Narrow string and number types in literal equality checks

src/compiler/checker.ts

@@ -8461,6 +8461,28 @@ namespace ts {
             return f(type) ? type : neverType;
         }
 
+        function mapType(type: Type, f: (t: Type) => Type): Type {
+            return type.flags & TypeFlags.Union ? getUnionType(map((<UnionType>type).types, f)) : f(type);
+        }
+
+        function extractTypesOfKind(type: Type, kind: TypeFlags) {
+            return filterType(type, t => (t.flags & kind) !== 0);
+        }
+
+        // Return a new type in which occurrences of the string and number primitive types in
+        // typeWithPrimitives have been replaced with occurrences of string literals and numeric
+        // literals in typeWithLiterals, respectively.
+        function replacePrimitivesWithLiterals(typeWithPrimitives: Type, typeWithLiterals: Type) {
+            if (isTypeSubsetOf(stringType, typeWithPrimitives) && maybeTypeOfKind(typeWithLiterals, TypeFlags.StringLiteral) ||
+                isTypeSubsetOf(numberType, typeWithPrimitives) && maybeTypeOfKind(typeWithLiterals, TypeFlags.NumberLiteral)) {
+                return mapType(typeWithPrimitives, t =>
+                    t.flags & TypeFlags.String ? extractTypesOfKind(typeWithLiterals, TypeFlags.String | TypeFlags.StringLiteral) :
+                    t.flags & TypeFlags.Number ? extractTypesOfKind(typeWithLiterals, TypeFlags.Number | TypeFlags.NumberLiteral) :
+                    t);
+            }
+            return typeWithPrimitives;
+        }
+
         function isIncomplete(flowType: FlowType) {
             return flowType.flags === 0;
         }
@@ -8796,7 +8818,7 @@ namespace ts {
                 }
                 if (assumeTrue) {
                     const narrowedType = filterType(type, t => areTypesComparable(t, valueType));
-                    return narrowedType.flags & TypeFlags.Never ? type : narrowedType;
+                    return narrowedType.flags & TypeFlags.Never ? type : replacePrimitivesWithLiterals(narrowedType, valueType);
                 }
                 if (isUnitType(valueType)) {
                     const regularType = getRegularTypeOfLiteralType(valueType);
@@ -8843,7 +8865,9 @@ namespace ts {
                 const clauseTypes = switchTypes.slice(clauseStart, clauseEnd);
                 const hasDefaultClause = clauseStart === clauseEnd || contains(clauseTypes, neverType);
                 const discriminantType = getUnionType(clauseTypes);
-                const caseType = discriminantType.flags & TypeFlags.Never ? neverType : filterType(type, t => isTypeComparableTo(discriminantType, t));
+                const caseType =
+                    discriminantType.flags & TypeFlags.Never ? neverType :
+                    replacePrimitivesWithLiterals(filterType(type, t => isTypeComparableTo(discriminantType, t)), discriminantType);
                 if (!hasDefaultClause) {
                     return caseType;
                 }

src/compiler/scanner.ts

@@ -1190,7 +1190,7 @@ namespace ts {
         }
 
         function scanBinaryOrOctalDigits(base: number): number {
-            Debug.assert(base !== 2 || base !== 8, "Expected either base 2 or base 8");
+            Debug.assert(base === 2 || base === 8, "Expected either base 2 or base 8");
 
             let value = 0;
             // For counting number of digits; Valid binaryIntegerLiteral must have at least one binary digit following B or b.

src/compiler/types.ts

@@ -2644,7 +2644,7 @@ namespace ts {
         // 'Narrowable' types are types where narrowing actually narrows.
         // This *should* be every type other than null, undefined, void, and never
         Narrowable = Any | StructuredType | TypeParameter | StringLike | NumberLike | BooleanLike | ESSymbol,
-        NotUnionOrUnit = Any | String | Number | ESSymbol | ObjectType,
+        NotUnionOrUnit = Any | ESSymbol | ObjectType,
         /* @internal */
         RequiresWidening = ContainsWideningType | ContainsObjectLiteral,
         /* @internal */

tests/baselines/reference/declFileTypeAnnotationStringLiteral.types

@@ -23,7 +23,7 @@ function foo(a: string): string | number {
 
         return a.length;
 >a.length : number
->a : string
+>a : "hello"
 >length : number
     }
 

tests/baselines/reference/literalTypes1.types

@@ -129,7 +129,7 @@ function f4(x: 0 | 1 | true | string) {
 >"def" : "def"
 
             x;
->x : string
+>x : "abc" | "def"
 
             break;
         case null:
@@ -163,7 +163,7 @@ function f5(x: string | number | boolean) {
 >"abc" : "abc"
 
             x;
->x : string
+>x : "abc"
 
