Add a mechanism for placing comments in Emit() calls that are not reproduced in the output.

PiperOrigin-RevId: 495059212

src/google/protobuf/io/printer.cc

@@ -49,7 +49,6 @@
 #include "google/protobuf/stubs/logging.h"
 #include "absl/strings/ascii.h"
 #include "absl/strings/escaping.h"
-#include "absl/strings/match.h"
 #include "absl/strings/str_cat.h"
 #include "absl/strings/str_format.h"
 #include "absl/strings/str_split.h"
@@ -156,22 +155,29 @@ Printer::Format Printer::TokenizeFormat(absl::string_view format_string,
   }
 
   // We now split the remaining format string into lines and discard:
-  //   1. All leading spaces to compute that line's indent.
+  //   1. A trailing Printer-discarded comment, if this is a raw string.
+  //
+  //   2. All leading spaces to compute that line's indent.
   //      We do not do this for the first line, so that Emit("  ") works
   //      correctly. We do this *regardless* of whether we are processing
   //      a raw string, because existing non-raw-string calls to cpp::Formatter
   //      rely on this. There is a test that validates this behavior.
   //
-  //   2. Set the indent for that line to max(0, line_indent -
+  //   3. Set the indent for that line to max(0, line_indent -
   //      raw_string_indent), if this is not a raw string.
   //
-  //   3. Trailing empty lines, if we know this is a raw string, except for
+  //   4. Trailing empty lines, if we know this is a raw string, except for
   //      a single extra newline at the end.
   //
   // Each line is itself split into chunks along the variable delimiters, e.g.
   // $...$.
   bool is_first = true;
   for (absl::string_view line_text : absl::StrSplit(format_string, '\n')) {
+    if (format.is_raw_string) {
+      size_t comment_index = line_text.find(options_.ignored_comment_start);
+      line_text = line_text.substr(0, comment_index);
+    }
+
     size_t line_indent = 0;
     while (!is_first && absl::ConsumePrefix(&line_text, " ")) {
       ++line_indent;

src/google/protobuf/io/printer.h

@@ -224,6 +224,17 @@ class AnnotationProtoCollector : public AnnotationCollector {
 //     }
 //   };
 //
+// # Comments
+//
+// It may be desirable to place comments in a raw string that are stripped out
+// before printing. The prefix for Printer-ignored comments can be configured
+// in Options. By default, this is `//~`.
+//
+//   p.Emit(R"cc(
+//     // Will be printed in the output.
+//     //~ Won't be.
+//   )cc");
+//
 // # Lookup Frames
 //
 // If many calls to Emit() use the same set of variables, they can be stored
@@ -445,6 +456,9 @@ class PROTOBUF_EXPORT Printer {
     // to allow the Printer to emit debugging annotations in the source code
     // output.
     absl::string_view comment_start = "//";
+    // The token for beginning comments that are discarded by Printer's internal
+    // formatter.
+    absl::string_view ignored_comment_start = "//~";
     // The number of spaces that a single level of indentation adds by default;
     // this is the amount that WithIndent() increases indentation by.
     size_t spaces_per_indent = 2;

src/google/protobuf/io/printer_unittest.cc

@@ -41,14 +41,12 @@
 
 #include "google/protobuf/descriptor.pb.h"
 #include <gmock/gmock.h>
-#include "google/protobuf/testing/googletest.h"
 #include <gtest/gtest.h>
 #include "absl/container/flat_hash_map.h"
 #include "google/protobuf/stubs/logging.h"
 #include "absl/strings/str_join.h"
 #include "absl/strings/string_view.h"
 #include "google/protobuf/io/zero_copy_stream.h"
-#include "google/protobuf/io/zero_copy_stream_impl.h"
 #include "google/protobuf/io/zero_copy_stream_impl_lite.h"
 
 namespace google {
@@ -56,7 +54,6 @@ namespace protobuf {
 namespace io {
 using ::testing::AllOf;
 using ::testing::ElementsAre;
-using ::testing::ExplainMatchResult;
 using ::testing::Field;
 using ::testing::IsEmpty;
 using ::testing::MatchesRegex;
@@ -565,6 +562,19 @@ TEST_F(PrinterTest, EmitWithSubs) {
             "};\n");
 }
 
+TEST_F(PrinterTest, EmitComments) {
+  {
+    Printer printer(output());
+    printer.Emit(R"cc(
+      // Yes.
+      //~ No.
+    )cc");
+    printer.Emit("//~ Not a raw string.");
+  }
+
+  EXPECT_EQ(written(), "// Yes.\n//~ Not a raw string.");
+}
+
 TEST_F(PrinterTest, EmitWithVars) {
   {
     Printer printer(output());