fix(generator): preserve comment introducers across embedded newlines

[colinmoy]

No description provided.

[gemini-code-assist]

Code Review

This pull request updates FormatCommentBlock in codegen_utils.cc to correctly handle multi-line comments and paragraph splitting, and adds corresponding unit tests. The review feedback recommends optimizing memory usage by using absl::string_view instead of std::string to avoid unnecessary heap allocations, and refactoring the final formatting loop to eliminate an unnecessary else block, aligning with the repository's style guide.

[gemini-code-assist]

Using std::vector<std::string> causes unnecessary memory allocations and copies for each line of the comment block. Since the comment parameter is passed as a const std::string& and its lifetime outlives this function, we can use std::vector<absl::string_view> instead to avoid these heap allocations.

  std::vector<absl::string_view> lines;
  std::vector<absl::string_view> paragraphs = absl::StrSplit(comment, '\n');
  for (auto const& paragraph : paragraphs) {
    if (paragraph.empty()) {
      lines.emplace_back();
      continue;
    }
    std::size_t start_pos = 0;
    while (start_pos != absl::string_view::npos) {
      std::size_t boundary = start_pos + comment_width;
      std::size_t end_pos = boundary;
      if (boundary < paragraph.length()) {
        // Look backward from the boundary for the last word
        end_pos = paragraph.rfind(' ', boundary);
        // If there is only one word, find and use its boundary
        if (end_pos == absl::string_view::npos || end_pos < start_pos) {
          end_pos = paragraph.find(' ', boundary);
        }
      }
      lines.push_back(paragraph.substr(start_pos, end_pos - start_pos));
      start_pos = paragraph.find_first_not_of(' ', end_pos);
    }
  }

References

1. Scrutinize copies of non-fundamental C++ types. Is it necessary to copy the data? ^(link)

[scotthart]

use std::string_view instead of absl::string_view

[colinmoy]

Done