From 8bcba2f8ff0e57a2ca336e03181cebd95b5f3c2a Mon Sep 17 00:00:00 2001
From: ernestognw <ernestognw@gmail.com>
Date: Fri, 14 Jul 2023 15:18:41 -0600
Subject: [PATCH 01/12] Allow reinitializers versions greater than 256

---
 contracts/mocks/InitializableMock.sol   |  8 +--
 contracts/proxy/utils/Initializable.sol | 84 +++++++++++++++++--------
 test/proxy/utils/Initializable.test.js  |  2 +-
 3 files changed, 63 insertions(+), 31 deletions(-)

diff --git a/contracts/mocks/InitializableMock.sol b/contracts/mocks/InitializableMock.sol
index 155aaefb799..456d2d1dfe5 100644
--- a/contracts/mocks/InitializableMock.sol
+++ b/contracts/mocks/InitializableMock.sol
@@ -79,7 +79,7 @@ contract ChildConstructorInitializableMock is ConstructorInitializableMock {
 contract ReinitializerMock is Initializable {
     uint256 public counter;
 
-    function getInitializedVersion() public view returns (uint8) {
+    function getInitializedVersion() public view returns (uint16) {
         return _getInitializedVersion();
     }
 
@@ -87,15 +87,15 @@ contract ReinitializerMock is Initializable {
         doStuff();
     }
 
-    function reinitialize(uint8 i) public reinitializer(i) {
+    function reinitialize(uint16 i) public reinitializer(i) {
         doStuff();
     }
 
-    function nestedReinitialize(uint8 i, uint8 j) public reinitializer(i) {
+    function nestedReinitialize(uint16 i, uint16 j) public reinitializer(i) {
         reinitialize(j);
     }
 
-    function chainReinitialize(uint8 i, uint8 j) public {
+    function chainReinitialize(uint16 i, uint16 j) public {
         reinitialize(i);
         reinitialize(j);
     }
diff --git a/contracts/proxy/utils/Initializable.sol b/contracts/proxy/utils/Initializable.sol
index 08171015d3c..8a99aca5917 100644
--- a/contracts/proxy/utils/Initializable.sol
+++ b/contracts/proxy/utils/Initializable.sol
@@ -1,7 +1,7 @@
 // SPDX-License-Identifier: MIT
 // OpenZeppelin Contracts (last updated v4.9.0) (proxy/utils/Initializable.sol)
 
-pragma solidity ^0.8.19;
+pragma solidity ^0.8.20;
 
 /**
  * @dev This is a base contract to aid in writing upgradeable contracts, or any kind of contract that will be deployed
@@ -55,14 +55,27 @@ pragma solidity ^0.8.19;
  */
 abstract contract Initializable {
     /**
-     * @dev Indicates that the contract has been initialized.
+     * @dev Storage of the initializable contract.
+     *
+     * It's implemented on a custom ERC-7201 namespace to reduce the risk of storage collisions
+     * when using with upgradeable contracts.
+     *
+     * @custom:storage-location erc7201:openzeppelin.storage.Initializable
      */
-    uint8 private _initialized;
+    struct InitializableStorage {
+        /**
+         * @dev Indicates that the contract has been initialized.
+         */
+        uint16 _initialized;
+        /**
+         * @dev Indicates that the contract is in the process of being initialized.
+         */
+        bool _initializing;
+    }
 
-    /**
-     * @dev Indicates that the contract is in the process of being initialized.
-     */
-    bool private _initializing;
+    // keccak256(abi.encode(uint256(keccak256("openzeppelin.storage.Initializable")) - 1))
+    bytes32 private constant _INITIALIZABLE_STORAGE =
+        0xf0c57e16840df040f15088dc2f81fe391c3923bec73e23a9662efc9c229c6a0e;
 
     /**
      * @dev The contract is already initialized.
@@ -77,7 +90,7 @@ abstract contract Initializable {
     /**
      * @dev Triggered when the contract has been initialized or reinitialized.
      */
-    event Initialized(uint8 version);
+    event Initialized(uint16 version);
 
     /**
      * @dev A modifier that defines a protected initializer function that can be invoked at most once. In its scope,
@@ -89,17 +102,20 @@ abstract contract Initializable {
      * Emits an {Initialized} event.
      */
     modifier initializer() {
-        bool isTopLevelCall = !_initializing;
-        if (!(isTopLevelCall && _initialized < 1) && !(address(this).code.length == 0 && _initialized == 1)) {
+        // solhint-disable-next-line var-name-mixedcase
+        InitializableStorage storage $ = _getInitializableStorage();
+
+        bool isTopLevelCall = !$._initializing;
+        if (!(isTopLevelCall && $._initialized < 1) && !(address(this).code.length == 0 && $._initialized == 1)) {
             revert AlreadyInitialized();
         }
-        _initialized = 1;
+        $._initialized = 1;
         if (isTopLevelCall) {
-            _initializing = true;
+            $._initializing = true;
         }
         _;
         if (isTopLevelCall) {
-            _initializing = false;
+            $._initializing = false;
             emit Initialized(1);
         }
     }
@@ -122,14 +138,17 @@ abstract contract Initializable {
      *
      * Emits an {Initialized} event.
      */
-    modifier reinitializer(uint8 version) {
-        if (_initializing || _initialized >= version) {
+    modifier reinitializer(uint16 version) {
+        // solhint-disable-next-line var-name-mixedcase
+        InitializableStorage storage $ = _getInitializableStorage();
+
+        if ($._initializing || $._initialized >= version) {
             revert AlreadyInitialized();
         }
-        _initialized = version;
-        _initializing = true;
+        $._initialized = version;
+        $._initializing = true;
         _;
-        _initializing = false;
+        $._initializing = false;
         emit Initialized(version);
     }
 
