private com.google.protobuf.SingleFieldBuilderV3<
              com.google.devtools.cloudtrace.v2.TruncatableString,
              com.google.devtools.cloudtrace.v2.TruncatableString.Builder,
              com.google.devtools.cloudtrace.v2.TruncatableStringOrBuilder>
          getFileNameFieldBuilder() {
        if (fileNameBuilder_ == null) {
          fileNameBuilder_ =
              new com.google.protobuf.SingleFieldBuilderV3<
                  com.google.devtools.cloudtrace.v2.TruncatableString,
                  com.google.devtools.cloudtrace.v2.TruncatableString.Builder,
                  com.google.devtools.cloudtrace.v2.TruncatableStringOrBuilder>(
                  getFileName(), getParentForChildren(), isClean());
          fileName_ = null;
        }
        return fileNameBuilder_;
      }
<pre>
The name of the source file where the function call appears (up to 256
bytes).
</pre>

<code>.google.devtools.cloudtrace.v2.TruncatableString file_name = 3;</code>
java-trace/proto-google-cloud-trace-v2/src/main/java/com/google/devtools/cloudtrace/v2/StackTrace.java