initial revision of reachability checks

src/compiler/checker.ts

@@ -160,6 +160,8 @@ namespace ts {
         let getGlobalPromiseConstructorLikeType: () => ObjectType;
         let getGlobalThenableType: () => ObjectType;
 
+        let jsxElementClassType: Type;
+
         let tupleTypes: Map<TupleType> = {};
         let unionTypes: Map<UnionType> = {};
         let intersectionTypes: Map<IntersectionType> = {};
@@ -7873,7 +7875,6 @@ namespace ts {
             return prop || unknownSymbol;
         }
 
-        let jsxElementClassType: Type = undefined;
         function getJsxGlobalElementClassType(): Type {
             if (!jsxElementClassType) {
                 jsxElementClassType = getExportedTypeFromNamespace(JsxNames.JSX, JsxNames.ElementClass);
@@ -9619,21 +9620,11 @@ 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;
             }
@@ -9644,26 +9635,20 @@ 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 {
@@ -9743,7 +9728,7 @@ namespace ts {
             }
 
             if (returnType && !node.asteriskToken) {
-                checkIfNonVoidFunctionHasReturnExpressionsOrSingleThrowStatment(node, isAsync ? promisedType : returnType);
+                checkAllCodePathsInNonVoidFunctionReturnOrThrow(node, isAsync ? promisedType : returnType);
             }
 
             if (node.body) {
@@ -10944,8 +10929,15 @@ 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);
+                        }
                     }
                 }
 
@@ -11876,7 +11868,7 @@ namespace ts {
                     promisedType = checkAsyncFunctionReturnType(node);
                 }
 
-                checkIfNonVoidFunctionHasReturnExpressionsOrSingleThrowStatment(node, isAsync ? promisedType : returnType);
+                checkAllCodePathsInNonVoidFunctionReturnOrThrow(node, isAsync ? promisedType : returnType);
             }
 
             if (produceDiagnostics && !node.type) {
@@ -14914,7 +14906,7 @@ 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

@@ -248,11 +248,31 @@ namespace ts {
             description: Diagnostics.Specifies_module_resolution_strategy_Colon_node_Node_js_or_classic_TypeScript_pre_1_6,
             error: Diagnostics.Argument_for_moduleResolution_option_must_be_node_or_classic,
         },
+        {
+            name: "allowUnusedLabels",
+            type: "boolean",
+            description: Diagnostics.Do_not_report_errors_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: "allowUnreachableCode",
+            type: "boolean",
+            description: Diagnostics.Do_not_report_errors_on_unreachable_code
+        },
         {
             name: "forceConsistentCasingInFileNames",
             type: "boolean",
             description: Diagnostics.Disallow_inconsistently_cased_references_to_the_same_file
-        },
+        }
     ];
 
     /* @internal */

src/compiler/diagnosticMessages.json

@@ -1012,7 +1012,7 @@
         "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
     },
@@ -1096,7 +1096,7 @@
         "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
     },
@@ -2298,6 +2298,22 @@
         "category": "Message",
         "code": 6073
     },
+    "Do not report errors on unused labels.": {
+        "category": "Message",
+        "code": 6074
+    },
+    "Report error when not all code paths in function return a value.": {
+        "category": "Message",
+        "code": 6075
+    },
+    "Report errors for fallthrough cases in switch statement.": {
+        "category": "Message",
+        "code": 6076
+    },
+    "Do not report errors on unreachable code.": {
+        "category": "Message",
+        "code": 6077
+    },
     "Variable '{0}' implicitly has an '{1}' type.": {
         "category": "Error",
         "code": 7005
@@ -2366,8 +2382,22 @@
         "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/emitter.ts

@@ -9,6 +9,12 @@ namespace ts {
 
     type DependencyGroup = Array<ImportDeclaration | ImportEqualsDeclaration | ExportDeclaration>;
 
+    const enum Jump {
+        Break       = 1 << 1,
+        Continue    = 1 << 2,
+        Return      = 1 << 3
+    }
+
     let entities: Map<number> = {
         "quot": 0x0022,
         "amp": 0x0026,
@@ -379,12 +385,6 @@ var __awaiter = (this && this.__awaiter) || function (thisArg, _arguments, Promi
             return true;
         }
 
-        const enum Jump {
-            Break       = 1 << 1,
-            Continue    = 1 << 2,
-            Return      = 1 << 3
-        }
-
         interface ConvertedLoopState {
             /*
              * set of labels that occured inside the converted loop

