Control flow analysis for implicit any variables

src/compiler/checker.ts

@@ -119,6 +119,7 @@ namespace ts {
         const resolvingSymbol = createSymbol(SymbolFlags.Transient, "__resolving__");
 
         const anyType = createIntrinsicType(TypeFlags.Any, "any");
+        const autoType = createIntrinsicType(TypeFlags.Any, "any");
         const unknownType = createIntrinsicType(TypeFlags.Any, "unknown");
         const undefinedType = createIntrinsicType(TypeFlags.Undefined, "undefined");
         const undefinedWideningType = strictNullChecks ? undefinedType : createIntrinsicType(TypeFlags.Undefined | TypeFlags.ContainsWideningType, "undefined");
@@ -3050,6 +3051,11 @@ namespace ts {
             return undefined;
         }
 
+        function isAutoVariableInitializer(initializer: Expression) {
+            const expr = initializer && skipParentheses(initializer);
+            return !expr || expr.kind === SyntaxKind.NullKeyword || expr.kind === SyntaxKind.Identifier && getResolvedSymbol(<Identifier>expr) === undefinedSymbol;
+        }
+
         function addOptionality(type: Type, optional: boolean): Type {
             return strictNullChecks && optional ? includeFalsyTypes(type, TypeFlags.Undefined) : type;
         }
@@ -3088,6 +3094,14 @@ namespace ts {
                 return addOptionality(getTypeFromTypeNode(declaration.type), /*optional*/ declaration.questionToken && includeOptionality);
             }
 
+            // Use control flow type inference for non-ambient, non-exported var or let variables with no initializer
+            // or a 'null' or 'undefined' initializer.
+            if (declaration.kind === SyntaxKind.VariableDeclaration && !isBindingPattern(declaration.name) &&
+                !(getCombinedNodeFlags(declaration) & NodeFlags.Const) && !(getCombinedModifierFlags(declaration) & ModifierFlags.Export) &&
+                !isInAmbientContext(declaration) && isAutoVariableInitializer(declaration.initializer)) {
+                return autoType;
+            }
+
             if (declaration.kind === SyntaxKind.Parameter) {
                 const func = <FunctionLikeDeclaration>declaration.parent;
                 // For a parameter of a set accessor, use the type of the get accessor if one is present
@@ -8432,7 +8446,9 @@ namespace ts {
             if (!reference.flowNode || assumeInitialized && !(declaredType.flags & TypeFlags.Narrowable)) {
                 return declaredType;
             }
-            const initialType = assumeInitialized ? declaredType : includeFalsyTypes(declaredType, TypeFlags.Undefined);
+            const initialType = assumeInitialized ? declaredType :
+                declaredType === autoType ? undefinedType :
+                includeFalsyTypes(declaredType, TypeFlags.Undefined);
             const visitedFlowStart = visitedFlowCount;
             const result = getTypeFromFlowType(getTypeAtFlowNode(reference.flowNode));
             visitedFlowCount = visitedFlowStart;
@@ -8506,9 +8522,12 @@ namespace ts {
                 // Assignments only narrow the computed type if the declared type is a union type. Thus, we
                 // only need to evaluate the assigned type if the declared type is a union type.
                 if (isMatchingReference(reference, node)) {
-                    const isIncrementOrDecrement = node.parent.kind === SyntaxKind.PrefixUnaryExpression || node.parent.kind === SyntaxKind.PostfixUnaryExpression;
-                    return declaredType.flags & TypeFlags.Union && !isIncrementOrDecrement ?
-                        getAssignmentReducedType(<UnionType>declaredType, getInitialOrAssignedType(node)) :
+                    if (node.parent.kind === SyntaxKind.PrefixUnaryExpression || node.parent.kind === SyntaxKind.PostfixUnaryExpression) {
+                        const flowType = getTypeAtFlowNode(flow.antecedent);
+                        return createFlowType(getBaseTypeOfLiteralType(getTypeFromFlowType(flowType)), isIncomplete(flowType));
+                    }
+                    return declaredType === autoType ? getBaseTypeOfLiteralType(getInitialOrAssignedType(node)) :
+                        declaredType.flags & TypeFlags.Union ? getAssignmentReducedType(<UnionType>declaredType, getInitialOrAssignedType(node)) :
                         declaredType;
                 }
                 // We didn't have a direct match. However, if the reference is a dotted name, this
@@ -8952,7 +8971,7 @@ namespace ts {
                 if (isRightSideOfQualifiedNameOrPropertyAccess(location)) {
                     location = location.parent;
                 }
-                if (isExpression(location) && !isAssignmentTarget(location)) {
+                if (isPartOfExpression(location) && !isAssignmentTarget(location)) {
                     const type = checkExpression(<Expression>location);
                     if (getExportSymbolOfValueSymbolIfExported(getNodeLinks(location).resolvedSymbol) === symbol) {
                         return type;
@@ -9123,13 +9142,23 @@ namespace ts {
             // We only look for uninitialized variables in strict null checking mode, and only when we can analyze
             // the entire control flow graph from the variable's declaration (i.e. when the flow container and
             // declaration container are the same).
-            const assumeInitialized = !strictNullChecks || (type.flags & TypeFlags.Any) !== 0 || isParameter ||
-                isOuterVariable || isInAmbientContext(declaration);
+            const assumeInitialized = isParameter || isOuterVariable ||
+                type !== autoType && (!strictNullChecks || (type.flags & TypeFlags.Any) !== 0) ||
+                isInAmbientContext(declaration);
             const flowType = getFlowTypeOfReference(node, type, assumeInitialized, flowContainer);
             // A variable is considered uninitialized when it is possible to analyze the entire control flow graph
             // from declaration to use, and when the variable's declared type doesn't include undefined but the
             // control flow based type does include undefined.
-            if (!assumeInitialized && !(getFalsyFlags(type) & TypeFlags.Undefined) && getFalsyFlags(flowType) & TypeFlags.Undefined) {
+            if (type === autoType) {
+                if (flowType === autoType) {
+                    if (compilerOptions.noImplicitAny) {
+                        error(declaration.name, Diagnostics.Variable_0_implicitly_has_type_any_in_some_locations_where_its_type_cannot_be_determined, symbolToString(symbol));
+                        error(node, Diagnostics.Variable_0_implicitly_has_an_1_type, symbolToString(symbol), typeToString(anyType));
+                    }
+                    return anyType;
+                }
+            }
+            else if (!assumeInitialized && !(getFalsyFlags(type) & TypeFlags.Undefined) && getFalsyFlags(flowType) & TypeFlags.Undefined) {
                 error(node, Diagnostics.Variable_0_is_used_before_being_assigned, symbolToString(symbol));
                 // Return the declared type to reduce follow-on errors
                 return type;
@@ -15874,6 +15903,10 @@ namespace ts {
             }
         }
 
