initial revision of reachability checks

src/compiler/checker.ts

@@ -158,6 +158,8 @@ namespace ts {
         let getGlobalPromiseConstructorLikeType: () => ObjectType;
         let getGlobalThenableType: () => ObjectType;
 
+        let jsxElementClassType: Type;
+
         let tupleTypes: Map<TupleType> = {};
         let unionTypes: Map<UnionType> = {};
         let intersectionTypes: Map<IntersectionType> = {};
@@ -7560,7 +7562,6 @@ namespace ts {
             return prop || unknownSymbol;
         }
 
-        let jsxElementClassType: Type = undefined;
         function getJsxGlobalElementClassType(): Type {
             if (!jsxElementClassType) {
                 jsxElementClassType = getExportedTypeFromNamespace(JsxNames.JSX, JsxNames.ElementClass);
@@ -9277,21 +9278,11 @@ namespace ts {
             return aggregatedTypes;
         }
 
-        function bodyContainsAReturnStatement(funcBody: Block) {
-            return forEachReturnStatement(funcBody, returnStatement => {
-                return true;
-            });
-        }
-
-        function bodyContainsSingleThrowStatement(body: Block) {
-            return (body.statements.length === 1) && (body.statements[0].kind === SyntaxKind.ThrowStatement);
-        }
-
         // TypeScript Specification 1.0 (6.3) - July 2014
         // An explicitly typed function whose return type isn't the Void or the Any type
         // must have at least one return statement somewhere in its body.
         // An exception to this rule is if the function implementation consists of a single 'throw' statement.
-        function checkIfNonVoidFunctionHasReturnExpressionsOrSingleThrowStatment(func: FunctionLikeDeclaration, returnType: Type): void {
+        function checkAllCodePathsInNonVoidFunctionReturnOrThrow(func: FunctionLikeDeclaration, returnType: Type): void {
             if (!produceDiagnostics) {
                 return;
             }
@@ -9302,26 +9293,20 @@ namespace ts {
             }
 
             // If all we have is a function signature, or an arrow function with an expression body, then there is nothing to check.
-            if (nodeIsMissing(func.body) || func.body.kind !== SyntaxKind.Block) {
+            // also if HasImplicitReturnValue flags is not set this means that all codepaths in function body end with return of throw
+            if (nodeIsMissing(func.body) || func.body.kind !== SyntaxKind.Block || !(func.flags & NodeFlags.HasImplicitReturn)) {
                 return;
             }
-
-            let bodyBlock = <Block>func.body;
-
-            // Ensure the body has at least one return expression.
-            if (bodyContainsAReturnStatement(bodyBlock)) {
-                return;
+
+            if (func.flags & NodeFlags.HasExplicitReturn) {
+                if (compilerOptions.noImplicitReturns) {
+                    error(func.type, Diagnostics.Not_all_code_paths_return_a_value);
+                }
             }
-
-            // If there are no return expressions, then we need to check if
-            // the function body consists solely of a throw statement;
-            // this is to make an exception for unimplemented functions.
-            if (bodyContainsSingleThrowStatement(bodyBlock)) {
-                return;
+            else {
+                // This function does not conform to the specification.
+                error(func.type, Diagnostics.A_function_whose_declared_type_is_neither_void_nor_any_must_return_a_value);
             }
-
-            // This function does not conform to the specification.
-            error(func.type, Diagnostics.A_function_whose_declared_type_is_neither_void_nor_any_must_return_a_value_or_consist_of_a_single_throw_statement);
         }
 
         function checkFunctionExpressionOrObjectLiteralMethod(node: FunctionExpression | MethodDeclaration, contextualMapper?: TypeMapper): Type {
@@ -9401,7 +9386,7 @@ namespace ts {
             }
 
             if (returnType && !node.asteriskToken) {
-                checkIfNonVoidFunctionHasReturnExpressionsOrSingleThrowStatment(node, isAsync ? promisedType : returnType);
+                checkAllCodePathsInNonVoidFunctionReturnOrThrow(node, isAsync ? promisedType : returnType);
             }
 
             if (node.body) {
@@ -10579,8 +10564,15 @@ namespace ts {
                 checkGrammarFunctionLikeDeclaration(node) || checkGrammarAccessor(node) || checkGrammarComputedPropertyName(node.name);
 
                 if (node.kind === SyntaxKind.GetAccessor) {
-                    if (!isInAmbientContext(node) && nodeIsPresent(node.body) && !(bodyContainsAReturnStatement(<Block>node.body) || bodyContainsSingleThrowStatement(<Block>node.body))) {
-                        error(node.name, Diagnostics.A_get_accessor_must_return_a_value_or_consist_of_a_single_throw_statement);
+                    if (!isInAmbientContext(node) && nodeIsPresent(node.body) && (node.flags & NodeFlags.HasImplicitReturn)) {
+                        if (node.flags & NodeFlags.HasExplicitReturn) {
+                            if (compilerOptions.noImplicitReturns) {
+                                error(node.name, Diagnostics.Not_all_code_paths_return_a_value);
+                            }
+                        }
+                        else {
+                            error(node.name, Diagnostics.A_get_accessor_must_return_a_value);
+                        }
                     }
                 }
 
