[clang-format] Improve brace wrapping and add an option to control indentation of export { ... } (#110381)

`export { ... }` blocks can get a bit long, so I thought it would make
sense to have an option that makes it so their contents are not indented
(basically the same argument as for namespaces).

This is based on the `NamespaceIndentation` option, except that there is
no option to control the behaviour of `export` blocks when nested because
nesting them doesn’t really make sense.

Additionally, brace wrapping of short `export { ... }` blocks is now controlled by the
`AllowShortBlocksOnASingleLine` option. There is no separate option just for `export`
blocks because you can just write e.g. `export int x;` instead of `export { int x; }`.

This closes #121723.

Author: Sirraide

clang/docs/ClangFormatStyleOptions.rst

@@ -3946,6 +3946,21 @@ the configuration (without a prefix: ``Auto``).
    This is an experimental flag, that might go away or be renamed. Do
    not use this in config files, etc. Use at your own risk.
 
+.. _ExportBlockIndentation:
+
+**ExportBlockIndentation** (``Boolean``) :versionbadge:`clang-format 20` :ref:`¶ <ExportBlockIndentation>`
+  If ``true``, clang-format will indent the body of an ``export { ... }``
+  block. This doesn't affect the formatting of anything else related to
+  exported declarations.
+
+  .. code-block:: c++
+
+     true:                     false:
+     export {          vs.     export {
+       void foo();             void foo();
+       void bar();             void bar();
+     }                         }
+
 .. _FixNamespaceComments:
 
 **FixNamespaceComments** (``Boolean``) :versionbadge:`clang-format 5` :ref:`¶ <FixNamespaceComments>`

clang/docs/ReleaseNotes.rst

@@ -1224,6 +1224,7 @@ clang-format
 - Adds ``VariableTemplates`` option.
 - Adds support for bash globstar in ``.clang-format-ignore``.
 - Adds ``WrapNamespaceBodyWithEmptyLines`` option.
+- Adds the ``ExportBlockIndentation`` option.
 
 libclang
 --------

clang/include/clang/Format/Format.h

@@ -2676,6 +2676,19 @@ struct FormatStyle {
   /// \version 3.7
   bool ExperimentalAutoDetectBinPacking;
 
+  /// If ``true``, clang-format will indent the body of an ``export { ... }``
+  /// block. This doesn't affect the formatting of anything else related to
+  /// exported declarations.
+  /// \code
+  ///    true:                     false:
+  ///    export {          vs.     export {
+  ///      void foo();             void foo();
+  ///      void bar();             void bar();
+  ///    }                         }
+  /// \endcode
+  /// \version 20
+  bool ExportBlockIndentation;
+
   /// If ``true``, clang-format adds missing namespace end comments for
   /// namespaces and fixes invalid existing ones. This doesn't affect short
   /// namespaces, which are controlled by ``ShortNamespaceLines``.
@@ -5254,6 +5267,7 @@ struct FormatStyle {
            EmptyLineBeforeAccessModifier == R.EmptyLineBeforeAccessModifier &&
            ExperimentalAutoDetectBinPacking ==
                R.ExperimentalAutoDetectBinPacking &&
+           ExportBlockIndentation == R.ExportBlockIndentation &&
            FixNamespaceComments == R.FixNamespaceComments &&
            ForEachMacros == R.ForEachMacros &&
            IncludeStyle.IncludeBlocks == R.IncludeStyle.IncludeBlocks &&

clang/lib/Format/Format.cpp

@@ -1040,6 +1040,7 @@ template <> struct MappingTraits<FormatStyle> {
                    Style.EmptyLineBeforeAccessModifier);
     IO.mapOptional("ExperimentalAutoDetectBinPacking",
                    Style.ExperimentalAutoDetectBinPacking);
+    IO.mapOptional("ExportBlockIndentation", Style.ExportBlockIndentation);
     IO.mapOptional("FixNamespaceComments", Style.FixNamespaceComments);
     IO.mapOptional("ForEachMacros", Style.ForEachMacros);
     IO.mapOptional("IfMacros", Style.IfMacros);
@@ -1550,6 +1551,7 @@ FormatStyle getLLVMStyle(FormatStyle::LanguageKind Language) {
   LLVMStyle.EmptyLineAfterAccessModifier = FormatStyle::ELAAMS_Never;
   LLVMStyle.EmptyLineBeforeAccessModifier = FormatStyle::ELBAMS_LogicalBlock;
   LLVMStyle.ExperimentalAutoDetectBinPacking = false;
+  LLVMStyle.ExportBlockIndentation = true;
   LLVMStyle.FixNamespaceComments = true;
   LLVMStyle.ForEachMacros.push_back("foreach");
   LLVMStyle.ForEachMacros.push_back("Q_FOREACH");

clang/lib/Format/TokenAnnotator.h

@@ -154,6 +154,11 @@ class AnnotatedLine {
            startsWith(tok::kw_export, tok::kw_namespace);
   }
 
