public com.google.devtools.cloudtrace.v2.TruncatableString getFileName() {
        if (fileNameBuilder_ == null) {
          return fileName_ == null
              ? com.google.devtools.cloudtrace.v2.TruncatableString.getDefaultInstance()
              : fileName_;
        } else {
          return fileNameBuilder_.getMessage();
        }
      }
<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>

@return The fileName.
java-trace/proto-google-cloud-trace-v2/src/main/java/com/google/devtools/cloudtrace/v2/StackTrace.java