[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.

1 files changed, 30 insertions, 19 deletions

diff --git a/clang/lib/Format/UnwrappedLineParser.cpp b/clang/lib/Format/UnwrappedLineParser.cpp
index 198c05f..834693e 100644
--- a/clang/lib/Format/UnwrappedLineParser.cpp
+++ b/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();