[clang-format] Ignore case and stable sort using-declarations

Summary:
This ignores case while sorting using-declarations, fixing a case where `_` would appear between lowercase and uppercase characters.
It also applies stable sort, so that replacements for the exact same using declarations are not generated.

Reviewers: klimek, alexfh

Reviewed By: alexfh

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D37263

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@313963 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Format/UsingDeclarationsSorter.cpp

@@ -34,7 +34,7 @@ struct UsingDeclaration {
       : Line(Line), Label(Label) {}
 
   bool operator<(const UsingDeclaration &Other) const {
-    return Label < Other.Label;
+    return StringRef(Label).compare_lower(Other.Label) < 0;
   }
 };
 
@@ -78,7 +78,8 @@ void endUsingDeclarationBlock(
     const SourceManager &SourceMgr, tooling::Replacements *Fixes) {
   SmallVector<UsingDeclaration, 4> SortedUsingDeclarations(
       UsingDeclarations->begin(), UsingDeclarations->end());
-  std::sort(SortedUsingDeclarations.begin(), SortedUsingDeclarations.end());
+  std::stable_sort(SortedUsingDeclarations.begin(),
+                   SortedUsingDeclarations.end());
   for (size_t I = 0, E = UsingDeclarations->size(); I < E; ++I) {
     if ((*UsingDeclarations)[I].Line == SortedUsingDeclarations[I].Line)
       continue;

unittests/Format/UsingDeclarationsSorterTest.cpp

@@ -86,6 +86,77 @@ TEST_F(UsingDeclarationsSorterTest, SwapsTwoConsecutiveUsingDeclarations) {
                                   "using a, b;"));
 }
 
+TEST_F(UsingDeclarationsSorterTest, SortsCaseInsensitively) {
+  EXPECT_EQ("using A;\n"
+            "using a;",
+            sortUsingDeclarations("using A;\n"
+                                  "using a;"));
+  EXPECT_EQ("using a;\n"
+            "using A;",
+            sortUsingDeclarations("using a;\n"
+                                  "using A;"));
+  EXPECT_EQ("using a;\n"
+            "using B;",
+            sortUsingDeclarations("using B;\n"
+                                  "using a;"));
+  EXPECT_EQ("using _;\n"
+            "using a;",
+            sortUsingDeclarations("using a;\n"
+                                  "using _;"));
+  EXPECT_EQ("using a::_;\n"
+            "using a::a;",
+            sortUsingDeclarations("using a::a;\n"
+                                  "using a::_;"));
+
+  EXPECT_EQ("using ::testing::_;\n"
+            "using ::testing::Aardvark;\n"
+            "using ::testing::apple::Honeycrisp;\n"
+            "using ::testing::Xylophone;\n"
+            "using ::testing::zebra::Stripes;",
+            sortUsingDeclarations("using ::testing::Aardvark;\n"
+                                  "using ::testing::Xylophone;\n"
+                                  "using ::testing::_;\n"
+                                  "using ::testing::apple::Honeycrisp;\n"
+                                  "using ::testing::zebra::Stripes;"));
+}
+
+TEST_F(UsingDeclarationsSorterTest, SortsStably) {
+  EXPECT_EQ("using a;\n"
+            "using a;\n"
+            "using A;\n"
+            "using a;\n"
+            "using A;\n"
+            "using a;\n"
+            "using A;\n"
+            "using a;\n"
+            "using B;\n"
+            "using b;\n"
+            "using b;\n"
+            "using B;\n"
+            "using b;\n"
+            "using b;\n"
+            "using b;\n"
+            "using B;\n"
+            "using b;",
+            sortUsingDeclarations("using a;\n"
+                                  "using B;\n"
+                                  "using a;\n"
+                                  "using b;\n"
+                                  "using A;\n"
+                                  "using a;\n"
+                                  "using b;\n"
+                                  "using B;\n"
+                                  "using b;\n"
+                                  "using A;\n"
+                                  "using a;\n"
+                                  "using b;\n"
+                                  "using b;\n"
+                                  "using B;\n"
+                                  "using b;\n"
+                                  "using A;\n"
+                                  "using a;"));
+}
+
 TEST_F(UsingDeclarationsSorterTest, SortsMultipleTopLevelDeclarations) {
   EXPECT_EQ("using a;\n"
             "using b;\n"