Add error message

src/compiler/checker.ts

@@ -6267,6 +6267,18 @@ namespace ts {
                 reportError(message, sourceType, targetType);
             }
 
+            function tryElaborateErrorsForPrimitivesAndObjects(source: Type, target: Type) {
+                const sourceType = typeToString(source);
+                const targetType = typeToString(target);
+
+                if ((globalStringType === source && stringType === target) ||
+                    (globalNumberType === source && numberType === target) ||
+                    (globalBooleanType === source && booleanType === target) ||
+                    (getGlobalESSymbolType() === source && esSymbolType === target)) {
+                        reportError(Diagnostics._0_is_a_primitive_but_1_is_a_wrapper_object_Prefer_using_0_when_possible, targetType, sourceType);
+                }
+            }
+
             // Compare two types and return
             // Ternary.True if they are related with no assumptions,
             // Ternary.Maybe if they are related with assumptions of other relationships, or
@@ -6390,6 +6402,9 @@ namespace ts {
                 }
 
                 if (reportErrors) {
+                    if (source.flags & TypeFlags.ObjectType && target.flags & TypeFlags.Primitive) {
+                        tryElaborateErrorsForPrimitivesAndObjects(source, target);
+                    }
                     reportRelationError(headMessage, source, target);
                 }
                 return Ternary.False;

src/compiler/diagnosticMessages.json

@@ -1955,6 +1955,10 @@
         "category": "Error",
         "code": 2691
     },
+    "'{0}' is a primitive, but '{1}' is a wrapper object. Prefer using '{0}' when possible.": {
+        "category": "Error",
+        "code": 2692
+    },
     "Import declaration '{0}' is using private name '{1}'.": {
         "category": "Error",
         "code": 4000

tests/baselines/reference/apparentTypeSubtyping.errors.txt

@@ -1,6 +1,7 @@
 tests/cases/conformance/types/typeRelationships/apparentType/apparentTypeSubtyping.ts(9,7): error TS2415: Class 'Derived<U>' incorrectly extends base class 'Base<string>'.
   Types of property 'x' are incompatible.
     Type 'String' is not assignable to type 'string'.
+      'string' is a primitive, but 'String' is a wrapper object. Prefer using 'string' when possible.
 
 
 ==== tests/cases/conformance/types/typeRelationships/apparentType/apparentTypeSubtyping.ts (1 errors) ====
@@ -17,6 +18,7 @@ tests/cases/conformance/types/typeRelationships/apparentType/apparentTypeSubtypi
 !!! error TS2415: Class 'Derived<U>' incorrectly extends base class 'Base<string>'.
 !!! error TS2415:   Types of property 'x' are incompatible.
 !!! error TS2415:     Type 'String' is not assignable to type 'string'.
+!!! error TS2415:       'string' is a primitive, but 'String' is a wrapper object. Prefer using 'string' when possible.
         x: String;
     }
 

tests/baselines/reference/apparentTypeSupertype.errors.txt

@@ -2,6 +2,7 @@ tests/cases/conformance/types/typeRelationships/apparentType/apparentTypeSuperty
   Types of property 'x' are incompatible.
     Type 'U' is not assignable to type 'string'.
       Type 'String' is not assignable to type 'string'.
+        'string' is a primitive, but 'String' is a wrapper object. Prefer using 'string' when possible.
 
 
 ==== tests/cases/conformance/types/typeRelationships/apparentType/apparentTypeSupertype.ts (1 errors) ====
@@ -19,5 +20,6 @@ tests/cases/conformance/types/typeRelationships/apparentType/apparentTypeSuperty
 !!! error TS2415:   Types of property 'x' are incompatible.
 !!! error TS2415:     Type 'U' is not assignable to type 'string'.
 !!! error TS2415:       Type 'String' is not assignable to type 'string'.
+!!! error TS2415:         'string' is a primitive, but 'String' is a wrapper object. Prefer using 'string' when possible.
         x: U;
     }

tests/baselines/reference/arrayLiterals3.errors.txt

@@ -18,6 +18,7 @@ tests/cases/conformance/expressions/arrayLiterals/arrayLiterals3.ts(34,5): error
       Types of parameters 'items' and 'items' are incompatible.
         Type 'Number' is not assignable to type 'string | number'.
           Type 'Number' is not assignable to type 'number'.
+            'number' is a primitive, but 'Number' is a wrapper object. Prefer using 'number' when possible.
 