@@ -11505,7 +11497,7 @@ namespace ts {
                     promisedType = checkAsyncFunctionReturnType(node);
                 }
 
-                checkIfNonVoidFunctionHasReturnExpressionsOrSingleThrowStatment(node, isAsync ? promisedType : returnType);
+                checkAllCodePathsInNonVoidFunctionReturnOrThrow(node, isAsync ? promisedType : returnType);
             }
 
             if (produceDiagnostics && !node.type) {
@@ -14524,7 +14516,7 @@ namespace ts {
         function initializeTypeChecker() {
             // Bind all source files and propagate errors
             forEach(host.getSourceFiles(), file => {
-                bindSourceFile(file);
+                bindSourceFile(file, compilerOptions);
             });
 
             // Initialize global symbol table

src/compiler/commandLineParser.ts

@@ -244,7 +244,27 @@ namespace ts {
                 "classic": ModuleResolutionKind.Classic
             },
             description: Diagnostics.Specifies_module_resolution_strategy_Colon_node_Node_or_classic_TypeScript_pre_1_6
-        }        
+        },
+        {
+            name: "noUnusedLabels",
+            type: "boolean",
+            description: Diagnostics.Report_error_on_unused_labels
+        },
+        {
+            name: "noImplicitReturns",
+            type: "boolean",
+            description: Diagnostics.Report_error_when_not_all_code_paths_in_function_return_a_value
+        },
+        {
+            name: "noFallthroughCasesInSwitch",
+            type: "boolean",
+            description: Diagnostics.Report_errors_for_fallthrough_cases_in_switch_statement
+        },
+        {
+            name: "noUnreachableCode",
+            type: "boolean",
+            description: Diagnostics.Report_errors_on_unreachable_code
+        }
     ];
 
