private com.google.protobuf.SingleFieldBuilderV3<
              com.google.devtools.cloudtrace.v2.TruncatableString,
              com.google.devtools.cloudtrace.v2.TruncatableString.Builder,
              com.google.devtools.cloudtrace.v2.TruncatableStringOrBuilder>
          getFunctionNameFieldBuilder() {
        if (functionNameBuilder_ == null) {
          functionNameBuilder_ =
              new com.google.protobuf.SingleFieldBuilderV3<
                  com.google.devtools.cloudtrace.v2.TruncatableString,
                  com.google.devtools.cloudtrace.v2.TruncatableString.Builder,
                  com.google.devtools.cloudtrace.v2.TruncatableStringOrBuilder>(
                  getFunctionName(), getParentForChildren(), isClean());
          functionName_ = null;
        }
        return functionNameBuilder_;
      }
<pre>
The fully-qualified name that uniquely identifies the function or
method that is active in this frame (up to 1024 bytes).
</pre>

<code>.google.devtools.cloudtrace.v2.TruncatableString function_name = 1;</code>
java-trace/proto-google-cloud-trace-v2/src/main/java/com/google/devtools/cloudtrace/v2/StackTrace.java