 
 ==== tests/cases/conformance/expressions/arrayLiterals/arrayLiterals3.ts (6 errors) ====
@@ -81,4 +82,5 @@ tests/cases/conformance/expressions/arrayLiterals/arrayLiterals3.ts(34,5): error
 !!! error TS2322:       Types of parameters 'items' and 'items' are incompatible.
 !!! error TS2322:         Type 'Number' is not assignable to type 'string | number'.
 !!! error TS2322:           Type 'Number' is not assignable to type 'number'.
+!!! error TS2322:             'number' is a primitive, but 'Number' is a wrapper object. Prefer using 'number' when possible.
 

tests/baselines/reference/assignFromBooleanInterface.errors.txt

@@ -1,4 +1,5 @@
 tests/cases/conformance/types/primitives/boolean/assignFromBooleanInterface.ts(3,1): error TS2322: Type 'Boolean' is not assignable to type 'boolean'.
+  'boolean' is a primitive, but 'Boolean' is a wrapper object. Prefer using 'boolean' when possible.
 
 
 ==== tests/cases/conformance/types/primitives/boolean/assignFromBooleanInterface.ts (1 errors) ====
@@ -7,4 +8,5 @@ tests/cases/conformance/types/primitives/boolean/assignFromBooleanInterface.ts(3
     x = a;
     ~
 !!! error TS2322: Type 'Boolean' is not assignable to type 'boolean'.
+!!! error TS2322:   'boolean' is a primitive, but 'Boolean' is a wrapper object. Prefer using 'boolean' when possible.
     a = x;

tests/baselines/reference/assignFromBooleanInterface2.errors.txt

@@ -3,6 +3,7 @@ tests/cases/conformance/types/primitives/boolean/assignFromBooleanInterface2.ts(
     Type '() => Object' is not assignable to type '() => boolean'.
       Type 'Object' is not assignable to type 'boolean'.
 tests/cases/conformance/types/primitives/boolean/assignFromBooleanInterface2.ts(19,1): error TS2322: Type 'Boolean' is not assignable to type 'boolean'.
+  'boolean' is a primitive, but 'Boolean' is a wrapper object. Prefer using 'boolean' when possible.
 tests/cases/conformance/types/primitives/boolean/assignFromBooleanInterface2.ts(20,1): error TS2322: Type 'NotBoolean' is not assignable to type 'boolean'.
 
 
@@ -33,6 +34,7 @@ tests/cases/conformance/types/primitives/boolean/assignFromBooleanInterface2.ts(
     x = a; // expected error
     ~
 !!! error TS2322: Type 'Boolean' is not assignable to type 'boolean'.
+!!! error TS2322:   'boolean' is a primitive, but 'Boolean' is a wrapper object. Prefer using 'boolean' when possible.
     x = b; // expected error
     ~
 !!! error TS2322: Type 'NotBoolean' is not assignable to type 'boolean'.

tests/baselines/reference/assignFromNumberInterface.errors.txt

@@ -1,4 +1,5 @@
 tests/cases/conformance/types/primitives/number/assignFromNumberInterface.ts(3,1): error TS2322: Type 'Number' is not assignable to type 'number'.
+  'number' is a primitive, but 'Number' is a wrapper object. Prefer using 'number' when possible.
 
