Merge pull request #8340 from Microsoft/nothingType

Display 'nothing' for the empty union type

Author: ahejlsberg

src/compiler/checker.ts

@@ -2014,7 +2014,12 @@ namespace ts {
                         writeUnionOrIntersectionType(<UnionOrIntersectionType>type, flags);
                     }
                     else if (type.flags & TypeFlags.Anonymous) {
-                        writeAnonymousType(<ObjectType>type, flags);
+                        if (type === emptyUnionType) {
+                            writer.writeKeyword("nothing");
+                        }
+                        else {
+                            writeAnonymousType(<ObjectType>type, flags);
+                        }
                     }
                     else if (type.flags & TypeFlags.StringLiteral) {
                         writer.writeStringLiteral(`"${escapeString((<StringLiteralType>type).text)}"`);
@@ -4247,7 +4252,9 @@ namespace ts {
                         propTypes.push(getTypeOfSymbol(prop));
                     }
                 }
-                return getUnionType(propTypes);
+                if (propTypes.length) {
+                    return getUnionType(propTypes);
+                }
             }
             return undefined;
         }

tests/baselines/reference/instanceOfAssignability.types

@@ -133,8 +133,8 @@ function fn5(x: Derived1) {
 		// 1.5: y: Derived1
 		// Want: ???
 		let y = x;
->y : {}
->x : {}
+>y : nothing
+>x : nothing
 	}
 }
 

tests/baselines/reference/stringLiteralTypesAsTags01.types

@@ -116,6 +116,6 @@ if (!hasKind(x, "B")) {
 }
 else {
     let d = x;
->d : {}
->x : {}
+>d : nothing
+>x : nothing
 }

tests/baselines/reference/stringLiteralTypesAsTags02.types

@@ -110,6 +110,6 @@ if (!hasKind(x, "B")) {
 }
 else {
     let d = x;
->d : {}
->x : {}
+>d : nothing
+>x : nothing
 }

tests/baselines/reference/stringLiteralTypesAsTags03.types

@@ -113,6 +113,6 @@ if (!hasKind(x, "B")) {
 }
 else {
     let d = x;
->d : {}
->x : {}
+>d : nothing
+>x : nothing
 }

tests/baselines/reference/typeGuardOfFormTypeOfBoolean.types

@@ -121,7 +121,7 @@ if (typeof strOrNum === "boolean") {
 
     let z1: {} = strOrNum; // {}
 >z1 : {}
->strOrNum : {}
+>strOrNum : nothing
 }
 else {
     let z2: string | number = strOrNum; // string | number
@@ -215,6 +215,6 @@ if (typeof strOrNum !== "boolean") {
 else {
     let z2: {} = strOrNum; // {}
 >z2 : {}
->strOrNum : {}
+>strOrNum : nothing
 }
 

tests/baselines/reference/typeGuardOfFormTypeOfNumber.types

@@ -120,7 +120,7 @@ if (typeof strOrBool === "number") {
 
     let y1: {} = strOrBool; // {}
 >y1 : {}
->strOrBool : {}
+>strOrBool : nothing
 }
 else {
     let y2: string | boolean = strOrBool; // string | boolean
@@ -212,6 +212,6 @@ if (typeof strOrBool !== "number") {
 else {
     let y2: {} = strOrBool; // {}
 >y2 : {}
->strOrBool : {}
+>strOrBool : nothing
 }
 

tests/baselines/reference/typeGuardOfFormTypeOfOther.types

@@ -105,7 +105,7 @@ if (typeof strOrNumOrBool === "Object") {
 
     let q1: {} = strOrNumOrBool; // {}
 >q1 : {}
->strOrNumOrBool : {}
+>strOrNumOrBool : nothing
 }
 else {
     let q2: string | number | boolean = strOrNumOrBool; // string | number | boolean
@@ -178,6 +178,6 @@ if (typeof strOrNumOrBool !== "Object") {
 else {
     let q2: {} = strOrNumOrBool; // {}
 >q2 : {}
->strOrNumOrBool : {}
+>strOrNumOrBool : nothing
 }
 

tests/baselines/reference/typeGuardOfFormTypeOfString.types

@@ -121,7 +121,7 @@ if (typeof numOrBool === "string") {
 
     let x1: {} = numOrBool; // {}
 >x1 : {}
->numOrBool : {}
+>numOrBool : nothing
 }
 else {
     let x2: number | boolean = numOrBool; // number | boolean
@@ -214,6 +214,6 @@ if (typeof numOrBool !== "string") {
 else {
     let x2: {} = numOrBool; // {}
 >x2 : {}
->numOrBool : {}
+>numOrBool : nothing
 }
 

tests/baselines/reference/typeGuardTautologicalConsistiency.types

@@ -15,7 +15,7 @@ if (typeof stringOrNumber === "number") {
 >"number" : string
 
         stringOrNumber;
->stringOrNumber : {}
+>stringOrNumber : nothing
     }
 }
 
@@ -31,6 +31,6 @@ if (typeof stringOrNumber === "number" && typeof stringOrNumber !== "number") {
 >"number" : string
 
     stringOrNumber;
->stringOrNumber : {}
+>stringOrNumber : nothing
 }