[clang-format] New flag - BraceWrapping.AfterExternBlock

[PriMee]

Summary

Bug: https://bugs.llvm.org/show_bug.cgi?id=34016 - "extern C part"

Problem:

Due to the lack of "brace wrapping extern" flag, clang format does parse the block after extern keyword moving the opening bracket to the header line always!

Patch description:

A new style added, new configuration flag - BraceWrapping.AfterExternBlock that allows us to decide whether we want a break before brace or not.

[krasimir]

docs/ClangFormatStyleOptions.rst

664

I think this is overly specific. The C++ standard also [[ http://en.cppreference.com/w/cpp/language/language_linkage | allows extern "C++" blocks ]]. I'd rename this to AfterExternBlock or something similar.

lib/Format/UnwrappedLineParser.cpp

1044

I think we should keep the old /*AddLevel=*/false when AfterExternC is false. That way you also don't have to change the following test case.

[PriMee]

Done :)

[krasimir]

lib/Format/UnwrappedLineParser.cpp

1047

Please clang-format the newly added lines.

[PriMee]

Sorry, forgot again...

[krasimir]

Looks great! Just one more nit: please add a line checking the parsing of the new option similar to the line CHECK_PARSE_NESTED_BOOL(BraceWrapping, AfterStruct); in unittests/Format/FormatTest.cpp.

[PriMee]

Thank you for noticing! Done.

[krasimir]

Looks good! Should I commit this for you?

[PriMee]

I would be grateful, thank you!

docs/ClangFormatStyleOptions.rst

.. code-block:: c++
         int x;
       }
 
       false:
       union foo {
         int x;
       }
 
+  * ``bool AfterExternBlock`` Wrap extern blocks.
+
+    .. code-block:: c++
+
+      true:
+      extern "C"
+      {
+        int foo();
+      }
+
+      false:
+      extern "C" {
+      int foo();
+      }
+
   * ``bool BeforeCatch`` Wrap before ``catch``.
 
     .. code-block:: c++
 
       true:
       try {
         foo();
       }

include/clang/Format/Format.h

struct BraceWrappingFlags {
     ///   }
     ///
     ///   false:
     ///   union foo {
     ///     int x;
     ///   }
     /// \endcode
     bool AfterUnion;
+    /// \brief Wrap extern blocks.
+    /// \code
+    ///   true:
+    ///   extern "C"
+    ///   {
+    ///     int foo();
+    ///   }
+    ///
+    ///   false:
+    ///   extern "C" {
+    ///   int foo();
+    ///   }
+    /// \endcode
+    bool AfterExternBlock;
     /// \brief Wrap before ``catch``.
     /// \code
     ///   true:
     ///   try {
     ///     foo();
     ///   }
     ///   catch () {
     ///   }

lib/Format/Format.cpp

static void mapping(IO &IO, FormatStyle::BraceWrappingFlags &Wrapping) {
     IO.mapOptional("AfterClass", Wrapping.AfterClass);
     IO.mapOptional("AfterControlStatement", Wrapping.AfterControlStatement);
     IO.mapOptional("AfterEnum", Wrapping.AfterEnum);
     IO.mapOptional("AfterFunction", Wrapping.AfterFunction);
     IO.mapOptional("AfterNamespace", Wrapping.AfterNamespace);
     IO.mapOptional("AfterObjCDeclaration", Wrapping.AfterObjCDeclaration);
     IO.mapOptional("AfterStruct", Wrapping.AfterStruct);
     IO.mapOptional("AfterUnion", Wrapping.AfterUnion);
+    IO.mapOptional("AfterExternBlock", Wrapping.AfterExternBlock);
     IO.mapOptional("BeforeCatch", Wrapping.BeforeCatch);
     IO.mapOptional("BeforeElse", Wrapping.BeforeElse);
     IO.mapOptional("IndentBraces", Wrapping.IndentBraces);
     IO.mapOptional("SplitEmptyFunction", Wrapping.SplitEmptyFunction);
     IO.mapOptional("SplitEmptyRecord", Wrapping.SplitEmptyRecord);
     IO.mapOptional("SplitEmptyNamespace", Wrapping.SplitEmptyNamespace);
   }
 };
std::string ParseErrorCategory::message(int EV) const {
   }
   llvm_unreachable("unexpected parse error");
 }
 
