Index: clang/lib/Format/FormatToken.h
===================================================================
--- clang/lib/Format/FormatToken.h
+++ clang/lib/Format/FormatToken.h
@@ -102,9 +102,11 @@
   TYPE(TypenameMacro)                                                          \
   TYPE(UnaryOperator)                                                          \
   TYPE(CSharpStringLiteral)                                                    \
-  TYPE(CSharpNullCoalescing)                                                   \
   TYPE(CSharpNamedArgumentColon)                                               \
-  TYPE(CSharpNullableTypeQuestionMark)                                         \
+  TYPE(CSharpNullable)                                                         \
+  TYPE(CSharpNullCoalescing)                                                   \
+  TYPE(CSharpNullConditional)                                                  \
+  TYPE(CSharpNullConditionalSq)                                                \
   TYPE(Unknown)
 
 enum TokenType {
Index: clang/lib/Format/FormatTokenLexer.h
===================================================================
--- clang/lib/Format/FormatTokenLexer.h
+++ clang/lib/Format/FormatTokenLexer.h
@@ -52,8 +52,8 @@
   bool tryMergeJSPrivateIdentifier();
   bool tryMergeCSharpStringLiteral();
   bool tryMergeCSharpKeywordVariables();
-  bool tryMergeCSharpNullConditionals();
   bool tryMergeCSharpDoubleQuestion();
+  bool tryMergeCSharpNullConditional();
   bool tryTransformCSharpForEach();
   bool tryMergeCSharpAttributeAndTarget();
 
Index: clang/lib/Format/FormatTokenLexer.cpp
===================================================================
--- clang/lib/Format/FormatTokenLexer.cpp
+++ clang/lib/Format/FormatTokenLexer.cpp
@@ -84,7 +84,7 @@
       return;
     if (tryMergeCSharpDoubleQuestion())
       return;
-    if (tryMergeCSharpNullConditionals())
+    if (tryMergeCSharpNullConditional())
       return;
     if (tryTransformCSharpForEach())
       return;
@@ -319,7 +319,7 @@
   auto &SecondQuestion = *(Tokens.end() - 1);
   if (!FirstQuestion->is(tok::question) || !SecondQuestion->is(tok::question))
     return false;
-  FirstQuestion->Tok.setKind(tok::question);
+  FirstQuestion->Tok.setKind(tok::question); // no '??' in clang tokens.
   FirstQuestion->TokenText = StringRef(FirstQuestion->TokenText.begin(),
                                        SecondQuestion->TokenText.end() -
                                            FirstQuestion->TokenText.begin());
@@ -329,6 +329,32 @@
   return true;
 }
 
+// Merge '?[' and '?.' pairs into single tokens.
+bool FormatTokenLexer::tryMergeCSharpNullConditional() {
+  if (Tokens.size() < 2)
+    return false;
+  auto &Question = *(Tokens.end() - 2);
+  auto &PeriodOrLSquare = *(Tokens.end() - 1);
+  if (!Question->is(tok::question) ||
+      !PeriodOrLSquare->isOneOf(tok::l_square, tok::period))
+    return false;
+  Question->TokenText =
+      StringRef(Question->TokenText.begin(),
+                PeriodOrLSquare->TokenText.end() - Question->TokenText.begin());
+  Question->ColumnWidth += PeriodOrLSquare->ColumnWidth;
+
+  if (PeriodOrLSquare->is(tok::l_square)) {
+    Question->Tok.setKind(tok::question); // no '?[' in clang tokens.
+    Question->Type = TT_CSharpNullConditionalSq;
+  } else {
+    Question->Tok.setKind(tok::question); // no '?.' in clang tokens.
+    Question->Type = TT_CSharpNullConditional;
+  }
+
+  Tokens.erase(Tokens.end() - 1);
+  return true;
+}
+
 bool FormatTokenLexer::tryMergeCSharpKeywordVariables() {
   if (Tokens.size() < 2)
     return false;
@@ -348,23 +374,6 @@
   return true;
 }
 
