[Diagnostics] Add a workaround for inability to diagnose name shadowing

Let's cover at least the most common cases - min/max. Fixing the
problem requires refactoring of `resolveDeclRefExpr`.

Author: xedin

lib/Sema/CSFix.cpp

@@ -499,6 +499,26 @@ bool RemoveExtraneousArguments::diagnose(Expr *root, bool asNote) const {
   return failure.diagnose(asNote);
 }
 
+bool RemoveExtraneousArguments::isMinMaxNameShadowing(
+    ConstraintSystem &cs, ConstraintLocatorBuilder locator) {
+  auto *anchor = dyn_cast_or_null<CallExpr>(locator.getAnchor());
+  if (!anchor)
+    return false;
+
+  if (auto *UDE = dyn_cast<UnresolvedDotExpr>(anchor->getFn())) {
+    if (auto *baseExpr = dyn_cast<DeclRefExpr>(UDE->getBase())) {
+      auto *decl = baseExpr->getDecl();
+      if (baseExpr->isImplicit() && decl &&
+          decl->getFullName() == cs.getASTContext().Id_self) {
+        auto memberName = UDE->getName();
+        return memberName.isSimpleName("min") || memberName.isSimpleName("max");
+      }
+    }
+  }
+
+  return false;
+}
+
 RemoveExtraneousArguments *RemoveExtraneousArguments::create(
     ConstraintSystem &cs, FunctionType *contextualType,
     llvm::ArrayRef<IndexedParam> extraArgs, ConstraintLocator *locator) {

lib/Sema/CSFix.h

@@ -1068,6 +1068,15 @@ class RemoveExtraneousArguments final
 
   bool diagnose(Expr *root, bool asNote = false) const override;
 
+  /// FIXME(diagnostics): Once `resolveDeclRefExpr` is gone this
+  /// logic would be obsolete.
+  ///
+  /// Determine whether presence of extraneous arguments indicates
+  /// potential name shadowing problem with local `min`/`max` shadowing
+  /// global definitions with different number of arguments.
+  static bool isMinMaxNameShadowing(ConstraintSystem &cs,
+                                    ConstraintLocatorBuilder locator);
+
   static RemoveExtraneousArguments *
   create(ConstraintSystem &cs, FunctionType *contextualType,
          llvm::ArrayRef<IndexedParam> extraArgs, ConstraintLocator *locator);

lib/Sema/CSSimplify.cpp

@@ -998,6 +998,9 @@ ConstraintSystem::TypeMatchResult constraints::matchCallArguments(
 
     auto extraArguments = listener.getExtraneousArguments();
     if (!extraArguments.empty()) {
+      if (RemoveExtraneousArguments::isMinMaxNameShadowing(cs, locator))
+        return cs.getTypeMatchFailure(locator);
+
       // First let's see whether this is a situation where a single
       // parameter is a tuple, but N distinct arguments were passed in.
       if (AllowTupleSplatForSingleParameter::attempt(

test/NameBinding/name_lookup_min_max_conditional_conformance.swift

@@ -17,7 +17,6 @@ extension ContainsMinMax {
 }
 
 func foo(_: Int, _: Int) {}
-// expected-note@-1 {{'foo' declared here}}
 
 protocol ContainsFoo {}
 extension ContainsFoo {
@@ -34,9 +33,10 @@ extension NonConditional {
         _ = min(3, 4)
         // expected-error@-1{{use of 'min' refers to instance method}}
         // expected-note@-2{{use 'Swift.' to reference the global function}}
-        _ = foo(5, 6)
-        // expected-error@-1{{use of 'foo' refers to instance method}}
-        // expected-note@-2{{use 'name_lookup_min_max_conditional_conformance.' to reference the global function}}
+
+        // FIXME(diagnostics): Better diagnostic in this case would be to suggest to add `name_lookup_min_max_conditional_conformance.`
+        // to call because name `foo` is shadowed by instance method without arguments. Would be fixed by `resolveDeclRefExpr` refactoring.
+        _ = foo(5, 6) // expected-error {{argument passed to call that takes no arguments}}
     }
 }
 
@@ -52,7 +52,10 @@ extension Conditional {
         _ = min(3, 4)
         // expected-warning@-1{{use of 'min' as reference to global function in module 'Swift' will change in future versions of Swift to reference instance method in generic struct 'Conditional' which comes via a conditional conformance}}
         // expected-note@-2{{use 'Swift.' to continue to reference the global function}}
+
+        // FIXME(diagnostics): Same as line 39, there should be only one error here about shadowing.
         _ = foo(5, 6)
-        // expected-error@-1{{referencing instance method 'foo()' on 'Conditional' requires that 'T' conform to 'ContainsFoo'}}
+        // expected-error@-1 {{referencing instance method 'foo()' on 'Conditional' requires that 'T' conform to 'ContainsFoo'}}
+        // expected-error@-2 {{argument passed to call that takes no arguments}}
     }
 }