Fix type conversion bug

Author: piscisaureus

demo.ts

@@ -1,9 +1,12 @@
 function demo(a: string, b: number, c: boolean, d: any[]): string {
-  return a + b;
+  return a + b + String(c) + d.join("");
 }
 
 // This should work correctly
 demo("hello", 42, true, ["world"]);
 
-// Let's uncomment this to see if we get a type error
-demo("hello", "42", true, ["world"]);
+// This should fail
+// demo("hello");
+// demo("hello", 0, true, ["world"], "extra");
+// demo("hello", 0, true, {});
+// demo(0, 0, true, []);

rust/src/compiler/mod.rs

@@ -423,11 +423,12 @@ impl TypeChecker {
                 self.is_assignable_to(src_elem_type, tgt_elem_type)
             }
 
-            // Number is assignable to String due to coercion
-            (Type::Number, Type::String) => true,
+            // In TypeScript, numbers can be coerced to strings during string concatenation,
+            // but a Number type is not assignable to a String parameter
+            (Type::Number, Type::String) => false,
 
-            // Boolean can be converted to String in JS
-            (Type::Boolean, Type::String) => true,
+            // Similarly, booleans are not assignable to strings in TypeScript
+            (Type::Boolean, Type::String) => false,
 
             // Add more special cases as needed
             // ...