     /* @internal */

src/compiler/diagnosticInformationMap.generated.ts

@@ -256,7 +256,7 @@ namespace ts {
         Neither_type_0_nor_type_1_is_assignable_to_the_other: { code: 2352, category: DiagnosticCategory.Error, key: "Neither type '{0}' nor type '{1}' is assignable to the other." },
         Object_literal_may_only_specify_known_properties_and_0_does_not_exist_in_type_1: { code: 2353, category: DiagnosticCategory.Error, key: "Object literal may only specify known properties, and '{0}' does not exist in type '{1}'." },
         No_best_common_type_exists_among_return_expressions: { code: 2354, category: DiagnosticCategory.Error, key: "No best common type exists among return expressions." },
-        A_function_whose_declared_type_is_neither_void_nor_any_must_return_a_value_or_consist_of_a_single_throw_statement: { code: 2355, category: DiagnosticCategory.Error, key: "A function whose declared type is neither 'void' nor 'any' must return a value or consist of a single 'throw' statement." },
+        A_function_whose_declared_type_is_neither_void_nor_any_must_return_a_value: { code: 2355, category: DiagnosticCategory.Error, key: "A function whose declared type is neither 'void' nor 'any' must return a value." },
         An_arithmetic_operand_must_be_of_type_any_number_or_an_enum_type: { code: 2356, category: DiagnosticCategory.Error, key: "An arithmetic operand must be of type 'any', 'number' or an enum type." },
         The_operand_of_an_increment_or_decrement_operator_must_be_a_variable_property_or_indexer: { code: 2357, category: DiagnosticCategory.Error, key: "The operand of an increment or decrement operator must be a variable, property or indexer." },
         The_left_hand_side_of_an_instanceof_expression_must_be_of_type_any_an_object_type_or_a_type_parameter: { code: 2358, category: DiagnosticCategory.Error, key: "The left-hand side of an 'instanceof' expression must be of type 'any', an object type or a type parameter." },
@@ -277,7 +277,7 @@ namespace ts {
         Duplicate_number_index_signature: { code: 2375, category: DiagnosticCategory.Error, key: "Duplicate number index signature." },
         A_super_call_must_be_the_first_statement_in_the_constructor_when_a_class_contains_initialized_properties_or_has_parameter_properties: { code: 2376, category: DiagnosticCategory.Error, key: "A 'super' call must be the first statement in the constructor when a class contains initialized properties or has parameter properties." },
         Constructors_for_derived_classes_must_contain_a_super_call: { code: 2377, category: DiagnosticCategory.Error, key: "Constructors for derived classes must contain a 'super' call." },
-        A_get_accessor_must_return_a_value_or_consist_of_a_single_throw_statement: { code: 2378, category: DiagnosticCategory.Error, key: "A 'get' accessor must return a value or consist of a single 'throw' statement." },
+        A_get_accessor_must_return_a_value: { code: 2378, category: DiagnosticCategory.Error, key: "A 'get' accessor must return a value." },
         Getter_and_setter_accessors_do_not_agree_in_visibility: { code: 2379, category: DiagnosticCategory.Error, key: "Getter and setter accessors do not agree in visibility." },
         get_and_set_accessor_must_have_the_same_type: { code: 2380, category: DiagnosticCategory.Error, key: "'get' and 'set' accessor must have the same type." },
         A_signature_with_an_implementation_cannot_use_a_string_literal_type: { code: 2381, category: DiagnosticCategory.Error, key: "A signature with an implementation cannot use a string literal type." },
@@ -570,6 +570,10 @@ namespace ts {
         Initializes_a_TypeScript_project_and_creates_a_tsconfig_json_file: { code: 6070, category: DiagnosticCategory.Message, key: "Initializes a TypeScript project and creates a tsconfig.json file." },
         Successfully_created_a_tsconfig_json_file: { code: 6071, category: DiagnosticCategory.Message, key: "Successfully created a tsconfig.json file." },
         Suppress_excess_property_checks_for_object_literals: { code: 6072, category: DiagnosticCategory.Message, key: "Suppress excess property checks for object literals." },
+        Report_error_on_unused_labels: { code: 6073, category: DiagnosticCategory.Message, key: "Report error on unused labels." },
+        Report_error_when_not_all_code_paths_in_function_return_a_value: { code: 6074, category: DiagnosticCategory.Message, key: "Report error when not all code paths in function return a value." },
+        Report_errors_for_fallthrough_cases_in_switch_statement: { code: 6075, category: DiagnosticCategory.Message, key: "Report errors for fallthrough cases in switch statement." },
+        Report_errors_on_unreachable_code: { code: 6076, category: DiagnosticCategory.Message, key: "Report errors on unreachable code." },
         Variable_0_implicitly_has_an_1_type: { code: 7005, category: DiagnosticCategory.Error, key: "Variable '{0}' implicitly has an '{1}' type." },
         Parameter_0_implicitly_has_an_1_type: { code: 7006, category: DiagnosticCategory.Error, key: "Parameter '{0}' implicitly has an '{1}' type." },
         Member_0_implicitly_has_an_1_type: { code: 7008, category: DiagnosticCategory.Error, key: "Member '{0}' implicitly has an '{1}' type." },
@@ -587,6 +591,10 @@ namespace ts {
         Function_implicitly_has_return_type_any_because_it_does_not_have_a_return_type_annotation_and_is_referenced_directly_or_indirectly_in_one_of_its_return_expressions: { code: 7024, category: DiagnosticCategory.Error, key: "Function implicitly has return type 'any' because it does not have a return type annotation and is referenced directly or indirectly in one of its return expressions." },
         Generator_implicitly_has_type_0_because_it_does_not_yield_any_values_Consider_supplying_a_return_type: { code: 7025, category: DiagnosticCategory.Error, key: "Generator implicitly has type '{0}' because it does not yield any values. Consider supplying a return type." },
         JSX_element_implicitly_has_type_any_because_no_interface_JSX_0_exists: { code: 7026, category: DiagnosticCategory.Error, key: "JSX element implicitly has type 'any' because no interface 'JSX.{0}' exists" },
+        Unreachable_code_detected: { code: 7027, category: DiagnosticCategory.Error, key: "Unreachable code detected." },
+        Unused_label: { code: 7028, category: DiagnosticCategory.Error, key: "Unused label." },
+        Fallthrough_case_in_switch: { code: 7029, category: DiagnosticCategory.Error, key: "Fallthrough case in switch." },
+        Not_all_code_paths_return_a_value: { code: 7030, category: DiagnosticCategory.Error, key: "Not all code paths return a value." },
         You_cannot_rename_this_element: { code: 8000, category: DiagnosticCategory.Error, key: "You cannot rename this element." },
         You_cannot_rename_elements_that_are_defined_in_the_standard_TypeScript_library: { code: 8001, category: DiagnosticCategory.Error, key: "You cannot rename elements that are defined in the standard TypeScript library." },
         import_can_only_be_used_in_a_ts_file: { code: 8002, category: DiagnosticCategory.Error, key: "'import ... =' can only be used in a .ts file." },

