feat: support negative forkblock numbers (#10263)

Author: mattsse

crates/anvil/src/cmd.rs

@@ -238,7 +238,12 @@ impl NodeArgs {
             .with_fork_choice(match (self.evm.fork_block_number, self.evm.fork_transaction_hash) {
                 (Some(block), None) => Some(ForkChoice::Block(block)),
                 (None, Some(hash)) => Some(ForkChoice::Transaction(hash)),
-                _ => self.evm.fork_url.as_ref().and_then(|f| f.block).map(ForkChoice::Block),
+                _ => self
+                    .evm
+                    .fork_url
+                    .as_ref()
+                    .and_then(|f| f.block)
+                    .map(|num| ForkChoice::Block(num as i128)),
             })
             .with_fork_headers(self.evm.fork_headers)
             .with_fork_chain_id(self.evm.fork_chain_id.map(u64::from).map(U256::from))
@@ -428,9 +433,17 @@ pub struct AnvilEvmArgs {
 
     /// Fetch state from a specific block number over a remote endpoint.
     ///
+    /// If a negative the the given value is subtracted from the `latest` block number.
+    ///
     /// See --fork-url.
-    #[arg(long, requires = "fork_url", value_name = "BLOCK", help_heading = "Fork config")]
-    pub fork_block_number: Option<u64>,
+    #[arg(
+        long,
+        requires = "fork_url",
+        value_name = "BLOCK",
+        help_heading = "Fork config",
+        allow_hyphen_values = true
+    )]
+    pub fork_block_number: Option<i128>,
 
     /// Fetch state from a specific transaction hash over a remote endpoint.
     ///

crates/anvil/src/config.rs

@@ -1361,7 +1361,16 @@ async fn derive_block_and_transactions(
     provider: &Arc<RetryProvider>,
 ) -> eyre::Result<(BlockNumber, Option<Vec<PoolTransaction>>)> {
     match fork_choice {
-        ForkChoice::Block(block_number) => Ok((block_number.to_owned(), None)),
+        ForkChoice::Block(block_number) => {
+            let block_number = *block_number;
+            if block_number >= 0 {
+                return Ok((block_number as u64, None))
+            }
+            // subtract from latest block number
+            let latest = provider.get_block_number().await?;
+
+            Ok((block_number.saturating_add(latest as i128) as u64, None))
+        }
         ForkChoice::Transaction(transaction_hash) => {
             // Determine the block that this transaction was mined in
             let transaction = provider
@@ -1400,15 +1409,17 @@ async fn derive_block_and_transactions(
 /// Fork delimiter used to specify which block or transaction to fork from
 #[derive(Clone, Copy, Debug, PartialEq, Eq)]
 pub enum ForkChoice {
-    /// Block number to fork from
-    Block(BlockNumber),
+    /// Block number to fork from.
+    ///
+    /// f a negative the the given value is subtracted from the `latest` block number.
+    Block(i128),
     /// Transaction hash to fork from
     Transaction(TxHash),
 }
 
 impl ForkChoice {
     /// Returns the block number to fork from
-    pub fn block_number(&self) -> Option<BlockNumber> {
+    pub fn block_number(&self) -> Option<i128> {
         match self {
             Self::Block(block_number) => Some(*block_number),
             Self::Transaction(_) => None,
@@ -1434,7 +1445,7 @@ impl From<TxHash> for ForkChoice {
 /// Convert a decimal block number into a ForkChoice
 impl From<u64> for ForkChoice {
     fn from(block: u64) -> Self {
-        Self::Block(block)
+        Self::Block(block as i128)
     }
 }
 

crates/anvil/src/eth/backend/mem/mod.rs

@@ -611,7 +611,7 @@ impl Backend {
         fork_block_number: u64,
     ) -> Result<(), BlockchainError> {
         let mut node_config = self.node_config.write().await;
-        node_config.fork_choice = Some(ForkChoice::Block(fork_block_number));
+        node_config.fork_choice = Some(ForkChoice::Block(fork_block_number as i128));
 
         let mut env = self.env.read().clone();
         let (forked_db, client_fork_config) =