completions: Add assertions that symbols are defined

Author: Andy Hanson

src/compiler/core.ts

@@ -2901,6 +2901,13 @@ namespace ts {
             return value;
         }
 
+        export function assertEachDefined<T, A extends ReadonlyArray<T>>(value: A): A {
+            for (const v of value) {
+                assertDefined(v);
+            }
+            return value;
+        }
+
         export function assertNever(member: never, message?: string, stackCrawlMark?: AnyFunction): never {
             return fail(message || `Illegal value: ${member}`, stackCrawlMark || assertNever);
         }

src/services/completions.ts

@@ -923,7 +923,7 @@ namespace ts.Completions {
         }
         else if (isStartingCloseTag) {
             const tagName = (<JsxElement>contextToken.parent.parent).openingElement.tagName;
-            const tagSymbol = typeChecker.getSymbolAtLocation(tagName);
+            const tagSymbol = Debug.assertDefined(typeChecker.getSymbolAtLocation(tagName));
 
             if (!typeChecker.isUnknownSymbol(tagSymbol)) {
                 symbols = [tagSymbol];
@@ -971,7 +971,7 @@ namespace ts.Completions {
 
                     if (symbol.flags & (SymbolFlags.Module | SymbolFlags.Enum)) {
                         // Extract module or enum members
-                        const exportedSymbols = typeChecker.getExportsOfModule(symbol);
+                        const exportedSymbols = Debug.assertEachDefined(typeChecker.getExportsOfModule(symbol));
                         const isValidValueAccess = (symbol: Symbol) => typeChecker.isValidPropertyAccess(<PropertyAccessExpression>(node.parent), symbol.name);
                         const isValidTypeAccess = (symbol: Symbol) => symbolCanBeReferencedAtTypeLocation(symbol);
                         const isValidAccess = isRhsOfImportDeclaration ?
@@ -1111,7 +1111,7 @@ namespace ts.Completions {
 
             const symbolMeanings = SymbolFlags.Type | SymbolFlags.Value | SymbolFlags.Namespace | SymbolFlags.Alias;
 
-            symbols = typeChecker.getSymbolsInScope(scopeNode, symbolMeanings);
+            symbols = Debug.assertEachDefined(typeChecker.getSymbolsInScope(scopeNode, symbolMeanings));
 
             // Need to insert 'this.' before properties of `this` type, so only do that if `includeInsertTextCompletions`
             if (options.includeInsertTextCompletions && scopeNode.kind !== SyntaxKind.SourceFile) {
@@ -2248,13 +2248,13 @@ namespace ts.Completions {
      */
     function getPropertiesForCompletion(type: Type, checker: TypeChecker, isForAccess: boolean): Symbol[] {
         if (!(type.flags & TypeFlags.Union)) {
-            return type.getApparentProperties();
+            return Debug.assertEachDefined(type.getApparentProperties());
         }
 
         const { types } = type as UnionType;
         // If we're providing completions for an object literal, skip primitive, array-like, or callable types since those shouldn't be implemented by object literals.
         const filteredTypes = isForAccess ? types : types.filter(memberType =>
             !(memberType.flags & TypeFlags.Primitive || checker.isArrayLikeType(memberType) || typeHasCallOrConstructSignatures(memberType, checker)));
-        return checker.getAllPossiblePropertiesOfTypes(filteredTypes);
+        return Debug.assertEachDefined(checker.getAllPossiblePropertiesOfTypes(filteredTypes));
     }
 }