public Builder setFileName(
          com.google.devtools.cloudtrace.v2.TruncatableString.Builder builderForValue) {
        if (fileNameBuilder_ == null) {
          fileName_ = builderForValue.build();
        } else {
          fileNameBuilder_.setMessage(builderForValue.build());
        }
        bitField0_ |= 0x00000004;
        onChanged();
        return this;
      }
<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