A written this: on a method annotates the receiver, it is not a parameter

tslang/lib/TypeScript/MLIRGenFunctions.cpp

@@ -51,6 +51,13 @@ namespace mlirgen
                 namePtr = getArgumentName(index);
             }
 
+            // A written `this:` on a method only annotates the receiver the method already has; as a
+            // parameter of its own it shifted every argument by one slot.
+            if (namePtr == THIS_NAME && !params.empty() && params.front()->getName() == THIS_NAME)
+            {
+                continue;
+            }
+
             auto isBindingPattern = arg->name == SyntaxKind::ObjectBindingPattern || arg->name == SyntaxKind::ArrayBindingPattern;
 
             mlir::Type type;

tslang/test/tester/CMakeLists.txt

@@ -553,6 +553,7 @@ tslang_add_test(NAME test-compile-00-try-catch-return-dispose COMMAND test-runne
 tslang_add_test(NAME test-compile-01-try-catch-return-dispose COMMAND test-runner "${PROJECT_SOURCE_DIR}/test/tester/tests/01try_catch_return_dispose.ts")
 tslang_add_test(NAME test-compile-00-property-access-conditional COMMAND test-runner "${PROJECT_SOURCE_DIR}/test/tester/tests/00property_access_cond.ts")
 tslang_add_test(NAME test-compile-00-method-access-conditional COMMAND test-runner "${PROJECT_SOURCE_DIR}/test/tester/tests/00method_access_cond.ts")
+tslang_add_test(NAME test-compile-00-method-this-param COMMAND test-runner "${PROJECT_SOURCE_DIR}/test/tester/tests/00method_this_param.ts")
 tslang_add_test(NAME test-compile-01-method-access-conditional COMMAND test-runner "${PROJECT_SOURCE_DIR}/test/tester/tests/01method_access_cond.ts")
 tslang_add_test(NAME test-compile-00-question-question COMMAND test-runner "${PROJECT_SOURCE_DIR}/test/tester/tests/00question_question.ts")
 tslang_add_test(NAME test-compile-00-spread-assignment COMMAND test-runner "${PROJECT_SOURCE_DIR}/test/tester/tests/00spread_assignment.ts")
@@ -998,6 +999,7 @@ tslang_add_test(NAME test-jit-01-try-catch-return-dispose COMMAND test-runner -j
 tslang_add_test(NAME test-jit-00-types COMMAND test-runner -jit "${PROJECT_SOURCE_DIR}/test/tester/tests/00types.ts")
 tslang_add_test(NAME test-jit-00-property-access-conditional COMMAND test-runner -jit "${PROJECT_SOURCE_DIR}/test/tester/tests/00property_access_cond.ts")
 tslang_add_test(NAME test-jit-00-method-access-conditional COMMAND test-runner -jit "${PROJECT_SOURCE_DIR}/test/tester/tests/00method_access_cond.ts")
+tslang_add_test(NAME test-jit-00-method-this-param COMMAND test-runner -jit "${PROJECT_SOURCE_DIR}/test/tester/tests/00method_this_param.ts")
 tslang_add_test(NAME test-jit-01-method-access-conditional COMMAND test-runner -jit "${PROJECT_SOURCE_DIR}/test/tester/tests/01method_access_cond.ts")
 tslang_add_test(NAME test-jit-00-question-question COMMAND test-runner -jit "${PROJECT_SOURCE_DIR}/test/tester/tests/00question_question.ts")
 tslang_add_test(NAME test-jit-00-spread-assignment COMMAND test-runner -jit "${PROJECT_SOURCE_DIR}/test/tester/tests/00spread_assignment.ts")
@@ -1686,6 +1688,7 @@ set(TSLANG_CORPUS
     00length.ts
     00map.ts
     00method_access_cond.ts
+    00method_this_param.ts
     00mixed_type_ops.ts
     00names_conflict.ts
     00nested_catch.ts
@@ -2275,6 +2278,7 @@ set(call_arity_cases
     "plain|Expected 2 arguments, but got 1\\."
     "optional|Expected 2\\-3 arguments, but got 1\\."
     "method|Expected 2 arguments, but got 1\\."
+    "method_this|Expected 2 arguments, but got 1\\."
     "constructor|Expected 2 arguments, but got 1\\."
     "closure|Expected 2 arguments, but got 1\\."
     "declared|Expected 2 arguments, but got 1\\."

tslang/test/tester/call-arity/method_this.ts

@@ -0,0 +1,12 @@
+class O {
+    x = 1;
+
+    m(this: O, a: number, b: number) {
+        return a + b + this.x;
+    }
+}
+
+function main() {
+    const o = new O();
+    print(o.m(1));
+}

tslang/test/tester/tests/00method_this_param.ts

@@ -0,0 +1,48 @@
+// A written `this:` parameter on a method annotates the receiver; it is not a parameter. It was
+// added next to the implicit receiver, which shifted every argument by one (#342).
+
+class O {
+    x = 1;
+
+    m(this: O, a: number, b: number) {
+        return a + b + this.x;
+    }
+}
+
+interface I {
+    x: number;
+    m(this: I, a: number, b: number): number;
+}
+
+class C implements I {
+    x: number = 10;
+
+    m(this: I, a: number, b: number) {
+        return a + b + this.x;
+    }
+}
+
+// a free function keeps its `this:` as the receiver it binds (the extension-function form)
+function ext(this: O, a: number) {
+    return this.x + a;
+}
+
+function main() {
+    const o = new O();
+    assert(o.m(1, 2) == 4);
+
+    const i: I = new C();
+    assert(i.m(1, 2) == 13);
+
+    const lit = {
+        x: 100,
+        m(this: { x: number }, a: number, b: number) {
+            return a + b + this.x;
+        }
+    };
+    assert(lit.m(1, 2) == 103);
+
+    assert(o.ext(5) == 6);
+
+    print("done.");
+}