TypeScriptToLua
diff --git a/‎src/LuaTransformer.ts‎
Lines changed: 2 additions & 4 deletions b/‎src/LuaTransformer.ts‎
Lines changed: 2 additions & 4 deletions
diff --git a/‎src/TSHelper.ts‎
Lines changed: 8 additions & 0 deletions b/‎src/TSHelper.ts‎
Lines changed: 8 additions & 0 deletions
diff --git a/‎test/unit/string.spec.ts‎
Lines changed: 14 additions & 0 deletions b/‎test/unit/string.spec.ts‎
Lines changed: 14 additions & 0 deletions
@@ -3918,10 +3918,8 @@ export class LuaTransformer {
             });
         }
 
-        switch (ownerType.flags) {
-            case ts.TypeFlags.String:
-            case ts.TypeFlags.StringLiteral:
-                return this.transformStringCallExpression(node);
+        if (tsHelper.isStringType(ownerType, this.checker, this.program)) {
+            return this.transformStringCallExpression(node);
         }
 
         // if ownerType is a array, use only supported functions
 
@@ -140,6 +140,14 @@ export function isStringType(type: ts.Type, checker: ts.TypeChecker, program: ts
         }
     }
 
+    if (type.isUnion()) {
+        return type.types.every(t => isStringType(t, checker, program));
+    }
+
+    if (type.isIntersection()) {
+        return type.types.some(t => isStringType(t, checker, program));
+    }
+
     return (
         (type.flags & ts.TypeFlags.String) !== 0 ||
         (type.flags & ts.TypeFlags.StringLike) !== 0 ||
 
@@ -349,6 +349,20 @@ test.each([`"foobar".length`, `"foobar".repeat(2)`, "`foo${'bar'}`.length", "`fo
     }
 );
 
+test.each(["foo"])("scoped string-union inference (%p)", inp => {
+    const result = util.transpileAndExecute(`
+        const union: string = "${inp}";
+
+        if (union === "foo" || union === "bar") {
+            return union.length;
+        }
+
+        return 0;
+    `);
+
+    expect(result).toBe(inp.length);
+});
+
 test.each([
     "function generic<T extends string>(string: T)",
     "type StringType = string; function generic<T extends StringType>(string: T)",
Original file line number	Diff line number	Diff line change
`@@ -3918,10 +3918,8 @@ export class LuaTransformer {`
`3918`	`3918`	`});`
`3919`	`3919`	`}`
`3920`	`3920`
`3921`		`- switch (ownerType.flags) {`
`3922`		`- case ts.TypeFlags.String:`
`3923`		`- case ts.TypeFlags.StringLiteral:`
`3924`		`- return this.transformStringCallExpression(node);`
	`3921`	`+ if (tsHelper.isStringType(ownerType, this.checker, this.program)) {`
	`3922`	`+ return this.transformStringCallExpression(node);`
`3925`	`3923`	`}`
`3926`	`3924`
`3927`	`3925`	`// if ownerType is a array, use only supported functions`
Original file line number	Diff line number	Diff line change
`@@ -140,6 +140,14 @@ export function isStringType(type: ts.Type, checker: ts.TypeChecker, program: ts`
`140`	`140`	`}`
`141`	`141`	`}`
`142`	`142`
	`143`	`+ if (type.isUnion()) {`
	`144`	`+ return type.types.every(t => isStringType(t, checker, program));`
	`145`	`+ }`
	`146`	`+`
	`147`	`+ if (type.isIntersection()) {`
	`148`	`+ return type.types.some(t => isStringType(t, checker, program));`
	`149`	`+ }`
	`150`	`+`
`143`	`151`	`return (`
`144`	`152`	`(type.flags & ts.TypeFlags.String) !== 0 \|\|`
`145`	`153`	`(type.flags & ts.TypeFlags.StringLike) !== 0 \|\|`