[clang-format] C# switch expression formatting differs from normal switch formatting

[MyDeveloperDay]

Summary

https://github.com/llvm/llvm-project/issues/52677

clang-format doesn't format C# switch expressions very well.

int x = a switch {
               1 => (0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0),
               2 => 1,
               _ => 2
           };

int x = a switch { 1 => (0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0), 2 => 1, _ => 2 };

Start with this small use case and try and improve the output. I'll look for other examples to add as tests

[curdeius]

LGTM. AFAIK (which is very limited when it comes to C#), the cases can have also other expressions, not only ints and _. But that can be left for a different patch.
Example from https://docs.microsoft.com/en-us/dotnet/csharp/fundamentals/functional/pattern-matching

public State PerformOperation(Operation command) =>
   command switch
   {
       Operation.SystemTest => RunDiagnostics(),
       Operation.Start => StartSystem(),
       Operation.Stop => StopSystem(),
       Operation.Reset => ResetToReady(),
       _ => throw new ArgumentException("Invalid enum value for command", nameof(command)),
   };

[MyDeveloperDay]

In D115673#3191408, @curdeius wrote:

LGTM. AFAIK (which is very limited when it comes to C#), the cases can have also other expressions, not only ints and _. But that can be left for a different patch.
Example from https://docs.microsoft.com/en-us/dotnet/csharp/fundamentals/functional/pattern-matching

public State PerformOperation(Operation command) =>
   command switch
   {
       Operation.SystemTest => RunDiagnostics(),
       Operation.Start => StartSystem(),
       Operation.Stop => StopSystem(),
       Operation.Reset => ResetToReady(),
       _ => throw new ArgumentException("Invalid enum value for command", nameof(command)),
   };

I thought that would be the case but actually I tried a load from the Microsoft docs and most where good, it seems to be the numerical ones that seems to be struggling.

clang/lib/Format/TokenAnnotator.cpp

if (Right.NewlinesBefore > 1 && Style.MaxEmptyLinesToKeep > 0)
     return true;
 
   if (Style.isCSharp()) {
     if (Right.is(TT_CSharpNamedArgumentColon) ||
         Left.is(TT_CSharpNamedArgumentColon))
       return false;
     if (Right.is(TT_CSharpGenericTypeConstraint))
       return true;
+    if (Right.Next && Right.Next->is(TT_FatArrow) &&
+        (Right.is(tok::numeric_constant) ||
+         (Right.is(tok::identifier) && Right.TokenText == "_")))
+      return true;
 
     // Break after C# [...] and before public/protected/private/internal.
     if (Left.is(TT_AttributeSquare) && Left.is(tok::r_square) &&
         (Right.isAccessSpecifier(/*ColonRequired=*/false) ||
          Right.is(Keywords.kw_internal)))
       return true;
     // Break between ] and [ but only when there are really 2 attributes.
     if (Left.is(TT_AttributeSquare) && Right.is(TT_AttributeSquare) &&

clang/unittests/Format/FormatTestCSharp.cpp

verifyFormat("namespace A\n"
                "        public interface Name1\n"
                "        {\n"
                "        }\n"
                "    }\n"
                "}\n",
                Style);
 }
 
+TEST_F(FormatTestCSharp, SwitchExpression) {
+  FormatStyle Style = getMicrosoftStyle(FormatStyle::LK_CSharp);
+  verifyFormat("int x = a switch {\n"
+               "    1 => (0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0),\n"
+               "    2 => 1,\n"
+               "    _ => 2\n"
+               "};\n",
+               Style);
+}
+
 } // namespace format
 } // end namespace clang