cargo-fuzz

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I was trying out cargo fuzz init on a rust project that only had a main.rs but no lib.rs. As a consequence, the generated file fuzz_target_1.rs failed to build:

$ cargo fuzz run fuzz_target_1
       Fresh cc v1.0.8
       Fresh arbitrary v0.1.0
       Fresh libfuzzer-sys v0.1.0 (https://github.com/rust-fuzz/libfuzzer-sys.git#4594b1f3)
   Compiling merge-dags-fuzz v0.0.1 (file:///Users/mstange/code/merge-dags/fuzz)
[...]
error[E0463]: can't find crate for `merge_dags`
 --> fuzz_targets/fuzz_target_1.rs:3:1
  |
3 | extern crate merge_dags;
  | ^^^^^^^^^^^^^^^^^^^^^^^^ can't find crate

error: aborting due to previous error

For more information about this error, try `rustc --explain E0463`.
error: Could not compile `merge-dags-fuzz`.

It would be nice to detect this condition and show a more helpful error message.

Yes! It would be nice :sweat_smile: I had this exact same problem and now I finally know what's up!

The way I'm working around this is by putting all my code in a lib crate and then just invoking the lib from src/main.rs and the specific function I want to fuzz from the fuzz target.

The way I'm working around this is by putting all my code in a lib crate and then just invoking the lib from src/main.rs and the specific function I want to fuzz from the fuzz target.

How can I do that? I assume you're making 2 distinct crates, then.

I'm barely a novice with cargo and the module system, though. Is there a tutorial for this? It would also be nice to be able to have my lib crate in a local directory, because I can't currently publish it.

@felix91gr it's as simple as creating both src/lib.rs and src/main.rs. This can be done within the same crate, you can have a look at an example project (that also uses cargo-fuzz) over here.