@@ -138,7 +157,7 @@ abstract contract Initializable {
      * {initializer} and {reinitializer} modifiers, directly or indirectly.
      */
     modifier onlyInitializing() {
-        if (!_initializing) {
+        if (!_isInitializing()) {
             revert NotInitializing();
         }
         _;
@@ -153,26 +172,39 @@ abstract contract Initializable {
      * Emits an {Initialized} event the first time it is successfully executed.
      */
     function _disableInitializers() internal virtual {
-        if (_initializing) {
+        // solhint-disable-next-line var-name-mixedcase
+        InitializableStorage storage $ = _getInitializableStorage();
+
+        if ($._initializing) {
             revert AlreadyInitialized();
         }
-        if (_initialized != type(uint8).max) {
-            _initialized = type(uint8).max;
-            emit Initialized(type(uint8).max);
+        if ($._initialized != type(uint16).max) {
+            $._initialized = type(uint16).max;
+            emit Initialized(type(uint16).max);
         }
     }
 
     /**
      * @dev Returns the highest version that has been initialized. See {reinitializer}.
      */
-    function _getInitializedVersion() internal view returns (uint8) {
-        return _initialized;
+    function _getInitializedVersion() internal view returns (uint16) {
+        return _getInitializableStorage()._initialized;
     }
 
     /**
      * @dev Returns `true` if the contract is currently initializing. See {onlyInitializing}.
      */
     function _isInitializing() internal view returns (bool) {
-        return _initializing;
+        return _getInitializableStorage()._initializing;
+    }
+
+    /**
+     * @dev Returns a pointer to the storage namespace.
+     */
+    // solhint-disable-next-line var-name-mixedcase
+    function _getInitializableStorage() private pure returns (InitializableStorage storage $) {
+        assembly {
+            $.slot := _INITIALIZABLE_STORAGE
+        }
     }
 }
diff --git a/test/proxy/utils/Initializable.test.js b/test/proxy/utils/Initializable.test.js
index e3e0fc02f77..fa8a0387b02 100644
--- a/test/proxy/utils/Initializable.test.js
+++ b/test/proxy/utils/Initializable.test.js
@@ -213,7 +213,7 @@ contract('Initializable', function () {
     it('old and new patterns in good sequence', async function () {
       const ok = await DisableOk.new();
       await expectEvent.inConstruction(ok, 'Initialized', { version: '1' });
-      await expectEvent.inConstruction(ok, 'Initialized', { version: '255' });
+      await expectEvent.inConstruction(ok, 'Initialized', { version: '65535' });
     });
   });
 });

From 6df8c25cfeb8ad645c6ac98234251d1cf095fb8e Mon Sep 17 00:00:00 2001
From: ernestognw <ernestognw@gmail.com>
Date: Fri, 14 Jul 2023 15:20:44 -0600
Subject: [PATCH 02/12] Use uint64 instead

---
 contracts/mocks/InitializableMock.sol   |  8 ++++----
 contracts/proxy/utils/Initializable.sol | 14 +++++++-------
 test/proxy/utils/Initializable.test.js  |  2 +-
 3 files changed, 12 insertions(+), 12 deletions(-)

diff --git a/contracts/mocks/InitializableMock.sol b/contracts/mocks/InitializableMock.sol
index 456d2d1dfe5..ab5ea031132 100644
--- a/contracts/mocks/InitializableMock.sol
+++ b/contracts/mocks/InitializableMock.sol
@@ -79,7 +79,7 @@ contract ChildConstructorInitializableMock is ConstructorInitializableMock {
 contract ReinitializerMock is Initializable {
     uint256 public counter;
 
-    function getInitializedVersion() public view returns (uint16) {
+    function getInitializedVersion() public view returns (uint64) {
         return _getInitializedVersion();
     }
 
@@ -87,15 +87,15 @@ contract ReinitializerMock is Initializable {
         doStuff();
     }
 
-    function reinitialize(uint16 i) public reinitializer(i) {
+    function reinitialize(uint64 i) public reinitializer(i) {
         doStuff();
     }
 
-    function nestedReinitialize(uint16 i, uint16 j) public reinitializer(i) {
+    function nestedReinitialize(uint64 i, uint64 j) public reinitializer(i) {
         reinitialize(j);
     }
 
