[CodeComplete] Ensure object is the same in compareOverloads()

[ilya-biryukov]

Summary

This fixes a regression that led to size() not being available in clangd
when completing 'deque().^' and using libc++.

[sammccall]

clang-tools-extra/clangd/unittests/CodeCompleteTests.cpp

2565

could you give the three methods different return types, so it's clearer which one is being selected?

clang/lib/Sema/SemaCodeComplete.cpp

1188

This comment is a little confusing: the very next line takes object type into account :-)

Maybe: // Base/derived shadowing is handled elsewhere.

[sammccall]

(oops, meant to accept with comments)

[ilya-biryukov]

• Address comments

clang/lib/Sema/SemaCodeComplete.cpp

1188

I also did not like it, thanks for the great suggestion.

clang-tools-extra/clangd/unittests/CodeCompleteTests.cpp

auto Results = completions(R"cpp(
     M(ns::ABC^
     }
   )cpp",
                              {cls("foo::ns::ABCDE")}, Opts);
   EXPECT_THAT(Results.Completions,
               UnorderedElementsAre(AllOf(Qualifier(""), Named("ABCDE"))));
 }
 
+TEST(CompletionTest, DerivedMethodsAreAlwaysVisible) {
+  // Despite the fact that base method matches the ref-qualifier better,
+  // completion results should only include the derived method.
+  auto Completions = completions(R"cpp(
+    struct deque_base {
+      int &size();
+      const int &size() const;
+    };
+    struct deque : deque_base {
+        int size() const;
+    };
+
+    auto x = deque().^
+  )cpp")
+                         .Completions;
+  EXPECT_THAT(Completions,
+              ElementsAre(AllOf(ReturnType("int"), Named("size"))));
+}
+
 TEST(NoCompileCompletionTest, Basic) {
   auto Results = completionsNoCompile(R"cpp(
     void func() {
       int xyz;
       int abc;
       ^
     }
   )cpp");

clang/lib/Sema/SemaCodeComplete.cpp

 // Will Candidate ever be called on the object, when overloaded with Incumbent?
 // Returns Dominates if Candidate is always called, Dominated if Incumbent is
 // always called, BothViable if either may be called dependending on arguments.
 // Precondition: must actually be overloads!
 static OverloadCompare compareOverloads(const CXXMethodDecl &Candidate,
                                         const CXXMethodDecl &Incumbent,
                                         const Qualifiers &ObjectQuals,
                                         ExprValueKind ObjectKind) {
+  // This function does not take object type into account.
+  if (Candidate.getDeclContext() != Incumbent.getDeclContext())
+    return OverloadCompare::BothViable;
   if (Candidate.isVariadic() != Incumbent.isVariadic() ||
       Candidate.getNumParams() != Incumbent.getNumParams() ||
       Candidate.getMinRequiredArguments() !=
           Incumbent.getMinRequiredArguments())
     return OverloadCompare::BothViable;
   for (unsigned I = 0, E = Candidate.getNumParams(); I != E; ++I)
     if (Candidate.parameters()[I]->getType().getCanonicalType() !=
         Incumbent.parameters()[I]->getType().getCanonicalType())

clang/test/CodeCompletion/member-access-qualifiers.cpp

+struct deque_base {
+  int &size();
+  const int &size() const;
+};
+
+struct deque : private deque_base {
+    int size() const;
+};
+
+auto x = deque().
+// RUN: %clang_cc1 -fsyntax-only -code-completion-at=%s:10:18 %s -o - | FileCheck %s
+// CHECK: COMPLETION: size : [#int#]size()[# const#]
+// CHECK: COMPLETION: size (Hidden,InBase,Inaccessible) : [#int &#]deque_base::size()