microsoft · DanielRosenwasser · Oct 10, 2019 · Sep 18, 2019 · Sep 18, 2019 · Sep 18, 2019
diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
@@ -32797,12 +32797,12 @@ namespace ts {
                         typeToString(node.type ? getTypeFromTypeNode(node.type) : anyType));
                 }
 
-                if (type.flags & TypeFlags.Union && allTypesAssignableToKind(type, TypeFlags.StringLiteral, /*strict*/ true)) {
+                if (type.flags & TypeFlags.Union && allTypesAssignableToKind(type, TypeFlags.StringOrNumberLiteral, /*strict*/ true)) {
                     return grammarErrorOnNode(parameter.name,
                         Diagnostics.An_index_signature_parameter_type_cannot_be_a_union_type_Consider_using_a_mapped_object_type_instead);
                 }
 
-                return grammarErrorOnNode(parameter.name, Diagnostics.An_index_signature_parameter_type_must_be_string_or_number);
+                return grammarErrorOnNode(parameter.name, Diagnostics.An_index_signature_parameter_type_must_be_either_string_or_number);
             }
             if (!node.type) {
                 return grammarErrorOnNode(node, Diagnostics.An_index_signature_must_have_a_type_annotation);

diff --git a/src/compiler/diagnosticMessages.json b/src/compiler/diagnosticMessages.json
@@ -71,7 +71,7 @@
         "category": "Error",
         "code": 1022
     },
-    "An index signature parameter type must be 'string' or 'number'.": {
+    "An index signature parameter type must be either 'string' or 'number'.": {
         "category": "Error",
         "code": 1023
     },

diff --git a/tests/baselines/reference/arraySigChecking.errors.txt b/tests/baselines/reference/arraySigChecking.errors.txt
@@ -1,4 +1,4 @@
-tests/cases/compiler/arraySigChecking.ts(11,17): error TS1023: An index signature parameter type must be 'string' or 'number'.
+tests/cases/compiler/arraySigChecking.ts(11,17): error TS1023: An index signature parameter type must be either 'string' or 'number'.
 tests/cases/compiler/arraySigChecking.ts(18,27): error TS2322: Type 'void' is not assignable to type 'string'.
 tests/cases/compiler/arraySigChecking.ts(22,13): error TS2322: Type 'number' is not assignable to type 'number[]'.
 tests/cases/compiler/arraySigChecking.ts(22,16): error TS2322: Type 'number' is not assignable to type 'number[]'.
@@ -17,7 +17,7 @@ tests/cases/compiler/arraySigChecking.ts(22,16): error TS2322: Type 'number' is
 
         var foo: { [index: any]; }; // expect an error here
                     ~~~~~
-!!! error TS1023: An index signature parameter type must be 'string' or 'number'.
+!!! error TS1023: An index signature parameter type must be either 'string' or 'number'.
     }
 
     interface myInt {

diff --git a/tests/baselines/reference/bigintIndex.errors.txt b/tests/baselines/reference/bigintIndex.errors.txt
@@ -1,4 +1,4 @@
-tests/cases/compiler/a.ts(2,6): error TS1023: An index signature parameter type must be 'string' or 'number'.
+tests/cases/compiler/a.ts(2,6): error TS1023: An index signature parameter type must be either 'string' or 'number'.
 tests/cases/compiler/a.ts(8,11): error TS2538: Type '1n' cannot be used as an index type.
 tests/cases/compiler/a.ts(14,1): error TS2322: Type '123n' is not assignable to type 'string | number | symbol'.
 tests/cases/compiler/a.ts(19,12): error TS2538: Type 'bigint' cannot be used as an index type.
@@ -13,7 +13,7 @@ tests/cases/compiler/b.ts(4,12): error TS2464: A computed property name must be
     interface BigIntIndex<E> {
         [index: bigint]: E; // should error
          ~~~~~
-!!! error TS1023: An index signature parameter type must be 'string' or 'number'.
+!!! error TS1023: An index signature parameter type must be either 'string' or 'number'.
     }
 
