[ConstraintSystem] Attach candidate notes either to decl (if it has valid loc) or AST node

Author: xedin

lib/Sema/ConstraintSystem.cpp

@@ -3229,6 +3229,9 @@ static bool diagnoseAmbiguity(
       if (!distinctChoices.insert(decl).second)
         continue;
 
+      auto noteLoc =
+          decl->getLoc().isInvalid() ? getLoc(commonAnchor) : decl->getLoc();
+
       if (solution.Fixes.size() == 1) {
         diagnosed &=
             solution.Fixes.front()->diagnose(solution, /*asNote*/ true);
@@ -3241,15 +3244,23 @@ static bool diagnoseAmbiguity(
         // lists.
         auto *fn = type->getAs<AnyFunctionType>();
         assert(fn);
-        DE.diagnose(decl->getLoc(), diag::candidate_partial_match,
-                    fn->getParamListAsString(fn->getParams()));
+
+        if (fn->getNumParams() == 1) {
+          const auto &param = fn->getParams()[0];
+          DE.diagnose(noteLoc, diag::candidate_has_invalid_argument_at_position,
+                      solution.simplifyType(param.getPlainType()),
+                      /*position=*/1, param.isInOut());
+        } else {
+          DE.diagnose(noteLoc, diag::candidate_partial_match,
+                      fn->getParamListAsString(fn->getParams()));
+        }
       } else {
         // Emit a general "found candidate" note
         if (decl->getLoc().isInvalid()) {
           if (candidateTypes.insert(type->getCanonicalType()).second)
             DE.diagnose(getLoc(commonAnchor), diag::found_candidate_type, type);
         } else {
-          DE.diagnose(decl->getLoc(), diag::found_candidate);
+          DE.diagnose(noteLoc, diag::found_candidate);
         }
       }
     }

test/Constraints/diagnostics.swift

@@ -399,9 +399,9 @@ enum Color {
   static func rainbow() -> Color {}
 
   static func overload(a : Int) -> Color {} // expected-note {{incorrect labels for candidate (have: '(_:)', expected: '(a:)')}}
-  // expected-note@-1 {{candidate has partially matching parameter list (a: Int)}}
+  // expected-note@-1 {{candidate expects value of type 'Int' for parameter #1}}
   static func overload(b : Int) -> Color {} // expected-note {{incorrect labels for candidate (have: '(_:)', expected: '(b:)')}}
-  // expected-note@-1 {{candidate has partially matching parameter list (b: Int)}}
+  // expected-note@-1 {{candidate expects value of type 'Int' for parameter #1}}
 
   static func frob(_ a : Int, b : inout Int) -> Color {}
   static var svar: Color { return .Red }

test/Constraints/super_constructor.swift

@@ -39,15 +39,15 @@ class B {
   init() {
   }
 
-  init(x:Int) { // expected-note{{candidate has partially matching parameter list (x: Int)}}
+  init(x:Int) { // expected-note{{candidate expects value of type 'Int' for parameter #1}}
   }
 
-  init(a:UnicodeScalar) { // expected-note {{candidate has partially matching parameter list (a: UnicodeScalar)}}
+  init(a:UnicodeScalar) { // expected-note {{candidate expects value of type 'UnicodeScalar' (aka 'Unicode.Scalar') for parameter #1}}
   }
-  init(b:UnicodeScalar) { // expected-note{{candidate has partially matching parameter list (b: UnicodeScalar)}}
+  init(b:UnicodeScalar) { // expected-note {{candidate expects value of type 'UnicodeScalar' (aka 'Unicode.Scalar') for parameter #1}}
   }
 
-  init(z:Float) { // expected-note{{candidate has partially matching parameter list (z: Float)}}
+  init(z:Float) { // expected-note{{candidate expects value of type 'Float' for parameter #1}}
     super.init() // expected-error{{'super' members cannot be referenced in a root class}}
   }
 }

test/expr/postfix/dot/init_ref_delegation.swift

@@ -323,12 +323,12 @@ class TestOverloadSets {
     self.init(5, 5) // expected-error{{extra argument in call}}
   }
 
-  convenience init(a : Z0) { // expected-note{{candidate has partially matching parameter list (a: Z0)}}
+  convenience init(a : Z0) { // expected-note{{candidate expects value of type 'Z0' for parameter #1}}
     self.init(42 as Int8) // expected-error{{no exact matches in call to initializer}}
   }
 
-  init(value: Int) { /* ... */ } // expected-note{{candidate has partially matching parameter list (value: Int)}}
-  init(value: Double) { /* ... */ } // expected-note{{candidate has partially matching parameter list (value: Double)}}
+  init(value: Int) { /* ... */ } // expected-note{{candidate expects value of type 'Int' for parameter #1}}
+  init(value: Double) { /* ... */ } // expected-note{{candidate expects value of type 'Double' for parameter #1}}
 }
 
 class TestNestedExpr {