Add simple hashbrown fuzzer.

This can (and will) be improved by adding more methods and by fuzzing HashSet.

Bug: 172274326
Test: Run fuzzer.
Change-Id: Icfb1fb0559821a952ff79bb9f32e3ccd6778f419
diff --git a/fuzzing/orphans/hashbrown/Android.bp b/fuzzing/orphans/hashbrown/Android.bp
new file mode 100644
index 0000000..d69b019
--- /dev/null
+++ b/fuzzing/orphans/hashbrown/Android.bp
@@ -0,0 +1,26 @@
+// Copyright 2021, The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+rust_fuzz {
+    name: "hashbrown_hashmap_fuzzer",
+    srcs: ["hashbrown_hashmap_fuzzer.rs"],
+    rustlibs: [
+        "libarbitrary",
+        "libhashbrown",
+    ],
+    fuzz_config: {
+        fuzz_on_haiku_device: true,
+        fuzz_on_haiku_host: true,
+    },
+}
\ No newline at end of file
diff --git a/fuzzing/orphans/hashbrown/hashbrown_hashmap_fuzzer.rs b/fuzzing/orphans/hashbrown/hashbrown_hashmap_fuzzer.rs
new file mode 100644
index 0000000..8267cf0
--- /dev/null
+++ b/fuzzing/orphans/hashbrown/hashbrown_hashmap_fuzzer.rs
@@ -0,0 +1,87 @@
+// Copyright 2021, The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#![allow(missing_docs)]
+#![no_main]
+#![feature(bench_black_box)]
+
+use hashbrown::HashMap;
+use libfuzzer_sys::arbitrary::Arbitrary;
+use libfuzzer_sys::fuzz_target;
+
+const MAX_RESERVE: usize = 1024;
+
+#[derive(Arbitrary, Debug, Eq, Hash, PartialEq)]
+enum Data {
+    A,
+    B,
+    Int { val: u8 },
+}
+
+#[derive(Arbitrary, Debug)]
+enum HashMapMethods {
+    Insert { key: Data, value: Data },
+    Remove { key: Data },
+    ContainsKey { key: Data },
+    Get { key: Data },
+    EntryOrInsert { key: Data, value: Data },
+    Iter,
+    Drain,
+    Clear,
+    Reserve { additional: usize },
+    ShrinkToFit,
+    ShrinkTo { min_capacity: usize },
+}
+
+fuzz_target!(|commands: Vec<HashMapMethods>| {
+    let mut map = HashMap::new();
+    for command in commands {
+        match command {
+            HashMapMethods::Insert { key, value } => {
+                map.insert(key, value);
+            }
+            HashMapMethods::Remove { key } => {
+                map.remove(&key);
+            }
+            HashMapMethods::ContainsKey { key } => {
+                map.contains_key(&key);
+            }
+            HashMapMethods::Get { key } => {
+                map.get(&key);
+            }
+            HashMapMethods::EntryOrInsert { key, value } => {
+                map.entry(key).or_insert(value);
+            }
+            HashMapMethods::Iter => {
+                std::hint::black_box(map.iter().count());
+            }
+            HashMapMethods::Drain => {
+                std::hint::black_box(map.drain().count());
+            }
+            HashMapMethods::Clear => {
+                map.clear();
+            }
+            HashMapMethods::Reserve { additional } => {
+                // Avoid allocating too much memory and crashing the fuzzer.
+                map.reserve(additional % MAX_RESERVE);
+            }
+            HashMapMethods::ShrinkToFit => {
+                map.shrink_to_fit();
+            }
+            HashMapMethods::ShrinkTo { min_capacity } => {
+                map.shrink_to(min_capacity % MAX_RESERVE);
+            }
+        }
+    }
+});