Allow missing return for unions containing any or void

masaeedu · masaeedu · commit e568892ea52e · 2016-01-15T23:50:30.000-05:00
diff --git a/doc/spec.md b/doc/spec.md
@@ -265,7 +265,7 @@ 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.
 
-&emsp;&emsp;![](images/image1.png)
+&emsp;&emsp;![](images/image1.png)
 
 In this example, the programmer benefits from type inference without providing type annotations. Some beneficial tools, however, do require the programmer to provide type annotations. In TypeScript, we can express a parameter requirement as in the following code fragment.
 
@@ -413,7 +413,7 @@ This signature denotes that a function may be passed as the parameter of the '$'
 
 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.
 
-&emsp;&emsp;![](images/image2.png)
+&emsp;&emsp;![](images/image2.png)
 
 Section [3.3](#3.3) provides additional information about object types.
 
@@ -630,7 +630,7 @@ An important goal of TypeScript is to provide accurate and straightforward types
 
 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.
 
-&emsp;&emsp;![](images/image3.png)
+&emsp;&emsp;![](images/image3.png)
 
 The following code fragment uses this feature. Because the 'span' variable is inferred to have the type 'HTMLSpanElement', the code can reference without static error the 'isMultiline' property of 'span'.
 
@@ -641,7 +641,7 @@ 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.
 
-&emsp;&emsp;![](images/image4.png)
+&emsp;&emsp;![](images/image4.png)
 
 Section [3.9.2.4](#3.9.2.4) provides details on how to use string literals in function signatures.
 
@@ -3885,7 +3885,7 @@ function g(x: number) {
 
 the inferred return type for 'f' and 'g' is Any because the functions reference themselves through a cycle with no return type annotations. Adding an explicit return type 'number' to either breaks the cycle and causes the return type 'number' to be inferred for the other.
 
-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.
+An explicitly typed function whose return type isn't the Void type, the Any type, or a union type containing the Void or Any type as a constituent 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.
 
 The type of 'this' in a function implementation is the Any type.
 
diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
@@ -2466,6 +2466,12 @@ namespace ts {
             return type && (type.flags & TypeFlags.Any) !== 0;
         }
 
+        function isUnionContaining(type: Type, kinds: TypeFlags) {
+            return type 
+                && (type.flags & TypeFlags.Union) 
+                && someConstituentTypeHasKind(type, kinds);
+        }
+
         // Return the type of a binding element parent. We check SymbolLinks first to see if a type has been
         // assigned by contextual typing.
         function getTypeForBindingElementParent(node: VariableLikeDeclaration) {
@@ -10201,7 +10207,8 @@ namespace ts {
 
         /*
          *TypeScript Specification 1.0 (6.3) - July 2014
-         * An explicitly typed function whose return type isn't the Void or the Any type
+         * An explicitly typed function whose return type isn't the Void type, 
+         * the Any type, or a union type containing the Void or Any type as a constituent
          * 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.
          * @param returnType - return type of the function, can be undefined if return type is not explicitly specified
@@ -10212,7 +10219,7 @@ namespace ts {
             }
 
             // Functions with with an explicitly specified 'void' or 'any' return type don't need any return expressions.
-            if (returnType === voidType || isTypeAny(returnType)) {
+            if (returnType === voidType || isTypeAny(returnType) || isUnionContaining(returnType, TypeFlags.Any) || isUnionContaining(returnType, TypeFlags.Void)) {
                 return;
             }
 
diff --git a/tests/baselines/reference/functionsMissingReturnStatementsAndExpressions.errors.txt b/tests/baselines/reference/functionsMissingReturnStatementsAndExpressions.errors.txt
@@ -1,11 +1,10 @@
 tests/cases/compiler/functionsMissingReturnStatementsAndExpressions.ts(3,16): error TS2355: A function whose declared type is neither 'void' nor 'any' must return a value.
-tests/cases/compiler/functionsMissingReturnStatementsAndExpressions.ts(93,17): error TS2355: A function whose declared type is neither 'void' nor 'any' must return a value.
 tests/cases/compiler/functionsMissingReturnStatementsAndExpressions.ts(101,17): error TS2355: A function whose declared type is neither 'void' nor 'any' must return a value.
 tests/cases/compiler/functionsMissingReturnStatementsAndExpressions.ts(106,16): error TS2378: A 'get' accessor must return a value.
 tests/cases/compiler/functionsMissingReturnStatementsAndExpressions.ts(129,5): error TS1003: Identifier expected.
 
 
-==== tests/cases/compiler/functionsMissingReturnStatementsAndExpressions.ts (5 errors) ====
+==== tests/cases/compiler/functionsMissingReturnStatementsAndExpressions.ts (4 errors) ====
     
     
     function f1(): string {
@@ -101,8 +100,6 @@ tests/cases/compiler/functionsMissingReturnStatementsAndExpressions.ts(129,5): e
     }
     
     function f19(): void | number {
-                    ~~~~~~~~~~~~~
-!!! error TS2355: A function whose declared type is neither 'void' nor 'any' must return a value.
         // Okay; function return type is union containing void
     }
     
