✨ Adds a means to bypass fixed addresses for LibMulticaller (#35)

* ✨ Adds a means to bypass fixed addresses for LibMulticaller (#34)

Co-authored-by: 3commascapital <3commascapital@github.com>

* Tidy

---------

Co-authored-by: 3commascapital <90629478+3commascapital@users.noreply.github.com>
Co-authored-by: 3commascapital <3commascapital@github.com>

.gas-snapshot

@@ -1,31 +1,31 @@
-MulticallerTest:testMultiCallerWithSignerIncrementNonceSalt(uint256) (runs: 256, μ: 83320, ~: 82376)
-MulticallerTest:testMultiCallerWithSignerIncrementNonceSaltWithERC1271(uint256) (runs: 256, μ: 614873, ~: 614814)
+MulticallerTest:testMultiCallerWithSignerIncrementNonceSalt(uint256) (runs: 256, μ: 83584, ~: 83538)
+MulticallerTest:testMultiCallerWithSignerIncrementNonceSaltWithERC1271(uint256) (runs: 256, μ: 614876, ~: 614922)
 MulticallerTest:testMulticallerCdFallback(string) (runs: 256, μ: 295907, ~: 281868)
 MulticallerTest:testMulticallerForwardsMessageValue() (gas: 214013)
 MulticallerTest:testMulticallerGetNames() (gas: 147637)
 MulticallerTest:testMulticallerReentrancyGuard() (gas: 19980)
-MulticallerTest:testMulticallerRefund(uint256) (runs: 256, μ: 170012, ~: 172026)
+MulticallerTest:testMulticallerRefund(uint256) (runs: 256, μ: 169488, ~: 171890)
 MulticallerTest:testMulticallerReturnDataIsProperlyEncoded() (gas: 122173)
-MulticallerTest:testMulticallerReturnDataIsProperlyEncoded(string,string,uint256) (runs: 256, μ: 506602, ~: 531965)
+MulticallerTest:testMulticallerReturnDataIsProperlyEncoded(string,string,uint256) (runs: 256, μ: 486042, ~: 450256)
 MulticallerTest:testMulticallerReturnDataIsProperlyEncoded(uint256,uint256,uint256,uint256) (runs: 256, μ: 122252, ~: 122252)
 MulticallerTest:testMulticallerRevertWithCustomError() (gas: 35485)
 MulticallerTest:testMulticallerRevertWithMessage() (gas: 38244)
 MulticallerTest:testMulticallerRevertWithMessage(string) (runs: 256, μ: 38922, ~: 38644)
 MulticallerTest:testMulticallerRevertWithNothing() (gas: 35306)
-MulticallerTest:testMulticallerSenderDoesNotRevertWithoutMulticallerDeployed() (gas: 3423)
-MulticallerTest:testMulticallerTargetGetMulticallerSender() (gas: 27448)
+MulticallerTest:testMulticallerSenderDoesNotRevertWithoutMulticallerDeployed() (gas: 3463)
+MulticallerTest:testMulticallerTargetGetMulticallerSender() (gas: 27523)
 MulticallerTest:testMulticallerWithNoData() (gas: 16213)
-MulticallerTest:testMulticallerWithSigner(uint256) (runs: 256, μ: 130354, ~: 119358)
+MulticallerTest:testMulticallerWithSigner(uint256) (runs: 256, μ: 128165, ~: 119136)
 MulticallerTest:testMulticallerWithSignerEIP712Domain() (gas: 12375)
-MulticallerTest:testMulticallerWithSignerGetMulticallerSigner() (gas: 136389)
-MulticallerTest:testMulticallerWithSignerInvalidateNonces(uint256) (runs: 256, μ: 80313, ~: 79643)
-MulticallerTest:testMulticallerWithSignerInvalidateNoncesWithERC1271(uint256) (runs: 256, μ: 616631, ~: 616541)
+MulticallerTest:testMulticallerWithSignerGetMulticallerSigner() (gas: 136504)
+MulticallerTest:testMulticallerWithSignerInvalidateNonces(uint256) (runs: 256, μ: 79177, ~: 77798)
+MulticallerTest:testMulticallerWithSignerInvalidateNoncesWithERC1271(uint256) (runs: 256, μ: 617027, ~: 616455)
 MulticallerTest:testMulticallerWithSignerNonPayableFunctions() (gas: 48884)
 MulticallerTest:testMulticallerWithSignerReentrancyGuard() (gas: 124909)
 MulticallerTest:testMulticallerWithSignerRevert() (gas: 206240)
-MulticallerTest:testMulticallerWithSignerWithERC1271(uint256) (runs: 256, μ: 657836, ~: 651346)
+MulticallerTest:testMulticallerWithSignerWithERC1271(uint256) (runs: 256, μ: 661769, ~: 651359)
 MulticallerTest:testMulticallerWithSignerWithNoData() (gas: 130147)
 MulticallerTest:testNastyCalldataRevert() (gas: 3420)
 MulticallerTest:testOffsetTrick(uint256,uint256,uint256) (runs: 256, μ: 571, ~: 571)
-MulticallerTest:test__codesize() (gas: 50276)
+MulticallerTest:test__codesize() (gas: 50297)
 TestPlus:test__codesize() (gas: 1102)

