fix: Adding duplicate identifier check in function signatures

src/compiler.ts

@@ -1471,6 +1471,26 @@ export class Compiler extends DiagnosticEmitter {
       }
     }
 
+    // ensure the function hasn't duplicate parameters
+    var parameters = instance.prototype.functionTypeNode.parameters;
+    var numParameters = parameters.length;
+    if (numParameters >= 2) {
+      let visited = new Set<string>();
+      visited.add(parameters[0].name.text);
+      for (let i = 1; i < numParameters; i++) {
+        let paramIdentifier = parameters[i].name;
+        let paramName = paramIdentifier.text;
+        if (!visited.has(paramName)) {
+          visited.add(paramName);
+        } else {
+          this.error(
+            DiagnosticCode.Duplicate_identifier_0,
+            paramIdentifier.range, paramName
+          );
+        }
+      }
+    }
+
     instance.set(CommonFlags.COMPILED);
     var pendingElements = this.pendingElements;
     pendingElements.add(instance);

src/parser.ts

@@ -845,7 +845,9 @@ export class Parser extends DiagnosticEmitter {
       return null;
     }
     this.tryParseSignatureIsSignature = true;
+
     if (!parameters) parameters = [];
+
     return Node.createFunctionType(
       parameters,
       returnType,

tests/compiler/function-expression.json

@@ -1,4 +1,7 @@
 {
   "asc_flags": [
+  ],
+  "stderr": [
+    "TS2300: Duplicate identifier 'a'"
   ]
-}
+}

tests/compiler/function-expression.ts

@@ -93,3 +93,7 @@ export function semanticallyAnonymous(): void {
   assert(fnDecl != exprDecl);
 }
 semanticallyAnonymous();
+
+var duplicateParams = (a: i32, a: i32): void => {};
+// TS2300: Duplicate identifier 'a'
+duplicateParams(1, 2);

tests/compiler/function.json

@@ -1,4 +1,7 @@
 {
   "asc_flags": [
+  ],
+  "stderr": [
+    "TS2300: Duplicate identifier 'a'"
   ]
-}
+}

tests/compiler/function.ts

@@ -39,3 +39,7 @@ iii(1, 2);
 jjj(1, 2);
 fff(1, 2);
 ddd(1, 2);
+
+function duplicateParams(a: i32, a: i32): void {}
+// TS2300: Duplicate identifier 'a'
+duplicateParams(1, 2);

tests/parser/function-type.ts

@@ -1,4 +1,5 @@
 var a: () => void;
 var b: (a: i32, b: i32) => void;
 var c: (a: i32, b: i32) => (a: i32, b: i32) => void;
-var d: (a) => void; // TS1110
+var d: (a: i32, a: i32) => void; // NOTE: duplicates in type signatures doesn't in TypeScript
+var e: (a) => void; // TS1110

tests/parser/function-type.ts.fixture.ts

@@ -1,5 +1,6 @@
 var a: () => void;
 var b: (a: i32, b: i32) => void;
 var c: (a: i32, b: i32) => (a: i32, b: i32) => void;
-var d: (a) => void;
-// ERROR 1110: "Type expected." in function-type.ts(4,10+0)
+var d: (a: i32, a: i32) => void;
+var e: (a) => void;
+// ERROR 1110: "Type expected." in function-type.ts(5,10+0)