Fix relevant warnings (#3685)

contracts/mocks/ERC165/ERC165ReturnBomb.sol

@@ -5,7 +5,7 @@ pragma solidity ^0.8.0;
 import "../../utils/introspection/IERC165.sol";
 
 contract ERC165ReturnBombMock is IERC165 {
-    function supportsInterface(bytes4 interfaceId) public view override returns (bool) {
+    function supportsInterface(bytes4 interfaceId) public pure override returns (bool) {
         if (interfaceId == type(IERC165).interfaceId) {
             assembly {
                 mstore(0, 1)

contracts/token/ERC20/extensions/ERC20Votes.sol

@@ -263,7 +263,7 @@ abstract contract ERC20Votes is IVotes, ERC20Permit {
         return a - b;
     }
 
-    function _unsafeAccess(Checkpoint[] storage ckpts, uint256 pos) private view returns (Checkpoint storage result) {
+    function _unsafeAccess(Checkpoint[] storage ckpts, uint256 pos) private pure returns (Checkpoint storage result) {
         assembly {
             mstore(0, ckpts.slot)
             result.slot := add(keccak256(0, 0x20), pos)

contracts/utils/Checkpoints.sol

@@ -34,8 +34,8 @@ library Checkpoints {
         require(blockNumber < block.number, "Checkpoints: block not yet mined");
         uint32 key = SafeCast.toUint32(blockNumber);
 
-        uint256 length = self._checkpoints.length;
-        uint256 pos = _upperBinaryLookup(self._checkpoints, key, 0, length);
+        uint256 len = self._checkpoints.length;
+        uint256 pos = _upperBinaryLookup(self._checkpoints, key, 0, len);
         return pos == 0 ? 0 : _unsafeAccess(self._checkpoints, pos - 1)._value;
     }
 
@@ -49,13 +49,13 @@ library Checkpoints {
         require(blockNumber < block.number, "Checkpoints: block not yet mined");
         uint32 key = SafeCast.toUint32(blockNumber);
 
-        uint256 length = self._checkpoints.length;
+        uint256 len = self._checkpoints.length;
 
         uint256 low = 0;
-        uint256 high = length;
+        uint256 high = len;
 
-        if (length > 5) {
-            uint256 mid = length - Math.sqrt(length);
+        if (len > 5) {
+            uint256 mid = len - Math.sqrt(len);
             if (key < _unsafeAccess(self._checkpoints, mid)._blockNumber) {
                 high = mid;
             } else {
@@ -205,7 +205,7 @@ library Checkpoints {
         return high;
     }
 
-    function _unsafeAccess(Checkpoint[] storage self, uint256 pos) private view returns (Checkpoint storage result) {
+    function _unsafeAccess(Checkpoint[] storage self, uint256 pos) private pure returns (Checkpoint storage result) {
         assembly {
             mstore(0, self.slot)
             result.slot := add(keccak256(0, 0x20), pos)
@@ -238,17 +238,17 @@ library Checkpoints {
      * @dev Returns the value in the oldest checkpoint with key greater or equal than the search key, or zero if there is none.
      */
     function lowerLookup(Trace224 storage self, uint32 key) internal view returns (uint224) {
-        uint256 length = self._checkpoints.length;
-        uint256 pos = _lowerBinaryLookup(self._checkpoints, key, 0, length);
-        return pos == length ? 0 : _unsafeAccess(self._checkpoints, pos)._value;
+        uint256 len = self._checkpoints.length;
+        uint256 pos = _lowerBinaryLookup(self._checkpoints, key, 0, len);
+        return pos == len ? 0 : _unsafeAccess(self._checkpoints, pos)._value;
     }
 
     /**
      * @dev Returns the value in the most recent checkpoint with key lower or equal than the search key.
      */
     function upperLookup(Trace224 storage self, uint32 key) internal view returns (uint224) {
-        uint256 length = self._checkpoints.length;
-        uint256 pos = _upperBinaryLookup(self._checkpoints, key, 0, length);
+        uint256 len = self._checkpoints.length;
+        uint256 pos = _upperBinaryLookup(self._checkpoints, key, 0, len);
         return pos == 0 ? 0 : _unsafeAccess(self._checkpoints, pos - 1)._value;
     }
 
@@ -368,7 +368,7 @@ library Checkpoints {
 
     function _unsafeAccess(Checkpoint224[] storage self, uint256 pos)
         private
-        view
+        pure
         returns (Checkpoint224 storage result)
     {
         assembly {
@@ -403,17 +403,17 @@ library Checkpoints {
      * @dev Returns the value in the oldest checkpoint with key greater or equal than the search key, or zero if there is none.
      */
     function lowerLookup(Trace160 storage self, uint96 key) internal view returns (uint160) {
-        uint256 length = self._checkpoints.length;
-        uint256 pos = _lowerBinaryLookup(self._checkpoints, key, 0, length);
-        return pos == length ? 0 : _unsafeAccess(self._checkpoints, pos)._value;
+        uint256 len = self._checkpoints.length;
+        uint256 pos = _lowerBinaryLookup(self._checkpoints, key, 0, len);
+        return pos == len ? 0 : _unsafeAccess(self._checkpoints, pos)._value;
     }
 