+  /// \c true if this line starts a C++ export block.
+  bool startsWithExportBlock() const {
+    return startsWith(tok::kw_export, tok::l_brace);
+  }
+
   FormatToken *getFirstNonComment() const {
     assert(First);
     return First->is(tok::comment) ? First->getNextNonComment() : First;

clang/lib/Format/UnwrappedLineFormatter.cpp

@@ -432,8 +432,9 @@ class LineJoiner {
 
     // Try to merge a control statement block with left brace unwrapped.
     if (TheLine->Last->is(tok::l_brace) && FirstNonComment != TheLine->Last &&
-        FirstNonComment->isOneOf(tok::kw_if, tok::kw_while, tok::kw_for,
-                                 TT_ForEachMacro)) {
+        (FirstNonComment->isOneOf(tok::kw_if, tok::kw_while, tok::kw_for,
+                                  TT_ForEachMacro) ||
+         TheLine->startsWithExportBlock())) {
       return Style.AllowShortBlocksOnASingleLine != FormatStyle::SBS_Never
                  ? tryMergeSimpleBlock(I, E, Limit)
                  : 0;
@@ -832,7 +833,8 @@ class LineJoiner {
     if (IsCtrlStmt(Line) ||
         Line.First->isOneOf(tok::kw_try, tok::kw___try, tok::kw_catch,
                             tok::kw___finally, tok::r_brace,
-                            Keywords.kw___except)) {
+                            Keywords.kw___except) ||
+        Line.startsWithExportBlock()) {
       if (IsSplitBlock)
         return 0;
       // Don't merge when we can't except the case when

clang/lib/Format/UnwrappedLineParser.cpp

@@ -1625,6 +1625,10 @@ void UnwrappedLineParser::parseStructuralElement(
         parseNamespace();
         return;
       }
+      if (FormatTok->is(tok::l_brace)) {
+        parseCppExportBlock();
+        return;
+      }
       if (FormatTok->is(Keywords.kw_import) && parseModuleImport())
         return;
     }
@@ -3105,6 +3109,26 @@ void UnwrappedLineParser::parseTryCatch() {
     addUnwrappedLine();
 }
 
+void UnwrappedLineParser::parseNamespaceOrExportBlock(unsigned AddLevels) {
+  bool ManageWhitesmithsBraces =
+      AddLevels == 0u && Style.BreakBeforeBraces == FormatStyle::BS_Whitesmiths;
+
+  // If we're in Whitesmiths mode, indent the brace if we're not indenting
+  // the whole block.
+  if (ManageWhitesmithsBraces)
+    ++Line->Level;
+
+  // Munch the semicolon after the block. This is more common than one would
+  // think. Putting the semicolon into its own line is very ugly.
+  parseBlock(/*MustBeDeclaration=*/true, AddLevels, /*MunchSemi=*/true,
+             /*KeepBraces=*/true, /*IfKind=*/nullptr, ManageWhitesmithsBraces);
+
+  addUnwrappedLine(AddLevels > 0 ? LineLevel::Remove : LineLevel::Keep);
+
+  if (ManageWhitesmithsBraces)
+    --Line->Level;
+}
+
 void UnwrappedLineParser::parseNamespace() {
   assert(FormatTok->isOneOf(tok::kw_namespace, TT_NamespaceMacro) &&
          "'namespace' expected");
@@ -3137,29 +3161,16 @@ void UnwrappedLineParser::parseNamespace() {
                  DeclarationScopeStack.size() > 1)
             ? 1u
             : 0u;
-    bool ManageWhitesmithsBraces =
-        AddLevels == 0u &&
-        Style.BreakBeforeBraces == FormatStyle::BS_Whitesmiths;
-
-    // If we're in Whitesmiths mode, indent the brace if we're not indenting
-    // the whole block.
-    if (ManageWhitesmithsBraces)
-      ++Line->Level;
-
-    // Munch the semicolon after a namespace. This is more common than one would
-    // think. Putting the semicolon into its own line is very ugly.
-    parseBlock(/*MustBeDeclaration=*/true, AddLevels, /*MunchSemi=*/true,
-               /*KeepBraces=*/true, /*IfKind=*/nullptr,
-               ManageWhitesmithsBraces);
-
-    addUnwrappedLine(AddLevels > 0 ? LineLevel::Remove : LineLevel::Keep);
-
-    if (ManageWhitesmithsBraces)
-      --Line->Level;
+    parseNamespaceOrExportBlock(AddLevels);
   }
   // FIXME: Add error handling.
 }
 
