Enum unification and improvements (#50528)

* Fix enum classification and evaluation

* References in literal enums must be to other enum members

* Accept new baselines

* Unify enum types + template literal constant expressions

* Accept new baselines

* Fix fourslash tests

* Fix new compiler errors

* Fix lint error

* Accept new API baselines

* Fix test

* Better error message + consistently check enum initializers

* Accept new baselines

Author: ahejlsberg

src/compiler/checker.ts

@@ -2256,7 +2256,7 @@
         "category": "Error",
         "code": 2473
     },
-    "const enum member initializers can only contain literal values and other computed enum values.": {
+    "const enum member initializers must be constant expressions.": {
         "category": "Error",
         "code": 2474
     },
@@ -2480,10 +2480,6 @@
         "category": "Error",
         "code": 2534
     },
-    "Enum type '{0}' has members with initializers that are not literals.": {
-        "category": "Error",
-        "code": 2535
-    },
     "Type '{0}' cannot be used to index type '{1}'.": {
         "category": "Error",
         "code": 2536
@@ -7481,7 +7477,7 @@
         "category": "Error",
         "code": 18032
     },
-    "Only numeric enums can have computed members, but this expression has type '{0}'. If you do not need exhaustiveness checks, consider using an object literal instead.": {
+    "Type '{0}' is not assignable to type '{1}' as required for computed enum member values.": {
         "category": "Error",
         "code": 18033
     },

src/compiler/diagnosticMessages.json

@@ -3922,8 +3922,8 @@ namespace ts {
     // is distinguished from a regular type by a flags value of zero. Incomplete type
     // objects are internal to the getFlowTypeOfReference function and never escape it.
     export interface IncompleteType {
-        flags: TypeFlags;  // No flags set
-        type: Type;        // The type marked incomplete
+        flags: TypeFlags | 0;  // No flags set
+        type: Type;            // The type marked incomplete
     }
 
     export interface AmdDependency {
@@ -5583,7 +5583,7 @@ namespace ts {
         String          = 1 << 2,
         Number          = 1 << 3,
         Boolean         = 1 << 4,
-        Enum            = 1 << 5,
+        Enum            = 1 << 5,   // Numeric computed enum member value
         BigInt          = 1 << 6,
         StringLiteral   = 1 << 7,
         NumberLiteral   = 1 << 8,

src/compiler/types.ts

@@ -82,35 +82,35 @@ declare enum E1 {
 >E1 : E1
 
     x,
->x : E1
+>x : E1.x
 
     y,
->y : E1
+>y : E1.y
 
     z
->z : E1
+>z : E1.z
 }
 
 // Ambient enum with integer literal initializer
 declare enum E2 {
 >E2 : E2
 
     q,
->q : E2
+>q : E2.q
 
     a = 1,
->a : E2
+>a : E2.a
 >1 : 1
 
     b,
->b : E2
+>b : E2.b
 
     c = 2,
->c : E2
+>c : E2.c
 >2 : 2
 
     d
->d : E2
+>d : E2.d
 }
 
 // Ambient enum members are always exported with or without export keyword

tests/baselines/reference/ambientDeclarations.types

@@ -5,28 +5,28 @@ declare enum E {
 >E : E
 
     a = 10,
->a : E
+>a : E.a
 >10 : 10
 
     b = 10 + 1,
->b : E
+>b : E.b
 >10 + 1 : number
 >10 : 10
 >1 : 1
 
     c = b,
->c : E
->b : E
+>c : E.b
+>b : E.b
 
     d = (c) + 1,
->d : E
+>d : E.d
 >(c) + 1 : number
->(c) : E
->c : E
+>(c) : E.b
+>c : E.b
 >1 : 1
 
     e = 10 << 2 * 8,
->e : E
+>e : E.e
 >10 << 2 * 8 : number
 >10 : 10
 >2 * 8 : number

