Function CreateUnifiedDiff

tests/gtest/gtest-all.cc:2696–2757

Create a list of diff hunks in Unified diff format. Each hunk has a header generated by PrintHeader above plus a body with lines prefixed with ' ' for no change, '-' for deletion and '+' for addition. 'context' represents the desired unchanged prefix/suffix around the diff. If two hunks are close enough that their contexts overlap, then they are joined into one hunk.

// If two hunks are close enough that their contexts overlap, then they are
// joined into one hunk.
std::string CreateUnifiedDiff(const std::vector<std::string>& left,
                              const std::vector<std::string>& right,
                              size_t context) {
  const std::vector<EditType> edits = CalculateOptimalEdits(left, right);

  size_t l_i = 0, r_i = 0, edit_i = 0;
  std::stringstream ss;
  while (edit_i < edits.size()) {
    // Find first edit.
    while (edit_i < edits.size() && edits[edit_i] == kMatch) {
      ++l_i;
      ++r_i;
      ++edit_i;
    }

    // Find the first line to include in the hunk.
    const size_t prefix_context = std::min(l_i, context);
    Hunk hunk(l_i - prefix_context + 1, r_i - prefix_context + 1);
    for (size_t i = prefix_context; i > 0; --i) {
      hunk.PushLine(' ', left[l_i - i].c_str());
    }

    // Iterate the edits until we found enough suffix for the hunk or the input
    // is over.
    size_t n_suffix = 0;
    for (; edit_i < edits.size(); ++edit_i) {
      if (n_suffix >= context) {
        // Continue only if the next hunk is very close.
        auto it = edits.begin() + static_cast<int>(edit_i);
        while (it != edits.end() && *it == kMatch) ++it;
        if (it == edits.end() ||
            static_cast<size_t>(it - edits.begin()) - edit_i >= context) {
          // There is no next edit or it is too far away.
          break;
        }
      }

      EditType edit = edits[edit_i];
      // Reset count when a non match is found.
      n_suffix = edit == kMatch ? n_suffix + 1 : 0;

      if (edit == kMatch || edit == kRemove || edit == kReplace) {
        hunk.PushLine(edit == kMatch ? ' ' : '-', left[l_i].c_str());
      }
      if (edit == kAdd || edit == kReplace) {
        hunk.PushLine('+', right[r_i].c_str());
      }

      // Advance indices, depending on edit type.
      l_i += edit != kAdd;
      r_i += edit != kRemove;
    }

    if (!hunk.has_edits()) {
      // We are done. We don't want this hunk.
      break;
    }