String literal apparent types with specific member types

src/compiler/checker.ts

@@ -6092,6 +6092,27 @@ namespace ts {
             return type.resolvedApparentType || (type.resolvedApparentType = getTypeWithThisArgument(type, type));
         }
 
+        function createStringLiteralApparentProperties(type: StringLiteralType): Type {
+            const propTable = createSymbolTable();
+            const possibleMembers: Type[] = [];
+            for (let i = 0; i < type.value.length; i++) {
+                const propName = "" + i as __String;
+                const prop = createSymbol(SymbolFlags.Property, propName);
+                prop.type = getLiteralType(type.value[i]);
+                propTable.set(propName, prop);
+                possibleMembers.push(prop.type);
+            }
+            if (strictNullChecks) {
+                possibleMembers.push(undefinedType);
+            }
+            copyEntries(resolveStructuredTypeMembers(globalStringType).members, propTable);
+            return createAnonymousType(type.symbol, propTable, emptyArray, emptyArray, /*stringIndexInfo*/ undefined, createIndexInfo(getUnionType(possibleMembers), /*isReadonly*/ true));
+        }
+
+        function getStringLiteralApparentProperties(type: StringLiteralType) {
+            return type.resolvedApparentType || (type.resolvedApparentType = createStringLiteralApparentProperties(type));
+        }
+
         function getResolvedTypeParameterDefault(typeParameter: TypeParameter): Type | undefined {
             if (!typeParameter.default) {
                 if (typeParameter.target) {
@@ -6147,6 +6168,7 @@ namespace ts {
         function getApparentType(type: Type): Type {
             const t = type.flags & TypeFlags.TypeVariable ? getBaseConstraintOfType(type) || emptyObjectType : type;
             return t.flags & TypeFlags.Intersection ? getApparentTypeOfIntersectionType(<IntersectionType>t) :
+                t.flags & TypeFlags.StringLiteral ? getStringLiteralApparentProperties(t as StringLiteralType) :
                 t.flags & TypeFlags.StringLike ? globalStringType :
                 t.flags & TypeFlags.NumberLike ? globalNumberType :
                 t.flags & TypeFlags.BooleanLike ? globalBooleanType :

src/compiler/types.ts

@@ -3347,6 +3347,7 @@ namespace ts {
 
     export interface StringLiteralType extends LiteralType {
         value: string;
+        /*@internal*/ resolvedApparentType?: Type; // Cached generated apparent properties
     }
 
     export interface NumberLiteralType extends LiteralType {

tests/baselines/reference/arrayLiteralContextualLiteralUnion.js

@@ -0,0 +1,5 @@
+//// [arrayLiteralContextualLiteralUnion.ts]
+const x: 'a' | 'a'[] = ['a'];
+
+//// [arrayLiteralContextualLiteralUnion.js]
+var x = ['a'];

tests/baselines/reference/arrayLiteralContextualLiteralUnion.symbols

@@ -0,0 +1,4 @@
+=== tests/cases/compiler/arrayLiteralContextualLiteralUnion.ts ===
+const x: 'a' | 'a'[] = ['a'];
+>x : Symbol(x, Decl(arrayLiteralContextualLiteralUnion.ts, 0, 5))
+

tests/baselines/reference/arrayLiteralContextualLiteralUnion.types

@@ -0,0 +1,6 @@
+=== tests/cases/compiler/arrayLiteralContextualLiteralUnion.ts ===
+const x: 'a' | 'a'[] = ['a'];
+>x : "a" | "a"[]
+>['a'] : ["a"]
+>'a' : "a"
+

tests/baselines/reference/defaultIndexProps2.symbols

@@ -21,4 +21,5 @@ var o = {v:"Yo2"};
 1[0];
 var q = "s"[0];
 >q : Symbol(q, Decl(defaultIndexProps2.ts, 13, 3))
+>0 : Symbol(0)
 

tests/baselines/reference/defaultIndexProps2.types

@@ -28,8 +28,8 @@ var o = {v:"Yo2"};
 >0 : 0
 
 var q = "s"[0];
->q : string
->"s"[0] : string
+>q : "s"
+>"s"[0] : "s"
 >"s" : "s"
 >0 : 0
 

