[ClangFormat] Future-proof Standard option, allow floating or pinning to arbitrary lang version

Summary:
The historical context:
- clang-format was written when C++11 was current,
  and the main language-version concern was >> vs > > template-closers.
  An option was added to allow selection of the 03/11 behavior, or auto-detection.
- there was no option to choose simply "latest standard" so anyone who didn't
  ever want 03 behavior or auto-detection specified Cpp11.
- In r185149 this option started to affect lexer mode.
- no options were added to cover c++14, as parsing/formatting
  didn't change that much. The usage of Cpp11 to mean "latest" became
  codified e.g. in r206263
- c++17 added some new constructs. These were mostly backwards-compatible and so
  not used in old programs, so having no way to turn them off was OK.
- c++20 added some new constructs and keywords (e.g. co_*) that changed the
  meaning of existing programs, and people started to complain that
  the c++20 parsing couldn't be turned off.

New plan:
 - Default ('Auto') behavior remains unchanged: parse as latest, format
   template-closers based on input.
 - Add new 'Latest' option that more clearly expresses the intent "use
   modern features" that many projects have chosen for their .clang-format files.
 - Allow pinning to *any* language version, using the same name as clang -std:
   c++03, c++11, c++14 etc. These set precise lexer options, and any
   clang-format code depending on these can use a >= check.
 - For backwards compatibility, `Cpp11` is an alias for `Latest`, not `c++11`.
   This matches the historical documented semantics of this option.
   This spelling (and `Cpp03`) are deprecated.

Reviewers: klimek, modocache

Subscribers: cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D67541

llvm-svn: 373439

1 files changed, 25 insertions, 12 deletions

diff --git a/clang/lib/Format/Format.cpp b/clang/lib/Format/Format.cpp
index e918e90cb9f..dd561cc0d89 100644
--- a/clang/lib/Format/Format.cpp
+++ b/clang/lib/Format/Format.cpp
@@ -67,10 +67,19 @@ template <> struct ScalarEnumerationTraits<FormatStyle::LanguageKind> {
 
 template <> struct ScalarEnumerationTraits<FormatStyle::LanguageStandard> {
   static void enumeration(IO &IO, FormatStyle::LanguageStandard &Value) {
-    IO.enumCase(Value, "Cpp03", FormatStyle::LS_Cpp03);
-    IO.enumCase(Value, "C++03", FormatStyle::LS_Cpp03);
-    IO.enumCase(Value, "Cpp11", FormatStyle::LS_Cpp11);
-    IO.enumCase(Value, "C++11", FormatStyle::LS_Cpp11);
+    IO.enumCase(Value, "c++03", FormatStyle::LS_Cpp03);
+    IO.enumCase(Value, "C++03", FormatStyle::LS_Cpp03); // Legacy alias
+    IO.enumCase(Value, "Cpp03", FormatStyle::LS_Cpp03); // Legacy alias
+
+    IO.enumCase(Value, "c++11", FormatStyle::LS_Cpp11);
+    IO.enumCase(Value, "C++11", FormatStyle::LS_Cpp11); // Legacy alias
+
+    IO.enumCase(Value, "c++14", FormatStyle::LS_Cpp14);
+    IO.enumCase(Value, "c++17", FormatStyle::LS_Cpp17);
+    IO.enumCase(Value, "c++20", FormatStyle::LS_Cpp20);
+
+    IO.enumCase(Value, "Latest", FormatStyle::LS_Latest);
+    IO.enumCase(Value, "Cpp11", FormatStyle::LS_Latest); // Legacy alias
     IO.enumCase(Value, "Auto", FormatStyle::LS_Auto);
   }
 };
@@ -756,7 +765,7 @@ FormatStyle getLLVMStyle(FormatStyle::LanguageKind Language) {
   LLVMStyle.ObjCSpaceBeforeProtocolList = true;
   LLVMStyle.PointerAlignment = FormatStyle::PAS_Right;
   LLVMStyle.SpacesBeforeTrailingComments = 1;
-  LLVMStyle.Standard = FormatStyle::LS_Cpp11;
+  LLVMStyle.Standard = FormatStyle::LS_Latest;
   LLVMStyle.UseTab = FormatStyle::UT_Never;
   LLVMStyle.ReflowComments = true;
   LLVMStyle.SpacesInParentheses = false;
@@ -1399,7 +1408,7 @@ private:
                                    : FormatStyle::PAS_Right;
     if (Style.Standard == FormatStyle::LS_Auto)
       Style.Standard = hasCpp03IncompatibleFormat(AnnotatedLines)
-                           ? FormatStyle::LS_Cpp11
+                           ? FormatStyle::LS_Latest
                            : FormatStyle::LS_Cpp03;
     BinPackInconclusiveFunctions =
         HasBinPackedFunction || !HasOnePerLineFunction;
@@ -2455,14 +2464,18 @@ tooling::Replacements sortUsingDeclarations(const FormatStyle &Style,
 
 LangOptions getFormattingLangOpts(const FormatStyle &Style) {
   LangOptions LangOpts;
-  FormatStyle::LanguageStandard LexingStd =
-      Style.Standard == FormatStyle::LS_Auto ? FormatStyle::LS_Cpp11
-                                             : Style.Standard;
+
+  FormatStyle::LanguageStandard LexingStd = Style.Standard;
+  if (LexingStd == FormatStyle::LS_Auto)
+    LexingStd = FormatStyle::LS_Latest;
+  if (LexingStd == FormatStyle::LS_Latest)
+    LexingStd = FormatStyle::LS_Cpp20;
   LangOpts.CPlusPlus = 1;
   LangOpts.CPlusPlus11 = LexingStd >= FormatStyle::LS_Cpp11;
-  LangOpts.CPlusPlus14 = LexingStd >= FormatStyle::LS_Cpp11;
-  LangOpts.CPlusPlus17 = LexingStd >= FormatStyle::LS_Cpp11;
-  LangOpts.CPlusPlus2a = LexingStd >= FormatStyle::LS_Cpp11;
+  LangOpts.CPlusPlus14 = LexingStd >= FormatStyle::LS_Cpp14;
+  LangOpts.CPlusPlus17 = LexingStd >= FormatStyle::LS_Cpp17;
+  LangOpts.CPlusPlus2a = LexingStd >= FormatStyle::LS_Cpp20;
+
   LangOpts.LineComment = 1;
   bool AlternativeOperators = Style.isCpp();
   LangOpts.CXXOperatorNames = AlternativeOperators ? 1 : 0;