clang-format: Handle "if constexpr".

c++1z adds the following constructions to the language:

  if constexpr (cond)
    statement1;
  else if constexpr (cond)
    statement2;
  else if constexpr (cond)
    statement3;
  else
    statement4;

A first version of this was proposed in reviews.llvm.org/D26953 by
Francis Visoiu Mistrih, but never commited. This patch additionally
fixes the behavior when allowing short if statements on a single line
and was authored by Jacob Bandes-Storch. Thank you to both authors.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@305666 91177308-0d34-0410-b5e6-96231b3b80d8

3 files changed, 10 insertions, 2 deletions

diff --git a/lib/Format/ContinuationIndenter.cpp b/lib/Format/ContinuationIndenter.cpp
index 387923031f..bc8fe54995 100644
--- a/lib/Format/ContinuationIndenter.cpp
+++ b/lib/Format/ContinuationIndenter.cpp
@@ -453,7 +453,8 @@ void ContinuationIndenter::addTokenOnCurrentLine(LineState &State, bool DryRun,
   State.Column += Spaces;
   if (Current.isNot(tok::comment) && Previous.is(tok::l_paren) &&
       Previous.Previous &&
-      Previous.Previous->isOneOf(tok::kw_if, tok::kw_for)) {
+      (Previous.Previous->isOneOf(tok::kw_if, tok::kw_for) ||
+       Previous.Previous->endsSequence(tok::kw_constexpr, tok::kw_if))) {
     // Treat the condition inside an if as if it was a second function
     // parameter, i.e. let nested calls have a continuation indent.
     State.Stack.back().LastSpace = State.Column;
diff --git a/lib/Format/TokenAnnotator.cpp b/lib/Format/TokenAnnotator.cpp
index 7ce699cf14..5e50268e3a 100644
--- a/lib/Format/TokenAnnotator.cpp
+++ b/lib/Format/TokenAnnotator.cpp
@@ -145,6 +145,7 @@ private:
         (Left->Previous->isOneOf(tok::kw_static_assert, tok::kw_decltype,
                                  tok::kw_if, tok::kw_while, tok::l_paren,
                                  tok::comma) ||
+         Left->Previous->endsSequence(tok::kw_constexpr, tok::kw_if) ||
          Left->Previous->is(TT_BinaryOperator))) {
       // static_assert, if and while usually contain expressions.
       Contexts.back().IsExpression = true;
@@ -572,6 +573,8 @@ private:
       break;
     case tok::kw_if:
     case tok::kw_while:
+      if (Tok->is(tok::kw_if) && CurrentToken && CurrentToken->is(tok::kw_constexpr))
+        next();
       if (CurrentToken && CurrentToken->is(tok::l_paren)) {
         next();
         if (!parseParens(/*LookForDecls=*/true))
@@ -2060,7 +2063,8 @@ unsigned TokenAnnotator::splitPenalty(const AnnotatedLine &Line,
       Style.AlignAfterOpenBracket != FormatStyle::BAS_DontAlign)
     return 100;
   if (Left.is(tok::l_paren) && Left.Previous &&
-      Left.Previous->isOneOf(tok::kw_if, tok::kw_for))
+      (Left.Previous->isOneOf(tok::kw_if, tok::kw_for)
+       || Left.Previous->endsSequence(tok::kw_constexpr, tok::kw_if)))
     return 1000;
   if (Left.is(tok::equal) && InFunctionDecl)
     return 110;
@@ -2211,6 +2215,7 @@ bool TokenAnnotator::spaceRequiredBetween(const AnnotatedLine &Line,
             (Left.isOneOf(tok::kw_if, tok::pp_elif, tok::kw_for, tok::kw_while,
                           tok::kw_switch, tok::kw_case, TT_ForEachMacro,
                           TT_ObjCForIn) ||
+             Left.endsSequence(tok::kw_constexpr, tok::kw_if) ||
              (Left.isOneOf(tok::kw_try, Keywords.kw___except, tok::kw_catch,
                            tok::kw_new, tok::kw_delete) &&
               (!Left.Previous || Left.Previous->isNot(tok::period))))) ||
diff --git a/lib/Format/UnwrappedLineParser.cpp b/lib/Format/UnwrappedLineParser.cpp
index 27436dda67..f7678bb6b2 100644
--- a/lib/Format/UnwrappedLineParser.cpp
+++ b/lib/Format/UnwrappedLineParser.cpp
@@ -1516,6 +1516,8 @@ void UnwrappedLineParser::parseSquare() {
 void UnwrappedLineParser::parseIfThenElse() {
   assert(FormatTok->Tok.is(tok::kw_if) && "'if' expected");
   nextToken();
+  if (FormatTok->Tok.is(tok::kw_constexpr))
+    nextToken();
   if (FormatTok->Tok.is(tok::l_paren))
     parseParens();
   bool NeedsUnwrappedLine = false;