src/compiler/types.ts

@@ -362,28 +362,31 @@ namespace ts {
 
     export const enum NodeFlags {
         None =              0,
-        Export =            0x00000001,  // Declarations
-        Ambient =           0x00000002,  // Declarations
-        Public =            0x00000010,  // Property/Method
-        Private =           0x00000020,  // Property/Method
-        Protected =         0x00000040,  // Property/Method
-        Static =            0x00000080,  // Property/Method
-        Abstract =          0x00000100,  // Class/Method/ConstructSignature
-        Async =             0x00000200,  // Property/Method/Function
-        Default =           0x00000400,  // Function/Class (export default declaration)
-        MultiLine =         0x00000800,  // Multi-line array or object literal
-        Synthetic =         0x00001000,  // Synthetic node (for full fidelity)
-        DeclarationFile =   0x00002000,  // Node is a .d.ts file
-        Let =               0x00004000,  // Variable declaration
-        Const =             0x00008000,  // Variable declaration
-        OctalLiteral =      0x00010000,  // Octal numeric literal
-        Namespace =         0x00020000,  // Namespace declaration
-        ExportContext =     0x00040000,  // Export context (initialized by binding)
-        ContainsThis =      0x00080000,  // Interface contains references to "this"
-
+        Export =            1 << 1,  // Declarations
+        Ambient =           1 << 2,  // Declarations
+        Public =            1 << 3,  // Property/Method
+        Private =           1 << 4,  // Property/Method
+        Protected =         1 << 5,  // Property/Method
+        Static =            1 << 6,  // Property/Method
+        Abstract =          1 << 7,  // Class/Method/ConstructSignature
+        Async =             1 << 8,  // Property/Method/Function
+        Default =           1 << 9,  // Function/Class (export default declaration)
+        MultiLine =         1 << 10,  // Multi-line array or object literal
+        Synthetic =         1 << 11,  // Synthetic node (for full fidelity)
+        DeclarationFile =   1 << 12,  // Node is a .d.ts file
+        Let =               1 << 13,  // Variable declaration
+        Const =             1 << 14,  // Variable declaration
+        OctalLiteral =      1 << 15,  // Octal numeric literal
+        Namespace =         1 << 16,  // Namespace declaration
+        ExportContext =     1 << 17,  // Export context (initialized by binding)
+        ContainsThis =      1 << 18,  // Interface contains references to "this"
+        HasImplicitReturn =     1 << 19,  // If function implicitly returns on one of codepaths (initialized by binding)
+        HasExplicitReturn =     1 << 20,  // 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,
-        BlockScoped = Let | Const
+        BlockScoped = Let | Const,
+
+        ReachabilityCheckFlags = HasImplicitReturn | HasExplicitReturn
     }
 
     /* @internal */
@@ -2092,6 +2095,10 @@ namespace ts {
         experimentalDecorators?: boolean;
         emitDecoratorMetadata?: boolean;
         moduleResolution?: ModuleResolutionKind;
+        allowUnusedLabels?: boolean;
+        allowUnreachableCode?: boolean;
+        noImplicitReturns?: boolean;
+        noFallthroughCasesInSwitch?: boolean;
         forceConsistentCasingInFileNames?: boolean;
         /* @internal */ stripInternal?: boolean;
 

src/compiler/utilities.ts

@@ -622,25 +622,26 @@ namespace ts {
     }
 
     export function isFunctionLike(node: Node): node is FunctionLikeDeclaration {
-        if (node) {
-            switch (node.kind) {
-                case SyntaxKind.Constructor:
-                case SyntaxKind.FunctionExpression:
-                case SyntaxKind.FunctionDeclaration:
-                case SyntaxKind.ArrowFunction:
-                case SyntaxKind.MethodDeclaration:
-                case SyntaxKind.MethodSignature:
-                case SyntaxKind.GetAccessor:
-                case SyntaxKind.SetAccessor:
-                case SyntaxKind.CallSignature:
-                case SyntaxKind.ConstructSignature:
-                case SyntaxKind.IndexSignature:
-                case SyntaxKind.FunctionType:
-                case SyntaxKind.ConstructorType:
-                    return true;
-            }
+        return node && isFunctionLikeKind(node.kind);
+    }
+
+    export function isFunctionLikeKind(kind: SyntaxKind): boolean {
+        switch (kind) {
+            case SyntaxKind.Constructor:
+            case SyntaxKind.FunctionExpression:
+            case SyntaxKind.FunctionDeclaration:
+            case SyntaxKind.ArrowFunction:
+            case SyntaxKind.MethodDeclaration:
+            case SyntaxKind.MethodSignature:
+            case SyntaxKind.GetAccessor:
+            case SyntaxKind.SetAccessor:
+            case SyntaxKind.CallSignature:
+            case SyntaxKind.ConstructSignature:
+            case SyntaxKind.IndexSignature:
+            case SyntaxKind.FunctionType:
+            case SyntaxKind.ConstructorType:
+                return true;
         }
-        return false;
     }
 
     export function introducesArgumentsExoticObject(node: Node) {
@@ -1228,7 +1229,7 @@ namespace ts {
             case SyntaxKind.LabeledStatement:
             case SyntaxKind.ReturnStatement:
             case SyntaxKind.SwitchStatement:
-            case SyntaxKind.ThrowKeyword:
+            case SyntaxKind.ThrowStatement:
             case SyntaxKind.TryStatement:
             case SyntaxKind.VariableStatement:
             case SyntaxKind.WhileStatement:

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

@@ -360,7 +360,6 @@ namespace ts.formatting {
                             return node;
                     }
                 }
-                return node;
             }
         }