. Your pull request should include a link to the bug that you are fixing. If you've submitted a PR for a bug, please post a comment in the bug to avoid duplication of effort.

Gulpfile.js

@@ -274,7 +274,7 @@ gulp.task(
 // Generate Markdown spec
 const specMd = "doc/spec.md";
 gulp.task(specMd, /*help*/ false, [word2mdJs], () =>
-    exec("cscript", ["//nologo", word2mdJs, path.resolve(specMd), path.resolve("doc/TypeScript Language Specification.docx")]));
+    exec("cscript", ["//nologo", word2mdJs, path.resolve("doc/TypeScript Language Specification.docx"), path.resolve(specMd)]));
 
 gulp.task(
     "generate-spec",
@@ -595,7 +595,7 @@ gulp.task(
                         project.waitForWorkToStart().then(() => {
                             source.cancel();
                         });
-                    
+
                         if (cmdLineOptions.tests || cmdLineOptions.failed) {
                             await runConsoleTests(runJs, "mocha-fivemat-progress-reporter", /*runInParallel*/ false, /*watchMode*/ true, source.token);
                         }

doc/spec.md

@@ -239,7 +239,7 @@ TypeScript is a trademark of Microsoft Corporation.
 
 # <a name="1"/>1 Introduction
 
-JavaScript applications such as web e-mail, maps, document editing, and collaboration tools are becoming an increasingly important part of the everyday computing. We designed TypeScript to meet the needs of the JavaScript programming teams that build and maintain large JavaScript programs. TypeScript helps programming teams to define interfaces between software components and to gain insight into the behavior of existing JavaScript libraries. TypeScript also enables teams to reduce naming conflicts by organizing their code into dynamically-loadable modules. TypeScript's optional type system enables JavaScript programmers to use highly-productive development tools and practices: static checking, symbol-based navigation, statement completion, and code re-factoring.
+JavaScript applications such as web e-mail, maps, document editing, and collaboration tools are becoming an increasingly important part of the everyday computing. We designed TypeScript to meet the needs of the JavaScript programming teams that build and maintain large JavaScript programs. TypeScript helps programming teams to define interfaces between software components and to gain insight into the behavior of existing JavaScript libraries. TypeScript also enables teams to reduce naming conflicts by organizing their code into dynamically-loadable modules. TypeScript's optional type system enables JavaScript programmers to use highly-productive development tools and practices: static checking, symbol-based navigation, statement completion, and code refactoring.
 
 TypeScript is a syntactic sugar for JavaScript. TypeScript syntax is a superset of ECMAScript 2015 (ES2015) syntax. Every JavaScript program is also a TypeScript program. The TypeScript compiler performs only file-local transformations on TypeScript programs and does not re-order variables declared in TypeScript. This leads to JavaScript output that closely matches the TypeScript input. TypeScript does not transform variable names, making tractable the direct debugging of emitted JavaScript. TypeScript optionally provides source maps, enabling source-level debugging. TypeScript tools typically emit JavaScript upon file save, preserving the test, edit, refresh cycle commonly used in JavaScript development.
 
@@ -263,7 +263,7 @@ function f() {
 }
 ```
 
-To benefit from this inference, a programmer can use the TypeScript language service. For example, a code editor can incorporate the TypeScript language service and use the service to find the members of a string object as in the following screen shot.
+To benefit from this inference, a programmer can use the TypeScript language service. For example, a code editor can incorporate the TypeScript language service and use the service to find the members of a string object as in the following screenshot.
 
 &emsp;&emsp;![](images/image1.png)
 
@@ -411,7 +411,7 @@ We mentioned above that the '$' function behaves differently depending on the ty
 
 This signature denotes that a function may be passed as the parameter of the '$' function. When a function is passed to '$', the jQuery library will invoke that function when a DOM document is ready. Because TypeScript supports overloading, tools can use TypeScript to show all available function signatures with their documentation tips and to give the correct documentation once a function has been called with a particular signature.
 
-A typical client would not need to add any additional typing but could just use a community-supplied typing to discover (through statement completion with documentation tips) and verify (through static checking) correct use of the library, as in the following screen shot.
+A typical client would not need to add any additional typing but could just use a community-supplied typing to discover (through statement completion with documentation tips) and verify (through static checking) correct use of the library, as in the following screenshot.
 
 &emsp;&emsp;![](images/image2.png)
 
@@ -628,7 +628,7 @@ JavaScript implementations can use these explicit constants to generate efficien
 
 An important goal of TypeScript is to provide accurate and straightforward types for existing JavaScript programming patterns. To that end, TypeScript includes generic types, discussed in the next section, and *overloading on string parameters*, the topic of this section.
 
-JavaScript programming interfaces often include functions whose behavior is discriminated by a string constant passed to the function. The Document Object Model makes heavy use of this pattern. For example, the following screen shot shows that the 'createElement' method of the 'document' object has multiple signatures, some of which identify the types returned when specific strings are passed into the method.
+JavaScript programming interfaces often include functions whose behavior is discriminated by a string constant passed to the function. The Document Object Model makes heavy use of this pattern. For example, the following screenshot shows that the 'createElement' method of the 'document' object has multiple signatures, some of which identify the types returned when specific strings are passed into the method.
 
 &emsp;&emsp;![](images/image3.png)
 
@@ -639,7 +639,7 @@ var span = document.createElement("span");
 span.isMultiLine = false;  // OK: HTMLSpanElement has isMultiline property
 ```
 
