Add simple fuzzing

Add infrastructure to automatically run fuzzers in CI,
and implement a simple fuzzing test based on triggering all (most)
public APIs in a randimized way.

As far as I was able to try it catches the previous unsoundness issues
in a matter of seconds. This can be tried by changing the `path = "../"` dependency to
`version = "=0.6.3"` etc. and running the fuzzer manually. (Note: You'll need
to tweak the `Cargo.lock` to allow downloading the yanked versions).

Related to #124

Author: dpc

.gitignore

@@ -1,2 +1,2 @@
 target
-Cargo.lock
+./Cargo.lock

.travis.yml

@@ -1,14 +1,36 @@
 language: rust
-rust:
-  - 1.20.0
-  - nightly
-  - beta
-  - stable
+addons:
+  apt:
+    update: true
+    packages:
+      - binutils-dev
+      - libunwind8-dev
+      - libcurl4-openssl-dev
+      - libelf-dev
+      - libdw-dev
+      - cmake
+      - gcc
+      - libiberty-dev
+matrix:
+  include:
+    - rust: 1.20.0
+    - rust: nightly
+    - rust: beta
+      env: DO_FUZZ=true
+    - rust: stable
+      env: DO_FUZZ=true
 script: |
   cargo build --verbose &&
   cargo test --verbose &&
   cargo test --verbose --features serde &&
   ([ $TRAVIS_RUST_VERSION != nightly ] || cargo check --verbose --no-default-features) &&
   ([ $TRAVIS_RUST_VERSION != nightly ] || cargo test --verbose --features union) &&
   ([ $TRAVIS_RUST_VERSION != nightly ] || cargo test --verbose --all-features) &&
-  ([ $TRAVIS_RUST_VERSION != nightly ] || cargo bench --verbose bench)
+  ([ $TRAVIS_RUST_VERSION != nightly ] || cargo bench --verbose bench) &&
+  if [ "$DO_FUZZ" = true ]
+  then
+  (
+    cd fuzz
+    ./travis-fuzz.sh
+  )
+  fi

fuzz/Cargo.lock

@@ -0,0 +1,26 @@
+[package]
+name = "smallvec-fuzz"
+version = "0.1.0"
+authors = ["Dawid Ciężarkiewicz <dpc@dpc.pw>"]
+edition = "2018"
+publish = false
+
+[package.metadata]
+cargo-fuzz = true
+
+[features]
+afl_fuzz = ["afl"]
+honggfuzz_fuzz = ["honggfuzz"]
+
+
+[dependencies]
+honggfuzz = { version = "0.5.45", optional = true }
+afl = { version = "0.4", optional = true }
+smallvec = { path = ".." }
+
+[workspace]
+members = ["."]
+
+[[bin]]
+name = "smallvec_ops"
+path = "fuzz_targets/smallvec_ops.rs"

fuzz/Cargo.toml

@@ -0,0 +1,12 @@
+# Fuzzer for smallvec
+
+Based on fuzzing in [rust-bitcoin](https://github.com/rust-bitcoin/rust-bitcoin/tree/c8ac25219a09bf9d017f1b05abe3e746e2136f73/fuzz)
+
+## Running manually with afl
+
+```
+cargo afl build --release --bin smallvec_ops --features afl   && cargo afl fuzz -i in -o out target/release/smallvec_ops
+```
+
+# Useful links:
+* https://rust-fuzz.github.io/book/afl.html