Don't Unnecessarily Invalidate Unreferenced Generic Parameters (#41128)

Author: philipturner

lib/Sema/TypeCheckGeneric.cpp

@@ -506,7 +506,6 @@ void TypeChecker::checkReferencedGenericParams(GenericContext *dc) {
       // Produce an error that this generic parameter cannot be bound.
       paramDecl->diagnose(diag::unreferenced_generic_parameter,
                           paramDecl->getNameStr());
-      decl->setInvalid();
     }
   }
 }

test/AutoDiff/Sema/derivative_attr_type_checking.swift

@@ -79,6 +79,16 @@ func vjpOriginalFunctionNotFound(_ x: Float) -> (value: Float, pullback: (Float)
   fatalError()
 }
 
+struct Q { }
+
+@derivative(of: remainder(_:_:)) // expected-error {{cannot find 'remainder' in scope}}
+// expected-error @+1 {{generic parameter 'T' is not used in function signature}}
+func _vjpRemainder<T: FloatingPoint>(_ x: Q, _ y: Q) -> (
+  value: Q, pullback: (Q) -> (Q, Q)
+) {
+  fatalError()
+}
+
 // Test `@derivative` attribute where `value:` result does not conform to `Differentiable`.
 // Invalid original function should be diagnosed first.
 // expected-error @+1 {{cannot find 'nonexistentFunction' in scope}}

test/Constraints/overload.swift

@@ -187,12 +187,12 @@ R_28051973().f(r28051973) // expected-error {{cannot use mutating member on immu
 // Fix for CSDiag vs CSSolver disagreement on what constitutes a
 // valid overload.
 
-func overloadedMethod(n: Int) {} // expected-note {{'overloadedMethod(n:)' declared here}}
-func overloadedMethod<T>() {}
+func overloadedMethod(n: Int) {}
+func overloadedMethod<T>() {} // expected-note {{in call to function 'overloadedMethod()'}}
 // expected-error@-1 {{generic parameter 'T' is not used in function signature}}
 
 overloadedMethod()
-// expected-error@-1 {{missing argument for parameter 'n' in call}}
+// expected-error@-1 {{generic parameter 'T' could not be inferred}}
 
 // Ensure we select the overload of '??' returning T? rather than T.
 func SR3817(_ d: [String : Any], _ s: String, _ t: String) -> Any {

test/Generics/unbound.swift

@@ -51,8 +51,10 @@ extension GC {
 
 
 class SomeClassWithInvalidMethod {
-  func method<T>() { // expected-error {{generic parameter 'T' is not used in function signature}}
+  func method<T>() { // expected-note {{in call to function 'method()'}}
+    // expected-error@-1 {{generic parameter 'T' is not used in function signature}}
     self.method()
+    // expected-error@-1 {{generic parameter 'T' could not be inferred}}
   }
 }