tests/baselines/reference/keyofAndIndexedAccessErrors.types

@@ -30,23 +30,23 @@ type T01 = keyof Object;
 >Object : Object
 
 type T02 = keyof keyof Object;
->T02 : "length" | "toString" | "valueOf" | "charAt" | "charCodeAt" | "concat" | "indexOf" | "lastIndexOf" | "localeCompare" | "match" | "replace" | "search" | "slice" | "split" | "substring" | "toLowerCase" | "toLocaleLowerCase" | "toUpperCase" | "toLocaleUpperCase" | "trim" | "substr"
+>T02 : "length" | "toString" | "valueOf" | "0" | "1" | "2" | "3" | "4" | "5" | "6" | "charAt" | "charCodeAt" | "concat" | "indexOf" | "lastIndexOf" | "localeCompare" | "match" | "replace" | "search" | "slice" | "split" | "substring" | "toLowerCase" | "toLocaleLowerCase" | "toUpperCase" | "toLocaleUpperCase" | "trim" | "substr"
 >Object : Object
 
 type T03 = keyof keyof keyof Object;
->T03 : "length" | "toString" | "valueOf" | "charAt" | "charCodeAt" | "concat" | "indexOf" | "lastIndexOf" | "localeCompare" | "match" | "replace" | "search" | "slice" | "split" | "substring" | "toLowerCase" | "toLocaleLowerCase" | "toUpperCase" | "toLocaleUpperCase" | "trim" | "substr"
+>T03 : "length" | "toString" | "valueOf" | "0" | "charAt" | "charCodeAt" | "concat" | "indexOf" | "lastIndexOf" | "localeCompare" | "match" | "replace" | "search" | "slice" | "split" | "substring" | "toLowerCase" | "toLocaleLowerCase" | "toUpperCase" | "toLocaleUpperCase" | "trim" | "substr"
 >Object : Object
 
 type T04 = keyof keyof keyof keyof Object;
->T04 : "length" | "toString" | "valueOf" | "charAt" | "charCodeAt" | "concat" | "indexOf" | "lastIndexOf" | "localeCompare" | "match" | "replace" | "search" | "slice" | "split" | "substring" | "toLowerCase" | "toLocaleLowerCase" | "toUpperCase" | "toLocaleUpperCase" | "trim" | "substr"
+>T04 : "length" | "toString" | "valueOf" | "0" | "charAt" | "charCodeAt" | "concat" | "indexOf" | "lastIndexOf" | "localeCompare" | "match" | "replace" | "search" | "slice" | "split" | "substring" | "toLowerCase" | "toLocaleLowerCase" | "toUpperCase" | "toLocaleUpperCase" | "trim" | "substr"
 >Object : Object
 
 type T05 = keyof keyof keyof keyof keyof Object;
->T05 : "length" | "toString" | "valueOf" | "charAt" | "charCodeAt" | "concat" | "indexOf" | "lastIndexOf" | "localeCompare" | "match" | "replace" | "search" | "slice" | "split" | "substring" | "toLowerCase" | "toLocaleLowerCase" | "toUpperCase" | "toLocaleUpperCase" | "trim" | "substr"
+>T05 : "length" | "toString" | "valueOf" | "0" | "charAt" | "charCodeAt" | "concat" | "indexOf" | "lastIndexOf" | "localeCompare" | "match" | "replace" | "search" | "slice" | "split" | "substring" | "toLowerCase" | "toLocaleLowerCase" | "toUpperCase" | "toLocaleUpperCase" | "trim" | "substr"
 >Object : Object
 
 type T06 = keyof keyof keyof keyof keyof keyof Object;
->T06 : "length" | "toString" | "valueOf" | "charAt" | "charCodeAt" | "concat" | "indexOf" | "lastIndexOf" | "localeCompare" | "match" | "replace" | "search" | "slice" | "split" | "substring" | "toLowerCase" | "toLocaleLowerCase" | "toUpperCase" | "toLocaleUpperCase" | "trim" | "substr"
+>T06 : "length" | "toString" | "valueOf" | "0" | "charAt" | "charCodeAt" | "concat" | "indexOf" | "lastIndexOf" | "localeCompare" | "match" | "replace" | "search" | "slice" | "split" | "substring" | "toLowerCase" | "toLocaleLowerCase" | "toUpperCase" | "toLocaleUpperCase" | "trim" | "substr"
 >Object : Object
 
 type T10 = Shape["name"];

tests/baselines/reference/stringHasStringValuedNumericIndexer.types

@@ -1,7 +1,7 @@
 === tests/cases/compiler/stringHasStringValuedNumericIndexer.ts ===
 var str: string = ""[0];
 >str : string
->""[0] : string
+>""[0] : never
 >"" : ""
 >0 : 0
 

tests/cases/compiler/arrayLiteralContextualLiteralUnion.ts

@@ -0,0 +1 @@
+const x: 'a' | 'a'[] = ['a'];