-In the following screen shot, a programming tool combines information from overloading on string parameters with contextual typing to infer that the type of the variable 'e' is 'MouseEvent' and that therefore 'e' has a 'clientX' property.
+In the following screenshot, a programming tool combines information from overloading on string parameters with contextual typing to infer that the type of the variable 'e' is 'MouseEvent' and that therefore 'e' has a 'clientX' property.
 
 &emsp;&emsp;![](images/image4.png)
 

src/compiler/checker.ts

@@ -4855,7 +4855,7 @@ namespace ts {
 
         function getLiteralPropertyNameText(name: PropertyName) {
             const type = getLiteralTypeFromPropertyName(name);
-            return type.flags & (TypeFlags.StringLiteral | TypeFlags.NumberLiteral) ? "" + (<LiteralType>type).value : undefined;
+            return type.flags & (TypeFlags.StringLiteral | TypeFlags.NumberLiteral) ? "" + (<StringLiteralType | NumberLiteralType>type).value : undefined;
         }
 
         /** Return the inferred type for a binding element */
@@ -6450,12 +6450,12 @@ namespace ts {
         /**
          * Gets the symbolic name for a late-bound member from its type.
          */
-        function getLateBoundNameFromType(type: LiteralType | UniqueESSymbolType): __String {
+        function getLateBoundNameFromType(type: StringLiteralType | NumberLiteralType | UniqueESSymbolType): __String {
             if (type.flags & TypeFlags.UniqueESSymbol) {
                 return `__@${type.symbol.escapedName}@${getSymbolId(type.symbol)}` as __String;
             }
             if (type.flags & (TypeFlags.StringLiteral | TypeFlags.NumberLiteral)) {
-                return escapeLeadingUnderscores("" + (<LiteralType>type).value);
+                return escapeLeadingUnderscores("" + (<StringLiteralType | NumberLiteralType>type).value);
             }
             return Debug.fail();
         }
@@ -6534,9 +6534,9 @@ namespace ts {
                         // If we have an existing early-bound member, combine its declarations so that we can
                         // report an error at each declaration.
                         const declarations = earlySymbol ? concatenate(earlySymbol.declarations, lateSymbol.declarations) : lateSymbol.declarations;
-                        const name = declarationNameToString(decl.name);
-                        forEach(declarations, declaration => error(getNameOfDeclaration(declaration) || declaration, Diagnostics.Duplicate_declaration_0, name));
-                        error(decl.name || decl, Diagnostics.Duplicate_declaration_0, name);
+                        const name = !(type.flags & TypeFlags.UniqueESSymbol) && unescapeLeadingUnderscores(memberName) || declarationNameToString(decl.name);
+                        forEach(declarations, declaration => error(getNameOfDeclaration(declaration) || declaration, Diagnostics.Property_0_was_also_declared_here, name));
+                        error(decl.name || decl, Diagnostics.Duplicate_property_0, name);
                         lateSymbol = createSymbol(SymbolFlags.None, memberName, CheckFlags.Late);
                     }
                     lateSymbol.nameType = type;
@@ -9824,7 +9824,7 @@ namespace ts {
             if (accessNode) {
                 const indexNode = getIndexNodeForAccessExpression(accessNode);
                 if (indexType.flags & (TypeFlags.StringLiteral | TypeFlags.NumberLiteral)) {
-                    error(indexNode, Diagnostics.Property_0_does_not_exist_on_type_1, "" + (<LiteralType>indexType).value, typeToString(objectType));
+                    error(indexNode, Diagnostics.Property_0_does_not_exist_on_type_1, "" + (<StringLiteralType | NumberLiteralType>indexType).value, typeToString(objectType));
                 }
                 else if (indexType.flags & (TypeFlags.String | TypeFlags.Number)) {
                     error(indexNode, Diagnostics.Type_0_has_no_matching_index_signature_for_type_1, typeToString(objectType), typeToString(indexType));
@@ -11769,11 +11769,11 @@ namespace ts {
             if (s & TypeFlags.StringLike && t & TypeFlags.String) return true;
             if (s & TypeFlags.StringLiteral && s & TypeFlags.EnumLiteral &&
                 t & TypeFlags.StringLiteral && !(t & TypeFlags.EnumLiteral) &&
-                (<LiteralType>source).value === (<LiteralType>target).value) return true;
+                (<StringLiteralType>source).value === (<StringLiteralType>target).value) return true;
             if (s & TypeFlags.NumberLike && t & TypeFlags.Number) return true;