     const arr: number[] = [1, 2, 3];

diff --git a/tests/baselines/reference/declarationEmitIndexTypeNotFound.errors.txt b/tests/baselines/reference/declarationEmitIndexTypeNotFound.errors.txt
@@ -1,4 +1,4 @@
-tests/cases/compiler/declarationEmitIndexTypeNotFound.ts(2,6): error TS1023: An index signature parameter type must be 'string' or 'number'.
+tests/cases/compiler/declarationEmitIndexTypeNotFound.ts(2,6): error TS1023: An index signature parameter type must be either 'string' or 'number'.
 tests/cases/compiler/declarationEmitIndexTypeNotFound.ts(2,13): error TS2304: Cannot find name 'TypeNotFound'.
 tests/cases/compiler/declarationEmitIndexTypeNotFound.ts(2,13): error TS4092: Parameter 'index' of index signature from exported interface has or is using private name 'TypeNotFound'.
 
@@ -7,7 +7,7 @@ tests/cases/compiler/declarationEmitIndexTypeNotFound.ts(2,13): error TS4092: Pa
     export interface Test {
         [index: TypeNotFound]: any;
          ~~~~~
-!!! error TS1023: An index signature parameter type must be 'string' or 'number'.
+!!! error TS1023: An index signature parameter type must be either 'string' or 'number'.
                 ~~~~~~~~~~~~
 !!! error TS2304: Cannot find name 'TypeNotFound'.
                 ~~~~~~~~~~~~

diff --git a/tests/baselines/reference/genericIndexTypeHasSensibleErrorMessage.errors.txt b/tests/baselines/reference/genericIndexTypeHasSensibleErrorMessage.errors.txt
@@ -1,7 +1,7 @@
-tests/cases/compiler/genericIndexTypeHasSensibleErrorMessage.ts(1,33): error TS1023: An index signature parameter type must be 'string' or 'number'.
+tests/cases/compiler/genericIndexTypeHasSensibleErrorMessage.ts(1,33): error TS1023: An index signature parameter type must be either 'string' or 'number'.
 
 
 ==== tests/cases/compiler/genericIndexTypeHasSensibleErrorMessage.ts (1 errors) ====
     type Wat<T extends string> = { [x: T]: string };
                                     ~
-!!! error TS1023: An index signature parameter type must be 'string' or 'number'.
+!!! error TS1023: An index signature parameter type must be either 'string' or 'number'.
diff --git a/tests/baselines/reference/genericTypeReferenceWithoutTypeArgument.d.errors.txt b/tests/baselines/reference/genericTypeReferenceWithoutTypeArgument.d.errors.txt
@@ -2,7 +2,7 @@ tests/cases/conformance/types/specifyingTypes/typeReferences/genericTypeReferenc
 tests/cases/conformance/types/specifyingTypes/typeReferences/genericTypeReferenceWithoutTypeArgument.d.ts(10,21): error TS2314: Generic type 'C<T>' requires 1 type argument(s).
 tests/cases/conformance/types/specifyingTypes/typeReferences/genericTypeReferenceWithoutTypeArgument.d.ts(11,22): error TS2314: Generic type 'C<T>' requires 1 type argument(s).
 tests/cases/conformance/types/specifyingTypes/typeReferences/genericTypeReferenceWithoutTypeArgument.d.ts(11,26): error TS2314: Generic type 'C<T>' requires 1 type argument(s).
-tests/cases/conformance/types/specifyingTypes/typeReferences/genericTypeReferenceWithoutTypeArgument.d.ts(12,19): error TS1023: An index signature parameter type must be 'string' or 'number'.
+tests/cases/conformance/types/specifyingTypes/typeReferences/genericTypeReferenceWithoutTypeArgument.d.ts(12,19): error TS1023: An index signature parameter type must be either 'string' or 'number'.
 tests/cases/conformance/types/specifyingTypes/typeReferences/genericTypeReferenceWithoutTypeArgument.d.ts(12,22): error TS2314: Generic type 'C<T>' requires 1 type argument(s).
 tests/cases/conformance/types/specifyingTypes/typeReferences/genericTypeReferenceWithoutTypeArgument.d.ts(12,26): error TS2314: Generic type 'C<T>' requires 1 type argument(s).
 tests/cases/conformance/types/specifyingTypes/typeReferences/genericTypeReferenceWithoutTypeArgument.d.ts(14,23): error TS2314: Generic type 'C<T>' requires 1 type argument(s).
@@ -36,7 +36,7 @@ tests/cases/conformance/types/specifyingTypes/typeReferences/genericTypeReferenc
 !!! error TS2314: Generic type 'C<T>' requires 1 type argument(s).
     declare var d: { [x: C]: C };
                       ~
-!!! error TS1023: An index signature parameter type must be 'string' or 'number'.
+!!! error TS1023: An index signature parameter type must be either 'string' or 'number'.
                          ~
 !!! error TS2314: Generic type 'C<T>' requires 1 type argument(s).
                              ~

