[clang-format] Add option for aligning requires clause body

Adds an option whether requires clause body should be aligned with
the `requires` keyword.
This option is now the default, both without configuration and in LLVM
style.

Fixes #56283

Differential Revision: https://reviews.llvm.org/D129443

Co-authored-by: Emilia Dreamer <emilia@rymiel.space>

clang/docs/ClangFormatStyleOptions.rst

@@ -3861,6 +3861,35 @@ the configuration (without a prefix: ``Auto``).
 
 
 
+**RequiresExpressionIndentation** (``RequiresExpressionIndentationKind``) :versionbadge:`clang-format 16`
+  The indentation used for requires expression bodies.
+
+  Possible values:
+
+  * ``REI_OuterScope`` (in configuration: ``OuterScope``)
+    Align requires expression body relative to the indentation level of the
+    outer scope the requires expression resides in.
+    This is the default.
+
+    .. code-block:: c++
+
+       template <typename T>
+       concept C = requires(T t) {
+         ...
+       }
+
+  * ``REI_Keyword`` (in configuration: ``Keyword``)
+    Align requires expression body relative to the `requires` keyword.
+
+    .. code-block:: c++
+
+       template <typename T>
+       concept C = requires(T t) {
+                     ...
+                   }
+
+
+
 **SeparateDefinitionBlocks** (``SeparateDefinitionStyle``) :versionbadge:`clang-format 14`
   Specifies the use of empty lines to separate definition blocks, including
   classes, structs, enums, and functions.

clang/docs/ReleaseNotes.rst

@@ -629,7 +629,10 @@ AST Matchers
 
 clang-format
 ------------
-- Add `RemoveSemicolon` option for removing `;` after a non-empty function definition.
+- Add ``RemoveSemicolon`` option for removing ``;`` after a non-empty function definition.
+- Add ``RequiresExpressionIndentation`` option for configuring the alignment of requires-expressions.
+  The default value of this option is ``OuterScope``, which differs in behavior from clang-format 15.
+  To match the default behavior of clang-format 15, use the ``Keyword`` value.
 
 clang-extdef-mapping
 --------------------

clang/include/clang/Format/Format.h

@@ -3153,6 +3153,32 @@ struct FormatStyle {
   /// \version 15
   RequiresClausePositionStyle RequiresClausePosition;
 
+  /// Indentation logic for requires expression bodies.
+  enum RequiresExpressionIndentationKind : int8_t {
+    /// Align requires expression body relative to the indentation level of the
+    /// outer scope the requires expression resides in.
+    /// This is the default.
+    /// \code
+    ///    template <typename T>
+    ///    concept C = requires(T t) {
+    ///      ...
+    ///    }
+    /// \endcode
+    REI_OuterScope,
+    /// Align requires expression body relative to the `requires` keyword.
+    /// \code
+    ///    template <typename T>
+    ///    concept C = requires(T t) {
+    ///                  ...
+    ///                }
+    /// \endcode
+    REI_Keyword,
+  };
+
+  /// The indentation used for requires expression bodies.
+  /// \version 16
+  RequiresExpressionIndentationKind RequiresExpressionIndentation;
+
   /// \brief The style if definition blocks should be separated.
   enum SeparateDefinitionStyle : int8_t {
     /// Leave definition blocks as they are.
@@ -3988,6 +4014,7 @@ struct FormatStyle {
            RemoveBracesLLVM == R.RemoveBracesLLVM &&
            RemoveSemicolon == R.RemoveSemicolon &&
            RequiresClausePosition == R.RequiresClausePosition &&
+           RequiresExpressionIndentation == R.RequiresExpressionIndentation &&
            SeparateDefinitionBlocks == R.SeparateDefinitionBlocks &&
            ShortNamespaceLines == R.ShortNamespaceLines &&
            SortIncludes == R.SortIncludes &&

clang/lib/Format/ContinuationIndenter.cpp

@@ -1406,8 +1406,10 @@ unsigned ContinuationIndenter::moveStateToNextToken(LineState &State,
     CurrentState.NestedBlockIndent = State.Column + Current.ColumnWidth + 1;
   if (Current.isOneOf(TT_LambdaLSquare, TT_LambdaArrow))
     CurrentState.LastSpace = State.Column;
-  if (Current.is(TT_RequiresExpression))
+  if (Current.is(TT_RequiresExpression) &&
+      Style.RequiresExpressionIndentation == FormatStyle::REI_Keyword) {
     CurrentState.NestedBlockIndent = State.Column;
+  }
 
   // Insert scopes created by fake parenthesis.
   const FormatToken *Previous = Current.getPreviousNonComment();

clang/lib/Format/Format.cpp

@@ -99,6 +99,15 @@ struct ScalarEnumerationTraits<FormatStyle::LambdaBodyIndentationKind> {
   }
 };
 
+template <>
+struct ScalarEnumerationTraits<FormatStyle::RequiresExpressionIndentationKind> {
+  static void
+  enumeration(IO &IO, FormatStyle::RequiresExpressionIndentationKind &Value) {
+    IO.enumCase(Value, "Keyword", FormatStyle::REI_Keyword);
+    IO.enumCase(Value, "OuterScope", FormatStyle::REI_OuterScope);
+  }
+};
+
 template <> struct ScalarEnumerationTraits<FormatStyle::UseTabStyle> {
   static void enumeration(IO &IO, FormatStyle::UseTabStyle &Value) {
     IO.enumCase(Value, "Never", FormatStyle::UT_Never);
@@ -854,6 +863,8 @@ template <> struct MappingTraits<FormatStyle> {
     IO.mapOptional("RemoveBracesLLVM", Style.RemoveBracesLLVM);
     IO.mapOptional("RemoveSemicolon", Style.RemoveSemicolon);
     IO.mapOptional("RequiresClausePosition", Style.RequiresClausePosition);
+    IO.mapOptional("RequiresExpressionIndentation",
+                   Style.RequiresExpressionIndentation);
     IO.mapOptional("SeparateDefinitionBlocks", Style.SeparateDefinitionBlocks);
     IO.mapOptional("ShortNamespaceLines", Style.ShortNamespaceLines);
     IO.mapOptional("SortIncludes", Style.SortIncludes);
@@ -1290,6 +1301,7 @@ FormatStyle getLLVMStyle(FormatStyle::LanguageKind Language) {
   LLVMStyle.PointerAlignment = FormatStyle::PAS_Right;
   LLVMStyle.ReferenceAlignment = FormatStyle::RAS_Pointer;
   LLVMStyle.RequiresClausePosition = FormatStyle::RCPS_OwnLine;
+  LLVMStyle.RequiresExpressionIndentation = FormatStyle::REI_OuterScope;
   LLVMStyle.SeparateDefinitionBlocks = FormatStyle::SDS_Leave;
   LLVMStyle.ShortNamespaceLines = 1;
   LLVMStyle.SpacesBeforeTrailingComments = 1;