 static FormatStyle expandPresets(const FormatStyle &Style) {
   if (Style.BreakBeforeBraces == FormatStyle::BS_Custom)
     return Style;
   FormatStyle Expanded = Style;
-  Expanded.BraceWrapping = {false, false, false, false, false, false,
-                            false, false, false, false, false, true,
-                            true,  true};
+  Expanded.BraceWrapping = {false, false, false, false, false, false, 
+                            false, false, false, false, false, false, 
+                            true,  true,  true};
   switch (Style.BreakBeforeBraces) {
   case FormatStyle::BS_Linux:
     Expanded.BraceWrapping.AfterClass = true;
     Expanded.BraceWrapping.AfterFunction = true;
     Expanded.BraceWrapping.AfterNamespace = true;
     break;
   case FormatStyle::BS_Mozilla:
     Expanded.BraceWrapping.AfterClass = true;
     Expanded.BraceWrapping.AfterEnum = true;
     Expanded.BraceWrapping.AfterFunction = true;
     Expanded.BraceWrapping.AfterStruct = true;
     Expanded.BraceWrapping.AfterUnion = true;
+    Expanded.BraceWrapping.AfterExternBlock = true;
     Expanded.BraceWrapping.SplitEmptyFunction = true;
     Expanded.BraceWrapping.SplitEmptyRecord = false;
     break;
   case FormatStyle::BS_Stroustrup:
     Expanded.BraceWrapping.AfterFunction = true;
     Expanded.BraceWrapping.BeforeCatch = true;
     Expanded.BraceWrapping.BeforeElse = true;
     break;
   case FormatStyle::BS_Allman:
     Expanded.BraceWrapping.AfterClass = true;
     Expanded.BraceWrapping.AfterControlStatement = true;
     Expanded.BraceWrapping.AfterEnum = true;
     Expanded.BraceWrapping.AfterFunction = true;
     Expanded.BraceWrapping.AfterNamespace = true;
     Expanded.BraceWrapping.AfterObjCDeclaration = true;
     Expanded.BraceWrapping.AfterStruct = true;
+    Expanded.BraceWrapping.AfterExternBlock = true;
     Expanded.BraceWrapping.BeforeCatch = true;
     Expanded.BraceWrapping.BeforeElse = true;
     break;
   case FormatStyle::BS_GNU:
-    Expanded.BraceWrapping = {true, true, true, true, true, true,
-                              true, true, true, true, true, true,
-                              true, true};
+    Expanded.BraceWrapping = {true, true, true, true, true, true, 
+                              true, true, true, true, true, true, 
+                              true, true, true};
     break;
   case FormatStyle::BS_WebKit:
     Expanded.BraceWrapping.AfterFunction = true;
     break;
   default:
     break;
   }
   return Expanded;
FormatStyle getLLVMStyle() {
   LLVMStyle.AlwaysBreakAfterDefinitionReturnType = FormatStyle::DRTBS_None;
   LLVMStyle.AlwaysBreakBeforeMultilineStrings = false;
   LLVMStyle.AlwaysBreakTemplateDeclarations = false;
   LLVMStyle.BinPackArguments = true;
   LLVMStyle.BinPackParameters = true;
   LLVMStyle.BreakBeforeBinaryOperators = FormatStyle::BOS_None;
   LLVMStyle.BreakBeforeTernaryOperators = true;
   LLVMStyle.BreakBeforeBraces = FormatStyle::BS_Attach;
-  LLVMStyle.BraceWrapping = {false, false, false, false, false, false,
-                             false, false, false, false, false, true,
-                             true,  true};
+  LLVMStyle.BraceWrapping = {false, false, false, false, false, false, 
+                             false, false, false, false, false, false, 
+                             true,  true,  true};
   LLVMStyle.BreakAfterJavaFieldAnnotations = false;
   LLVMStyle.BreakConstructorInitializers = FormatStyle::BCIS_BeforeColon;
   LLVMStyle.BreakBeforeInheritanceComma = false;
   LLVMStyle.BreakStringLiterals = true;
   LLVMStyle.ColumnLimit = 80;
   LLVMStyle.CommentPragmas = "^ IWYU pragma:";
   LLVMStyle.CompactNamespaces = false;
   LLVMStyle.ConstructorInitializerAllOnOneLineOrOnePerLine = false;

