[Diagnostics] Implement MissingArgumentsFailure::diagnoseAsNote in order

to diagnose ambiguities due to missing arguments.

Author: hborla

lib/Sema/CSDiagnostics.cpp

@@ -3809,6 +3809,21 @@ bool MissingArgumentsFailure::diagnoseAsError() {
   return true;
 }
 
+bool MissingArgumentsFailure::diagnoseAsNote() {
+  auto *locator = getLocator();
+  if (auto overload = getChoiceFor(locator)) {
+    auto *fn = resolveType(overload->openedType)->getAs<AnyFunctionType>();
+    auto loc = overload->choice.getDecl()->getLoc();
+    if (loc.isInvalid())
+      loc = getAnchor()->getLoc();
+    emitDiagnostic(loc, diag::candidate_partial_match,
+                   fn->getParamListAsString(fn->getParams()));
+    return true;
+  }
+
+  return false;
+}
+
 bool MissingArgumentsFailure::diagnoseSingleMissingArgument() const {
   auto &ctx = getASTContext();
 

lib/Sema/CSDiagnostics.h

@@ -1210,6 +1210,8 @@ class MissingArgumentsFailure final : public FailureDiagnostic {
 
   bool diagnoseAsError() override;
 
+  bool diagnoseAsNote() override;
+
   bool diagnoseSingleMissingArgument() const;
 
 private:

test/decl/subscript/subscripting.swift

@@ -398,12 +398,13 @@ func testSubscript1(_ s1 : SubscriptTest1) {
 struct SubscriptTest2 {
   subscript(a : String, b : Int) -> Int { return 0 } // expected-note {{candidate expects value of type 'Int' for parameter #2}}
   // expected-note@-1 {{declared here}}
+  // expected-note@-2 {{candidate has partially matching parameter list (String, Int)}}
     subscript(a : String, b : String) -> Int { return 0 } // expected-note {{candidate expects value of type 'String' for parameter #2}}
+  // expected-note@-1 {{candidate has partially matching parameter list (String, String)}}
 }
 
 func testSubscript1(_ s2 : SubscriptTest2) {
-  _ = s2["foo"] // expected-error {{cannot subscript a value of type 'SubscriptTest2' with an argument of type 'String'}}
-  // expected-note @-1 {{overloads for 'subscript' exist with these partially matching parameter lists: (String, Int), (String, String)}}
+  _ = s2["foo"] // expected-error {{no exact matches in call to subscript}}
 
   let a = s2["foo", 1.0] // expected-error {{no exact matches in call to subscript}}
 

test/type/types.swift

@@ -19,8 +19,12 @@ var d3 : () -> Float = { 4 }
 var d4 : () -> Int = { d2 }  // expected-error{{function produces expected type 'Int'; did you mean to call it with '()'?}} {{26-26=()}}
 
 var e0 : [Int]
-e0[] // expected-error {{cannot subscript a value of type '[Int]' with an argument of type '()'}}
-  // expected-note @-1 {{overloads for 'subscript' exist with these partially matching parameter lists: ((UnboundedRange_) -> ()), (Int), (R), (Range<Int>), (Range<Self.Index>)}}
+e0[] // expected-error {{no exact matches in call to subscript}}
+// expected-note@-1 {{candidate has partially matching parameter list (Int)}}
+// expected-note@-2 {{candidate has partially matching parameter list (Range<Int>)}}
+// expected-note@-3 {{candidate has partially matching parameter list ((UnboundedRange_) -> ())}}
+// expected-note@-4 {{candidate has partially matching parameter list (Range<Array<Int>.Index>)}}
+// expected-note@-5 {{candidate has partially matching parameter list ((UnboundedRange_) -> ())}}
 
 var f0 : [Float]
 var f1 : [(Int,Int)]