diff --git a/tests/baselines/reference/genericTypeReferenceWithoutTypeArgument.errors.txt b/tests/baselines/reference/genericTypeReferenceWithoutTypeArgument.errors.txt
@@ -2,7 +2,7 @@ tests/cases/conformance/types/specifyingTypes/typeReferences/genericTypeReferenc
 tests/cases/conformance/types/specifyingTypes/typeReferences/genericTypeReferenceWithoutTypeArgument.ts(10,13): error TS2314: Generic type 'C<T>' requires 1 type argument(s).
 tests/cases/conformance/types/specifyingTypes/typeReferences/genericTypeReferenceWithoutTypeArgument.ts(11,14): error TS2314: Generic type 'C<T>' requires 1 type argument(s).
 tests/cases/conformance/types/specifyingTypes/typeReferences/genericTypeReferenceWithoutTypeArgument.ts(11,18): error TS2314: Generic type 'C<T>' requires 1 type argument(s).
-tests/cases/conformance/types/specifyingTypes/typeReferences/genericTypeReferenceWithoutTypeArgument.ts(12,11): error TS1023: An index signature parameter type must be 'string' or 'number'.
+tests/cases/conformance/types/specifyingTypes/typeReferences/genericTypeReferenceWithoutTypeArgument.ts(12,11): error TS1023: An index signature parameter type must be either 'string' or 'number'.
 tests/cases/conformance/types/specifyingTypes/typeReferences/genericTypeReferenceWithoutTypeArgument.ts(12,14): error TS2314: Generic type 'C<T>' requires 1 type argument(s).
 tests/cases/conformance/types/specifyingTypes/typeReferences/genericTypeReferenceWithoutTypeArgument.ts(12,18): error TS2314: Generic type 'C<T>' requires 1 type argument(s).
 tests/cases/conformance/types/specifyingTypes/typeReferences/genericTypeReferenceWithoutTypeArgument.ts(14,13): error TS2314: Generic type 'C<T>' requires 1 type argument(s).
@@ -46,7 +46,7 @@ tests/cases/conformance/types/specifyingTypes/typeReferences/genericTypeReferenc
 !!! error TS2314: Generic type 'C<T>' requires 1 type argument(s).
     var d: { [x: C]: C };
               ~
-!!! error TS1023: An index signature parameter type must be 'string' or 'number'.
+!!! error TS1023: An index signature parameter type must be either 'string' or 'number'.
                  ~
 !!! error TS2314: Generic type 'C<T>' requires 1 type argument(s).
                      ~

