Add initial support for cargo-fuzz

fuzz/.gitignore

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+Cargo.lock
+target
+corpus
+artifacts

fuzz/Cargo.toml

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+
+[package]
+name = "tectonic-fuzz"
+version = "0.0.1"
+authors = ["Automatically generated"]
+publish = false
+
+[package.metadata]
+cargo-fuzz = true
+
+[dependencies.tectonic]
+path = ".."
+[dependencies.libfuzzer-sys]
+git = "https://github.com/rust-fuzz/libfuzzer-sys.git"
+
+# Prevent this from interfering with workspaces
+[workspace]
+members = ["."]
+
+[[bin]]
+name = "compile"
+path = "fuzz_targets/compile.rs"

fuzz/fuzz_targets/compile.rs

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+#![no_main]
+#[macro_use] extern crate libfuzzer_sys;
+extern crate tectonic;
+
+fuzz_target!(|data: &[u8]| {
+    if let Ok(data) = std::str::from_utf8(data) {
+        let _ = tectonic::latex_to_pdf(data);
+    }
+});

fuzz/run-fuzzer.sh

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+#!/usr/bin/env bash
+set -e
+set -o pipefail
+HERE="$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )"
+PARENT="$HERE/../"
+
+(test -x "${HOME}/.cargo/bin/cargo-fuzz" || cargo install cargo-fuzz)
+
+# it is important for `cargo fuzz` to be run from the project root
+cd "$PARENT"
+
+mkdir -p "$HERE/corpus"
+rustup override set nightly
+
+# run `compile` target using `seeds` as a start point and put new corpus state into `corpus` using 4 parallel jobs
+cargo fuzz run compile "$HERE/corpus" "$HERE/seeds" -j 4 --all-features

fuzz/seeds/hello.tex

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+\documentclass{article}
+\begin{document}
+Hello, world!
+\end{document}