[Diagnostics] Introduce extraneous call fix

lib/Sema/CSDiagnostics.cpp

@@ -5453,3 +5453,41 @@ bool ExpandArrayIntoVarargsFailure::diagnoseAsNote() {
   }
   return false;
 }
+
+bool ExtraneousCallFailure::diagnoseAsError() {
+  auto &cs = getConstraintSystem();
+
+  auto *anchor = getAnchor();
+  auto *locator = getLocator();
+
+  // If this is something like `foo()` where `foo` is a variable
+  // or a property, let's suggest dropping `()`.
+  auto removeParensFixIt = [&](InFlightDiagnostic &diagnostic) {
+    auto *argLoc = cs.getConstraintLocator(getRawAnchor(),
+                                           ConstraintLocator::ApplyArgument);
+
+    if (auto *TE =
+            dyn_cast_or_null<TupleExpr>(simplifyLocatorToAnchor(argLoc))) {
+      if (TE->getNumElements() == 0) {
+        diagnostic.fixItRemove(TE->getSourceRange());
+      }
+    }
+  };
+
+  if (auto overload = getChoiceFor(cs.getCalleeLocator(locator))) {
+    if (auto *decl = overload->choice.getDeclOrNull()) {
+      if (auto *enumCase = dyn_cast<EnumElementDecl>(decl)) {
+        auto diagnostic = emitDiagnostic(
+            anchor->getLoc(), diag::unexpected_arguments_in_enum_case,
+            enumCase->getName());
+        removeParensFixIt(diagnostic);
+        return true;
+      }
+    }
+  }
+
+  auto diagnostic = emitDiagnostic(
+      anchor->getLoc(), diag::cannot_call_non_function_value, getType(anchor));
+  removeParensFixIt(diagnostic);
+  return true;
+}

lib/Sema/CSDiagnostics.h

@@ -1912,6 +1912,15 @@ class MissingForcedDowncastFailure final : public ContextualFailure {
   bool diagnoseAsError() override;
 };
 
+class ExtraneousCallFailure final : public FailureDiagnostic {
+public:
+  ExtraneousCallFailure(Expr *expr, ConstraintSystem &cs,
+                        ConstraintLocator *locator)
+      : FailureDiagnostic(expr, cs, locator) {}
+
+  bool diagnoseAsError() override;
+};
+
 } // end namespace constraints
 } // end namespace swift
 

lib/Sema/CSFix.cpp

@@ -984,3 +984,13 @@ AllowArgumentMismatch::create(ConstraintSystem &cs, Type argType,
   return new (cs.getAllocator())
       AllowArgumentMismatch(cs, argType, paramType, locator);
 }
+
+bool RemoveInvalidCall::diagnose(Expr *root, bool asNote) const {
+  ExtraneousCallFailure failure(root, getConstraintSystem(), getLocator());
+  return failure.diagnose(asNote);
+}
+
+RemoveInvalidCall *RemoveInvalidCall::create(ConstraintSystem &cs,
+                                             ConstraintLocator *locator) {
+  return new (cs.getAllocator()) RemoveInvalidCall(cs, locator);
+}

lib/Sema/CSFix.h

@@ -211,6 +211,10 @@ enum class FixKind : uint8_t {
   /// If an array was passed to a variadic argument, give a specific diagnostic
   /// and offer to drop the brackets if it's a literal.
   ExpandArrayIntoVarargs,
+
+  /// Remove extraneous call to something which can't be invoked e.g.
+  /// a variable, a property etc.
+  RemoveCall,
 };
 
 class ConstraintFix {
@@ -1469,6 +1473,21 @@ class CoerceToCheckedCast final : public ContextualMismatch {
                                       Type toType, ConstraintLocator *locator);
 };
 
+class RemoveInvalidCall final : public ConstraintFix {
+  RemoveInvalidCall(ConstraintSystem &cs, ConstraintLocator *locator)
+      : ConstraintFix(cs, FixKind::RemoveCall, locator) {}
+
+public:
+  std::string getName() const {
+    return "remove extraneous call from value of non-function type";
+  }
+
+  bool diagnose(Expr *root, bool asNote = false) const;
+
+  static RemoveInvalidCall *create(ConstraintSystem &cs,
+                                   ConstraintLocator *locator);
+};
+
 } // end namespace constraints
 } // end namespace swift
 

