Add empty tuple type

Author: lefb766

src/compiler/checker.ts

@@ -332,6 +332,7 @@ namespace ts {
 
         const emptyStringType = getLiteralType("");
         const zeroType = getLiteralType(0);
+        const emptyTupleType = createTupleType([]);
 
         const resolutionTargets: TypeSystemEntity[] = [];
         const resolutionResults: boolean[] = [];
@@ -2621,16 +2622,8 @@ namespace ts {
                         return createArrayTypeNode(elementType);
                     }
                     else if (type.target.objectFlags & ObjectFlags.Tuple) {
-                        if (typeArguments.length > 0) {
-                            const tupleConstituentNodes = mapToTypeNodes(typeArguments.slice(0, getTypeReferenceArity(type)), context);
-                            if (tupleConstituentNodes && tupleConstituentNodes.length > 0) {
-                                return createTupleTypeNode(tupleConstituentNodes);
-                            }
-                        }
-                        if (!context.encounteredError && !(context.flags & NodeBuilderFlags.AllowEmptyTuple)) {
-                            context.encounteredError = true;
-                        }
-                        return undefined;
+                        const tupleConstituentNodes = mapToTypeNodes(typeArguments.slice(0, getTypeReferenceArity(type)), context) || [];
+                        return createTupleTypeNode(tupleConstituentNodes);
                     }
                     else {
                         const outerTypeParameters = type.target.outerTypeParameters;
@@ -9898,7 +9891,7 @@ namespace ts {
         }
 
         function isTupleLikeType(type: Type): boolean {
-            return !!getPropertyOfType(type, "0" as __String);
+            return !!getPropertyOfType(type, "0" as __String) || type === emptyTupleType;
         }
 
         function isUnitType(type: Type): boolean {
@@ -13204,9 +13197,7 @@ namespace ts {
                             }
                         }
                     }
-                    if (elementTypes.length) {
-                        return createTupleType(elementTypes);
-                    }
+                    return createTupleType(elementTypes);
                 }
             }
             return createArrayType(elementTypes.length ?
@@ -18493,10 +18484,7 @@ namespace ts {
 
         function checkTupleType(node: TupleTypeNode) {
             // Grammar checking
-            const hasErrorFromDisallowedTrailingComma = checkGrammarForDisallowedTrailingComma(node.elementTypes);
-            if (!hasErrorFromDisallowedTrailingComma && node.elementTypes.length === 0) {
-                grammarErrorOnNode(node, Diagnostics.A_tuple_type_element_list_cannot_be_empty);
-            }
+            checkGrammarForDisallowedTrailingComma(node.elementTypes);
 
             forEach(node.elementTypes, checkSourceElement);
         }

src/compiler/diagnosticMessages.json

@@ -355,10 +355,6 @@
         "category": "Error",
         "code": 1121
     },
-    "A tuple type element list cannot be empty.": {
-        "category": "Error",
-        "code": 1122
-    },
     "Variable declaration list cannot be empty.": {
         "category": "Error",
         "code": 1123

src/compiler/types.ts

@@ -2692,9 +2692,8 @@ namespace ts {
         AllowQualifedNameInPlaceOfIdentifier    = 1 << 11,
         AllowAnonymousIdentifier                = 1 << 13,
         AllowEmptyUnionOrIntersection           = 1 << 14,
-        AllowEmptyTuple                         = 1 << 15,
 
-        IgnoreErrors = AllowThisInObjectLiteral | AllowQualifedNameInPlaceOfIdentifier | AllowAnonymousIdentifier | AllowEmptyUnionOrIntersection | AllowEmptyTuple,
+        IgnoreErrors = AllowThisInObjectLiteral | AllowQualifedNameInPlaceOfIdentifier | AllowAnonymousIdentifier | AllowEmptyUnionOrIntersection,
 
         // State
         InObjectTypeLiteral                     = 1 << 20,

tests/baselines/reference/TupleType3.errors.txt

@@ -0,0 +1,4 @@
+=== tests/cases/conformance/parser/ecmascript5/TupleTypes/TupleType3.ts ===
+var v: []
+>v : Symbol(v, Decl(TupleType3.ts, 0, 3))
+

tests/baselines/reference/TupleType3.symbols

@@ -0,0 +1,4 @@
+=== tests/cases/conformance/parser/ecmascript5/TupleTypes/TupleType3.ts ===
+var v: []
+>v : []
+

tests/baselines/reference/TupleType3.types

@@ -1,5 +1,5 @@
-tests/cases/conformance/expressions/arrayLiterals/arrayLiterals3.ts(10,5): error TS2322: Type 'undefined[]' is not assignable to type '[any, any, any]'.
-  Property '0' is missing in type 'undefined[]'.
+tests/cases/conformance/expressions/arrayLiterals/arrayLiterals3.ts(10,5): error TS2322: Type '[]' is not assignable to type '[any, any, any]'.
+  Property '0' is missing in type '[]'.
 tests/cases/conformance/expressions/arrayLiterals/arrayLiterals3.ts(11,5): error TS2322: Type '["string", number, boolean]' is not assignable to type '[boolean, string, number]'.
   Type '"string"' is not assignable to type 'boolean'.
 tests/cases/conformance/expressions/arrayLiterals/arrayLiterals3.ts(17,5): error TS2322: Type '[number, number, string, boolean]' is not assignable to type '[number, number]'.
@@ -32,8 +32,8 @@ tests/cases/conformance/expressions/arrayLiterals/arrayLiterals3.ts(34,5): error
 
     var a0: [any, any, any] = [];                             // Error
         ~~
-!!! error TS2322: Type 'undefined[]' is not assignable to type '[any, any, any]'.
-!!! error TS2322:   Property '0' is missing in type 'undefined[]'.
+!!! error TS2322: Type '[]' is not assignable to type '[any, any, any]'.
+!!! error TS2322:   Property '0' is missing in type '[]'.
     var a1: [boolean, string, number] = ["string", 1, true];  // Error
         ~~
 !!! error TS2322: Type '["string", number, boolean]' is not assignable to type '[boolean, string, number]'.

tests/baselines/reference/arrayLiterals3.errors.txt

@@ -0,0 +1,8 @@
+=== tests/cases/conformance/types/tuple/emptyTuples/emptyTuplesTypeAssertion01.ts ===
+let x = <[]>[];
+>x : Symbol(x, Decl(emptyTuplesTypeAssertion01.ts, 0, 3))
+
+let y = x[0];
+>y : Symbol(y, Decl(emptyTuplesTypeAssertion01.ts, 1, 3))
+>x : Symbol(x, Decl(emptyTuplesTypeAssertion01.ts, 0, 3))
+

tests/baselines/reference/emptyTuplesTypeAssertion01.errors.txt

@@ -0,0 +1,12 @@
+=== tests/cases/conformance/types/tuple/emptyTuples/emptyTuplesTypeAssertion01.ts ===
+let x = <[]>[];
+>x : []
+><[]>[] : []
+>[] : []
+
+let y = x[0];
+>y : never
+>x[0] : never
+>x : []
+>0 : 0
+