-// In C# merge the Identifier and the ? together e.g. arg?.
-bool FormatTokenLexer::tryMergeCSharpNullConditionals() {
-  if (Tokens.size() < 2)
-    return false;
-  auto &Identifier = *(Tokens.end() - 2);
-  auto &Question = *(Tokens.end() - 1);
-  if (!Identifier->isOneOf(tok::r_square, tok::identifier) ||
-      !Question->is(tok::question))
-    return false;
-  Identifier->TokenText =
-      StringRef(Identifier->TokenText.begin(),
-                Question->TokenText.end() - Identifier->TokenText.begin());
-  Identifier->ColumnWidth += Question->ColumnWidth;
-  Tokens.erase(Tokens.end() - 1);
-  return true;
-}
-
 // In C# transform identifier foreach into kw_foreach
 bool FormatTokenLexer::tryTransformCSharpForEach() {
   if (Tokens.size() < 1)
Index: clang/lib/Format/TokenAnnotator.cpp
===================================================================
--- clang/lib/Format/TokenAnnotator.cpp
+++ clang/lib/Format/TokenAnnotator.cpp
@@ -972,6 +972,13 @@
       }
       break;
     case tok::question:
+      if (Tok->is(TT_CSharpNullConditionalSq)) {
+        if (!parseSquare())
+          return false;
+        break;
+      }
+      if (Tok->isOneOf(TT_CSharpNullConditional, TT_CSharpNullCoalescing))
+        break;
       if (Style.Language == FormatStyle::LK_JavaScript && Tok->Next &&
           Tok->Next->isOneOf(tok::semi, tok::comma, tok::colon, tok::r_paren,
                              tok::r_brace)) {
@@ -987,9 +994,11 @@
       if (Line.MustBeDeclaration && !Contexts.back().IsExpression &&
           Style.Language == FormatStyle::LK_JavaScript)
         break;
-      if (Style.isCSharp() && Line.MustBeDeclaration) {
-        Tok->Type = TT_CSharpNullableTypeQuestionMark;
-        break;
+      if (Style.isCSharp()) {
+        if (Line.MustBeDeclaration && !Contexts.back().IsExpression) {
+          Tok->Type = TT_CSharpNullable;
+          break;
+        }
       }
       parseConditional();
       break;
@@ -1437,6 +1446,21 @@
       // The token type is already known.
       return;
 
+    if (Style.isCSharp() && CurrentToken->is(tok::question)) {
+      if (CurrentToken->TokenText == "??") {
+        Current.Type = TT_CSharpNullCoalescing;
+        return;
+      }
+      if (CurrentToken->TokenText == "?.") {
+        Current.Type = TT_CSharpNullConditional;
+        return;
+      }
+      if (CurrentToken->TokenText == "?[") {
+        Current.Type = TT_CSharpNullConditionalSq;
+        return;
+      }
+    }
+
     if (Style.Language == FormatStyle::LK_JavaScript) {
       if (Current.is(tok::exclaim)) {
         if (Current.Previous &&
@@ -2907,9 +2931,29 @@
       return Style.SpacesInSquareBrackets;
 
     // No space before ? in nullable types.
-    if (Right.is(TT_CSharpNullableTypeQuestionMark))
+    if (Right.is(TT_CSharpNullable))
+      return false;
+
+    // Require space after ? in nullable types.
+    if (Left.is(TT_CSharpNullable))
+      return true;
+
+    // No space before or after '?.'.
+    if (Left.is(TT_CSharpNullConditional) || Right.is(TT_CSharpNullConditional))
       return false;
 
+    // Space before and after '??'.
+    if (Left.is(TT_CSharpNullCoalescing) || Right.is(TT_CSharpNullCoalescing))
+      return true;
+
+    // No space before '?['.
+    if (Right.is(TT_CSharpNullConditionalSq))
+      return false;
+
+    // Possible space inside `?[ 0 ]`.
+    if (Left.is(TT_CSharpNullConditionalSq))
+      return Style.SpacesInSquareBrackets;
+
     // space between keywords and paren e.g. "using ("
     if (Right.is(tok::l_paren))
       if (Left.isOneOf(tok::kw_using, Keywords.kw_async, Keywords.kw_when))
Index: clang/unittests/Format/FormatTestCSharp.cpp
===================================================================
--- clang/unittests/Format/FormatTestCSharp.cpp
+++ clang/unittests/Format/FormatTestCSharp.cpp
@@ -170,6 +170,12 @@
   verifyFormat("public override string ToString() => \"{Name}\\{Age}\";");
 }
 
+TEST_F(FormatTestCSharp, CSharpConditionalExpressions) {
+  FormatStyle Style = getGoogleStyle(FormatStyle::LK_CSharp);
+  // conditional expression is not seen as a NullConditional.
+  verifyFormat("var y = A < B ? -1 : 1;", Style);
+}
+
 TEST_F(FormatTestCSharp, CSharpNullConditional) {
   FormatStyle Style = getGoogleStyle(FormatStyle::LK_CSharp);
   Style.SpaceBeforeParens = FormatStyle::SBPO_Always;