[Sema] Handle coercion in ambiguity note emission

Author: LucianoPAlmeida

lib/Sema/ConstraintSystem.cpp

@@ -4687,10 +4687,25 @@ static bool diagnoseAmbiguity(
           fixes.push_back(entry.second);
       }
 
+      auto emitGeneralFoundCandidateNote = [&]() {
+        // 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(noteLoc, diag::found_candidate);
+        }
+      };
+
       if (fixes.size() == 1) {
         diagnosed &= fixes.front()->diagnose(solution, /*asNote*/ true);
       } else if (!fixes.empty() &&
                  llvm::all_of(fixes, [&](const ConstraintFix *fix) {
+                   // Ignore coercion fixes in this context, to
+                   // focus on the argument mismatches.
+                   if (fix->getLocator()->isForCoercion())
+                     return true;
+
                    return fix->getLocator()
                        ->findLast<LocatorPathElt::ApplyArgument>()
                        .has_value();
@@ -4704,28 +4719,34 @@ static bool diagnoseAmbiguity(
             type->lookThroughAllOptionalTypes()->getAs<AnyFunctionType>();
         assert(fn);
 
-        auto *argList = solution.getArgumentList(fixes.front()->getLocator());
-        assert(argList);
-
-        if (fn->getNumParams() == 1 && argList->isUnary()) {
-          const auto &param = fn->getParams()[0];
-          auto argTy = solution.getResolvedType(argList->getUnaryExpr());
+        auto first = llvm::find_if(fixes, [&](const ConstraintFix *fix) {
+          return fix->getLocator()
+              ->findLast<LocatorPathElt::ApplyArgument>()
+              .has_value();
+        });
 
-          DE.diagnose(noteLoc, diag::candidate_has_invalid_argument_at_position,
-                      solution.simplifyType(param.getPlainType()),
-                      /*position=*/1, param.isInOut(), argTy);
+        if (first != fixes.end()) {
+          auto *argList = solution.getArgumentList((*first)->getLocator());
+          assert(argList);
+
+          if (fn->getNumParams() == 1 && argList->isUnary()) {
+            const auto &param = fn->getParams()[0];
+            auto argTy = solution.getResolvedType(argList->getUnaryExpr());
+
+            DE.diagnose(noteLoc,
+                        diag::candidate_has_invalid_argument_at_position,
+                        solution.simplifyType(param.getPlainType()),
+                        /*position=*/1, param.isInOut(), argTy);
+          } else {
+            DE.diagnose(noteLoc, diag::candidate_partial_match,
+                        fn->getParamListAsString(fn->getParams()));
+          }
         } else {
-          DE.diagnose(noteLoc, diag::candidate_partial_match,
-                      fn->getParamListAsString(fn->getParams()));
+          // Only coercion ambiguity fixes.
+          emitGeneralFoundCandidateNote();
         }
       } 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(noteLoc, diag::found_candidate);
-        }
+        emitGeneralFoundCandidateNote();
       }
     }
 

test/Constraints/overload.swift

@@ -324,3 +324,8 @@ func f63834_D(_ x: Int = 0) {}
 func f63834_D(_ x: String) {}
 
 (f63834_D as Magic)() // expected-error{{missing argument for parameter #1 in call}}
+
+func fn63834_3() -> String {} // expected-note {{found candidate with type 'String'}}
+func fn63834_3() -> Double {} // expected-note {{found candidate with type 'Double'}}
+
+fn63834_3() as Int // expected-error {{no exact matches in call to global function 'fn63834_3'}}