-    function chainReinitialize(uint16 i, uint16 j) public {
+    function chainReinitialize(uint64 i, uint64 j) public {
         reinitialize(i);
         reinitialize(j);
     }
diff --git a/contracts/proxy/utils/Initializable.sol b/contracts/proxy/utils/Initializable.sol
index 8a99aca5917..897e9eff87f 100644
--- a/contracts/proxy/utils/Initializable.sol
+++ b/contracts/proxy/utils/Initializable.sol
@@ -66,7 +66,7 @@ abstract contract Initializable {
         /**
          * @dev Indicates that the contract has been initialized.
          */
-        uint16 _initialized;
+        uint64 _initialized;
         /**
          * @dev Indicates that the contract is in the process of being initialized.
          */
@@ -90,7 +90,7 @@ abstract contract Initializable {
     /**
      * @dev Triggered when the contract has been initialized or reinitialized.
      */
-    event Initialized(uint16 version);
+    event Initialized(uint64 version);
 
     /**
      * @dev A modifier that defines a protected initializer function that can be invoked at most once. In its scope,
@@ -138,7 +138,7 @@ abstract contract Initializable {
      *
      * Emits an {Initialized} event.
      */
-    modifier reinitializer(uint16 version) {
+    modifier reinitializer(uint64 version) {
         // solhint-disable-next-line var-name-mixedcase
         InitializableStorage storage $ = _getInitializableStorage();
 
@@ -178,16 +178,16 @@ abstract contract Initializable {
         if ($._initializing) {
             revert AlreadyInitialized();
         }
-        if ($._initialized != type(uint16).max) {
-            $._initialized = type(uint16).max;
-            emit Initialized(type(uint16).max);
+        if ($._initialized != type(uint64).max) {
+            $._initialized = type(uint64).max;
+            emit Initialized(type(uint64).max);
         }
     }
 
     /**
      * @dev Returns the highest version that has been initialized. See {reinitializer}.
      */
-    function _getInitializedVersion() internal view returns (uint16) {
+    function _getInitializedVersion() internal view returns (uint64) {
         return _getInitializableStorage()._initialized;
     }
 
diff --git a/test/proxy/utils/Initializable.test.js b/test/proxy/utils/Initializable.test.js
index fa8a0387b02..cb45995ea44 100644
--- a/test/proxy/utils/Initializable.test.js
+++ b/test/proxy/utils/Initializable.test.js
@@ -213,7 +213,7 @@ contract('Initializable', function () {
     it('old and new patterns in good sequence', async function () {
       const ok = await DisableOk.new();
       await expectEvent.inConstruction(ok, 'Initialized', { version: '1' });
-      await expectEvent.inConstruction(ok, 'Initialized', { version: '65535' });
+      await expectEvent.inConstruction(ok, 'Initialized', { version: '18446744073709551615' }); // MAX_UINT64
     });
   });
 });

From 2a6e2f67368749c079cf2f8566551714f87e42ae Mon Sep 17 00:00:00 2001
From: ernestognw <ernestognw@gmail.com>
Date: Fri, 14 Jul 2023 15:23:46 -0600
Subject: [PATCH 03/12] Add changeset

---
 .changeset/thick-pumpkins-exercise.md | 5 +++++
 1 file changed, 5 insertions(+)
 create mode 100644 .changeset/thick-pumpkins-exercise.md

diff --git a/.changeset/thick-pumpkins-exercise.md b/.changeset/thick-pumpkins-exercise.md
new file mode 100644
index 00000000000..52966efe8ad
--- /dev/null
+++ b/.changeset/thick-pumpkins-exercise.md
@@ -0,0 +1,5 @@
+---
+'openzeppelin-solidity': major
+---
+
+`Initializable`: Allow versions greater than 256.

From 54395dadcf45269a386a2d7ee9024a6573c40ede Mon Sep 17 00:00:00 2001
From: ernestognw <ernestognw@gmail.com>
Date: Sat, 15 Jul 2023 01:39:58 -0600
Subject: [PATCH 04/12] Simplify initializer

---
 contracts/mocks/InitializableMock.sol   | 28 +----------
 contracts/proxy/utils/Initializable.sol | 64 +++++++++++++++----------
 test/proxy/utils/Initializable.test.js  | 27 +++--------
 3 files changed, 47 insertions(+), 72 deletions(-)

diff --git a/contracts/mocks/InitializableMock.sol b/contracts/mocks/InitializableMock.sol
index ab5ea031132..29fa56ebc8c 100644
--- a/contracts/mocks/InitializableMock.sol
+++ b/contracts/mocks/InitializableMock.sol
@@ -25,10 +25,6 @@ contract InitializableMock is Initializable {
         onlyInitializingRan = true;
     }
 
-    function initializerNested() public initializer {
-        initialize();
-    }
-
     function onlyInitializingNested() public initializer {
         initializeOnlyInitializing();
     }
@@ -64,18 +60,6 @@ contract ConstructorInitializableMock is Initializable {
     }
 }
 
-contract ChildConstructorInitializableMock is ConstructorInitializableMock {
-    bool public childInitializerRan;
-
-    constructor() initializer {
-        childInitialize();
-    }
-
-    function childInitialize() public initializer {
-        childInitializerRan = true;
-    }
-}
-
 contract ReinitializerMock is Initializable {
     uint256 public counter;
 
@@ -109,22 +93,14 @@ contract ReinitializerMock is Initializable {
     }
 }
 
-contract DisableNew is Initializable {
+contract DisableOk is Initializable {
     constructor() {
         _disableInitializers();
     }
 }
 
