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

clang/include/clang/Format/Format.h

@@ -688,6 +688,18 @@ struct FormatStyle {
     bool BeforeElse;
     /// \brief Indent the wrapped braces themselves.
     bool IndentBraces;
+    /// \brief If ``false``, empty function body can be put on a single line.
+    /// This option is used only if the opening brace of the function has
+    /// already been wrapped, i.e. the `AfterFunction` brace wrapping mode is
+    /// set, and the function could/should not be put on a single line (as per
+    /// `AllowShortFunctionsOnASingleLine` and constructor formatting options).
+    /// \code
+    ///   int f()   vs.   inf f()
+    ///   {}              {
+    ///                   }
+    /// \endcode
+    ///
+    bool SplitEmptyFunctionBody;
   };
 
   /// \brief Control of individual brace wrapping cases.

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;

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.

clang/unittests/Format/FormatTest.cpp

@@ -6239,6 +6239,35 @@ TEST_F(FormatTest, PullTrivialFunctionDefinitionsIntoSingleLine) {
                getLLVMStyleWithColumns(23));
 }
 
+TEST_F(FormatTest, PullEmptyFunctionDefinitionsIntoSingleLine) {
+  FormatStyle MergeEmptyOnly = getLLVMStyle();
+  MergeEmptyOnly.AllowShortFunctionsOnASingleLine = FormatStyle::SFS_Empty;
+  verifyFormat("class C {\n"
+               "  int f() {}\n"
+               "};",
+               MergeEmptyOnly);
+  verifyFormat("class C {\n"
+               "  int f() {\n"
+               "    return 42;\n"
+               "  }\n"
+               "};",
+               MergeEmptyOnly);
+  verifyFormat("int f() {}", MergeEmptyOnly);
+  verifyFormat("int f() {\n"
+               "  return 42;\n"
+               "}",
+               MergeEmptyOnly);
+
+  // Also verify behavior when BraceWrapping.AfterFunction = true
+  MergeEmptyOnly.BreakBeforeBraces = FormatStyle::BS_Custom;
+  MergeEmptyOnly.BraceWrapping.AfterFunction = true;
+  verifyFormat("int f() {}", MergeEmptyOnly);
+  verifyFormat("class C {\n"
+               "  int f() {}\n"
+               "};",
+               MergeEmptyOnly);
+}
+
 TEST_F(FormatTest, PullInlineFunctionDefinitionsIntoSingleLine) {
   FormatStyle MergeInlineOnly = getLLVMStyle();
   MergeInlineOnly.AllowShortFunctionsOnASingleLine = FormatStyle::SFS_Inline;
@@ -6250,6 +6279,101 @@ TEST_F(FormatTest, PullInlineFunctionDefinitionsIntoSingleLine) {
                "  return 42;\n"
                "}",
                MergeInlineOnly);
+
+  // SFS_Inline implies SFS_Empty
+  verifyFormat("class C {\n"
+               "  int f() {}\n"
+               "};",
+               MergeInlineOnly);
+  verifyFormat("int f() {}", MergeInlineOnly);
+
+  // Also verify behavior when BraceWrapping.AfterFunction = true
+  MergeInlineOnly.BreakBeforeBraces = FormatStyle::BS_Custom;
+  MergeInlineOnly.BraceWrapping.AfterFunction = true;
+  verifyFormat("class C {\n"
+               "  int f() { return 42; }\n"
+               "};",
+               MergeInlineOnly);
+  verifyFormat("int f()\n"
+               "{\n"
+               "  return 42;\n"
+               "}",
+               MergeInlineOnly);
+
+  // SFS_Inline implies SFS_Empty
+  verifyFormat("int f() {}", MergeInlineOnly);
+  verifyFormat("class C {\n"
+               "  int f() {}\n"
+               "};",
+               MergeInlineOnly);
+}
+
+TEST_F(FormatTest, SplitEmptyFunctionBody) {
+  FormatStyle Style = getLLVMStyle();
+  Style.AllowShortFunctionsOnASingleLine = FormatStyle::SFS_None;
+  Style.BreakBeforeBraces = FormatStyle::BS_Custom;
+  Style.BraceWrapping.AfterFunction = true;
+  Style.BraceWrapping.SplitEmptyFunctionBody = false;
+  Style.ColumnLimit = 40;
+
+  verifyFormat("int f()\n"
+               "{}",
+               Style);
+  verifyFormat("int f()\n"
+               "{\n"
+               "  return 42;\n"
+               "}",
+               Style);
+  verifyFormat("int f()\n"
+               "{\n"
+               "  // some comment\n"
+               "}",
+               Style);
+
+  Style.AllowShortFunctionsOnASingleLine = FormatStyle::SFS_Empty;
+  verifyFormat("int f() {}", Style);
+  verifyFormat("int aaaaaaaaaaaaaa(int bbbbbbbbbbbbbb)\n"
+               "{}",
+               Style);
+  verifyFormat("int f()\n"
+               "{\n"
+               "  return 0;\n"
+               "}",
+               Style);
+
+  Style.AllowShortFunctionsOnASingleLine = FormatStyle::SFS_Inline;
+  verifyFormat("class Foo {\n"
+               "  int f() {}\n"
+               "};\n",
+               Style);
+  verifyFormat("class Foo {\n"
+               "  int f() { return 0; }\n"
+               "};\n",
+               Style);
+  verifyFormat("class Foo {\n"
+               "  int aaaaaaaaaaaaaa(int bbbbbbbbbbbbbb)\n"
+               "  {}\n"
+               "};\n",
+               Style);
+  verifyFormat("class Foo {\n"
+               "  int aaaaaaaaaaaaaa(int bbbbbbbbbbbbbb)\n"
+               "  {\n"
+               "    return 0;\n"
+               "  }\n"
+               "};\n",
+               Style);
+
+  Style.AllowShortFunctionsOnASingleLine = FormatStyle::SFS_All;
+  verifyFormat("int f() {}", Style);
+  verifyFormat("int f() { return 0; }", Style);
+  verifyFormat("int aaaaaaaaaaaaaa(int bbbbbbbbbbbbbb)\n"
+               "{}",
+               Style);
+  verifyFormat("int aaaaaaaaaaaaaa(int bbbbbbbbbbbbbb)\n"
+               "{\n"
+               "  return 0;\n"
+               "}",
+               Style);
 }
 
 TEST_F(FormatTest, UnderstandContextOfRecordTypeKeywords) {
@@ -8960,6 +9084,7 @@ TEST_F(FormatTest, ParsesConfigurationBools) {
   CHECK_PARSE_NESTED_BOOL(BraceWrapping, BeforeCatch);
   CHECK_PARSE_NESTED_BOOL(BraceWrapping, BeforeElse);
   CHECK_PARSE_NESTED_BOOL(BraceWrapping, IndentBraces);
+  CHECK_PARSE_NESTED_BOOL(BraceWrapping, SplitEmptyFunctionBody);
 }
 
 #undef CHECK_PARSE_BOOL