Index: clang/docs/ReleaseNotes.rst
===================================================================
--- clang/docs/ReleaseNotes.rst
+++ clang/docs/ReleaseNotes.rst
@@ -221,6 +221,23 @@
 ------------
 
 
+- Option ``IndentExternBlock`` has been added to optionally apply indenting inside extern "C" blocks.
+  
+  The ``BraceWrapping.AfterExternBlock`` option has been modified so it no longer indents when set to true, now it just wraps the braces around extern blocks.
+
+  .. code-block:: c++
+
+    true:                         false:
+      #ifdef __cplusplus          #ifdef __cplusplus
+      extern "C" {                extern "C" {
+      #endif                      #endif
+  
+          void f(void);           void f(void);
+  
+      #ifdef __cplusplus          #ifdef __cplusplus
+      }                           }
+      #endif                      #endif
+
 - Option ``IndentCaseBlocks`` has been added to support treating the block
   following a switch case label as a scope block which gets indented itself.
   It helps avoid having the closing bracket align with the switch statement's
Index: clang/include/clang/Format/Format.h
===================================================================
--- clang/include/clang/Format/Format.h
+++ clang/include/clang/Format/Format.h
@@ -953,7 +953,7 @@
     ///   true:
     ///   extern "C"
     ///   {
-    ///     int foo();
+    ///   int foo();
     ///   }
     ///
     ///   false:
@@ -1462,6 +1462,32 @@
   /// \endcode
   bool IndentWrappedFunctionNames;
 
+  /// Indent extern blocks; indent size = IndentWidth
+  /// \code
+  /// true:
+  /// #ifdef __cplusplus
+  /// extern "C" {
+  /// #endif
+  ///
+  ///     void f(void);
+  ///
+  /// #ifdef __cplusplus
+  /// }
+  /// #endif
+  ///
+  /// false:
+  /// #ifdef __cplusplus
+  /// extern "C" {
+  /// #endif
+  ///
+  /// void f(void);
+  ///
+  /// #ifdef __cplusplus
+  /// }
+  /// #endif
+  /// \endcode
+  bool IndentExternBlock;
+
   /// A vector of prefixes ordered by the desired groups for Java imports.
   ///
   /// Each group is separated by a newline. Static imports will also follow the
@@ -2206,6 +2232,7 @@
            IndentPPDirectives == R.IndentPPDirectives &&
            IndentWidth == R.IndentWidth && Language == R.Language &&
            IndentWrappedFunctionNames == R.IndentWrappedFunctionNames &&
+           IndentExternBlock == R.IndentExternBlock &&
            JavaImportGroups == R.JavaImportGroups &&
            JavaScriptQuotes == R.JavaScriptQuotes &&
            JavaScriptWrapImports == R.JavaScriptWrapImports &&
Index: clang/lib/Format/Format.cpp
===================================================================
--- clang/lib/Format/Format.cpp
+++ clang/lib/Format/Format.cpp
@@ -493,6 +493,7 @@
     IO.mapOptional("IndentWidth", Style.IndentWidth);
     IO.mapOptional("IndentWrappedFunctionNames",
                    Style.IndentWrappedFunctionNames);
+    IO.mapOptional("IndentExternBlock", Style.IndentExternBlock);
     IO.mapOptional("InsertTrailingCommas", Style.InsertTrailingCommas);
     IO.mapOptional("JavaImportGroups", Style.JavaImportGroups);
     IO.mapOptional("JavaScriptQuotes", Style.JavaScriptQuotes);
@@ -801,6 +802,7 @@
   LLVMStyle.IndentGotoLabels = true;
   LLVMStyle.IndentPPDirectives = FormatStyle::PPDIS_None;
   LLVMStyle.IndentWrappedFunctionNames = false;
+  LLVMStyle.IndentExternBlock = false;
   LLVMStyle.IndentWidth = 2;
   LLVMStyle.InsertTrailingCommas = FormatStyle::TCS_None;
   LLVMStyle.JavaScriptQuotes = FormatStyle::JSQS_Leave;
@@ -888,6 +890,7 @@
   GoogleStyle.IncludeStyle.IncludeIsMainRegex = "([-_](test|unittest))?$";
   GoogleStyle.IncludeStyle.IncludeBlocks = tooling::IncludeStyle::IBS_Regroup;
   GoogleStyle.IndentCaseLabels = true;
+  GoogleStyle.IndentExternBlock = false;
   GoogleStyle.KeepEmptyLinesAtTheStartOfBlocks = false;
   GoogleStyle.ObjCBinPackProtocolList = FormatStyle::BPS_Never;
   GoogleStyle.ObjCSpaceAfterProperty = false;
@@ -1023,6 +1026,7 @@
     ChromiumStyle.BreakAfterJavaFieldAnnotations = true;
     ChromiumStyle.ContinuationIndentWidth = 8;
     ChromiumStyle.IndentWidth = 4;
+    ChromiumStyle.IndentExternBlock = false;
     // See styleguide for import groups:
     // https://chromium.googlesource.com/chromium/src/+/master/styleguide/java/java.md#Import-Order
     ChromiumStyle.JavaImportGroups = {
@@ -1072,6 +1076,7 @@
   MozillaStyle.Cpp11BracedListStyle = false;
   MozillaStyle.FixNamespaceComments = false;
   MozillaStyle.IndentCaseLabels = true;
+  MozillaStyle.IndentExternBlock = false;
   MozillaStyle.ObjCSpaceAfterProperty = true;
   MozillaStyle.ObjCSpaceBeforeProtocolList = false;
   MozillaStyle.PenaltyReturnTypeOnItsOwnLine = 200;
@@ -1094,6 +1099,7 @@
   Style.ColumnLimit = 0;
   Style.FixNamespaceComments = false;
   Style.IndentWidth = 4;
+  Style.IndentExternBlock = true;
   Style.NamespaceIndentation = FormatStyle::NI_Inner;
   Style.ObjCBlockIndentWidth = 4;
   Style.ObjCSpaceAfterProperty = true;
@@ -1113,6 +1119,7 @@
   Style.Cpp11BracedListStyle = false;
   Style.ColumnLimit = 79;
   Style.FixNamespaceComments = false;
+  Style.IndentExternBlock = false;
   Style.SpaceBeforeParens = FormatStyle::SBPO_Always;
   Style.Standard = FormatStyle::LS_Cpp03;
   return Style;
@@ -1123,6 +1130,7 @@
   Style.ColumnLimit = 120;
   Style.TabWidth = 4;
   Style.IndentWidth = 4;
+  Style.IndentExternBlock = false;
   Style.UseTab = FormatStyle::UT_Never;
   Style.BreakBeforeBraces = FormatStyle::BS_Custom;
   Style.BraceWrapping.AfterClass = true;
Index: clang/lib/Format/UnwrappedLineParser.cpp
===================================================================
--- clang/lib/Format/UnwrappedLineParser.cpp
+++ clang/lib/Format/UnwrappedLineParser.cpp
@@ -1114,11 +1114,9 @@
       if (FormatTok->Tok.is(tok::l_brace)) {
         if (Style.BraceWrapping.AfterExternBlock) {
           addUnwrappedLine();
-          parseBlock(/*MustBeDeclaration=*/true);
-        } else {
-          parseBlock(/*MustBeDeclaration=*/true, /*AddLevel=*/false);
         }
-        addUnwrappedLine();
+        parseBlock(/*MustBeDeclaration=*/true,
+        /*AddLevel=*/Style.IndentExternBlock);
         return;
       }
     }
Index: clang/unittests/Format/FormatTest.cpp
===================================================================
--- clang/unittests/Format/FormatTest.cpp
+++ clang/unittests/Format/FormatTest.cpp
@@ -2491,11 +2491,43 @@
                Style);
   verifyFormat("extern \"C\"\n"
                "{\n"
-               "  int foo();\n"
+               "int foo();\n"
                "}",
                Style);
 }
 
