[ConstraintSystem] Extend function type conversion mismatch coverage

lib/Sema/CSSimplify.cpp

@@ -2160,6 +2160,17 @@ ConstraintSystem::matchExistentialTypes(Type type1, Type type2,
 
             break;
           }
+
+          // TODO(diagnostics): If there are any requirement failures associated
+          // with result types which are part of a function type conversion,
+          // let's record general conversion mismatch in order for it to capture
+          // and display complete function types.
+          //
+          // Once either reacher locators or better diagnostic presentation for
+          // nested type failures is available this check could be removed.
+          if (last->is<LocatorPathElt::FunctionResult>())
+            return getTypeMatchFailure(locator);
+
         } else { // There are no elements in the path
           auto *anchor = locator.getAnchor();
           if (!(anchor &&
@@ -4083,21 +4094,8 @@ ConstraintSystem::matchTypes(Type type1, Type type2, ConstraintKind kind,
 
       auto result = matchFunctionTypes(func1, func2, kind, flags, locator);
 
-      if (shouldAttemptFixes() && result.isFailure()) {
-        // If this is a contextual type mismatch failure
-        // let's give the solver a chance to "fix" it.
-        if (auto last = locator.last()) {
-          if (last->is<LocatorPathElt::ContextualType>())
-            break;
-        }
-
-        // If this is a type mismatch in assignment, we don't really care
-        // (yet) was it argument or result type mismatch, let's produce a
-        // diagnostic which mentions both function types.
-        auto *anchor = locator.getAnchor();
-        if (anchor && isa<AssignExpr>(anchor))
-          break;
-      }
+      if (shouldAttemptFixes() && result.isFailure())
+        break;
 
       return result;
     }

test/Constraints/enum_cases.swift

@@ -22,14 +22,14 @@ let _ = arr.map(E.bar) // Ok
 let _ = arr.map(E.two) // expected-error {{cannot invoke 'map' with an argument list of type '(@escaping (Int, Int) -> E)'}}
 // expected-note@-1{{expected an argument list of type '((Self.Element) throws -> T)'}}
 
-let _ = arr.map(E.tuple) // expected-error {{cannot invoke 'map' with an argument list of type '(@escaping ((x: Int, y: Int)) -> E)'}}
-// expected-note@-1{{expected an argument list of type '((Self.Element) throws -> T)'}}
+let _ = arr.map(E.tuple) // expected-error {{cannot convert value of type '((x: Int, y: Int)) -> E' to expected argument type '(String) throws -> T'}}
+// expected-error@-1 {{generic parameter 'T' could not be inferred}}
 
 let _ = arr.map(G_E<String>.foo) // Ok
 let _ = arr.map(G_E<String>.bar) // Ok
 let _ = arr.map(G_E<String>.two) // expected-error {{cannot convert value of type '(String, String) -> G_E<String>' to expected argument type '(String) throws -> G_E<String>'}}
-let _ = arr.map(G_E<Int>.tuple) // expected-error {{cannot invoke 'map' with an argument list of type '(@escaping ((x: Int, y: Int)) -> G_E<Int>)'}}
-// expected-note@-1{{expected an argument list of type '((Self.Element) throws -> T)'}}
+let _ = arr.map(G_E<Int>.tuple) // expected-error {{cannot convert value of type '((x: Int, y: Int)) -> G_E<Int>' to expected argument type '(String) throws -> T'}}
+// expected-error@-1 {{generic parameter 'T' could not be inferred}}
 
 let _ = E.foo("hello") // expected-error {{missing argument label 'bar:' in call}}
 let _ = E.bar("hello") // Ok

test/Constraints/tuple_arguments.swift

@@ -1702,7 +1702,8 @@ _ = x.map { (_: ()) in () }
 // https://bugs.swift.org/browse/SR-9470
 do {
   func f(_: Int...) {}
-  let _ = [(1, 2, 3)].map(f) // expected-error {{cannot invoke 'map' with an argument list of type '(@escaping (Int...) -> ())'}}
+  let _ = [(1, 2, 3)].map(f) // expected-error {{cannot convert value of type '(Int...) -> ()' to expected argument type '((Int, Int, Int)) throws -> T'}}
+  // expected-error@-1 {{generic parameter 'T' could not be inferred}}
 }
 
 // rdar://problem/48443263 - cannot convert value of type '() -> Void' to expected argument type '(_) -> Void'