 
 ==== tests/cases/conformance/types/primitives/number/assignFromNumberInterface.ts (1 errors) ====
@@ -7,4 +8,5 @@ tests/cases/conformance/types/primitives/number/assignFromNumberInterface.ts(3,1
     x = a;
     ~
 !!! error TS2322: Type 'Number' is not assignable to type 'number'.
+!!! error TS2322:   'number' is a primitive, but 'Number' is a wrapper object. Prefer using 'number' when possible.
     a = x;

tests/baselines/reference/assignFromNumberInterface2.errors.txt

@@ -1,4 +1,5 @@
 tests/cases/conformance/types/primitives/number/assignFromNumberInterface2.ts(24,1): error TS2322: Type 'Number' is not assignable to type 'number'.
+  'number' is a primitive, but 'Number' is a wrapper object. Prefer using 'number' when possible.
 tests/cases/conformance/types/primitives/number/assignFromNumberInterface2.ts(25,1): error TS2322: Type 'NotNumber' is not assignable to type 'number'.
 
 
@@ -29,6 +30,7 @@ tests/cases/conformance/types/primitives/number/assignFromNumberInterface2.ts(25
     x = a; // expected error
     ~
 !!! error TS2322: Type 'Number' is not assignable to type 'number'.
+!!! error TS2322:   'number' is a primitive, but 'Number' is a wrapper object. Prefer using 'number' when possible.
     x = b; // expected error
     ~
 !!! error TS2322: Type 'NotNumber' is not assignable to type 'number'.

tests/baselines/reference/assignFromStringInterface.errors.txt

@@ -1,4 +1,5 @@
 tests/cases/conformance/types/primitives/string/assignFromStringInterface.ts(3,1): error TS2322: Type 'String' is not assignable to type 'string'.
+  'string' is a primitive, but 'String' is a wrapper object. Prefer using 'string' when possible.
 
 
 ==== tests/cases/conformance/types/primitives/string/assignFromStringInterface.ts (1 errors) ====
@@ -7,4 +8,5 @@ tests/cases/conformance/types/primitives/string/assignFromStringInterface.ts(3,1
     x = a;
     ~
 !!! error TS2322: Type 'String' is not assignable to type 'string'.
+!!! error TS2322:   'string' is a primitive, but 'String' is a wrapper object. Prefer using 'string' when possible.
     a = x;

tests/baselines/reference/assignFromStringInterface2.errors.txt

@@ -1,4 +1,5 @@
 tests/cases/conformance/types/primitives/string/assignFromStringInterface2.ts(47,1): error TS2322: Type 'String' is not assignable to type 'string'.
+  'string' is a primitive, but 'String' is a wrapper object. Prefer using 'string' when possible.
 tests/cases/conformance/types/primitives/string/assignFromStringInterface2.ts(48,1): error TS2322: Type 'NotString' is not assignable to type 'string'.
 
 
@@ -52,6 +53,7 @@ tests/cases/conformance/types/primitives/string/assignFromStringInterface2.ts(48
     x = a; // expected error
     ~
 !!! error TS2322: Type 'String' is not assignable to type 'string'.
+!!! error TS2322:   'string' is a primitive, but 'String' is a wrapper object. Prefer using 'string' when possible.
     x = b; // expected error
     ~
 !!! error TS2322: Type 'NotString' is not assignable to type 'string'.

