Can one exempt generated files from formatting?

[8573]

I'm using LALRPOP, which generates a Rust file from a build script,
which I then reference with a mod <filename> item.

The generated file is large and densely formatted, with many long
lines, and rustfmt always emits error messages about being unable to
wrap some of the lines. It does, however, reformat much of the file —
enough to expand the 3010-line file to 8265 lines.

How, if at all, could I instruct rustfmt to ignore this file?

[8573]

Apologies for posting this issue twice (the other instance being
#1399); my client claimed that the first submission failed.