-contract DisableOld is Initializable {
-    constructor() initializer {}
-}
-
-contract DisableBad1 is DisableNew, DisableOld {}
-
-contract DisableBad2 is Initializable {
+contract DisableBad is Initializable {
     constructor() initializer {
         _disableInitializers();
     }
 }
-
-contract DisableOk is DisableOld, DisableNew {}
diff --git a/contracts/proxy/utils/Initializable.sol b/contracts/proxy/utils/Initializable.sol
index 897e9eff87f..f5f9f81b9cd 100644
--- a/contracts/proxy/utils/Initializable.sol
+++ b/contracts/proxy/utils/Initializable.sol
@@ -102,22 +102,9 @@ abstract contract Initializable {
      * Emits an {Initialized} event.
      */
     modifier initializer() {
-        // solhint-disable-next-line var-name-mixedcase
-        InitializableStorage storage $ = _getInitializableStorage();
-
-        bool isTopLevelCall = !$._initializing;
-        if (!(isTopLevelCall && $._initialized < 1) && !(address(this).code.length == 0 && $._initialized == 1)) {
-            revert AlreadyInitialized();
-        }
-        $._initialized = 1;
-        if (isTopLevelCall) {
-            $._initializing = true;
-        }
+        bool isTopLevelCall = _beforeInitialize(1);
         _;
-        if (isTopLevelCall) {
-            $._initializing = false;
-            emit Initialized(1);
-        }
+        _afterInitialize(isTopLevelCall, 1);
     }
 
     /**
@@ -139,17 +126,9 @@ abstract contract Initializable {
      * Emits an {Initialized} event.
      */
     modifier reinitializer(uint64 version) {
-        // solhint-disable-next-line var-name-mixedcase
-        InitializableStorage storage $ = _getInitializableStorage();
-
-        if ($._initializing || $._initialized >= version) {
-            revert AlreadyInitialized();
-        }
-        $._initialized = version;
-        $._initializing = true;
+        bool isTopLevelCall = _beforeInitialize(version);
         _;
-        $._initializing = false;
-        emit Initialized(version);
+        _afterInitialize(isTopLevelCall, version);
     }
 
     /**
@@ -207,4 +186,39 @@ abstract contract Initializable {
             $.slot := _INITIALIZABLE_STORAGE
         }
     }
+
+    function _setInitializedVersion(uint64 version) private returns (bool) {
+        // solhint-disable-next-line var-name-mixedcase
+        InitializableStorage storage $ = _getInitializableStorage();
+
+        // Cache values
+        bool initializing = $._initializing;
+        uint64 initialized = $._initialized;
+
+        bool reinitializing = version > 1;
+        bool increasing = version > initialized;
+
+        if (initializing ? reinitializing : !increasing) {
+            revert AlreadyInitialized();
+        }
+
+        $._initialized = version;
+
+        return !initializing;
+    }
+
+    function _beforeInitialize(uint64 version) private returns (bool) {
+        bool isTopLevelCall = _setInitializedVersion(version);
+        if (isTopLevelCall) {
+            _getInitializableStorage()._initializing = true;
+        }
+        return isTopLevelCall;
+    }
+
+    function _afterInitialize(bool isTopLevelCall, uint64 version) private {
+        if (isTopLevelCall) {
+            _getInitializableStorage()._initializing = false;
+            emit Initialized(version);
+        }
+    }
 }
diff --git a/test/proxy/utils/Initializable.test.js b/test/proxy/utils/Initializable.test.js
index cb45995ea44..3e50111a42a 100644
--- a/test/proxy/utils/Initializable.test.js
+++ b/test/proxy/utils/Initializable.test.js
@@ -4,11 +4,9 @@ const { expectRevertCustomError } = require('../../helpers/customError');
 
 const InitializableMock = artifacts.require('InitializableMock');
 const ConstructorInitializableMock = artifacts.require('ConstructorInitializableMock');
-const ChildConstructorInitializableMock = artifacts.require('ChildConstructorInitializableMock');
 const ReinitializerMock = artifacts.require('ReinitializerMock');
 const SampleChild = artifacts.require('SampleChild');
-const DisableBad1 = artifacts.require('DisableBad1');
-const DisableBad2 = artifacts.require('DisableBad2');
+const DisableBad = artifacts.require('DisableBad');
 const DisableOk = artifacts.require('DisableOk');
 
 contract('Initializable', function () {
@@ -46,10 +44,6 @@ contract('Initializable', function () {
     });
 
     describe('nested under an initializer', function () {
-      it('initializer modifier reverts', async function () {
-        await expectRevertCustomError(this.contract.initializerNested(), 'AlreadyInitialized', []);
-      });
-
       it('onlyInitializing modifier succeeds', async function () {
         await this.contract.onlyInitializingNested();
         expect(await this.contract.onlyInitializingRan()).to.equal(true);
@@ -67,13 +61,6 @@ contract('Initializable', function () {
     expect(await contract2.onlyInitializingRan()).to.equal(true);
   });
 