src/compiler/diagnosticMessages.json

@@ -1013,7 +1013,7 @@
         "category": "Error",
         "code": 2354
     },
-    "A function whose declared type is neither 'void' nor 'any' must return a value or consist of a single 'throw' statement.": {
+    "A function whose declared type is neither 'void' nor 'any' must return a value.": {
         "category": "Error",
         "code": 2355
     },
@@ -1097,7 +1097,7 @@
         "category": "Error",
         "code": 2377
     },
-    "A 'get' accessor must return a value or consist of a single 'throw' statement.": {
+    "A 'get' accessor must return a value.": {
         "category": "Error",
         "code": 2378
     },
@@ -2270,7 +2270,22 @@
         "category": "Message",
         "code": 6072
     },
-
+    "Report error on unused labels.": {
+        "category": "Message",
+        "code": 6073
+    },
+    "Report error when not all code paths in function return a value.": {
+        "category": "Message",
+        "code": 6074
+    },
+    "Report errors for fallthrough cases in switch statement.": {
+        "category": "Message",
+        "code": 6075
+    },
+    "Report errors on unreachable code.": {
+        "category": "Message",
+        "code": 6076
+    },
     "Variable '{0}' implicitly has an '{1}' type.": {
         "category": "Error",
         "code": 7005
@@ -2339,8 +2354,22 @@
         "category": "Error",
         "code": 7026
     },
-
-
+    "Unreachable code detected.": {
+        "category": "Error",
+        "code": 7027
+    },
+    "Unused label.": {
+        "category": "Error",
+        "code": 7028
+    },
+    "Fallthrough case in switch.": {
+        "category": "Error",
+        "code": 7029
+    },
+    "Not all code paths return a value.": {
+        "category": "Error",
+        "code": 7030
+    },    
     "You cannot rename this element.": {
         "category": "Error",
         "code": 8000

src/compiler/types.ts

@@ -376,6 +376,8 @@ namespace ts {
         OctalLiteral =      0x00010000,  // Octal numeric literal
         Namespace =         0x00020000,  // Namespace declaration
         ExportContext =     0x00040000,  // Export context (initialized by binding)
+        HasImplicitReturn =     0x00080000,  // If function implicitly returns on one of codepaths (initialized by binding)
+        HasExplicitReturn =     0x00100000,  // If function has explicit reachable return on one of codepaths (initialized by binding)
 
         Modifier = Export | Ambient | Public | Private | Protected | Static | Abstract | Default | Async,
         AccessibilityModifier = Public | Private | Protected,
@@ -2057,7 +2059,11 @@ namespace ts {
         experimentalDecorators?: boolean;
         experimentalAsyncFunctions?: boolean;
         emitDecoratorMetadata?: boolean;
-        moduleResolution?: ModuleResolutionKind
+        moduleResolution?: ModuleResolutionKind,
+        noUnusedLabels?: boolean,
+        noImplicitReturns?: boolean,
+        noFallthroughCasesInSwitch?: boolean,
+        noUnreachableCode?: boolean,
         /* @internal */ stripInternal?: boolean;
 
         // Skip checking lib.d.ts to help speed up tests.

src/harness/harness.ts

@@ -1242,6 +1242,18 @@ module Harness {
                                           setting.value.toLowerCase() === "preserve" ? ts.JsxEmit.Preserve :
                                           ts.JsxEmit.None;
                             break;
+                        case "nounusedlabels":
+                            options.noUnusedLabels = setting.value === "true"
+                            break;
+                        case "noimplicitreturns":
+                            options.noImplicitReturns = setting.value === "true"
+                            break;
+                        case "nofallthroughcasesinswitch":
+                            options.noFallthroughCasesInSwitch = setting.value === "true"
+                            break;
+                        case "nounreachablecode":
+                            options.noUnreachableCode = setting.value === "true"
+                            break;
 
                         default:
                             throw new Error("Unsupported compiler setting " + setting.flag);

src/services/breakpoints.ts

@@ -446,7 +446,7 @@ namespace ts.BreakpointResolver {
                         // fall through.
 
                     case SyntaxKind.CatchClause:
-                        return spanInNode(lastOrUndefined((<Block>node.parent).statements));;
+                        return spanInNode(lastOrUndefined((<Block>node.parent).statements));
 
                     case SyntaxKind.CaseBlock:
                         // breakpoint in last statement of the last clause
@@ -493,9 +493,6 @@ namespace ts.BreakpointResolver {
                     default:
                         return spanInNode(node.parent);
                 }
-
-                // Default to parent node
-                return spanInNode(node.parent);
             }
 
             function spanInColonToken(node: Node): TextSpan {

src/services/formatting/smartIndenter.ts

@@ -340,7 +340,6 @@ namespace ts.formatting {
                             return node;
                     }
                 }
-                return node;
             }
         }