[clang-format] Add PPIndentWidth option

This allows to set a different indent width for preprocessor statements.

Example:

 #ifdef __linux_
 # define FOO
 #endif

int main(void)
{
    return 0;
}

Differential Revision: https://reviews.llvm.org/D103286

clang/docs/ClangFormatStyleOptions.rst

@@ -3033,6 +3033,21 @@ the configuration (without a prefix: ``Auto``).
   Add a space in front of an Objective-C protocol list, i.e. use
   ``Foo <Protocol>`` instead of ``Foo<Protocol>``.
 
+**PPIndentWidth** (``int``)
+  The number of columns to use for indentation of preprocessor statements.
+  When set to -1 (default) ``IndentWidth`` is used also for preprocessor
+  statements.
+
+  .. code-block:: c++
+
+     PPIndentWidth: 1
+
+     #ifdef __linux__
+     # define FOO
+     #else
+     # define BAR
+     #endif
+
 **PenaltyBreakAssignment** (``unsigned``)
   The penalty for breaking around an assignment operator.
 

clang/docs/ReleaseNotes.rst

@@ -233,6 +233,9 @@ clang-format
 - Option ``IndentAccessModifiers`` has been added to be able to give access
   modifiers their own indentation level inside records.
 
+- Option ``PPIndentWidth`` has been added to be able to configure pre-processor
+  indentation independent from regular code.
+
 - Option ``ShortNamespaceLines`` has been added to give better control
   over ``FixNamespaceComments`` when determining a namespace length.
 

clang/include/clang/Format/Format.h

@@ -2666,6 +2666,20 @@ struct FormatStyle {
   /// Pointer and reference alignment style.
   PointerAlignmentStyle PointerAlignment;
 
+  /// The number of columns to use for indentation of preprocessor statements.
+  /// When set to -1 (default) ``IndentWidth`` is used also for preprocessor
+  /// statements.
+  /// \code
+  ///    PPIndentWidth: 1
+  ///
+  ///    #ifdef __linux__
+  ///    # define FOO
+  ///    #else
+  ///    # define BAR
+  ///    #endif
+  /// \endcode
+  int PPIndentWidth;
+
   /// See documentation of ``RawStringFormats``.
   struct RawStringFormat {
     /// The language of this raw string.

clang/lib/Format/Format.cpp

@@ -665,6 +665,7 @@ template <> struct MappingTraits<FormatStyle> {
     IO.mapOptional("PenaltyIndentedWhitespace",
                    Style.PenaltyIndentedWhitespace);
     IO.mapOptional("PointerAlignment", Style.PointerAlignment);
+    IO.mapOptional("PPIndentWidth", Style.PPIndentWidth);
     IO.mapOptional("RawStringFormats", Style.RawStringFormats);
     IO.mapOptional("ReflowComments", Style.ReflowComments);
     IO.mapOptional("ShortNamespaceLines", Style.ShortNamespaceLines);
@@ -1022,6 +1023,7 @@ FormatStyle getLLVMStyle(FormatStyle::LanguageKind Language) {
   LLVMStyle.IndentRequires = false;
   LLVMStyle.IndentWrappedFunctionNames = false;
   LLVMStyle.IndentWidth = 2;
+  LLVMStyle.PPIndentWidth = -1;
   LLVMStyle.InsertTrailingCommas = FormatStyle::TCS_None;
   LLVMStyle.JavaScriptQuotes = FormatStyle::JSQS_Leave;
   LLVMStyle.JavaScriptWrapImports = true;

clang/lib/Format/UnwrappedLineFormatter.cpp

@@ -57,7 +57,9 @@ public:
     while (IndentForLevel.size() <= Line.Level)
       IndentForLevel.push_back(-1);
     if (Line.InPPDirective) {
-      Indent = Line.Level * Style.IndentWidth + AdditionalIndent;
+      unsigned IndentWidth =
+          (Style.PPIndentWidth >= 0) ? Style.PPIndentWidth : Style.IndentWidth;
+      Indent = Line.Level * IndentWidth + AdditionalIndent;
     } else {
       IndentForLevel.resize(Line.Level + 1);
       Indent = getIndent(IndentForLevel, Line.Level);

clang/unittests/Format/FormatTest.cpp

@@ -3453,6 +3453,48 @@ TEST_F(FormatTest, DoesntRemoveUnknownTokens) {
   verifyFormat("a\f\\");
 }
 
+TEST_F(FormatTest, IndentsPPDirectiveWithPPIndentWidth) {
+  FormatStyle style = getChromiumStyle(FormatStyle::LK_Cpp);
+  style.IndentWidth = 4;
+  style.PPIndentWidth = 1;
+
+  style.IndentPPDirectives = FormatStyle::PPDIS_None;
+  verifyFormat("#ifdef __linux__\n"
+               "void foo() {\n"
+               "    int x = 0;\n"
+               "}\n"
+               "#define FOO\n"
+               "#endif\n"
+               "void bar() {\n"
+               "    int y = 0;\n"
+               "}\n",
+               style);
+
+  style.IndentPPDirectives = FormatStyle::PPDIS_AfterHash;
+  verifyFormat("#ifdef __linux__\n"
+               "void foo() {\n"
+               "    int x = 0;\n"
+               "}\n"
+               "# define FOO foo\n"
+               "#endif\n"
+               "void bar() {\n"
+               "    int y = 0;\n"
+               "}\n",
+               style);
+
+  style.IndentPPDirectives = FormatStyle::PPDIS_BeforeHash;
+  verifyFormat("#ifdef __linux__\n"
+               "void foo() {\n"
+               "    int x = 0;\n"
+               "}\n"
+               " #define FOO foo\n"
+               "#endif\n"
+               "void bar() {\n"
+               "    int y = 0;\n"
+               "}\n",
+               style);
+}
+
 TEST_F(FormatTest, IndentsPPDirectiveInReducedSpace) {
   verifyFormat("#define A(BB)", getLLVMStyleWithColumns(13));
   verifyFormat("#define A( \\\n    BB)", getLLVMStyleWithColumns(12));