-  it('multiple constructor levels can be initializers', async function () {
-    const contract2 = await ChildConstructorInitializableMock.new();
-    expect(await contract2.initializerRan()).to.equal(true);
-    expect(await contract2.childInitializerRan()).to.equal(true);
-    expect(await contract2.onlyInitializingRan()).to.equal(true);
-  });
-
   describe('reinitialization', function () {
     beforeEach('deploying', async function () {
       this.contract = await ReinitializerMock.new();
@@ -205,15 +192,13 @@ contract('Initializable', function () {
   });
 
   describe('disabling initialization', function () {
-    it('old and new patterns in bad sequence', async function () {
-      await expectRevertCustomError(DisableBad1.new(), 'AlreadyInitialized', []);
-      await expectRevertCustomError(DisableBad2.new(), 'AlreadyInitialized', []);
-    });
-
-    it('old and new patterns in good sequence', async function () {
+    it('disables initializers', async function () {
       const ok = await DisableOk.new();
-      await expectEvent.inConstruction(ok, 'Initialized', { version: '1' });
       await expectEvent.inConstruction(ok, 'Initialized', { version: '18446744073709551615' }); // MAX_UINT64
     });
+
+    it('reverts disabling initializers and using the initializer modifier', async function () {
+      await expectRevertCustomError(DisableBad.new(), 'AlreadyInitialized', []);
+    });
   });
 });

From eabc9c00e7a35d46d04b1532134b3e32bb398d3f Mon Sep 17 00:00:00 2001
From: ernestognw <ernestognw@gmail.com>
Date: Mon, 17 Jul 2023 21:08:22 -0600
Subject: [PATCH 05/12] Improve gas (?)

---
 contracts/proxy/utils/Initializable.sol | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/contracts/proxy/utils/Initializable.sol b/contracts/proxy/utils/Initializable.sol
index f5f9f81b9cd..87a2701a80d 100644
--- a/contracts/proxy/utils/Initializable.sol
+++ b/contracts/proxy/utils/Initializable.sol
@@ -191,14 +191,11 @@ abstract contract Initializable {
         // solhint-disable-next-line var-name-mixedcase
         InitializableStorage storage $ = _getInitializableStorage();
 
-        // Cache values
         bool initializing = $._initializing;
-        uint64 initialized = $._initialized;
 
-        bool reinitializing = version > 1;
-        bool increasing = version > initialized;
-
-        if (initializing ? reinitializing : !increasing) {
+        // When it's initializing check if it's a reinitializer, otherwise check if
+        // the intended version is not already set.
+        if (initializing ? version > 1 : version <= $._initialized) {
             revert AlreadyInitialized();
         }
 

From 9777b62972df08dfc1515cea53ecfeb66a53029e Mon Sep 17 00:00:00 2001
From: ernestognw <ernestognw@gmail.com>
Date: Thu, 20 Jul 2023 15:31:55 -0600
Subject: [PATCH 06/12] Improved function docs

---
 contracts/proxy/utils/Initializable.sol | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/contracts/proxy/utils/Initializable.sol b/contracts/proxy/utils/Initializable.sol
index 87a2701a80d..9c4297c0157 100644
--- a/contracts/proxy/utils/Initializable.sol
+++ b/contracts/proxy/utils/Initializable.sol
@@ -187,6 +187,14 @@ abstract contract Initializable {
         }
     }
 
+    /**
+     * @dev Sets the initialized version.
+     *
+     * Requirements:
+     *
+     * - If the contract is initializing the version set must not be that of an reinitializer.
+     * - If the contract is not initializing the version must not be already set.
+     */
     function _setInitializedVersion(uint64 version) private returns (bool) {
         // solhint-disable-next-line var-name-mixedcase
         InitializableStorage storage $ = _getInitializableStorage();
@@ -204,6 +212,10 @@ abstract contract Initializable {
         return !initializing;
     }
 
+    /**
+     * @dev Runs before initialization.
+     * It sets the initialized version and sets the initializing flag to true.
+     */
     function _beforeInitialize(uint64 version) private returns (bool) {
         bool isTopLevelCall = _setInitializedVersion(version);
         if (isTopLevelCall) {
@@ -212,6 +224,10 @@ abstract contract Initializable {
         return isTopLevelCall;
     }
 
+    /**
+     * @dev Runs after initialization.
+     * It clears the initializing flag and emits an {Initialized} event if it is a top level call.
+     */
     function _afterInitialize(bool isTopLevelCall, uint64 version) private {
         if (isTopLevelCall) {
             _getInitializableStorage()._initializing = false;

From aa0bb6f3024098958d7850cd415e51fd17ddb972 Mon Sep 17 00:00:00 2001
From: ernestognw <ernestognw@gmail.com>
Date: Thu, 27 Jul 2023 15:53:54 -0600
Subject: [PATCH 07/12] Revert #3950 fix

---
 contracts/mocks/InitializableMock.sol   | 28 ++++++++-
 contracts/proxy/utils/Initializable.sol | 77 ++++++++-----------------
 test/proxy/utils/Initializable.test.js  | 27 +++++++--
 3 files changed, 72 insertions(+), 60 deletions(-)

diff --git a/contracts/mocks/InitializableMock.sol b/contracts/mocks/InitializableMock.sol
index 29fa56ebc8c..ab5ea031132 100644
--- a/contracts/mocks/InitializableMock.sol
+++ b/contracts/mocks/InitializableMock.sol
@@ -25,6 +25,10 @@ contract InitializableMock is Initializable {
         onlyInitializingRan = true;
     }
 