diff --git a/tests/baselines/reference/genericTypeReferenceWithoutTypeArgument2.errors.txt b/tests/baselines/reference/genericTypeReferenceWithoutTypeArgument2.errors.txt
@@ -2,7 +2,7 @@ tests/cases/conformance/types/specifyingTypes/typeReferences/genericTypeReferenc
 tests/cases/conformance/types/specifyingTypes/typeReferences/genericTypeReferenceWithoutTypeArgument2.ts(10,13): error TS2314: Generic type 'I<T>' requires 1 type argument(s).
 tests/cases/conformance/types/specifyingTypes/typeReferences/genericTypeReferenceWithoutTypeArgument2.ts(11,14): error TS2314: Generic type 'I<T>' requires 1 type argument(s).
 tests/cases/conformance/types/specifyingTypes/typeReferences/genericTypeReferenceWithoutTypeArgument2.ts(11,18): error TS2314: Generic type 'I<T>' requires 1 type argument(s).
-tests/cases/conformance/types/specifyingTypes/typeReferences/genericTypeReferenceWithoutTypeArgument2.ts(12,11): error TS1023: An index signature parameter type must be 'string' or 'number'.
+tests/cases/conformance/types/specifyingTypes/typeReferences/genericTypeReferenceWithoutTypeArgument2.ts(12,11): error TS1023: An index signature parameter type must be either 'string' or 'number'.
 tests/cases/conformance/types/specifyingTypes/typeReferences/genericTypeReferenceWithoutTypeArgument2.ts(12,14): error TS2314: Generic type 'I<T>' requires 1 type argument(s).
 tests/cases/conformance/types/specifyingTypes/typeReferences/genericTypeReferenceWithoutTypeArgument2.ts(12,18): error TS2314: Generic type 'I<T>' requires 1 type argument(s).
 tests/cases/conformance/types/specifyingTypes/typeReferences/genericTypeReferenceWithoutTypeArgument2.ts(14,13): error TS2314: Generic type 'I<T>' requires 1 type argument(s).
@@ -46,7 +46,7 @@ tests/cases/conformance/types/specifyingTypes/typeReferences/genericTypeReferenc
 !!! error TS2314: Generic type 'I<T>' requires 1 type argument(s).
     var d: { [x: I]: I };
               ~
-!!! error TS1023: An index signature parameter type must be 'string' or 'number'.
+!!! error TS1023: An index signature parameter type must be either 'string' or 'number'.
                  ~
 !!! error TS2314: Generic type 'I<T>' requires 1 type argument(s).
                      ~

diff --git a/tests/baselines/reference/genericTypeReferenceWithoutTypeArgument3.errors.txt b/tests/baselines/reference/genericTypeReferenceWithoutTypeArgument3.errors.txt
@@ -2,7 +2,7 @@ tests/cases/conformance/types/specifyingTypes/typeReferences/genericTypeReferenc
 tests/cases/conformance/types/specifyingTypes/typeReferences/genericTypeReferenceWithoutTypeArgument3.ts(10,21): error TS2314: Generic type 'C<T>' requires 1 type argument(s).
 tests/cases/conformance/types/specifyingTypes/typeReferences/genericTypeReferenceWithoutTypeArgument3.ts(11,22): error TS2314: Generic type 'C<T>' requires 1 type argument(s).
 tests/cases/conformance/types/specifyingTypes/typeReferences/genericTypeReferenceWithoutTypeArgument3.ts(11,26): error TS2314: Generic type 'C<T>' requires 1 type argument(s).
-tests/cases/conformance/types/specifyingTypes/typeReferences/genericTypeReferenceWithoutTypeArgument3.ts(12,19): error TS1023: An index signature parameter type must be 'string' or 'number'.
+tests/cases/conformance/types/specifyingTypes/typeReferences/genericTypeReferenceWithoutTypeArgument3.ts(12,19): error TS1023: An index signature parameter type must be either 'string' or 'number'.
 tests/cases/conformance/types/specifyingTypes/typeReferences/genericTypeReferenceWithoutTypeArgument3.ts(12,22): error TS2314: Generic type 'C<T>' requires 1 type argument(s).
 tests/cases/conformance/types/specifyingTypes/typeReferences/genericTypeReferenceWithoutTypeArgument3.ts(12,26): error TS2314: Generic type 'C<T>' requires 1 type argument(s).
 tests/cases/conformance/types/specifyingTypes/typeReferences/genericTypeReferenceWithoutTypeArgument3.ts(14,23): error TS2314: Generic type 'C<T>' requires 1 type argument(s).
@@ -36,7 +36,7 @@ tests/cases/conformance/types/specifyingTypes/typeReferences/genericTypeReferenc
 !!! error TS2314: Generic type 'C<T>' requires 1 type argument(s).
     declare var d: { [x: C]: C };
                       ~
-!!! error TS1023: An index signature parameter type must be 'string' or 'number'.
+!!! error TS1023: An index signature parameter type must be either 'string' or 'number'.
                          ~
 !!! error TS2314: Generic type 'C<T>' requires 1 type argument(s).
                              ~

