Fix csharp doc commments (#15955)

Fix C# document comments when there is an extra `/` at the start of a comment line.
See https://github.com/grpc/grpc/issues/35905

Related to https://github.com/grpc/grpc/pull/36000 which also fixes the issue in the gRPC C# plugin

Closes #15955

COPYBARA_INTEGRATE_REVIEW=https://github.com/protocolbuffers/protobuf/pull/15955 from tonydnewell:csharp-comment-fix d80e09ae20
PiperOrigin-RevId: 610784971

src/google/protobuf/compiler/csharp/csharp_doc_comment.cc

@@ -21,31 +21,35 @@ namespace compiler {
 namespace csharp {
 
 // Functions to create C# XML documentation comments.
-// Currently this only includes documentation comments containing text specified as comments
-// in the .proto file; documentation comments generated just from field/message/enum/proto names
-// is inlined in the relevant code. If more control is required, that code can be moved here.
+// Currently this only includes documentation comments containing text specified
+// as comments in the .proto file; documentation comments generated just from
+// field/message/enum/proto names is inlined in the relevant code. If more
+// control is required, that code can be moved here.
 
 void WriteDocCommentBodyImpl(io::Printer* printer, SourceLocation location) {
-    std::string comments = location.leading_comments.empty() ?
-        location.trailing_comments : location.leading_comments;
+  std::string comments = location.leading_comments.empty()
+                             ? location.trailing_comments
+                             : location.leading_comments;
   if (comments.empty()) {
     return;
   }
-    // XML escaping... no need for apostrophes etc as the whole text is going to be a child
-    // node of a summary element, not part of an attribute.
+  // XML escaping... no need for apostrophes etc as the whole text is going to
+  // be a child node of a summary element, not part of an attribute.
   comments = absl::StrReplaceAll(comments, {{"&", "&amp;"}, {"<", "&lt;"}});
   std::vector<std::string> lines;
   lines = absl::StrSplit(comments, "\n", absl::AllowEmpty());
-    // TODO: We really should work out which part to put in the summary and which to put in the remarks...
-    // but that needs to be part of a bigger effort to understand the markdown better anyway.
+  // TODO: We really should work out which part to put in the summary and which
+  // to put in the remarks... but that needs to be part of a bigger effort to
+  // understand the markdown better anyway.
   printer->Print("/// <summary>\n");
   bool last_was_empty = false;
-    // We squash multiple blank lines down to one, and remove any trailing blank lines. We need
-    // to preserve the blank lines themselves, as this is relevant in the markdown.
-    // Note that we can't remove leading or trailing whitespace as *that's* relevant in markdown too.
-    // (We don't skip "just whitespace" lines, either.)
-    for (std::vector<std::string>::iterator it = lines.begin();
-         it != lines.end(); ++it) {
+  // We squash multiple blank lines down to one, and remove any trailing blank
+  // lines. We need to preserve the blank lines themselves, as this is relevant
+  // in the markdown. Note that we can't remove leading or trailing whitespace
+  // as *that's* relevant in markdown too. (We don't skip "just whitespace"
+  // lines, either.)
+  for (std::vector<std::string>::iterator it = lines.begin(); it != lines.end();
+       ++it) {
     std::string line = *it;
     if (line.empty()) {
       last_was_empty = true;
@@ -54,15 +58,21 @@ void WriteDocCommentBodyImpl(io::Printer* printer, SourceLocation location) {
         printer->Print("///\n");
       }
       last_was_empty = false;
-        printer->Print("///$line$\n", "line", *it);
+      // If the comment has an extra slash at the start then this can cause the
+      // C# compiler to complain when generating the XML documentation Issue
+      // https://github.com/grpc/grpc/issues/35905
+      if (line[0] == '/') {
+        line.replace(0, 1, "&#x2F;");
+      }
+      printer->Print("///$line$\n", "line", line);
     }
   }
   printer->Print("/// </summary>\n");
 }
 
 template <typename DescriptorType>
-static void WriteDocCommentBody(
-    io::Printer* printer, const DescriptorType* descriptor) {
+static void WriteDocCommentBody(io::Printer* printer,
+                                const DescriptorType* descriptor) {
   SourceLocation location;
   if (descriptor->GetSourceLocation(&location)) {
     WriteDocCommentBodyImpl(printer, location);
@@ -73,18 +83,22 @@ void WriteMessageDocComment(io::Printer* printer, const Descriptor* message) {
   WriteDocCommentBody(printer, message);
 }
 
-void WritePropertyDocComment(io::Printer* printer, const FieldDescriptor* field) {
+void WritePropertyDocComment(io::Printer* printer,
+                             const FieldDescriptor* field) {
   WriteDocCommentBody(printer, field);
 }
 
-void WriteEnumDocComment(io::Printer* printer, const EnumDescriptor* enumDescriptor) {
+void WriteEnumDocComment(io::Printer* printer,
+                         const EnumDescriptor* enumDescriptor) {
   WriteDocCommentBody(printer, enumDescriptor);
 }
-void WriteEnumValueDocComment(io::Printer* printer, const EnumValueDescriptor* value) {
+void WriteEnumValueDocComment(io::Printer* printer,
+                              const EnumValueDescriptor* value) {
   WriteDocCommentBody(printer, value);
 }
 
-void WriteMethodDocComment(io::Printer* printer, const MethodDescriptor* method) {
+void WriteMethodDocComment(io::Printer* printer,
+                           const MethodDescriptor* method) {
   WriteDocCommentBody(printer, method);
 }