[clang-format] Switch to case-insensitive header matching and use it to

improve support for LLVM-style include sorting.

This really is a collection of improvements to the rules for LLVM
include sorting:
- We have gmock headers now, so it adds support for those to one of the
  categories.
- LLVM does use 'FooTest.cpp' files to test 'Foo.h' so it adds that
  suffix for finding a main header.
- At times the test file's case may not match the header file's case, so
  switch to case-insensitive regex matching of header names.

With this set of changes, I can't spot any misbehaviors when re-sorting
all of LLVM's unittest '#include' lines.

Thanks to Eric and Daniel for help testing and refining the patch during
review!

Differential Revision: https://reviews.llvm.org/D33932

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@306759 91177308-0d34-0410-b5e6-96231b3b80d8

include/clang/Format/Format.h

@@ -966,7 +966,7 @@ struct FormatStyle {
   ///   IncludeCategories:
   ///     - Regex:           '^"(llvm|llvm-c|clang|clang-c)/'
   ///       Priority:        2
-  ///     - Regex:           '^(<|"(gtest|isl|json)/)'
+  ///     - Regex:           '^(<|"(gtest|gmock|isl|json)/)'
   ///       Priority:        3
   ///     - Regex:           '.*'
   ///       Priority:        1

lib/Format/Format.cpp

@@ -579,9 +579,9 @@ FormatStyle getLLVMStyle() {
   LLVMStyle.ForEachMacros.push_back("Q_FOREACH");
   LLVMStyle.ForEachMacros.push_back("BOOST_FOREACH");
   LLVMStyle.IncludeCategories = {{"^\"(llvm|llvm-c|clang|clang-c)/", 2},
-                                 {"^(<|\"(gtest|isl|json)/)", 3},
+                                 {"^(<|\"(gtest|gmock|isl|json)/)", 3},
                                  {".*", 1}};
-  LLVMStyle.IncludeIsMainRegex = "$";
+  LLVMStyle.IncludeIsMainRegex = "(Test)?$";
   LLVMStyle.IndentCaseLabels = false;
   LLVMStyle.IndentWrappedFunctionNames = false;
   LLVMStyle.IndentWidth = 2;
@@ -1409,7 +1409,7 @@ public:
       : Style(Style), FileName(FileName) {
     FileStem = llvm::sys::path::stem(FileName);
     for (const auto &Category : Style.IncludeCategories)
-      CategoryRegexs.emplace_back(Category.Regex);
+      CategoryRegexs.emplace_back(Category.Regex, llvm::Regex::IgnoreCase);
     IsMainFile = FileName.endswith(".c") || FileName.endswith(".cc") ||
                  FileName.endswith(".cpp") || FileName.endswith(".c++") ||
                  FileName.endswith(".cxx") || FileName.endswith(".m") ||
@@ -1437,9 +1437,11 @@ private:
       return false;
     StringRef HeaderStem =
         llvm::sys::path::stem(IncludeName.drop_front(1).drop_back(1));
-    if (FileStem.startswith(HeaderStem)) {
+    if (FileStem.startswith(HeaderStem) ||
+        FileStem.startswith_lower(HeaderStem)) {
       llvm::Regex MainIncludeRegex(
-          (HeaderStem + Style.IncludeIsMainRegex).str());
+          (HeaderStem + Style.IncludeIsMainRegex).str(),
+          llvm::Regex::IgnoreCase);
       if (MainIncludeRegex.match(FileStem))
         return true;
     }

unittests/Format/SortIncludesTest.cpp

@@ -266,6 +266,29 @@ TEST_F(SortIncludesTest, LeavesMainHeaderFirst) {
                  "a.cc"));
 }
 
+TEST_F(SortIncludesTest, SupportCaseInsensitiveMatching) {
+  // Setup an regex for main includes so we can cover those as well.
+  Style.IncludeIsMainRegex = "([-_](test|unittest))?$";
+
+  // Ensure both main header detection and grouping work in a case insensitive
+  // manner.
+  EXPECT_EQ("#include \"llvm/A.h\"\n"
+            "#include \"b.h\"\n"
+            "#include \"c.h\"\n"
+            "#include \"LLVM/z.h\"\n"
+            "#include \"llvm/X.h\"\n"
+            "#include \"GTest/GTest.h\"\n"
+            "#include \"gmock/gmock.h\"\n",
+            sort("#include \"c.h\"\n"
+                 "#include \"b.h\"\n"
+                 "#include \"GTest/GTest.h\"\n"
+                 "#include \"llvm/A.h\"\n"
+                 "#include \"gmock/gmock.h\"\n"
+                 "#include \"llvm/X.h\"\n"
+                 "#include \"LLVM/z.h\"\n",
+                 "a_TEST.cc"));
+}
+
 TEST_F(SortIncludesTest, NegativePriorities) {
   Style.IncludeCategories = {{".*important_os_header.*", -1}, {".*", 1}};
   EXPECT_EQ("#include \"important_os_header.h\"\n"