feat(invariant): on failures show original and current sequence len (foundry-rs#9816)

Author: grandizzy

crates/evm/fuzz/src/lib.rs

@@ -35,8 +35,8 @@ pub use inspector::Fuzzer;
 pub enum CounterExample {
     /// Call used as a counter example for fuzz tests.
     Single(BaseCounterExample),
-    /// Sequence of calls used as a counter example for invariant tests.
-    Sequence(Vec<BaseCounterExample>),
+    /// Original sequence size and sequence of calls used as a counter example for invariant tests.
+    Sequence(usize, Vec<BaseCounterExample>),
 }
 
 #[derive(Clone, Debug, Serialize, Deserialize)]

crates/forge/src/result.rs

@@ -446,8 +446,14 @@ impl fmt::Display for TestResult {
                             CounterExample::Single(ex) => {
                                 write!(s, "; counterexample: {ex}]").unwrap();
                             }
-                            CounterExample::Sequence(sequence) => {
-                                s.push_str("]\n\t[Sequence]\n");
+                            CounterExample::Sequence(original, sequence) => {
+                                s.push_str(
+                                    format!(
+                                        "]\n\t[Sequence] (original: {original}, shrunk: {})\n",
+                                        sequence.len()
+                                    )
+                                    .as_str(),
+                                );
                                 for ex in sequence {
                                     writeln!(s, "\t\t{ex}").unwrap();
                                 }
@@ -593,7 +599,7 @@ impl TestResult {
         } else {
             Some(format!("{invariant_name} persisted failure revert"))
         };
-        self.counterexample = Some(CounterExample::Sequence(call_sequence));
+        self.counterexample = Some(CounterExample::Sequence(call_sequence.len(), call_sequence));
     }
 
     /// Returns the fail result for invariant test setup.

crates/forge/src/runner.rs

@@ -31,7 +31,7 @@ use foundry_evm::{
     traces::{load_contracts, TraceKind, TraceMode},
 };
 use proptest::test_runner::{
-    FailurePersistence, FileFailurePersistence, RngAlgorithm, TestRng, TestRunner,
+    FailurePersistence, FileFailurePersistence, RngAlgorithm, TestError, TestRng, TestRunner,
 };
 use rayon::prelude::*;
 use std::{borrow::Cow, cmp::min, collections::BTreeMap, sync::Arc, time::Instant};
@@ -686,7 +686,16 @@ impl<'a> FunctionRunner<'a> {
                                 ) {
                                     error!(%err, "Failed to record call sequence");
                                 }
-                                counterexample = Some(CounterExample::Sequence(call_sequence))
+
+                                let original_seq_len =
+                                    if let TestError::Fail(_, calls) = &case_data.test_error {
+                                        calls.len()
+                                    } else {
+                                        call_sequence.len()
+                                    };
+
+                                counterexample =
+                                    Some(CounterExample::Sequence(original_seq_len, call_sequence))
                             }
                         }
                         Err(err) => {

crates/forge/tests/it/invariant.rs

@@ -266,7 +266,7 @@ async fn test_invariant_shrink() {
     match get_counterexample!(runner, &filter) {
         CounterExample::Single(_) => panic!("CounterExample should be a sequence."),
         // `fuzz_seed` at 119 makes this sequence shrinkable from 4 to 2.
-        CounterExample::Sequence(sequence) => {
+        CounterExample::Sequence(_, sequence) => {
             assert!(sequence.len() <= 3);
 
             if sequence.len() == 2 {
@@ -314,7 +314,7 @@ async fn check_shrink_sequence(test_pattern: &str, expected_len: usize) {
 
     match get_counterexample!(runner, &filter) {
         CounterExample::Single(_) => panic!("CounterExample should be a sequence."),
-        CounterExample::Sequence(sequence) => {
+        CounterExample::Sequence(_, sequence) => {
             assert_eq!(sequence.len(), expected_len);
         }
     };
@@ -346,7 +346,7 @@ async fn test_shrink_big_sequence() {
 
     let initial_sequence = match initial_counterexample {
         CounterExample::Single(_) => panic!("CounterExample should be a sequence."),
-        CounterExample::Sequence(sequence) => sequence,
+        CounterExample::Sequence(_, sequence) => sequence,
     };
     // ensure shrinks to same sequence of 77
     assert_eq!(initial_sequence.len(), 77);
@@ -379,7 +379,7 @@ async fn test_shrink_big_sequence() {
         .unwrap()
     {
         CounterExample::Single(_) => panic!("CounterExample should be a sequence."),
-        CounterExample::Sequence(sequence) => sequence,
+        CounterExample::Sequence(_, sequence) => sequence,
     };
     // ensure shrinks to same sequence of 77
     assert_eq!(new_sequence.len(), 77);
@@ -407,7 +407,7 @@ async fn test_shrink_fail_on_revert() {
 
     match get_counterexample!(runner, &filter) {
         CounterExample::Single(_) => panic!("CounterExample should be a sequence."),
-        CounterExample::Sequence(sequence) => {
+        CounterExample::Sequence(_, sequence) => {
             // ensure shrinks to sequence of 10
             assert_eq!(sequence.len(), 10);
         }
@@ -696,7 +696,7 @@ async fn test_no_reverts_in_counterexample() {
 
     match get_counterexample!(runner, &filter) {
         CounterExample::Single(_) => panic!("CounterExample should be a sequence."),
-        CounterExample::Sequence(sequence) => {
+        CounterExample::Sequence(_, sequence) => {
             // ensure original counterexample len is 10 (even without shrinking)
             assert_eq!(sequence.len(), 10);
         }
@@ -1064,3 +1064,39 @@ contract InvariantSelectorsWeightTest is Test {
 
     cmd.args(["test", "--fuzz-seed", "119", "--mt", "invariant_selectors_weight"]).assert_success();
 });
+
+// Tests original and new counterexample lengths are displayed on failure.
+forgetest_init!(invariant_sequence_len, |prj, cmd| {
+    prj.update_config(|config| {
+        config.fuzz.seed = Some(U256::from(100u32));
+    });
+
+    prj.add_test(
+        "InvariantSequenceLenTest.t.sol",
+        r#"
+import {Test} from "forge-std/Test.sol";
+import "src/Counter.sol";
+
+contract InvariantSequenceLenTest is Test {
+    Counter public counter;
+
+    function setUp() public {
+        counter = new Counter();
+        targetContract(address(counter));
+    }
+
+    function invariant_increment() public {
+        require(counter.number() / 2 < 100000000000000000000000000000000, "invariant increment failure");
+    }
+}
+   "#,
+    )
+    .unwrap();
+
+    cmd.args(["test", "--mt", "invariant_increment"]).assert_failure().stdout_eq(str![[r#"
+...
+[FAIL: revert: invariant increment failure]
+	[Sequence] (original: 4, shrunk: 1)
+...
+"#]]);
+});