+    function initializerNested() public initializer {
+        initialize();
+    }
+
     function onlyInitializingNested() public initializer {
         initializeOnlyInitializing();
     }
@@ -60,6 +64,18 @@ contract ConstructorInitializableMock is Initializable {
     }
 }
 
+contract ChildConstructorInitializableMock is ConstructorInitializableMock {
+    bool public childInitializerRan;
+
+    constructor() initializer {
+        childInitialize();
+    }
+
+    function childInitialize() public initializer {
+        childInitializerRan = true;
+    }
+}
+
 contract ReinitializerMock is Initializable {
     uint256 public counter;
 
@@ -93,14 +109,22 @@ contract ReinitializerMock is Initializable {
     }
 }
 
-contract DisableOk is Initializable {
+contract DisableNew is Initializable {
     constructor() {
         _disableInitializers();
     }
 }
 
-contract DisableBad is Initializable {
+contract DisableOld is Initializable {
+    constructor() initializer {}
+}
+
+contract DisableBad1 is DisableNew, DisableOld {}
+
+contract DisableBad2 is Initializable {
     constructor() initializer {
         _disableInitializers();
     }
 }
+
+contract DisableOk is DisableOld, DisableNew {}
diff --git a/contracts/proxy/utils/Initializable.sol b/contracts/proxy/utils/Initializable.sol
index 9c4297c0157..897e9eff87f 100644
--- a/contracts/proxy/utils/Initializable.sol
+++ b/contracts/proxy/utils/Initializable.sol
@@ -102,9 +102,22 @@ abstract contract Initializable {
      * Emits an {Initialized} event.
      */
     modifier initializer() {
-        bool isTopLevelCall = _beforeInitialize(1);
+        // solhint-disable-next-line var-name-mixedcase
+        InitializableStorage storage $ = _getInitializableStorage();
+
+        bool isTopLevelCall = !$._initializing;
+        if (!(isTopLevelCall && $._initialized < 1) && !(address(this).code.length == 0 && $._initialized == 1)) {
+            revert AlreadyInitialized();
+        }
+        $._initialized = 1;
+        if (isTopLevelCall) {
+            $._initializing = true;
+        }
         _;
-        _afterInitialize(isTopLevelCall, 1);
+        if (isTopLevelCall) {
+            $._initializing = false;
+            emit Initialized(1);
+        }
     }
 
     /**
@@ -126,9 +139,17 @@ abstract contract Initializable {
      * Emits an {Initialized} event.
      */
     modifier reinitializer(uint64 version) {
-        bool isTopLevelCall = _beforeInitialize(version);
+        // solhint-disable-next-line var-name-mixedcase
+        InitializableStorage storage $ = _getInitializableStorage();
+
+        if ($._initializing || $._initialized >= version) {
+            revert AlreadyInitialized();
+        }
+        $._initialized = version;
+        $._initializing = true;
         _;
-        _afterInitialize(isTopLevelCall, version);
+        $._initializing = false;
+        emit Initialized(version);
     }
 
     /**
@@ -186,52 +207,4 @@ abstract contract Initializable {
             $.slot := _INITIALIZABLE_STORAGE
         }
     }
-
-    /**
-     * @dev Sets the initialized version.
-     *
-     * Requirements:
-     *
-     * - If the contract is initializing the version set must not be that of an reinitializer.
-     * - If the contract is not initializing the version must not be already set.
-     */
-    function _setInitializedVersion(uint64 version) private returns (bool) {
-        // solhint-disable-next-line var-name-mixedcase
-        InitializableStorage storage $ = _getInitializableStorage();
-
-        bool initializing = $._initializing;
-
-        // When it's initializing check if it's a reinitializer, otherwise check if
-        // the intended version is not already set.
-        if (initializing ? version > 1 : version <= $._initialized) {
-            revert AlreadyInitialized();
-        }
-
-        $._initialized = version;
-
-        return !initializing;
-    }
-
-    /**
-     * @dev Runs before initialization.
-     * It sets the initialized version and sets the initializing flag to true.
-     */
-    function _beforeInitialize(uint64 version) private returns (bool) {
-        bool isTopLevelCall = _setInitializedVersion(version);
-        if (isTopLevelCall) {
-            _getInitializableStorage()._initializing = true;
-        }
-        return isTopLevelCall;
-    }
-
-    /**
-     * @dev Runs after initialization.
-     * It clears the initializing flag and emits an {Initialized} event if it is a top level call.
-     */
-    function _afterInitialize(bool isTopLevelCall, uint64 version) private {
-        if (isTopLevelCall) {
-            _getInitializableStorage()._initializing = false;
-            emit Initialized(version);
-        }
-    }
 }
diff --git a/test/proxy/utils/Initializable.test.js b/test/proxy/utils/Initializable.test.js
index 3e50111a42a..cb45995ea44 100644
--- a/test/proxy/utils/Initializable.test.js
+++ b/test/proxy/utils/Initializable.test.js
@@ -4,9 +4,11 @@ const { expectRevertCustomError } = require('../../helpers/customError');
 
