public Builder setFunctionName(
          com.google.devtools.cloudtrace.v2.TruncatableString.Builder builderForValue) {
        if (functionNameBuilder_ == null) {
          functionName_ = builderForValue.build();
        } else {
          functionNameBuilder_.setMessage(builderForValue.build());
        }
        bitField0_ |= 0x00000001;
        onChanged();
        return this;
      }
<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