Add gix-commitgraph::File fuzzer

gix-commitgraph/fuzz/.gitignore

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+target
+corpus
+artifacts
+coverage

gix-commitgraph/fuzz/Cargo.toml

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+[package]
+name = "gix-commitgraph-fuzz"
+version = "0.0.0"
+publish = false
+edition = "2021"
+
+[package.metadata]
+cargo-fuzz = true
+
+[dependencies]
+anyhow = "1.0.76"
+arbitrary = { version = "1.3.2", features = ["derive"] }
+libfuzzer-sys = "0.4"
+tempfile = "3.8.1"
+
+[dependencies.gix-commitgraph]
+path = ".."
+
+# Prevent this from interfering with workspaces
+[workspace]
+members = ["."]
+
+[profile.release]
+debug = 1
+
+[[bin]]
+name = "fuzz_file"
+path = "fuzz_targets/fuzz_file.rs"
+test = false
+doc = false

gix-commitgraph/fuzz/fuzz_targets/fuzz_file.rs

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+#![no_main]
+
+use anyhow::Result;
+use arbitrary::Arbitrary;
+use gix_commitgraph::File;
+use libfuzzer_sys::fuzz_target;
+use std::fs;
+use std::hint::black_box;
+use tempfile::NamedTempFile;
+
+fn fuzz(data: &[u8]) -> Result<()> {
+    let named_temp_file = NamedTempFile::new()?;
+    fs::write(named_temp_file.path(), data).expect("Unable to write fuzzed file");
+    let file = File::try_from(named_temp_file.path())?;
+
+    _ = black_box(file.iter_base_graph_ids().count());
+    _ = black_box(file.iter_commits().count());
+    _ = black_box(file.iter_ids().count());
+
+    let _ = black_box(file.checksum());
+    let _ = black_box(file.verify_checksum());
+    let _ = black_box(file.object_hash());
+
+    Ok(())
+}
+
+fuzz_target!(|data: &[u8]| {
+    _ = black_box(fuzz(data));
+});