 const InitializableMock = artifacts.require('InitializableMock');
 const ConstructorInitializableMock = artifacts.require('ConstructorInitializableMock');
+const ChildConstructorInitializableMock = artifacts.require('ChildConstructorInitializableMock');
 const ReinitializerMock = artifacts.require('ReinitializerMock');
 const SampleChild = artifacts.require('SampleChild');
-const DisableBad = artifacts.require('DisableBad');
+const DisableBad1 = artifacts.require('DisableBad1');
+const DisableBad2 = artifacts.require('DisableBad2');
 const DisableOk = artifacts.require('DisableOk');
 
 contract('Initializable', function () {
@@ -44,6 +46,10 @@ contract('Initializable', function () {
     });
 
     describe('nested under an initializer', function () {
+      it('initializer modifier reverts', async function () {
+        await expectRevertCustomError(this.contract.initializerNested(), 'AlreadyInitialized', []);
+      });
+
       it('onlyInitializing modifier succeeds', async function () {
         await this.contract.onlyInitializingNested();
         expect(await this.contract.onlyInitializingRan()).to.equal(true);
@@ -61,6 +67,13 @@ contract('Initializable', function () {
     expect(await contract2.onlyInitializingRan()).to.equal(true);
   });
 
+  it('multiple constructor levels can be initializers', async function () {
+    const contract2 = await ChildConstructorInitializableMock.new();
+    expect(await contract2.initializerRan()).to.equal(true);
+    expect(await contract2.childInitializerRan()).to.equal(true);
+    expect(await contract2.onlyInitializingRan()).to.equal(true);
+  });
+
   describe('reinitialization', function () {
     beforeEach('deploying', async function () {
       this.contract = await ReinitializerMock.new();
@@ -192,13 +205,15 @@ contract('Initializable', function () {
   });
 
   describe('disabling initialization', function () {
-    it('disables initializers', async function () {
-      const ok = await DisableOk.new();
-      await expectEvent.inConstruction(ok, 'Initialized', { version: '18446744073709551615' }); // MAX_UINT64
+    it('old and new patterns in bad sequence', async function () {
+      await expectRevertCustomError(DisableBad1.new(), 'AlreadyInitialized', []);
+      await expectRevertCustomError(DisableBad2.new(), 'AlreadyInitialized', []);
     });
 
-    it('reverts disabling initializers and using the initializer modifier', async function () {
-      await expectRevertCustomError(DisableBad.new(), 'AlreadyInitialized', []);
+    it('old and new patterns in good sequence', async function () {
+      const ok = await DisableOk.new();
+      await expectEvent.inConstruction(ok, 'Initialized', { version: '1' });
+      await expectEvent.inConstruction(ok, 'Initialized', { version: '18446744073709551615' }); // MAX_UINT64
     });
   });
 });

From 1b27b496ab8bc58050d63f13c45fd8648924ee4f Mon Sep 17 00:00:00 2001
From: ernestognw <ernestognw@gmail.com>
Date: Thu, 27 Jul 2023 18:51:34 -0600
Subject: [PATCH 08/12] Fix conflict

---
 contracts/proxy/utils/Initializable.sol | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/contracts/proxy/utils/Initializable.sol b/contracts/proxy/utils/Initializable.sol
index 4aa7fe4f52d..7f33a6267c0 100644
--- a/contracts/proxy/utils/Initializable.sol
+++ b/contracts/proxy/utils/Initializable.sol
@@ -165,7 +165,9 @@ abstract contract Initializable {
      * @dev Reverts if the contract is not in an initializing state. See {onlyInitializing}.
      */
     function _checkInitializing() internal view virtual {
-        if (!_initializing) revert NotInitializing();
+        if (!_isInitializing()) {
+            revert NotInitializing();
+        }
     }
 
     /**

From f106f034bf515c59276a3bdb436ce5dc6df2fbf2 Mon Sep 17 00:00:00 2001
From: ernestognw <ernestognw@gmail.com>
Date: Sat, 29 Jul 2023 19:23:02 -0600
Subject: [PATCH 09/12] Use 0xFFFFFFFFFFFFFFFF in tests

---
 test/proxy/utils/Initializable.test.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/test/proxy/utils/Initializable.test.js b/test/proxy/utils/Initializable.test.js
index cb45995ea44..e42850c07b5 100644
--- a/test/proxy/utils/Initializable.test.js
+++ b/test/proxy/utils/Initializable.test.js
@@ -213,7 +213,7 @@ contract('Initializable', function () {
     it('old and new patterns in good sequence', async function () {
       const ok = await DisableOk.new();
       await expectEvent.inConstruction(ok, 'Initialized', { version: '1' });
-      await expectEvent.inConstruction(ok, 'Initialized', { version: '18446744073709551615' }); // MAX_UINT64
+      await expectEvent.inConstruction(ok, 'Initialized', { version: BigInt('0xFFFFFFFFFFFFFFFF').toString() }); // MAX_UINT64
     });
   });
 });

From eb7699133cebbd22c8d6edf7ea701e187db4bad5 Mon Sep 17 00:00:00 2001
From: ernestognw <ernestognw@gmail.com>
Date: Sun, 30 Jul 2023 18:26:49 -0600
Subject: [PATCH 10/12] Use 2n ** 64n - 1n in tests