lib/Format/UnwrappedLineFormatter.cpp

if (TheLine->Last->is(tok::l_brace) && TheLine->First == TheLine->Last &&
 
       if (Tok && Tok->getNamespaceToken())
         return !Style.BraceWrapping.SplitEmptyNamespace && EmptyBlock
             ? tryMergeSimpleBlock(I, E, Limit) : 0;
 
       if (Tok && Tok->is(tok::kw_typedef))
         Tok = Tok->getNextNonComment();
       if (Tok && Tok->isOneOf(tok::kw_class, tok::kw_struct, tok::kw_union,
-                              Keywords.kw_interface))
+                              tok::kw_extern, Keywords.kw_interface))
         return !Style.BraceWrapping.SplitEmptyRecord && EmptyBlock
-            ? tryMergeSimpleBlock(I, E, Limit) : 0;
+                   ? tryMergeSimpleBlock(I, E, Limit)
+                   : 0;
     }
 
     // FIXME: TheLine->Level != 0 might or might not be the right check to do.
     // If necessary, change to something smarter.
     bool MergeShortFunctions =
         Style.AllowShortFunctionsOnASingleLine == FormatStyle::SFS_All ||
         (Style.AllowShortFunctionsOnASingleLine >= FormatStyle::SFS_Empty &&
          I[1]->First->is(tok::r_brace)) ||

lib/Format/UnwrappedLineParser.cpp

void UnwrappedLineParser::parseStructuralElement() {
   case tok::kw___try:
     parseTryCatch();
     return;
   case tok::kw_extern:
     nextToken();
     if (FormatTok->Tok.is(tok::string_literal)) {
       nextToken();
       if (FormatTok->Tok.is(tok::l_brace)) {
+        if (Style.BraceWrapping.AfterExternBlock) {
+          addUnwrappedLine();
+          parseBlock(/*MustBeDeclaration=*/true);
+        } else {
           parseBlock(/*MustBeDeclaration=*/true, /*AddLevel=*/false);
+        }
         addUnwrappedLine();
         return;
       }
     }
     break;
   case tok::kw_export:
     if (Style.Language == FormatStyle::LK_JavaScript) {
       parseJavaScriptEs6ImportExport();

unittests/Format/FormatTest.cpp

EXPECT_EQ("namespace out { namespace mid { namespace in {\n"
                    "namespace in {\n"
                    "int i;\n"
                    "} // namespace in\n"
                    "} // namespace mid\n"
                    "} // namespace out",
                    Style));
 }
 
-TEST_F(FormatTest, FormatsExternC) { verifyFormat("extern \"C\" {\nint a;"); }
+TEST_F(FormatTest, FormatsExternC) {
+  verifyFormat("extern \"C\" {\nint a;");
+  verifyFormat("extern \"C\" {}");
+  verifyFormat("extern \"C\" {\n"
+               "int foo();\n"
+               "}");
+  verifyFormat("extern \"C\" int foo() {}");
+  verifyFormat("extern \"C\" int foo();");
+  verifyFormat("extern \"C\" int foo() {\n"
+               "  int i = 42;\n"
+               "  return i;\n"
+               "}");
+
+  FormatStyle Style = getLLVMStyle();
+  Style.BreakBeforeBraces = FormatStyle::BS_Custom;
+  Style.BraceWrapping.AfterFunction = true;
+  verifyFormat("extern \"C\" int foo() {}", Style);
+  verifyFormat("extern \"C\" int foo();", Style);
+  verifyFormat("extern \"C\" int foo()\n"
+               "{\n"
+               "  int i = 42;\n"
+               "  return i;\n"
+               "}",
+               Style);
+
+  Style.BraceWrapping.AfterExternBlock = true;
+  Style.BraceWrapping.SplitEmptyRecord = false;
+  verifyFormat("extern \"C\"\n"
+               "{}",
+               Style);
+  verifyFormat("extern \"C\"\n"
+               "{\n"
+               "  int foo();\n"
+               "}",
+               Style);
+}
 
 TEST_F(FormatTest, FormatsInlineASM) {
   verifyFormat("asm(\"xyz\" : \"=a\"(a), \"=d\"(b) : \"a\"(data));");
   verifyFormat("asm(\"nop\" ::: \"memory\");");
   verifyFormat(
       "asm(\"movq\\t%%rbx, %%rsi\\n\\t\"\n"
       "    \"cpuid\\n\\t\"\n"
       "    \"xchgq\\t%%rbx, %%rsi\\n\\t\"\n"