diff --git a/tests/baselines/reference/indexTypeCheck.errors.txt b/tests/baselines/reference/indexTypeCheck.errors.txt
@@ -4,7 +4,7 @@ tests/cases/compiler/indexTypeCheck.ts(17,2): error TS2413: Numeric index type '
 tests/cases/compiler/indexTypeCheck.ts(22,2): error TS2413: Numeric index type 'Orange' is not assignable to string index type 'Yellow'.
 tests/cases/compiler/indexTypeCheck.ts(27,2): error TS2413: Numeric index type 'number' is not assignable to string index type 'string'.
 tests/cases/compiler/indexTypeCheck.ts(32,3): error TS1096: An index signature must have exactly one parameter.
-tests/cases/compiler/indexTypeCheck.ts(36,3): error TS1023: An index signature parameter type must be 'string' or 'number'.
+tests/cases/compiler/indexTypeCheck.ts(36,3): error TS1023: An index signature parameter type must be either 'string' or 'number'.
 tests/cases/compiler/indexTypeCheck.ts(51,8): error TS2538: Type 'Blue' cannot be used as an index type.
 
 
@@ -58,7 +58,7 @@ tests/cases/compiler/indexTypeCheck.ts(51,8): error TS2538: Type 'Blue' cannot b
     interface Magenta {
     	[p:Purple]; // error
     	 ~
-!!! error TS1023: An index signature parameter type must be 'string' or 'number'.
+!!! error TS1023: An index signature parameter type must be either 'string' or 'number'.
     }
 
     var yellow: Yellow;

diff --git a/tests/baselines/reference/indexerConstraints2.errors.txt b/tests/baselines/reference/indexerConstraints2.errors.txt
@@ -3,11 +3,11 @@ tests/cases/compiler/indexerConstraints2.ts(17,5): error TS2413: Numeric index t
 tests/cases/compiler/indexerConstraints2.ts(26,5): error TS2413: Numeric index type 'A' is not assignable to string index type 'B'.
 tests/cases/compiler/indexerConstraints2.ts(34,6): error TS1336: An index signature parameter type cannot be a type alias. Consider writing '[n: number]: A' instead.
 tests/cases/compiler/indexerConstraints2.ts(40,6): error TS1336: An index signature parameter type cannot be a type alias. Consider writing '[s: string]: A' instead.
-tests/cases/compiler/indexerConstraints2.ts(46,6): error TS1023: An index signature parameter type must be 'string' or 'number'.
+tests/cases/compiler/indexerConstraints2.ts(46,6): error TS1023: An index signature parameter type must be either 'string' or 'number'.
 tests/cases/compiler/indexerConstraints2.ts(52,6): error TS1337: An index signature parameter type cannot be a union type. Consider using a mapped object type instead.
-tests/cases/compiler/indexerConstraints2.ts(58,6): error TS1023: An index signature parameter type must be 'string' or 'number'.
-tests/cases/compiler/indexerConstraints2.ts(64,6): error TS1023: An index signature parameter type must be 'string' or 'number'.
-tests/cases/compiler/indexerConstraints2.ts(70,6): error TS1023: An index signature parameter type must be 'string' or 'number'.
+tests/cases/compiler/indexerConstraints2.ts(58,6): error TS1023: An index signature parameter type must be either 'string' or 'number'.
+tests/cases/compiler/indexerConstraints2.ts(64,6): error TS1337: An index signature parameter type cannot be a union type. Consider using a mapped object type instead.
+tests/cases/compiler/indexerConstraints2.ts(70,6): error TS1337: An index signature parameter type cannot be a union type. Consider using a mapped object type instead.
 tests/cases/compiler/indexerConstraints2.ts(74,6): error TS1337: An index signature parameter type cannot be a union type. Consider using a mapped object type instead.
 tests/cases/compiler/indexerConstraints2.ts(79,6): error TS1336: An index signature parameter type cannot be a type alias. Consider writing '[key: string]: any' instead.
 