             break;
         case 0:
@@ -173,7 +173,7 @@ function f5(x: string | number | boolean) {
 >1 : 1
 
             x;
->x : number
+>x : 0 | 1
 
             break;
         case true:
@@ -190,7 +190,7 @@ function f5(x: string | number | boolean) {
 >123 : 123
 
             x;
->x : string | number
+>x : "hello" | 123
 
             break;
         default:

tests/baselines/reference/literalTypes3.js

@@ -0,0 +1,125 @@
+//// [literalTypes3.ts]
+
+function f1(s: string) {
+    if (s === "foo") {
+        s;  // "foo"
+    }
+    if (s === "foo" || s === "bar") {
+        s;  // "foo" | "bar"
+    }
+}
+
+function f2(s: string) {
+    switch (s) {
+        case "foo":
+        case "bar":
+            s;  // "foo" | "bar"
+        case "baz":
+            s;  // "foo" | "bar" | "baz"
+            break;
+        default:
+            s;  // string
+    }
+}
+
+function f3(s: string) {
+    return s === "foo" || s === "bar" ? s : undefined;  // "foo" | "bar" | undefined
+}
+
+function f4(x: number) {
+    if (x === 1 || x === 2) {
+        return x;  // 1 | 2
+    }
+    throw new Error();
+}
+
+function f5(x: number, y: 1 | 2) {
+    if (x === 0 || x === y) {
+        x;  // 0 | 1 | 2
+    }
+}
+
+function f6(x: number, y: 1 | 2) {
+    if (y === x || 0 === x) {
+        x;  // 0 | 1 | 2
+    }
+}
+
+function f7(x: number | "foo" | "bar", y: 1 | 2 | string) {
+    if (x === y) {
+        x;  // "foo" | "bar" | 1 | 2
+    }
+}
+
+function f8(x: number | "foo" | "bar") {
+    switch (x) {
+        case 1:
+        case 2:
+            x;  // 1 | 2
+            break;
+        case "foo":
+            x;  // "foo"
+            break;
+        default:
+            x;  // number | "bar"
+    }
+}
+
+//// [literalTypes3.js]
+function f1(s) {
+    if (s === "foo") {
+        s; // "foo"
+    }
+    if (s === "foo" || s === "bar") {
+        s; // "foo" | "bar"
+    }
+}
+function f2(s) {
+    switch (s) {
+        case "foo":
+        case "bar":
+            s; // "foo" | "bar"
+        case "baz":
+            s; // "foo" | "bar" | "baz"
+            break;
+        default:
+            s; // string
+    }
+}
+function f3(s) {
+    return s === "foo" || s === "bar" ? s : undefined; // "foo" | "bar" | undefined
+}
+function f4(x) {
+    if (x === 1 || x === 2) {
+        return x; // 1 | 2
+    }
+    throw new Error();
+}
+function f5(x, y) {
+    if (x === 0 || x === y) {
+        x; // 0 | 1 | 2
+    }
+}
+function f6(x, y) {
+    if (y === x || 0 === x) {
+        x; // 0 | 1 | 2
+    }
+}
+function f7(x, y) {
+    if (x === y) {
+        x; // "foo" | "bar" | 1 | 2
+    }
+}
+function f8(x) {
+    switch (x) {
+        case 1:
+        case 2:
+            x; // 1 | 2
+            break;
+        case "foo":
+            x; // "foo"
+            break;
+        default:
+            x; // number | "bar"
+    }
+}

