Properly reduce intersections of string literal and template literal types (microsoft#41162)

* Properly reduce single element intersections

* Add regression test

* Accept new baselines

Author: ahejlsberg

src/compiler/checker.ts

@@ -13373,6 +13373,9 @@ namespace ts {
                 includes & TypeFlags.VoidLike && includes & (TypeFlags.DisjointDomains & ~TypeFlags.VoidLike)) {
                 return neverType;
             }
+            if (includes & TypeFlags.TemplateLiteral && includes & TypeFlags.StringLiteral && extractRedundantTemplateLiterals(typeSet)) {
+                return neverType;
+            }
             if (includes & TypeFlags.Any) {
                 return includes & TypeFlags.IncludesWildcard ? wildcardType : anyType;
             }
@@ -13424,12 +13427,7 @@ namespace ts {
                     }
                 }
                 else {
-                    if (includes & TypeFlags.TemplateLiteral && includes & TypeFlags.StringLiteral && extractRedundantTemplateLiterals(typeSet)) {
-                        result = neverType;
-                    }
-                    else {
-                        result = createIntersectionType(typeSet, aliasSymbol, aliasTypeArguments);
-                    }
+                    result = createIntersectionType(typeSet, aliasSymbol, aliasTypeArguments);
                 }
                 intersectionTypes.set(id, result);
             }

tests/baselines/reference/templateLiteralTypesPatterns.errors.txt

@@ -332,4 +332,10 @@ tests/cases/conformance/types/literal/templateLiteralTypesPatterns.ts(160,7): er
     const exampleBad: B = "anything"; // fails
           ~~~~~~~~~~
 !!! error TS2322: Type '"anything"' is not assignable to type '`${number} ${number}`'.
-    const exampleGood: B = "1 2"; // ok
+    const exampleGood: B = "1 2"; // ok
+    
+    // Repro from #41161
+    
+    var aa: '0';
+    var aa: '0' & `${number}`;
+    

tests/baselines/reference/templateLiteralTypesPatterns.js

@@ -159,7 +159,13 @@ const shouldWork2: AGen<string> = null as any as AGen<number>;
 type A = `${number}`;
 type B = `${A} ${A}`;
 const exampleBad: B = "anything"; // fails
-const exampleGood: B = "1 2"; // ok
+const exampleGood: B = "1 2"; // ok
+
+// Repro from #41161
+
+var aa: '0';
+var aa: '0' & `${number}`;
+
 
 //// [templateLiteralTypesPatterns.js]
 "use strict";
@@ -280,3 +286,6 @@ var shouldWork1 = null;
 var shouldWork2 = null;
 var exampleBad = "anything"; // fails
 var exampleGood = "1 2"; // ok
+// Repro from #41161
+var aa;
+var aa;

tests/baselines/reference/templateLiteralTypesPatterns.symbols

@@ -393,3 +393,11 @@ const exampleGood: B = "1 2"; // ok
 >exampleGood : Symbol(exampleGood, Decl(templateLiteralTypesPatterns.ts, 160, 5))
 >B : Symbol(B, Decl(templateLiteralTypesPatterns.ts, 157, 21))
 
+// Repro from #41161
+
+var aa: '0';
+>aa : Symbol(aa, Decl(templateLiteralTypesPatterns.ts, 164, 3), Decl(templateLiteralTypesPatterns.ts, 165, 3))
+
+var aa: '0' & `${number}`;
+>aa : Symbol(aa, Decl(templateLiteralTypesPatterns.ts, 164, 3), Decl(templateLiteralTypesPatterns.ts, 165, 3))
+

tests/baselines/reference/templateLiteralTypesPatterns.types

@@ -552,3 +552,11 @@ const exampleGood: B = "1 2"; // ok
 >exampleGood : `${number} ${number}`
 >"1 2" : "1 2"
 
+// Repro from #41161
+
+var aa: '0';
+>aa : "0"
+
+var aa: '0' & `${number}`;
+>aa : "0"
+

tests/cases/conformance/types/literal/templateLiteralTypesPatterns.ts

@@ -159,4 +159,9 @@ const shouldWork2: AGen<string> = null as any as AGen<number>;
 type A = `${number}`;
 type B = `${A} ${A}`;
 const exampleBad: B = "anything"; // fails
-const exampleGood: B = "1 2"; // ok
+const exampleGood: B = "1 2"; // ok
+
+// Repro from #41161
+
+var aa: '0';
+var aa: '0' & `${number}`;