tests/baselines/reference/ambientEnumDeclaration1.types

@@ -6,18 +6,18 @@ declare enum E {
 >E : E
 
     a, // E.a
->a : E
+>a : E.a
 
     b, // E.b
->b : E
+>b : E.b
 }
 
 declare const enum E1 {
 >E1 : E1
 
     a, // E.a = 0
->a : E1
+>a : E1.a
 
     b, // E.b = 1
->b : E1
+>b : E1.b
 }

tests/baselines/reference/ambientEnumDeclaration2.types

@@ -2063,7 +2063,7 @@ declare namespace ts {
     }
     export type FlowType = Type | IncompleteType;
     export interface IncompleteType {
-        flags: TypeFlags;
+        flags: TypeFlags | 0;
         type: Type;
     }
     export interface AmdDependency {

tests/baselines/reference/api/tsserverlibrary.d.ts

@@ -2063,7 +2063,7 @@ declare namespace ts {
     }
     export type FlowType = Type | IncompleteType;
     export interface IncompleteType {
-        flags: TypeFlags;
+        flags: TypeFlags | 0;
         type: Type;
     }
     export interface AmdDependency {

tests/baselines/reference/api/typescript.d.ts

@@ -1,8 +1,8 @@
 tests/cases/conformance/expressions/functions/arrowFunctionContexts.ts(2,1): error TS2410: The 'with' statement is not supported. All symbols in a 'with' block will have type 'any'.
-tests/cases/conformance/expressions/functions/arrowFunctionContexts.ts(30,9): error TS18033: Only numeric enums can have computed members, but this expression has type '() => number'. If you do not need exhaustiveness checks, consider using an object literal instead.
+tests/cases/conformance/expressions/functions/arrowFunctionContexts.ts(30,9): error TS18033: Type '() => number' is not assignable to type 'number' as required for computed enum member values.
 tests/cases/conformance/expressions/functions/arrowFunctionContexts.ts(31,16): error TS2332: 'this' cannot be referenced in current location.
 tests/cases/conformance/expressions/functions/arrowFunctionContexts.ts(43,5): error TS2410: The 'with' statement is not supported. All symbols in a 'with' block will have type 'any'.
-tests/cases/conformance/expressions/functions/arrowFunctionContexts.ts(71,13): error TS18033: Only numeric enums can have computed members, but this expression has type '() => number'. If you do not need exhaustiveness checks, consider using an object literal instead.
+tests/cases/conformance/expressions/functions/arrowFunctionContexts.ts(71,13): error TS18033: Type '() => number' is not assignable to type 'number' as required for computed enum member values.
 tests/cases/conformance/expressions/functions/arrowFunctionContexts.ts(72,20): error TS2332: 'this' cannot be referenced in current location.
 
 
@@ -40,7 +40,7 @@ tests/cases/conformance/expressions/functions/arrowFunctionContexts.ts(72,20): e
     enum E {
         x = () => 4, // Error expected
             ~~~~~~~
-!!! error TS18033: Only numeric enums can have computed members, but this expression has type '() => number'. If you do not need exhaustiveness checks, consider using an object literal instead.
+!!! error TS18033: Type '() => number' is not assignable to type 'number' as required for computed enum member values.
         y = (() => this).length // error, can't use this in enum
                    ~~~~
 !!! error TS2332: 'this' cannot be referenced in current location.
@@ -87,7 +87,7 @@ tests/cases/conformance/expressions/functions/arrowFunctionContexts.ts(72,20): e
         enum E {
             x = () => 4, // Error expected
                 ~~~~~~~
-!!! error TS18033: Only numeric enums can have computed members, but this expression has type '() => number'. If you do not need exhaustiveness checks, consider using an object literal instead.
+!!! error TS18033: Type '() => number' is not assignable to type 'number' as required for computed enum member values.
             y = (() => this).length
                        ~~~~
 !!! error TS2332: 'this' cannot be referenced in current location.