             if (s & TypeFlags.NumberLiteral && s & TypeFlags.EnumLiteral &&
                 t & TypeFlags.NumberLiteral && !(t & TypeFlags.EnumLiteral) &&
-                (<LiteralType>source).value === (<LiteralType>target).value) return true;
+                (<NumberLiteralType>source).value === (<NumberLiteralType>target).value) return true;
             if (s & TypeFlags.BigIntLike && t & TypeFlags.BigInt) return true;
             if (s & TypeFlags.BooleanLike && t & TypeFlags.Boolean) return true;
             if (s & TypeFlags.ESSymbolLike && t & TypeFlags.ESSymbol) return true;
@@ -13697,8 +13697,8 @@ namespace ts {
         // no flags for all other types (including non-falsy literal types).
         function getFalsyFlags(type: Type): TypeFlags {
             return type.flags & TypeFlags.Union ? getFalsyFlagsOfTypes((<UnionType>type).types) :
-                type.flags & TypeFlags.StringLiteral ? (<LiteralType>type).value === "" ? TypeFlags.StringLiteral : 0 :
-                type.flags & TypeFlags.NumberLiteral ? (<LiteralType>type).value === 0 ? TypeFlags.NumberLiteral : 0 :
+                type.flags & TypeFlags.StringLiteral ? (<StringLiteralType>type).value === "" ? TypeFlags.StringLiteral : 0 :
+                type.flags & TypeFlags.NumberLiteral ? (<NumberLiteralType>type).value === 0 ? TypeFlags.NumberLiteral : 0 :
                 type.flags & TypeFlags.BigIntLiteral ? isZeroBigInt(<BigIntLiteralType>type) ? TypeFlags.BigIntLiteral : 0 :
                 type.flags & TypeFlags.BooleanLiteral ? (type === falseType || type === regularFalseType) ? TypeFlags.BooleanLiteral : 0 :
                 type.flags & TypeFlags.PossiblyFalsy;
@@ -13721,8 +13721,8 @@ namespace ts {
                 type === regularFalseType ||
                 type === falseType ||
                 type.flags & (TypeFlags.Void | TypeFlags.Undefined | TypeFlags.Null) ||
-                type.flags & TypeFlags.StringLiteral && (<LiteralType>type).value === "" ||
-                type.flags & TypeFlags.NumberLiteral && (<LiteralType>type).value === 0 ||
+                type.flags & TypeFlags.StringLiteral && (<StringLiteralType>type).value === "" ||
+                type.flags & TypeFlags.NumberLiteral && (<NumberLiteralType>type).value === 0 ||
                 type.flags & TypeFlags.BigIntLiteral && isZeroBigInt(<BigIntLiteralType>type) ? type :
                 neverType;
         }
@@ -15110,7 +15110,7 @@ namespace ts {
                 return strictNullChecks ? TypeFacts.StringStrictFacts : TypeFacts.StringFacts;
             }
             if (flags & TypeFlags.StringLiteral) {
-                const isEmpty = (<LiteralType>type).value === "";
+                const isEmpty = (<StringLiteralType>type).value === "";
                 return strictNullChecks ?
                     isEmpty ? TypeFacts.EmptyStringStrictFacts : TypeFacts.NonEmptyStringStrictFacts :
                     isEmpty ? TypeFacts.EmptyStringFacts : TypeFacts.NonEmptyStringFacts;
@@ -15119,7 +15119,7 @@ namespace ts {
                 return strictNullChecks ? TypeFacts.NumberStrictFacts : TypeFacts.NumberFacts;
             }
             if (flags & TypeFlags.NumberLiteral) {
-                const isZero = (<LiteralType>type).value === 0;
+                const isZero = (<NumberLiteralType>type).value === 0;
                 return strictNullChecks ?
                     isZero ? TypeFacts.ZeroNumberStrictFacts : TypeFacts.NonZeroNumberStrictFacts :
                     isZero ? TypeFacts.ZeroNumberFacts : TypeFacts.NonZeroNumberFacts;

src/compiler/diagnosticMessages.json

@@ -2433,7 +2433,7 @@
         "category": "Error",
         "code": 2717
     },
-    "Duplicate declaration '{0}'.": {
+    "Duplicate property '{0}'.": {
         "category": "Error",
         "code": 2718
     },
@@ -2493,6 +2493,10 @@
         "category": "Error",
         "code": 2732
     },
+    "Property '{0}' was also declared here.": {
+        "category": "Error",
+        "code": 2733
+    },
     "It is highly likely that you are missing a semicolon.": {
         "category": "Error",
         "code": 2734

src/lib/README.md

@@ -4,5 +4,5 @@ The files within this directory are used to generate `lib.d.ts` and `lib.es6.d.t
 
 ## Generated files
 
-Any files ending in `.generated.d.ts` aren't mean to be edited by hand.
+Any files ending in `.generated.d.ts` aren't meant to be edited by hand.
 If you need to make changes to such files, make a change to the input files for [**our library generator**](https://github.com/Microsoft/TSJS-lib-generator).