clang-format: add option to merge empty function body

Summary:
This option supplements the AllowShortFunctionsOnASingleLine flag, to
merge empty function body at the beginning of the line: e.g. when the
function is not short-enough and breaking braces after function.

  int f()
  {}

Reviewers: krasimir, djasper

Reviewed By: djasper

Subscribers: klimek, cfe-commits

Differential Revision: https://reviews.llvm.org/D33447

llvm-svn: 305272

2 files changed, 15 insertions, 4 deletions

diff --git a/clang/lib/Format/Format.cpp b/clang/lib/Format/Format.cpp
index 2ef6516e02e..0eaf44d2048 100644
--- a/clang/lib/Format/Format.cpp
+++ b/clang/lib/Format/Format.cpp
@@ -410,6 +410,7 @@ template <> struct MappingTraits<FormatStyle::BraceWrappingFlags> {
     IO.mapOptional("BeforeCatch", Wrapping.BeforeCatch);
     IO.mapOptional("BeforeElse", Wrapping.BeforeElse);
     IO.mapOptional("IndentBraces", Wrapping.IndentBraces);
+    IO.mapOptional("SplitEmptyFunctionBody", Wrapping.SplitEmptyFunctionBody);
   }
 };
 
@@ -485,7 +486,7 @@ static FormatStyle expandPresets(const FormatStyle &Style) {
     return Style;
   FormatStyle Expanded = Style;
   Expanded.BraceWrapping = {false, false, false, false, false, false,
-                            false, false, false, false, false};
+                            false, false, false, false, false, true};
   switch (Style.BreakBeforeBraces) {
   case FormatStyle::BS_Linux:
     Expanded.BraceWrapping.AfterClass = true;
@@ -498,6 +499,7 @@ static FormatStyle expandPresets(const FormatStyle &Style) {
     Expanded.BraceWrapping.AfterFunction = true;
     Expanded.BraceWrapping.AfterStruct = true;
     Expanded.BraceWrapping.AfterUnion = true;
+    Expanded.BraceWrapping.SplitEmptyFunctionBody = false;
     break;
   case FormatStyle::BS_Stroustrup:
     Expanded.BraceWrapping.AfterFunction = true;
@@ -517,7 +519,7 @@ static FormatStyle expandPresets(const FormatStyle &Style) {
     break;
   case FormatStyle::BS_GNU:
     Expanded.BraceWrapping = {true, true, true, true, true, true,
-                              true, true, true, true, true};
+                              true, true, true, true, true, true};
     break;
   case FormatStyle::BS_WebKit:
     Expanded.BraceWrapping.AfterFunction = true;
@@ -554,7 +556,7 @@ FormatStyle getLLVMStyle() {
   LLVMStyle.BreakBeforeTernaryOperators = true;
   LLVMStyle.BreakBeforeBraces = FormatStyle::BS_Attach;
   LLVMStyle.BraceWrapping = {false, false, false, false, false, false,
-                             false, false, false, false, false};
+                             false, false, false, false, false, true};
   LLVMStyle.BreakAfterJavaFieldAnnotations = false;
   LLVMStyle.BreakConstructorInitializers = FormatStyle::BCIS_BeforeColon;
   LLVMStyle.BreakBeforeInheritanceComma = false;
diff --git a/clang/lib/Format/UnwrappedLineFormatter.cpp b/clang/lib/Format/UnwrappedLineFormatter.cpp
index 01504da0a29..eb8de6598eb 100644
--- a/clang/lib/Format/UnwrappedLineFormatter.cpp
+++ b/clang/lib/Format/UnwrappedLineFormatter.cpp
@@ -186,6 +186,12 @@ private:
                 ? 0
                 : Limit - TheLine->Last->TotalLength;
 
+    if (TheLine->Last->is(TT_FunctionLBrace) &&
+        TheLine->First == TheLine->Last &&
+        !Style.BraceWrapping.SplitEmptyFunctionBody &&
+        I[1]->First->is(tok::r_brace))
+      return tryMergeSimpleBlock(I, E, Limit);
+
     // FIXME: TheLine->Level != 0 might or might not be the right check to do.
     // If necessary, change to something smarter.
     bool MergeShortFunctions =
@@ -215,7 +221,10 @@ private:
       Limit -= 2;
 
       unsigned MergedLines = 0;
-      if (MergeShortFunctions) {
+      if (MergeShortFunctions ||
+          (Style.AllowShortFunctionsOnASingleLine >= FormatStyle::SFS_Empty &&
+           I[1]->First == I[1]->Last && I + 2 != E &&
+           I[2]->First->is(tok::r_brace))) {
         MergedLines = tryMergeSimpleBlock(I + 1, E, Limit);
         // If we managed to merge the block, count the function header, which is
         // on a separate line.