---
 test/proxy/utils/Initializable.test.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/test/proxy/utils/Initializable.test.js b/test/proxy/utils/Initializable.test.js
index e42850c07b5..52d3031da01 100644
--- a/test/proxy/utils/Initializable.test.js
+++ b/test/proxy/utils/Initializable.test.js
@@ -213,7 +213,7 @@ contract('Initializable', function () {
     it('old and new patterns in good sequence', async function () {
       const ok = await DisableOk.new();
       await expectEvent.inConstruction(ok, 'Initialized', { version: '1' });
-      await expectEvent.inConstruction(ok, 'Initialized', { version: BigInt('0xFFFFFFFFFFFFFFFF').toString() }); // MAX_UINT64
+      await expectEvent.inConstruction(ok, 'Initialized', { version: (2n ** 64n - 1n).toString() }); // MAX_UINT64
     });
   });
 });

From 4d6d20505ed032217ecf57a0b31443434f6fbcf3 Mon Sep 17 00:00:00 2001
From: ernestognw <ernestognw@gmail.com>
Date: Wed, 2 Aug 2023 14:54:53 -0600
Subject: [PATCH 11/12] Used web3.utils.toBN for tests

---
 test/helpers/constants.js              | 7 +++++++
 test/metatx/ERC2771Context.test.js     | 3 +--
 test/proxy/utils/Initializable.test.js | 3 ++-
 3 files changed, 10 insertions(+), 3 deletions(-)
 create mode 100644 test/helpers/constants.js

diff --git a/test/helpers/constants.js b/test/helpers/constants.js
new file mode 100644
index 00000000000..0f4d028cfce
--- /dev/null
+++ b/test/helpers/constants.js
@@ -0,0 +1,7 @@
+const MAX_UINT48 = web3.utils.toBN(1).shln(48).subn(1).toString();
+const MAX_UINT64 = web3.utils.toBN(1).shln(64).subn(1).toString();
+
+module.exports = {
+  MAX_UINT48,
+  MAX_UINT64,
+};
diff --git a/test/metatx/ERC2771Context.test.js b/test/metatx/ERC2771Context.test.js
index 0ec8d98dde6..678deb5addb 100644
--- a/test/metatx/ERC2771Context.test.js
+++ b/test/metatx/ERC2771Context.test.js
@@ -1,6 +1,7 @@
 const ethSigUtil = require('eth-sig-util');
 const Wallet = require('ethereumjs-wallet').default;
 const { getDomain, domainType } = require('../helpers/eip712');
+const { MAX_UINT48 } = require('../helpers/constants');
 
 const { expectEvent } = require('@openzeppelin/test-helpers');
 const { expect } = require('chai');
@@ -14,8 +15,6 @@ const { shouldBehaveLikeRegularContext } = require('../utils/Context.behavior');
 contract('ERC2771Context', function (accounts) {
   const [, trustedForwarder] = accounts;
 
-  const MAX_UINT48 = web3.utils.toBN(1).shln(48).subn(1).toString();
-
   beforeEach(async function () {
     this.forwarder = await ERC2771Forwarder.new('ERC2771Forwarder');
     this.recipient = await ERC2771ContextMock.new(this.forwarder.address);
diff --git a/test/proxy/utils/Initializable.test.js b/test/proxy/utils/Initializable.test.js
index 52d3031da01..98ed19d36a2 100644
--- a/test/proxy/utils/Initializable.test.js
+++ b/test/proxy/utils/Initializable.test.js
@@ -1,6 +1,7 @@
 const { expectEvent } = require('@openzeppelin/test-helpers');
 const { expect } = require('chai');
 const { expectRevertCustomError } = require('../../helpers/customError');
+const { MAX_UINT64 } = require('../../helpers/constants');
 
 const InitializableMock = artifacts.require('InitializableMock');
 const ConstructorInitializableMock = artifacts.require('ConstructorInitializableMock');
@@ -213,7 +214,7 @@ contract('Initializable', function () {
     it('old and new patterns in good sequence', async function () {
       const ok = await DisableOk.new();
       await expectEvent.inConstruction(ok, 'Initialized', { version: '1' });
-      await expectEvent.inConstruction(ok, 'Initialized', { version: (2n ** 64n - 1n).toString() }); // MAX_UINT64
+      await expectEvent.inConstruction(ok, 'Initialized', { version: MAX_UINT64 });
     });
   });
 });

From 593509064f3730883671d234879eb88c78345be5 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ernesto=20Garc=C3=ADa?= <ernestognw@gmail.com>
Date: Wed, 2 Aug 2023 21:30:04 -0600
Subject: [PATCH 12/12] Update .changeset/thick-pumpkins-exercise.md

Co-authored-by: Francisco <fg@frang.io>
---
 .changeset/thick-pumpkins-exercise.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/.changeset/thick-pumpkins-exercise.md b/.changeset/thick-pumpkins-exercise.md
index 52966efe8ad..8df8b51cc47 100644
--- a/.changeset/thick-pumpkins-exercise.md
+++ b/.changeset/thick-pumpkins-exercise.md
@@ -2,4 +2,4 @@
 'openzeppelin-solidity': major
 ---
 
-`Initializable`: Allow versions greater than 256.
+`Initializable`: Use the namespaced storage pattern to avoid putting critical variables in slot 0. Allow reinitializer versions greater than 256.