tests/baselines/reference/nativeToBoxedTypes.errors.txt

@@ -0,0 +1,36 @@
+tests/cases/compiler/nativeToBoxedTypes.ts(3,1): error TS2322: Type 'Number' is not assignable to type 'number'.
+  'number' is a primitive, but 'Number' is a wrapper object. Prefer using 'number' when possible.
+tests/cases/compiler/nativeToBoxedTypes.ts(7,1): error TS2322: Type 'String' is not assignable to type 'string'.
+  'string' is a primitive, but 'String' is a wrapper object. Prefer using 'string' when possible.
+tests/cases/compiler/nativeToBoxedTypes.ts(11,1): error TS2322: Type 'Boolean' is not assignable to type 'boolean'.
+  'boolean' is a primitive, but 'Boolean' is a wrapper object. Prefer using 'boolean' when possible.
+tests/cases/compiler/nativeToBoxedTypes.ts(14,10): error TS2304: Cannot find name 'Symbol'.
+
+
+==== tests/cases/compiler/nativeToBoxedTypes.ts (4 errors) ====
+    var N = new Number();
+    var n = 100;
+    n = N;
+    ~
+!!! error TS2322: Type 'Number' is not assignable to type 'number'.
+!!! error TS2322:   'number' is a primitive, but 'Number' is a wrapper object. Prefer using 'number' when possible.
+
+    var S = new String();
+    var s = "foge";
+    s = S;
+    ~
+!!! error TS2322: Type 'String' is not assignable to type 'string'.
+!!! error TS2322:   'string' is a primitive, but 'String' is a wrapper object. Prefer using 'string' when possible.
+
+    var B = new Boolean();
+    var b = true;
+    b = B;
+    ~
+!!! error TS2322: Type 'Boolean' is not assignable to type 'boolean'.
+!!! error TS2322:   'boolean' is a primitive, but 'Boolean' is a wrapper object. Prefer using 'boolean' when possible.
+
+    var sym: symbol; 
+    var Sym: Symbol;
+             ~~~~~~
+!!! error TS2304: Cannot find name 'Symbol'.
+    sym = Sym;

tests/baselines/reference/nativeToBoxedTypes.js

@@ -0,0 +1,30 @@
+//// [nativeToBoxedTypes.ts]
+var N = new Number();
+var n = 100;
+n = N;
+
+var S = new String();
+var s = "foge";
+s = S;
+
+var B = new Boolean();
+var b = true;
+b = B;
+
+var sym: symbol; 
+var Sym: Symbol;
+sym = Sym;
+
+//// [nativeToBoxedTypes.js]
+var N = new Number();
+var n = 100;
+n = N;
+var S = new String();
+var s = "foge";
+s = S;
+var B = new Boolean();
+var b = true;
+b = B;
+var sym;
+var Sym;
+sym = Sym;

tests/baselines/reference/primitiveMembers.errors.txt

@@ -1,5 +1,6 @@
 tests/cases/compiler/primitiveMembers.ts(5,3): error TS2339: Property 'toBAZ' does not exist on type 'number'.
 tests/cases/compiler/primitiveMembers.ts(11,1): error TS2322: Type 'Number' is not assignable to type 'number'.
+  'number' is a primitive, but 'Number' is a wrapper object. Prefer using 'number' when possible.
 
 
 ==== tests/cases/compiler/primitiveMembers.ts (2 errors) ====
@@ -18,6 +19,7 @@ tests/cases/compiler/primitiveMembers.ts(11,1): error TS2322: Type 'Number' is n
     n = N;  // should not work, as 'number' has a different brand
     ~
 !!! error TS2322: Type 'Number' is not assignable to type 'number'.
+!!! error TS2322:   'number' is a primitive, but 'Number' is a wrapper object. Prefer using 'number' when possible.
     N = n; // should work
 
     var o: Object = {}

tests/baselines/reference/symbolType15.errors.txt

@@ -1,4 +1,5 @@
 tests/cases/conformance/es6/Symbols/symbolType15.ts(5,1): error TS2322: Type 'Symbol' is not assignable to type 'symbol'.
+  'symbol' is a primitive, but 'Symbol' is a wrapper object. Prefer using 'symbol' when possible.
 
 
 ==== tests/cases/conformance/es6/Symbols/symbolType15.ts (1 errors) ====
@@ -8,4 +9,5 @@ tests/cases/conformance/es6/Symbols/symbolType15.ts(5,1): error TS2322: Type 'Sy
     symObj = sym;
     sym = symObj;
     ~~~
-!!! error TS2322: Type 'Symbol' is not assignable to type 'symbol'.
+!!! error TS2322: Type 'Symbol' is not assignable to type 'symbol'.
+!!! error TS2322:   'symbol' is a primitive, but 'Symbol' is a wrapper object. Prefer using 'symbol' when possible.

tests/cases/compiler/nativeToBoxedTypes.ts

@@ -0,0 +1,15 @@
+var N = new Number();
+var n = 100;
+n = N;
+
+var S = new String();
+var s = "foge";
+s = S;
+
+var B = new Boolean();
+var b = true;
+b = B;
+
+var sym: symbol; 
+var Sym: Symbol;
+sym = Sym;