feat: add Clarity4 keyword current-contract

Author: obycode

CHANGELOG.md

@@ -15,6 +15,7 @@ and this project adheres to the versioning scheme outlined in the [README.md](RE
 - Creates epoch 3.3 and costs-4 in preparation for a hardfork to activate Clarity 4
 - Adds support for new Clarity 4 builtins (not activated until epoch 3.3):
   - `contract-hash?`
+  - `current-contract`
 
 ### Changed
 

clarity/src/vm/analysis/arithmetic_checker/mod.rs

@@ -144,9 +144,8 @@ impl ArithmeticOnlyChecker<'_> {
         {
             match native_var {
                 ContractCaller | TxSender | TotalLiquidMicroSTX | BlockHeight | BurnBlockHeight
-                | Regtest | TxSponsor | Mainnet | ChainId | StacksBlockHeight | TenureHeight => {
-                    Err(Error::VariableForbidden(native_var))
-                }
+                | Regtest | TxSponsor | Mainnet | ChainId | StacksBlockHeight | TenureHeight
+                | CurrentContract => Err(Error::VariableForbidden(native_var)),
                 NativeNone | NativeTrue | NativeFalse => Ok(()),
             }
         } else {

clarity/src/vm/analysis/type_checker/v2_05/mod.rs

@@ -318,9 +318,9 @@ fn type_reserved_variable(variable_name: &str) -> CheckResult<Option<TypeSignatu
             NativeFalse => TypeSignature::BoolType,
             TotalLiquidMicroSTX => TypeSignature::UIntType,
             Regtest => TypeSignature::BoolType,
-            TxSponsor | Mainnet | ChainId | StacksBlockHeight | TenureHeight => {
+            TxSponsor | Mainnet | ChainId | StacksBlockHeight | TenureHeight | CurrentContract => {
                 return Err(CheckErrors::Expects(
-                    "tx-sponsor, mainnet, chain-id, stacks-block-height, and tenure-height should not reach here in 2.05".into(),
+                    "tx-sponsor, mainnet, chain-id, stacks-block-height, tenure-height, and current-contract should not reach here in 2.05".into(),
                 )
                 .into())
             }

clarity/src/vm/analysis/type_checker/v2_1/mod.rs

@@ -991,6 +991,7 @@ fn type_reserved_variable(
             Regtest => TypeSignature::BoolType,
             Mainnet => TypeSignature::BoolType,
             ChainId => TypeSignature::UIntType,
+            CurrentContract => TypeSignature::PrincipalType,
         };
         Ok(Some(var_type))
     } else {

clarity/src/vm/docs/mod.rs

@@ -125,6 +125,15 @@ to the same contract principal.",
     example: "(print contract-caller) ;; Will print out a Stacks address of the transaction sender",
 };
 
+const CURRENT_CONTRACT_KEYWORD: SimpleKeywordAPI = SimpleKeywordAPI {
+    name: "current-contract",
+    snippet: "current-contract",
+    output_type: "principal",
+    description: "Returns the principal of the current contract.",
+    example:
+        "(print current-contract) ;; Will print out the Stacks address of the current contract",
+};
+
 const STACKS_BLOCK_HEIGHT_KEYWORD: SimpleKeywordAPI = SimpleKeywordAPI {
     name: "stacks-block-height",
     snippet: "stacks-block-height",
@@ -2660,6 +2669,7 @@ pub fn make_keyword_reference(variable: &NativeVariables) -> Option<KeywordAPI>
         NativeVariables::Mainnet => MAINNET_KEYWORD.clone(),
         NativeVariables::ChainId => CHAINID_KEYWORD.clone(),
         NativeVariables::TxSponsor => TX_SPONSOR_KEYWORD.clone(),
+        NativeVariables::CurrentContract => CURRENT_CONTRACT_KEYWORD.clone(),
     };
     Some(KeywordAPI {
         name: keyword.name,