     /**
      * @dev Returns the value in the most recent checkpoint with key lower or equal than the search key.
      */
     function upperLookup(Trace160 storage self, uint96 key) internal view returns (uint160) {
-        uint256 length = self._checkpoints.length;
-        uint256 pos = _upperBinaryLookup(self._checkpoints, key, 0, length);
+        uint256 len = self._checkpoints.length;
+        uint256 pos = _upperBinaryLookup(self._checkpoints, key, 0, len);
         return pos == 0 ? 0 : _unsafeAccess(self._checkpoints, pos - 1)._value;
     }
 
@@ -533,7 +533,7 @@ library Checkpoints {
 
     function _unsafeAccess(Checkpoint160[] storage self, uint256 pos)
         private
-        view
+        pure
         returns (Checkpoint160 storage result)
     {
         assembly {

scripts/generate/templates/Checkpoints.js

@@ -49,17 +49,17 @@ function push(
  * @dev Returns the value in the oldest checkpoint with key greater or equal than the search key, or zero if there is none.
  */
 function lowerLookup(${opts.historyTypeName} storage self, ${opts.keyTypeName} key) internal view returns (${opts.valueTypeName}) {
-    uint256 length = self.${opts.checkpointFieldName}.length;
-    uint256 pos = _lowerBinaryLookup(self.${opts.checkpointFieldName}, key, 0, length);
-    return pos == length ? 0 : _unsafeAccess(self.${opts.checkpointFieldName}, pos).${opts.valueFieldName};
+    uint256 len = self.${opts.checkpointFieldName}.length;
+    uint256 pos = _lowerBinaryLookup(self.${opts.checkpointFieldName}, key, 0, len);
+    return pos == len ? 0 : _unsafeAccess(self.${opts.checkpointFieldName}, pos).${opts.valueFieldName};
 }
 
 /**
  * @dev Returns the value in the most recent checkpoint with key lower or equal than the search key.
  */
 function upperLookup(${opts.historyTypeName} storage self, ${opts.keyTypeName} key) internal view returns (${opts.valueTypeName}) {
-    uint256 length = self.${opts.checkpointFieldName}.length;
-    uint256 pos = _upperBinaryLookup(self.${opts.checkpointFieldName}, key, 0, length);
+    uint256 len = self.${opts.checkpointFieldName}.length;
+    uint256 pos = _upperBinaryLookup(self.${opts.checkpointFieldName}, key, 0, len);
     return pos == 0 ? 0 : _unsafeAccess(self.${opts.checkpointFieldName}, pos - 1).${opts.valueFieldName};
 }
 `;
@@ -73,8 +73,8 @@ function getAtBlock(${opts.historyTypeName} storage self, uint256 blockNumber) i
     require(blockNumber < block.number, "Checkpoints: block not yet mined");
     uint32 key = SafeCast.toUint32(blockNumber);
 
-    uint256 length = self.${opts.checkpointFieldName}.length;
-    uint256 pos = _upperBinaryLookup(self.${opts.checkpointFieldName}, key, 0, length);
+    uint256 len = self.${opts.checkpointFieldName}.length;
+    uint256 pos = _upperBinaryLookup(self.${opts.checkpointFieldName}, key, 0, len);
     return pos == 0 ? 0 : _unsafeAccess(self.${opts.checkpointFieldName}, pos - 1).${opts.valueFieldName};
 }
 
@@ -88,13 +88,13 @@ function getAtProbablyRecentBlock(${opts.historyTypeName} storage self, uint256
     require(blockNumber < block.number, "Checkpoints: block not yet mined");
     uint32 key = SafeCast.toUint32(blockNumber);
 
-    uint256 length = self.${opts.checkpointFieldName}.length;
+    uint256 len = self.${opts.checkpointFieldName}.length;
 
     uint256 low = 0;
-    uint256 high = length;
+    uint256 high = len;
 
-    if (length > 5) {
-        uint256 mid = length - Math.sqrt(length);
+    if (len > 5) {
+        uint256 mid = len - Math.sqrt(len);
         if (key < _unsafeAccess(self.${opts.checkpointFieldName}, mid)._blockNumber) {
             high = mid;
         } else {
@@ -248,7 +248,7 @@ function _lowerBinaryLookup(
 
 function _unsafeAccess(${opts.checkpointTypeName}[] storage self, uint256 pos)
     private
-    view
+    pure
     returns (${opts.checkpointTypeName} storage result)
 {
     assembly {