cabana(DBCFile): preserve original header (#31900)

* cabana(DBCFile): preserve original header

* add trailing space
old-commit-hash: 5a805df340

tools/cabana/dbc/dbcfile.cc

@@ -98,10 +98,13 @@ void DBCFile::parse(const QString &content) {
   QTextStream stream((QString *)&content);
   cabana::Msg *current_msg = nullptr;
   int multiplexor_cnt = 0;
+  bool seen_first = false;
   while (!stream.atEnd()) {
     ++line_num;
     QString raw_line = stream.readLine();
     line = raw_line.trimmed();
+
+    bool seen = true;
     if (line.startsWith("BO_ ")) {
       multiplexor_cnt = 0;
       auto match = bo_regexp.match(line);
@@ -182,6 +185,14 @@ void DBCFile::parse(const QString &content) {
       if (auto s = get_sig(match.captured(1).toUInt(), match.captured(2))) {
         s->comment = match.captured(3).trimmed();
       }
+    } else {
+      seen = false;
+    }
+
+    if (seen) {
+      seen_first = true;
+    } else if (!seen_first) {
+      header += raw_line + "\n";
     }
   }
 
@@ -231,5 +242,5 @@ QString DBCFile::generateDBC() {
     }
     dbc_string += "\n";
   }
-  return dbc_string + comment + val_desc;
+  return header + dbc_string + comment + val_desc;
 }

tools/cabana/dbc/dbcfile.h

@@ -34,6 +34,7 @@ public:
 
 private:
   void parse(const QString &content);
+  QString header;
   std::map<uint32_t, cabana::Msg> msgs;
   QString name_;
 };

tools/cabana/tests/test_cabana.cc

@@ -45,6 +45,26 @@ CM_ SG_ 162 signal_2 "signal comment";
   REQUIRE(dbc.generateDBC() == content);
 }
 
+TEST_CASE("DBCFile::generateDBC -- preserve original header") {
+  QString content = R"(VERSION "1.0"
+
+NS_ :
+ CM_
+
+BS_:
+
+BU_: EON
+
+BO_ 160 message_1: 8 EON
+ SG_ signal_1 : 0|12@1+ (1,0) [0|4095] "unit" XXX
+
+CM_ BO_ 160 "message comment";
+CM_ SG_ 160 signal_1 "signal comment";
+)";
+  DBCFile dbc("", content);
+  REQUIRE(dbc.generateDBC() == content);
+}
+
 TEST_CASE("parse_dbc") {
   QString content = R"(
 BO_ 160 message_1: 8 EON