lib/Sema/CSSimplify.cpp

@@ -7097,8 +7097,37 @@ ConstraintSystem::simplifyApplicableFnConstraint(
   }
 
   // Handle applications of @dynamicCallable types.
-  return simplifyDynamicCallableApplicableFnConstraint(type1, origType2,
-                                                       subflags, locator);
+  auto result = simplifyDynamicCallableApplicableFnConstraint(
+      type1, origType2, subflags, locator);
+
+  if (shouldAttemptFixes() && result == SolutionKind::Error) {
+    // Skip this fix if the type is not yet resolved or
+    // it's a function type/metatype which points to argument mismatches.
+    if (desugar2->is<TypeVariableType>() || desugar2->is<FunctionType>() ||
+        desugar2->is<AnyMetatypeType>())
+      return SolutionKind::Error;
+
+    if (auto objectTy = desugar2->lookThroughAllOptionalTypes()) {
+      if (objectTy->isAny() || objectTy->isAnyObject())
+        return SolutionKind::Error;
+    }
+
+    // If there are any type variables associated with arguments/result
+    // they have to be marked as "holes".
+    type1.visit([&](Type subType) {
+      if (auto *typeVar = subType->getAs<TypeVariableType>())
+        recordHole(typeVar);
+    });
+
+    auto *fix = RemoveInvalidCall::create(*this, getConstraintLocator(locator));
+    // Let's make this fix as high impact so if there is a function or member
+    // overload with e.g. argument-to-parameter type mismatches it would take
+    // a higher priority.
+    return recordFix(fix, /*impact=*/10) ? SolutionKind::Error
+                                         : SolutionKind::Solved;
+  }
+
+  return result;
 }
 
 /// Looks up and returns the @dynamicCallable required methods (if they exist)
@@ -8012,6 +8041,7 @@ ConstraintSystem::SolutionKind ConstraintSystem::simplifyFixConstraint(
   case FixKind::UseSubscriptOperator:
   case FixKind::ExplicitlyEscaping:
   case FixKind::RelabelArguments:
+  case FixKind::RemoveCall:
   case FixKind::RemoveUnwrap:
   case FixKind::DefineMemberBasedOnUse:
   case FixKind::AllowMemberRefOnExistential:

test/Constraints/closures.swift

@@ -100,8 +100,8 @@ func r21544303() {
   inSubcall = false
 
   var v2 : Bool = false
-  v2 = inSubcall
-  {  // expected-error {{cannot call value of non-function type 'Bool'}} expected-note {{did you mean to use a 'do' statement?}} {{3-3=do }}
+  v2 = inSubcall // expected-error {{cannot call value of non-function type 'Bool'}}
+  {
   }
 }
 
@@ -114,56 +114,56 @@ func SR3671() {
   { consume($0) }(42)
   ;
 
-  ({ $0(42) } { consume($0) }) // expected-note {{callee is here}}
+  ({ $0(42) } { consume($0) }) // expected-error {{cannot call value of non-function type '()'}} expected-note {{callee is here}}
 
-  { print(42) }  // expected-warning {{braces here form a trailing closure separated from its callee by multiple newlines}} expected-note {{did you mean to use a 'do' statement?}} {{3-3=do }} expected-error {{cannot call value of non-function type '()'}}
+  { print(42) }  // expected-warning {{braces here form a trailing closure separated from its callee by multiple newlines}} expected-note {{did you mean to use a 'do' statement?}} {{3-3=do }}
   ;
 
-  ({ $0(42) } { consume($0) }) // expected-note {{callee is here}}
+  ({ $0(42) } { consume($0) }) // expected-error {{cannot call value of non-function type '()'}} expected-note {{callee is here}}
 
-  { print($0) }  // expected-warning {{braces here form a trailing closure separated from its callee by multiple newlines}} expected-error {{cannot call value of non-function type '()'}}
+  { print($0) }  // expected-warning {{braces here form a trailing closure separated from its callee by multiple newlines}}
   ;
 
-  ({ $0(42) } { consume($0) }) // expected-note {{callee is here}}
+  ({ $0(42) } { consume($0) }) // expected-error {{cannot call value of non-function type '()'}} expected-note {{callee is here}}
 
-  { [n] in print(42) }  // expected-warning {{braces here form a trailing closure separated from its callee by multiple newlines}} expected-error {{cannot call value of non-function type '()'}}
+  { [n] in print(42) }  // expected-warning {{braces here form a trailing closure separated from its callee by multiple newlines}}
   ;
 
-  ({ $0(42) } { consume($0) }) // expected-note {{callee is here}}
+  ({ $0(42) } { consume($0) }) // expected-error {{cannot call value of non-function type '()'}} expected-note {{callee is here}}
 
-  { consume($0) }(42)  // expected-warning {{braces here form a trailing closure separated from its callee by multiple newlines}} expected-error {{cannot call value of non-function type '()'}}
+  { consume($0) }(42)  // expected-warning {{braces here form a trailing closure separated from its callee by multiple newlines}}
   ;
 
-  ({ $0(42) } { consume($0) }) // expected-note {{callee is here}}
+  ({ $0(42) } { consume($0) }) // expected-error {{cannot call value of non-function type '()'}} expected-note {{callee is here}}
 