+TEST_F(FormatTest, FormatsExternBlock) {
+  FormatStyle Style = getLLVMStyle();
+  Style.IndentWidth = 2;
+  Style.BraceWrapping.AfterExternBlock = true;
+  Style.IndentExternBlock = true;
+  verifyFormat("extern \"C\" {}", Style);
+  verifyFormat("extern \"C\" {\n"
+               "  int foo();"
+               "\n}", Style);
+
+  Style.BraceWrapping.AfterExternBlock = false;
+  Style.IndentExternBlock = true;
+  verifyFormat("extern \"C\" {}", Style);
+  verifyFormat("extern \"C\" {\n"
+               "  int foo();"
+               "\n}", Style);
+
+  Style.BraceWrapping.AfterExternBlock = true;
+  Style.IndentExternBlock = false;
+  verifyFormat("extern \"C\" {}", Style);
+  verifyFormat("extern \"C\" {\n"
+               "int foo();"
+               "\n}", Style);
+
+  Style.BraceWrapping.AfterExternBlock = false;
+  Style.IndentExternBlock = false;
+  verifyFormat("extern \"C\" {}", Style);
+  verifyFormat("extern \"C\" {\n"
+               "int foo();"
+               "\n}", Style);
+}
+
 TEST_F(FormatTest, FormatsInlineASM) {
   verifyFormat("asm(\"xyz\" : \"=a\"(a), \"=d\"(b) : \"a\"(data));");
   verifyFormat("asm(\"nop\" ::: \"memory\");");
@@ -12660,6 +12692,7 @@
   CHECK_PARSE_BOOL(IndentCaseBlocks);
   CHECK_PARSE_BOOL(IndentGotoLabels);
   CHECK_PARSE_BOOL(IndentWrappedFunctionNames);
+  CHECK_PARSE_BOOL(IndentExternBlock);
   CHECK_PARSE_BOOL(KeepEmptyLinesAtTheStartOfBlocks);
   CHECK_PARSE_BOOL(ObjCSpaceAfterProperty);
   CHECK_PARSE_BOOL(ObjCSpaceBeforeProtocolList);