+        function convertAutoToAny(type: Type) {
+            return type === autoType ? anyType : type;
+        }
+
         // Check variable, parameter, or property declaration
         function checkVariableLikeDeclaration(node: VariableLikeDeclaration) {
             checkDecorators(node);
@@ -15924,7 +15957,7 @@ namespace ts {
                 return;
             }
             const symbol = getSymbolOfNode(node);
-            const type = getTypeOfVariableOrParameterOrProperty(symbol);
+            const type = convertAutoToAny(getTypeOfVariableOrParameterOrProperty(symbol));
             if (node === symbol.valueDeclaration) {
                 // Node is the primary declaration of the symbol, just validate the initializer
                 // Don't validate for-in initializer as it is already an error
@@ -15936,7 +15969,7 @@ namespace ts {
             else {
                 // Node is a secondary declaration, check that type is identical to primary declaration and check that
                 // initializer is consistent with type associated with the node
-                const declarationType = getWidenedTypeForVariableLikeDeclaration(node);
+                const declarationType = convertAutoToAny(getWidenedTypeForVariableLikeDeclaration(node));
                 if (type !== unknownType && declarationType !== unknownType && !isTypeIdenticalTo(type, declarationType)) {
                     error(node.name, Diagnostics.Subsequent_variable_declarations_must_have_the_same_type_Variable_0_must_be_of_type_1_but_here_has_type_2, declarationNameToString(node.name), typeToString(type), typeToString(declarationType));
                 }

src/compiler/diagnosticMessages.json

@@ -2953,6 +2953,10 @@
         "category": "Error",
         "code": 7033
     },
+    "Variable '{0}' implicitly has type 'any' in some locations where its type cannot be determined.": {
+        "category": "Error",
+        "code": 7034
+    },
     "You cannot rename this element.": {
         "category": "Error",
         "code": 8000

tests/baselines/reference/ES5SymbolProperty2.errors.txt

@@ -4,7 +4,7 @@ tests/cases/conformance/Symbols/ES5SymbolProperty2.ts(10,11): error TS2304: Cann
 
 ==== tests/cases/conformance/Symbols/ES5SymbolProperty2.ts (2 errors) ====
     module M {
-        var Symbol;
+        var Symbol: any;
 
         export class C {
             [Symbol.iterator]() { }

tests/baselines/reference/ES5SymbolProperty2.js

@@ -1,6 +1,6 @@
 //// [ES5SymbolProperty2.ts]
 module M {
-    var Symbol;
+    var Symbol: any;
 
     export class C {
         [Symbol.iterator]() { }

tests/baselines/reference/ES5SymbolProperty3.errors.txt

@@ -2,7 +2,7 @@ tests/cases/conformance/Symbols/ES5SymbolProperty3.ts(4,6): error TS2471: A comp
 