-  { (x: Int) in consume(x) }(42)  // expected-warning {{braces here form a trailing closure separated from its callee by multiple newlines}} expected-error {{cannot call value of non-function type '()'}}
+  { (x: Int) in consume(x) }(42)  // expected-warning {{braces here form a trailing closure separated from its callee by multiple newlines}}
   ;
 
   // This is technically a valid call, so nothing goes wrong until (42)
 
-  { $0(3) }
-  { consume($0) }(42)  // expected-error {{cannot call value of non-function type '()'}}
+  { $0(3) } // expected-error {{cannot call value of non-function type '()'}}
+  { consume($0) }(42)
   ;
-  ({ $0(42) })
-  { consume($0) }(42)  // expected-error {{cannot call value of non-function type '()'}}
+  ({ $0(42) }) // expected-error {{cannot call value of non-function type '()'}}
+  { consume($0) }(42)
   ;
-  { $0(3) }
-  { [n] in consume($0) }(42)  // expected-error {{cannot call value of non-function type '()'}}
+  { $0(3) } // expected-error {{cannot call value of non-function type '()'}}
+  { [n] in consume($0) }(42)
   ;
-  ({ $0(42) })
-  { [n] in consume($0) }(42)  // expected-error {{cannot call value of non-function type '()'}}
+  ({ $0(42) }) // expected-error {{cannot call value of non-function type '()'}}
+  { [n] in consume($0) }(42)
   ;
 
   // Equivalent but more obviously unintended.
 
-  { $0(3) }  // expected-note {{callee is here}}
+  { $0(3) }  // expected-error {{cannot call value of non-function type '()'}} expected-note {{callee is here}}
 
-  { consume($0) }(42)  // expected-error {{cannot call value of non-function type '()'}}
+  { consume($0) }(42)
   // expected-warning@-1 {{braces here form a trailing closure separated from its callee by multiple newlines}}
 
-  ({ $0(3) })  // expected-note {{callee is here}}
+  ({ $0(3) })  // expected-error {{cannot call value of non-function type '()'}} expected-note {{callee is here}}
 
-  { consume($0) }(42)  // expected-error {{cannot call value of non-function type '()'}}
+  { consume($0) }(42)
   // expected-warning@-1 {{braces here form a trailing closure separated from its callee by multiple newlines}}
   ;
 
@@ -407,6 +407,7 @@ func r20789423() {
 
   let p: C
   print(p.f(p)())  // expected-error {{cannot convert value of type 'C' to expected argument type 'Int'}}
+  // expected-error@-1:11 {{cannot call value of non-function type '()'}}
 
   let _f = { (v: Int) in  // expected-error {{unable to infer complex closure return type; add explicit type to disambiguate}} {{23-23=-> String }}
     print("a")

test/Constraints/diagnostics.swift

@@ -169,7 +169,7 @@ func rdar20142523() {
 func rdar21080030() {
   var s = "Hello"
   // SR-7599: This should be `cannot_call_non_function_value`
-  if s.count() == 0 {} // expected-error{{cannot invoke 'count' with no arguments}}
+  if s.count() == 0 {} // expected-error{{cannot call value of non-function type 'Int'}} {{13-15=}}
 }
 
 // <rdar://problem/21248136> QoI: problem with return type inference mis-diagnosed as invalid arguments
@@ -530,8 +530,8 @@ let _: Color = .frob(1, &d) // expected-error {{missing argument label 'b:' in c
 let _: Color = .frob(1, b: &d) // expected-error {{cannot convert value of type 'Double' to expected argument type 'Int'}}
 var someColor : Color = .red // expected-error {{enum type 'Color' has no case 'red'; did you mean 'Red'}}
 someColor = .red  // expected-error {{enum type 'Color' has no case 'red'; did you mean 'Red'}}
-someColor = .svar() // expected-error {{static property 'svar' is not a function}}
-someColor = .svar(1) // expected-error {{static property 'svar' is not a function}}
+someColor = .svar() // expected-error {{cannot call value of non-function type 'Color'}}
+someColor = .svar(1) // expected-error {{cannot call value of non-function type 'Color'}}
 
 func testTypeSugar(_ a : Int) {
   typealias Stride = Int

test/Index/invalid_code.swift

@@ -17,7 +17,7 @@ class CrashTest {
   init() { }
 }
 // CHECK: [[@LINE+1]]:13 | instance-method/Swift | returnSelf
-CrashTest().returnSelf(["": 0]).something()
+CrashTest().returnSelf(["": 0]).something
 
 class CrashTest2 {
 // CHECK: [[@LINE+1]]:8 | instance-method/Swift | bar
@@ -48,4 +48,4 @@ extension Protector where T: RangeReplaceableCollection {
       _ = newElement
     }
   }
-}
+}