src/LibMulticaller.sol

@@ -36,28 +36,14 @@ library LibMulticaller {
      * @dev Returns the caller of `aggregateWithSender` on `MULTICALLER_WITH_SENDER`.
      */
     function multicallerSender() internal view returns (address result) {
-        /// @solidity memory-safe-assembly
-        assembly {
-            mstore(0x00, 0x00)
-            if iszero(staticcall(gas(), MULTICALLER_WITH_SENDER, codesize(), 0x00, 0x00, 0x20)) {
-                revert(codesize(), codesize()) // For better gas estimation.
-            }
-            result := mload(0x00)
-        }
+        return at(MULTICALLER_WITH_SENDER);
     }
 
     /**
      * @dev Returns the signer of `aggregateWithSigner` on `MULTICALLER_WITH_SIGNER`.
      */
     function multicallerSigner() internal view returns (address result) {
-        /// @solidity memory-safe-assembly
-        assembly {
-            mstore(0x00, 0x00)
-            if iszero(staticcall(gas(), MULTICALLER_WITH_SIGNER, codesize(), 0x00, 0x00, 0x20)) {
-                revert(codesize(), codesize()) // For better gas estimation.
-            }
-            result := mload(0x00)
-        }
+        return at(MULTICALLER_WITH_SIGNER);
     }
 
     /**
@@ -66,31 +52,43 @@ library LibMulticaller {
      *      Otherwise, returns `msg.sender`.
      */
     function sender() internal view returns (address result) {
+        return resolve(MULTICALLER_WITH_SENDER);
+    }
+
+    /**
+     * @dev Returns the caller of `aggregateWithSigner` on `MULTICALLER_WITH_SIGNER`,
+     *      if the current context's `msg.sender` is `MULTICALLER_WITH_SIGNER`.
+     *      Otherwise, returns `msg.sender`.
+     */
+    function signer() internal view returns (address) {
+        return resolve(MULTICALLER_WITH_SIGNER);
+    }
+
+    /**
+     * @dev Returns the caller or signer at `a`.
+     * @param a The multicaller with sender / signer.
+     */
+    function at(address a) internal view returns (address result) {
         /// @solidity memory-safe-assembly
         assembly {
-            mstore(0x00, caller())
-            let withSender := MULTICALLER_WITH_SENDER
-            if eq(caller(), withSender) {
-                if iszero(staticcall(gas(), withSender, codesize(), 0x00, 0x00, 0x20)) {
-                    revert(codesize(), codesize()) // For better gas estimation.
-                }
+            mstore(0x00, 0x00)
+            if iszero(staticcall(gas(), a, codesize(), 0x00, 0x00, 0x20)) {
+                revert(codesize(), codesize()) // For better gas estimation.
             }
             result := mload(0x00)
         }
     }
 
     /**
-     * @dev Returns the caller of `aggregateWithSigner` on `MULTICALLER_WITH_SIGNER`,
-     *      if the current context's `msg.sender` is `MULTICALLER_WITH_SIGNER`.
-     *      Otherwise, returns `msg.sender`.
+     * @dev Returns the caller or signer at `a`, if the caller is `a`.
+     * @param a The multicaller with sender / signer.
      */
-    function signer() internal view returns (address result) {
+    function resolve(address a) internal view returns (address result) {
         /// @solidity memory-safe-assembly
         assembly {
             mstore(0x00, caller())
-            let withSigner := MULTICALLER_WITH_SIGNER
-            if eq(caller(), withSigner) {
-                if iszero(staticcall(gas(), withSigner, codesize(), 0x00, 0x00, 0x20)) {
+            if eq(caller(), a) {
+                if iszero(staticcall(gas(), a, codesize(), 0x00, 0x00, 0x20)) {
                     revert(codesize(), codesize()) // For better gas estimation.
                 }
             }