 
 ==== tests/cases/conformance/Symbols/ES5SymbolProperty3.ts (1 errors) ====
-    var Symbol;
+    var Symbol: any;
 
     class C {
         [Symbol.iterator]() { }

tests/baselines/reference/ES5SymbolProperty3.js

@@ -1,5 +1,5 @@
 //// [ES5SymbolProperty3.ts]
-var Symbol;
+var Symbol: any;
 
 class C {
     [Symbol.iterator]() { }

tests/baselines/reference/anyPlusAny1.js

@@ -1,5 +1,5 @@
 //// [anyPlusAny1.ts]
-var x;
+var x: any;
 x.name = "hello";
 var z = x + x;
 

tests/baselines/reference/anyPlusAny1.symbols

@@ -1,5 +1,5 @@
 === tests/cases/compiler/anyPlusAny1.ts ===
-var x;
+var x: any;
 >x : Symbol(x, Decl(anyPlusAny1.ts, 0, 3))
 
 x.name = "hello";

tests/baselines/reference/anyPlusAny1.types

@@ -1,5 +1,5 @@
 === tests/cases/compiler/anyPlusAny1.ts ===
-var x;
+var x: any;
 >x : any
 
 x.name = "hello";

tests/baselines/reference/asiPreventsParsingAsTypeAlias01.types

@@ -10,10 +10,10 @@ var Foo;
 >Foo : any
 
 type
->type : any
+>type : undefined
 
 Foo = string;
->Foo = string : any
+>Foo = string : undefined
 >Foo : any
->string : any
+>string : undefined
 

tests/baselines/reference/assignEveryTypeToAny.types

@@ -59,9 +59,9 @@ var e = undefined;
 >undefined : undefined
 
 x = e;
->x = e : any
+>x = e : undefined
 >x : any
->e : any
+>e : undefined
 
 var e2: typeof undefined;
 >e2 : any

tests/baselines/reference/assignmentLHSIsReference.js

@@ -1,5 +1,5 @@
 //// [assignmentLHSIsReference.ts]
-var value;
+var value: any;
 
 // identifiers: variable and parameter
 var x1: number;

tests/baselines/reference/assignmentLHSIsReference.symbols

@@ -1,5 +1,5 @@
 === tests/cases/conformance/expressions/assignmentOperator/assignmentLHSIsReference.ts ===
-var value;
+var value: any;
 >value : Symbol(value, Decl(assignmentLHSIsReference.ts, 0, 3))
 
 // identifiers: variable and parameter

tests/baselines/reference/assignmentLHSIsReference.types

@@ -1,5 +1,5 @@
 === tests/cases/conformance/expressions/assignmentOperator/assignmentLHSIsReference.ts ===
-var value;
+var value: any;
 >value : any
 
 // identifiers: variable and parameter

tests/baselines/reference/assignmentLHSIsValue.errors.txt

@@ -41,7 +41,7 @@ tests/cases/conformance/expressions/assignmentOperator/assignmentLHSIsValue.ts(7
 
 ==== tests/cases/conformance/expressions/assignmentOperator/assignmentLHSIsValue.ts (39 errors) ====
     // expected error for all the LHS of assignments
-    var value;
+    var value: any;
 
     // this
     class C {

tests/baselines/reference/assignmentLHSIsValue.js

@@ -1,6 +1,6 @@
 //// [assignmentLHSIsValue.ts]
 // expected error for all the LHS of assignments
-var value;
+var value: any;
 
 // this
 class C {

tests/baselines/reference/capturedLetConstInLoop9.types

@@ -39,7 +39,7 @@ for (let x = 0; x < 1; ++x) {
     }
 
     switch (x) {
->x : any
+>x : undefined
 
         case 1:
 >1 : 1

tests/baselines/reference/capturedLetConstInLoop9_ES6.types

@@ -40,7 +40,7 @@ for (let x = 0; x < 1; ++x) {
     }
 
     switch (x) {
->x : any
+>x : undefined
 
         case 1:
 >1 : 1

tests/baselines/reference/commentsArgumentsOfCallExpression2.types

@@ -17,7 +17,7 @@ foo(/*c2*/ 1, /*d2*/ 1 + 2, /*e1*/ a + b);
 >1 : 1
 >2 : 2
 >a + b : any
->a : any
+>a : undefined
 >b : any
 
 foo(/*c3*/ function () { }, /*d2*/() => { }, /*e2*/ a + /*e3*/ b);
@@ -26,7 +26,7 @@ foo(/*c3*/ function () { }, /*d2*/() => { }, /*e2*/ a + /*e3*/ b);
 >function () { } : () => void
 >() => { } : () => void
 >a + /*e3*/ b : any
->a : any
+>a : undefined
 >b : any
 
 foo(/*c3*/ function () { }, /*d3*/() => { }, /*e3*/(a + b));
@@ -36,7 +36,7 @@ foo(/*c3*/ function () { }, /*d3*/() => { }, /*e3*/(a + b));
 >() => { } : () => void
 >(a + b) : any
 >a + b : any
->a : any
+>a : undefined
 >b : any
 
 foo(