Index: clang/docs/ClangFormatStyleOptions.rst
===================================================================
--- clang/docs/ClangFormatStyleOptions.rst
+++ clang/docs/ClangFormatStyleOptions.rst
@@ -2289,6 +2289,27 @@
 
   For example: BOOST_FOREACH.
 
+**IfMacros** (``std::vector<std::string>``)
+  A vector of macros that should be interpreted as conditionals
+  instead of as function calls.
+
+  These are expected to be macros of the form:
+
+  .. code-block:: c++
+
+    IF(...)
+      <conditional-body>
+    else IF(...)
+      <conditional-body>
+
+  In the .clang-format configuration file, this can be configured like:
+
+  .. code-block:: yaml
+
+    IfMacros: ['IF']
+
+  For example: KJ_IF_MAYBE.
+
 **IncludeBlocks** (``IncludeBlocksStyle``)
   Dependent on the value, multiple ``#include`` blocks can be sorted
   as one and divided based on category.
Index: clang/include/clang/Format/Format.h
===================================================================
--- clang/include/clang/Format/Format.h
+++ clang/include/clang/Format/Format.h
@@ -2079,6 +2079,25 @@
   /// For example: BOOST_FOREACH.
   std::vector<std::string> ForEachMacros;
 
+  /// A vector of macros that should be interpreted as conditionals
+  /// instead of as function calls.
+  ///
+  /// These are expected to be macros of the form:
+  /// \code
+  ///   IF(...) {
+  ///     <if body>
+  ///   } else {
+  ///   }
+  /// \endcode
+  ///
+  /// In the .clang-format configuration file, this can be configured like:
+  /// \code{.yaml}
+  ///   IfMacros: ['IF']
+  /// \endcode
+  ///
+  /// For example: KJ_IF_MAYBE.
+  std::vector<std::string> IfMacros;
+
   /// \brief A vector of macros that should be interpreted as type declarations
   /// instead of as function calls.
   ///
Index: clang/lib/Format/Format.cpp
===================================================================
--- clang/lib/Format/Format.cpp
+++ clang/lib/Format/Format.cpp
@@ -616,6 +616,7 @@
                    Style.ExperimentalAutoDetectBinPacking);
     IO.mapOptional("FixNamespaceComments", Style.FixNamespaceComments);
     IO.mapOptional("ForEachMacros", Style.ForEachMacros);
+    IO.mapOptional("IfMacros", Style.IfMacros);
     IO.mapOptional("StatementAttributeLikeMacros",
                    Style.StatementAttributeLikeMacros);
     IO.mapOptional("IncludeBlocks", Style.IncludeStyle.IncludeBlocks);
Index: clang/lib/Format/FormatToken.h
===================================================================
--- clang/lib/Format/FormatToken.h
+++ clang/lib/Format/FormatToken.h
@@ -52,6 +52,7 @@
   TYPE(FunctionDeclarationName)                                                \
   TYPE(FunctionLBrace)                                                         \
   TYPE(FunctionTypeLParen)                                                     \
+  TYPE(IfMacro)                                                                \
   TYPE(ImplicitStringLiteral)                                                  \
   TYPE(InheritanceColon)                                                       \
   TYPE(InheritanceComma)                                                       \
Index: clang/lib/Format/FormatTokenLexer.cpp
===================================================================
--- clang/lib/Format/FormatTokenLexer.cpp
+++ clang/lib/Format/FormatTokenLexer.cpp
@@ -39,6 +39,8 @@
 
   for (const std::string &ForEachMacro : Style.ForEachMacros)
     Macros.insert({&IdentTable.get(ForEachMacro), TT_ForEachMacro});
+  for (const std::string &IfMacro : Style.IfMacros)
+    Macros.insert({&IdentTable.get(IfMacro), TT_IfMacro});
   for (const std::string &AttributeMacro : Style.AttributeMacros)
     Macros.insert({&IdentTable.get(AttributeMacro), TT_AttributeMacro});
   for (const std::string &StatementMacro : Style.StatementMacros)
@@ -1014,6 +1016,9 @@
               tok::pp_define) &&
         it != Macros.end()) {
       FormatTok->setType(it->second);
+      if (it->second == TT_IfMacro) {
+        FormatTok->Tok.setKind(tok::kw_if);
+      }
     } else if (FormatTok->is(tok::identifier)) {
       if (MacroBlockBeginRegex.match(Text)) {
         FormatTok->setType(TT_MacroBlockBegin);
Index: clang/lib/Format/TokenAnnotator.cpp
===================================================================
--- clang/lib/Format/TokenAnnotator.cpp
+++ clang/lib/Format/TokenAnnotator.cpp
@@ -1363,7 +1363,7 @@
     // Reset token type in case we have already looked at it and then
     // recovered from an error (e.g. failure to find the matching >).
     if (!CurrentToken->isOneOf(
-            TT_LambdaLSquare, TT_LambdaLBrace, TT_AttributeMacro,
+            TT_LambdaLSquare, TT_LambdaLBrace, TT_AttributeMacro, TT_IfMacro,
             TT_ForEachMacro, TT_TypenameMacro, TT_FunctionLBrace,
             TT_ImplicitStringLiteral, TT_InlineASMBrace, TT_FatArrow,
             TT_LambdaArrow, TT_NamespaceMacro, TT_OverloadedOperator,
@@ -3022,6 +3022,9 @@
             FormatStyle::SBPO_ControlStatementsExceptForEachMacros &&
         Left.is(TT_ForEachMacro))
       return false;
+    if (Left.is(TT_IfMacro)) {
+      return false;
+    }
     return Line.Type == LT_ObjCDecl || Left.is(tok::semi) ||
            (Style.SpaceBeforeParens != FormatStyle::SBPO_Never &&
             (Left.isOneOf(tok::pp_elif, tok::kw_for, tok::kw_while,
Index: clang/unittests/Format/FormatTest.cpp
===================================================================
--- clang/unittests/Format/FormatTest.cpp
+++ clang/unittests/Format/FormatTest.cpp
@@ -17111,6 +17111,11 @@
   CHECK_PARSE("ForEachMacros: [BOOST_FOREACH, Q_FOREACH]", ForEachMacros,
               BoostAndQForeach);
 
+  Style.IfMacros.clear();
+  std::vector<std::string> CustomIfs;
+  CustomIfs.push_back("MYIF");
+  CHECK_PARSE("IfMacros: [MYIF]", IfMacros, CustomIfs);
+
   Style.AttributeMacros.clear();
   CHECK_PARSE("BasedOnStyle: LLVM", AttributeMacros,
               std::vector<std::string>{"__capability"});
@@ -19684,11 +19689,14 @@
 
 TEST_F(FormatTest, SpacesInConditionalStatement) {
   FormatStyle Spaces = getLLVMStyle();
+  Spaces.IfMacros.clear();
+  Spaces.IfMacros.push_back("MYIF");
   Spaces.SpacesInConditionalStatement = true;
   verifyFormat("for ( int i = 0; i; i++ )\n  continue;", Spaces);
   verifyFormat("if ( !a )\n  return;", Spaces);
   verifyFormat("if ( a )\n  return;", Spaces);
   verifyFormat("if constexpr ( a )\n  return;", Spaces);
+  verifyFormat("MYIF( a )\n  return;", Spaces);
   verifyFormat("switch ( a )\ncase 1:\n  return;", Spaces);
   verifyFormat("while ( a )\n  return;", Spaces);
   verifyFormat("while ( (a && b) )\n  return;", Spaces);