@@ -70,7 +70,7 @@ tests/cases/compiler/indexerConstraints2.ts(79,6): error TS1336: An index signat
     interface N {
         [b: AliasedBoolean]: A;
          ~
-!!! error TS1023: An index signature parameter type must be 'string' or 'number'.
+!!! error TS1023: An index signature parameter type must be either 'string' or 'number'.
     }
 
     type IndexableUnion = "foo" | "bar";
@@ -86,23 +86,23 @@ tests/cases/compiler/indexerConstraints2.ts(79,6): error TS1336: An index signat
     interface P {
         [u: NonIndexableUnion]: A;
          ~
-!!! error TS1023: An index signature parameter type must be 'string' or 'number'.
+!!! error TS1023: An index signature parameter type must be either 'string' or 'number'.
     }
 
     type NonIndexableUnion2 = string | number;
 
     interface Q {
         [u: NonIndexableUnion2]: A;
          ~
-!!! error TS1023: An index signature parameter type must be 'string' or 'number'.
+!!! error TS1337: An index signature parameter type cannot be a union type. Consider using a mapped object type instead.
     }
 
     type NonIndexableUnion3 = "foo" | 42;
 
     interface R {
         [u: NonIndexableUnion3]: A;
          ~
-!!! error TS1023: An index signature parameter type must be 'string' or 'number'.
+!!! error TS1337: An index signature parameter type cannot be a union type. Consider using a mapped object type instead.
     }
 
     interface S {

diff --git a/tests/baselines/reference/parserES5SymbolIndexer1.errors.txt b/tests/baselines/reference/parserES5SymbolIndexer1.errors.txt
@@ -1,9 +1,9 @@
-tests/cases/conformance/parser/ecmascript5/Symbols/parserES5SymbolIndexer1.ts(2,6): error TS1023: An index signature parameter type must be 'string' or 'number'.
+tests/cases/conformance/parser/ecmascript5/Symbols/parserES5SymbolIndexer1.ts(2,6): error TS1023: An index signature parameter type must be either 'string' or 'number'.
 
 
 ==== tests/cases/conformance/parser/ecmascript5/Symbols/parserES5SymbolIndexer1.ts (1 errors) ====
     interface I {
         [s: symbol]: string;
          ~
-!!! error TS1023: An index signature parameter type must be 'string' or 'number'.
+!!! error TS1023: An index signature parameter type must be either 'string' or 'number'.
     }
diff --git a/tests/baselines/reference/parserES5SymbolIndexer2.errors.txt b/tests/baselines/reference/parserES5SymbolIndexer2.errors.txt
@@ -1,9 +1,9 @@
-tests/cases/conformance/parser/ecmascript5/Symbols/parserES5SymbolIndexer2.ts(2,6): error TS1023: An index signature parameter type must be 'string' or 'number'.
+tests/cases/conformance/parser/ecmascript5/Symbols/parserES5SymbolIndexer2.ts(2,6): error TS1023: An index signature parameter type must be either 'string' or 'number'.
 
 
 ==== tests/cases/conformance/parser/ecmascript5/Symbols/parserES5SymbolIndexer2.ts (1 errors) ====
     class C {
         [s: symbol]: string;
          ~
-!!! error TS1023: An index signature parameter type must be 'string' or 'number'.
+!!! error TS1023: An index signature parameter type must be either 'string' or 'number'.
     }