+void UnwrappedLineParser::parseCppExportBlock() {
+  parseNamespaceOrExportBlock(/*AddLevels=*/Style.ExportBlockIndentation ? 1
+                                                                         : 0);
+}
+
 void UnwrappedLineParser::parseNew() {
   assert(FormatTok->is(tok::kw_new) && "'new' expected");
   nextToken();

clang/lib/Format/UnwrappedLineParser.h

@@ -171,6 +171,8 @@ class UnwrappedLineParser {
   void parseRequiresClause(FormatToken *RequiresToken);
   void parseRequiresExpression(FormatToken *RequiresToken);
   void parseConstraintExpression();
+  void parseCppExportBlock();
+  void parseNamespaceOrExportBlock(unsigned AddLevels);
   void parseJavaEnumBody();
   // Parses a record (aka class) as a top level element. If ParseAsExpr is true,
   // parses the record as a child block, i.e. if the class declaration is an

clang/unittests/Format/FormatTest.cpp

@@ -9059,6 +9059,121 @@ TEST_F(FormatTest, AdaptiveOnePerLineFormatting) {
                Style);
 }
 
+TEST_F(FormatTest, ExportBlockIndentation) {
+  FormatStyle Style = getLLVMStyleWithColumns(80);
+  Style.ExportBlockIndentation = true;
+  verifyFormat("export {\n"
+               "  int x;\n"
+               "  int y;\n"
+               "}",
+               "export {\n"
+               "int x;\n"
+               "int y;\n"
+               "}",
+               Style);
+
+  Style.ExportBlockIndentation = false;
+  verifyFormat("export {\n"
+               "int x;\n"
+               "int y;\n"
+               "}",
+               "export {\n"
+               "  int x;\n"
+               "  int y;\n"
+               "}",
+               Style);
+}
+
+TEST_F(FormatTest, ShortExportBlocks) {
+  FormatStyle Style = getLLVMStyleWithColumns(80);
+  Style.ExportBlockIndentation = false;
+
+  Style.AllowShortBlocksOnASingleLine = FormatStyle::SBS_Never;
+  verifyFormat("export {\n"
+               "}",
+               Style);
+
+  verifyFormat("export {\n"
+               "int x;\n"
+               "}",
+               Style);
+
+  verifyFormat("export {\n"
+               "int x;\n"
+               "}",
+               "export\n"
+               "{\n"
+               "int x;\n"
+               "}",
+               Style);
+
+  verifyFormat("export {\n"
+               "}",
+               "export {}", Style);
+
+  verifyFormat("export {\n"
+               "int x;\n"
+               "}",
+               "export { int x; }", Style);
+
+  Style.AllowShortBlocksOnASingleLine = FormatStyle::SBS_Always;
+  verifyFormat("export {}",
+               "export {\n"
+               "}",
+               Style);
+
+  verifyFormat("export { int x; }",
+               "export {\n"
+               "int x;\n"
+               "}",
+               Style);
+
+  verifyFormat("export { int x; }",
+               "export\n"
+               "{\n"
+               "int x;\n"
+               "}",
+               Style);
+
+  verifyFormat("export {}",
+               "export {\n"
+               "}",
+               Style);
+
+  verifyFormat("export { int x; }",
+               "export {\n"
+               "int x;\n"
+               "}",
+               Style);
+
+  Style.AllowShortBlocksOnASingleLine = FormatStyle::SBS_Empty;
+  verifyFormat("export {}",
+               "export {\n"
+               "}",
+               Style);
+
+  verifyFormat("export {\n"
+               "int x;\n"
+               "}",
+               Style);
+
+  verifyFormat("export {\n"
+               "int x;\n"
+               "}",
+               "export\n"
+               "{\n"
+               "int x;\n"
+               "}",
+               Style);
+
+  verifyFormat("export {}", Style);
+
+  verifyFormat("export {\n"
+               "int x;\n"
+               "}",
+               "export { int x; }", Style);
+}
+
 TEST_F(FormatTest, FormatsBuilderPattern) {
   verifyFormat("return llvm::StringSwitch<Reference::Kind>(name)\n"
                "    .StartsWith(\".eh_frame_hdr\", ORDER_EH_FRAMEHDR)\n"