feat(cast): Implemented cast index (seth feature parity #29) (#676)

* feat(cast): Implemented cast index (seth feature parity #29)

* made the suggested changes after review #676

cast/src/lib.rs

@@ -1175,6 +1175,32 @@ impl SimpleCast {
 
         Ok(code)
     }
+    /// Prints the slot number for the specified mapping type and input data
+    /// Uses abi_encode to pad the data to 32 bytes.
+    /// For value types v, slot number of v is keccak256(concat(h(v) , p)) where h is the padding
+    /// function and p is slot number of the mapping.
+    /// ```
+    /// # use cast::SimpleCast as Cast;
+    ///
+    /// # fn main() -> eyre::Result<()> {
+    ///    
+    ///    assert_eq!(Cast::index("address", "uint256" ,"0xD0074F4E6490ae3f888d1d4f7E3E43326bD3f0f5" ,"2").unwrap().as_str(),"0x9525a448a9000053a4d151336329d6563b7e80b24f8e628e95527f218e8ab5fb");
+    ///    assert_eq!(Cast::index("uint256", "uint256" ,"42" ,"6").unwrap().as_str(),"0xfc808b0f31a1e6b9cf25ff6289feae9b51017b392cc8e25620a94a38dcdafcc1");
+    /// #    Ok(())
+    /// # }
+    /// ```
+
+    pub fn index(
+        from_type: &str,
+        to_type: &str,
+        from_value: &str,
+        slot_number: &str,
+    ) -> Result<String> {
+        let sig = format!("x({},{})", from_type, to_type);
+        let encoded = Self::abi_encode(&sig, &[from_value, slot_number])?;
+        let location: String = Self::keccak(&encoded)?;
+        Ok(location)
+    }
 }
 
 fn strip_0x(s: &str) -> &str {

cli/src/cast.rs

@@ -319,6 +319,10 @@ async fn main() -> eyre::Result<()> {
         Subcommands::AbiEncode { sig, args } => {
             println!("{}", SimpleCast::abi_encode(&sig, &args)?);
         }
+        Subcommands::Index { from_type, to_type, from_value, slot_number } => {
+            let encoded = SimpleCast::index(&from_type, &to_type, &from_value, &slot_number)?;
+            println!("{}", encoded);
+        }
         Subcommands::FourByte { selector } => {
             let sigs = foundry_utils::fourbyte(&selector).await?;
             sigs.iter().for_each(|sig| println!("{}", sig.0));

cli/src/opts/cast.rs

@@ -271,6 +271,20 @@ pub enum Subcommands {
         #[clap(allow_hyphen_values = true)]
         args: Vec<String>,
     },
+    #[clap(name = "index")]
+    #[clap(
+        about = "Get storage slot of value from mapping type, mapping slot number and input value"
+    )]
+    Index {
+        #[clap(help = "mapping key type")]
+        from_type: String,
+        #[clap(help = "mapping value type")]
+        to_type: String,
+        #[clap(help = "the value")]
+        from_value: String,
+        #[clap(help = "storage slot of the mapping")]
+        slot_number: String,
+    },
     #[clap(name = "4byte")]
     #[clap(about = "Fetches function signatures given the selector from 4byte.directory")]
     FourByte {