fuzz: add fuzzing that tests pruning

.github/workflows/fuzz.yml

@@ -9,6 +9,20 @@ on:
   pull_request:
 
 jobs:
+  test:
+    name: Test Fuzz Library
+    if: ${{ !github.event.act }}
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout Crate
+        uses: actions/checkout@v4
+
+      - name: Install Toolchain
+        uses: dtolnay/rust-toolchain@stable
+
+      - name: Run Tests
+        run: cargo test -p simplicity-fuzz --lib
+
   fuzz:
     name: Run Fuzz Target
     if: ${{ !github.event.act }}
@@ -23,6 +37,7 @@ c_rust_merkle,
 decode_natural,
 decode_program,
 parse_human,
+prune_generated,
 regression_286,
 regression_value,
         ]

Cargo-recent.lock

@@ -589,6 +589,7 @@ dependencies = [
 name = "simplicity-fuzz"
 version = "0.0.1"
 dependencies = [
+ "arbitrary",
  "base64 0.22.1",
  "libfuzzer-sys",
  "simplicity-lang 0.3.1",

fuzz/Cargo.toml

@@ -13,6 +13,7 @@ cargo-fuzz = true
 path = "fuzz_lib/lib.rs"
 
 [dependencies]
+arbitrary = "1.4.2"
 libfuzzer-sys = "0.4"
 # We shouldn't need an explicit version on the next line, but Andrew's tools
 # choke on it otherwise. See https://github.com/nix-community/crate2nix/issues/373
@@ -67,6 +68,13 @@ test = false
 doc = false
 bench = false
 
+[[bin]]
+name = "prune_generated"
+path = "fuzz_targets/prune_generated.rs"
+test = false
+doc = false
+bench = false
+
 [[bin]]
 name = "regression_286"
 path = "fuzz_targets/regression_286.rs"

fuzz/fuzz.sh

@@ -22,5 +22,11 @@ rustc --version
 # Run fuzz target
 for targetFile in $targetFiles; do
   targetName=$(targetFileToName "$targetFile")
-  cargo-fuzz run "$targetName" -- -max_total_time=30
+  # prune_generated builds a program from its input, and only long inputs give
+  # large programs, which libFuzzer otherwise tries only after a long time.
+  extraArgs=()
+  if [ "$targetName" == "prune_generated" ]; then
+    extraArgs=(-len_control=0 -max_len=4096)
+  fi
+  cargo-fuzz run "$targetName" -- -max_total_time=30 "${extraArgs[@]}"
 done