tests/baselines/reference/arrowFunctionContexts.errors.txt

@@ -68,12 +68,12 @@ enum E {
 >E : E
 
     x = () => 4, // Error expected
->x : E
+>x : E.x
 >() => 4 : () => number
 >4 : 4
 
     y = (() => this).length // error, can't use this in enum
->y : E
+>y : E.y
 >(() => this).length : number
 >(() => this) : () => any
 >() => this : () => any
@@ -171,12 +171,12 @@ module M2 {
 >E : E
 
         x = () => 4, // Error expected
->x : E
+>x : E.x
 >() => 4 : () => number
 >4 : 4
 
         y = (() => this).length
->y : E
+>y : E.y
 >(() => this).length : number
 >(() => this) : () => any
 >() => this : () => any

tests/baselines/reference/arrowFunctionContexts.types

@@ -3,19 +3,19 @@ export declare enum require {
 >require : require
 
     _thisVal1,
->_thisVal1 : require
+>_thisVal1 : require._thisVal1
 
     _thisVal2,
->_thisVal2 : require
+>_thisVal2 : require._thisVal2
 }
 export declare enum exports {
 >exports : exports
 
     _thisVal1,
->_thisVal1 : exports
+>_thisVal1 : exports._thisVal1
 
     _thisVal2,
->_thisVal2 : exports
+>_thisVal2 : exports._thisVal2
 }
 declare module m1 {
 >m1 : typeof m1
@@ -24,19 +24,19 @@ declare module m1 {
 >require : require
 
         _thisVal1,
->_thisVal1 : require
+>_thisVal1 : require._thisVal1
 
         _thisVal2,
->_thisVal2 : require
+>_thisVal2 : require._thisVal2
     }
     enum exports {
 >exports : exports
 
         _thisVal1,
->_thisVal1 : exports
+>_thisVal1 : exports._thisVal1
 
         _thisVal2,
->_thisVal2 : exports
+>_thisVal2 : exports._thisVal2
     }
 }
 module m2 {
@@ -46,19 +46,19 @@ module m2 {
 >require : require
 
         _thisVal1,
->_thisVal1 : require
+>_thisVal1 : require._thisVal1
 
         _thisVal2,
->_thisVal2 : require
+>_thisVal2 : require._thisVal2
     }
     export declare enum exports {
 >exports : exports
 
         _thisVal1,
->_thisVal1 : exports
+>_thisVal1 : exports._thisVal1
 
         _thisVal2,
->_thisVal2 : exports
+>_thisVal2 : exports._thisVal2
     }
 }
 
@@ -67,19 +67,19 @@ declare enum require {
 >require : require
 
     _thisVal1,
->_thisVal1 : require
+>_thisVal1 : require._thisVal1
 
     _thisVal2,
->_thisVal2 : require
+>_thisVal2 : require._thisVal2
 }
 declare enum exports {
 >exports : exports
 
     _thisVal1,
->_thisVal1 : exports
+>_thisVal1 : exports._thisVal1
 
     _thisVal2,
->_thisVal2 : exports
+>_thisVal2 : exports._thisVal2
 }
 declare module m3 {
 >m3 : typeof m3
@@ -88,19 +88,19 @@ declare module m3 {
 >require : require
 
         _thisVal1,
->_thisVal1 : require
+>_thisVal1 : require._thisVal1
 
         _thisVal2,
->_thisVal2 : require
+>_thisVal2 : require._thisVal2
     }
     enum exports {
 >exports : exports
 
         _thisVal1,
->_thisVal1 : exports
+>_thisVal1 : exports._thisVal1
 
         _thisVal2,
->_thisVal2 : exports
+>_thisVal2 : exports._thisVal2
     }
 }
 module m4 {
@@ -110,18 +110,18 @@ module m4 {
 >require : require
 
         _thisVal1,
->_thisVal1 : require
+>_thisVal1 : require._thisVal1
 
         _thisVal2,
->_thisVal2 : require
+>_thisVal2 : require._thisVal2
     }
     export declare enum exports {
 >exports : exports
 
         _thisVal1,
->_thisVal1 : exports
+>_thisVal1 : exports._thisVal1
 
         _thisVal2,
->_thisVal2 : exports
+>_thisVal2 : exports._thisVal2
     }
 }

tests/baselines/reference/collisionExportsRequireAndAmbientEnum.types

@@ -14,13 +14,13 @@ declare enum C {
 >C : C
 
     a,
->a : C
+>a : C.a
 
     b,
->b : C
+>b : C.b
 
     c
->c : C
+>c : C.c
 }
 
 // Don't keep this comment.