tests/baselines/reference/literalTypes3.symbols

@@ -0,0 +1,137 @@
+=== tests/cases/conformance/types/literal/literalTypes3.ts ===
+
+function f1(s: string) {
+>f1 : Symbol(f1, Decl(literalTypes3.ts, 0, 0))
+>s : Symbol(s, Decl(literalTypes3.ts, 1, 12))
+
+    if (s === "foo") {
+>s : Symbol(s, Decl(literalTypes3.ts, 1, 12))
+
+        s;  // "foo"
+>s : Symbol(s, Decl(literalTypes3.ts, 1, 12))
+    }
+    if (s === "foo" || s === "bar") {
+>s : Symbol(s, Decl(literalTypes3.ts, 1, 12))
+>s : Symbol(s, Decl(literalTypes3.ts, 1, 12))
+
+        s;  // "foo" | "bar"
+>s : Symbol(s, Decl(literalTypes3.ts, 1, 12))
+    }
+}
+
+function f2(s: string) {
+>f2 : Symbol(f2, Decl(literalTypes3.ts, 8, 1))
+>s : Symbol(s, Decl(literalTypes3.ts, 10, 12))
+
+    switch (s) {
+>s : Symbol(s, Decl(literalTypes3.ts, 10, 12))
+
+        case "foo":
+        case "bar":
+            s;  // "foo" | "bar"
+>s : Symbol(s, Decl(literalTypes3.ts, 10, 12))
+
+        case "baz":
+            s;  // "foo" | "bar" | "baz"
+>s : Symbol(s, Decl(literalTypes3.ts, 10, 12))
+
+            break;
+        default:
+            s;  // string
+>s : Symbol(s, Decl(literalTypes3.ts, 10, 12))
+    }
+}
+
+function f3(s: string) {
+>f3 : Symbol(f3, Decl(literalTypes3.ts, 21, 1))
+>s : Symbol(s, Decl(literalTypes3.ts, 23, 12))
+
+    return s === "foo" || s === "bar" ? s : undefined;  // "foo" | "bar" | undefined
+>s : Symbol(s, Decl(literalTypes3.ts, 23, 12))
+>s : Symbol(s, Decl(literalTypes3.ts, 23, 12))
+>s : Symbol(s, Decl(literalTypes3.ts, 23, 12))
+>undefined : Symbol(undefined)
+}
+
+function f4(x: number) {
+>f4 : Symbol(f4, Decl(literalTypes3.ts, 25, 1))
+>x : Symbol(x, Decl(literalTypes3.ts, 27, 12))
+
+    if (x === 1 || x === 2) {
+>x : Symbol(x, Decl(literalTypes3.ts, 27, 12))
+>x : Symbol(x, Decl(literalTypes3.ts, 27, 12))
+
+        return x;  // 1 | 2
+>x : Symbol(x, Decl(literalTypes3.ts, 27, 12))
+    }
+    throw new Error();
+>Error : Symbol(Error, Decl(lib.d.ts, --, --), Decl(lib.d.ts, --, --))
+}
+
+function f5(x: number, y: 1 | 2) {
+>f5 : Symbol(f5, Decl(literalTypes3.ts, 32, 1))
+>x : Symbol(x, Decl(literalTypes3.ts, 34, 12))
+>y : Symbol(y, Decl(literalTypes3.ts, 34, 22))
+
+    if (x === 0 || x === y) {
+>x : Symbol(x, Decl(literalTypes3.ts, 34, 12))
+>x : Symbol(x, Decl(literalTypes3.ts, 34, 12))
+>y : Symbol(y, Decl(literalTypes3.ts, 34, 22))
+
+        x;  // 0 | 1 | 2
+>x : Symbol(x, Decl(literalTypes3.ts, 34, 12))
+    }
+}
+
+function f6(x: number, y: 1 | 2) {
+>f6 : Symbol(f6, Decl(literalTypes3.ts, 38, 1))
+>x : Symbol(x, Decl(literalTypes3.ts, 40, 12))
+>y : Symbol(y, Decl(literalTypes3.ts, 40, 22))
+
+    if (y === x || 0 === x) {
+>y : Symbol(y, Decl(literalTypes3.ts, 40, 22))
+>x : Symbol(x, Decl(literalTypes3.ts, 40, 12))
+>x : Symbol(x, Decl(literalTypes3.ts, 40, 12))
+
+        x;  // 0 | 1 | 2
+>x : Symbol(x, Decl(literalTypes3.ts, 40, 12))
+    }
+}
+
+function f7(x: number | "foo" | "bar", y: 1 | 2 | string) {
+>f7 : Symbol(f7, Decl(literalTypes3.ts, 44, 1))
+>x : Symbol(x, Decl(literalTypes3.ts, 46, 12))
+>y : Symbol(y, Decl(literalTypes3.ts, 46, 38))
+
+    if (x === y) {
+>x : Symbol(x, Decl(literalTypes3.ts, 46, 12))
+>y : Symbol(y, Decl(literalTypes3.ts, 46, 38))
+
+        x;  // "foo" | "bar" | 1 | 2
+>x : Symbol(x, Decl(literalTypes3.ts, 46, 12))
+    }
+}
+
+function f8(x: number | "foo" | "bar") {
+>f8 : Symbol(f8, Decl(literalTypes3.ts, 50, 1))
+>x : Symbol(x, Decl(literalTypes3.ts, 52, 12))
+
+    switch (x) {
+>x : Symbol(x, Decl(literalTypes3.ts, 52, 12))
+
+        case 1:
+        case 2:
+            x;  // 1 | 2
+>x : Symbol(x, Decl(literalTypes3.ts, 52, 12))
+
+            break;
+        case "foo":
+            x;  // "foo"
+>x : Symbol(x, Decl(literalTypes3.ts, 52, 12))
+
+            break;
+        default:
+            x;  // number | "bar"
+>x : Symbol(x, Decl(literalTypes3.ts, 52, 12))
+    }
+}