feat(lang): support solidity contracts (#318)

Fixes sourcerer-io/awesome-libraries#21.

Author: asurkov

src/main/kotlin/app/extractors/Heuristics.kt

@@ -985,6 +985,9 @@ val HeuristicsMap = mapOf<String, (String) -> ExtractorInterface?>(
     "sls" to { _ ->
         CommonExtractor(Lang.SCHEME)
     },
+    "sol" to { _ ->
+        CommonExtractor(Lang.SOLIDITY)
+    },
     "spc" to { _ ->
         CommonExtractor(Lang.PLSQL)
     },

src/main/kotlin/app/extractors/Languages.kt

@@ -88,9 +88,10 @@ object Lang {
     const val SCHEME = "scheme"  // Scheme
     const val SHELL = "shell"  // Shell
     const val SMALLTALK = "smalltalk"  // Smalltalk
-    const val STANDARDML = "standard_ml"  // Standard ML
+    const val SOLIDITY = "solidity"  // Solidity
     const val SQL = "sql"  // SQL
     const val SQLPL = "sqlpl"  // SQLPL
+    const val STANDARDML = "standard_ml"  // Standard ML
     const val SUPERCOLLIDER = "supercollider"  // SuperCollider
     const val SWIFT = "swift"  // Swift
     const val TCL = "tcl"  // Tcl

src/test/resources/samples/Solidity/VotingContract.sol

@@ -0,0 +1,149 @@
+pragma solidity ^0.4.22;
+
+/// @title Voting with delegation.
+contract Ballot {
+    // This declares a new complex type which will
+    // be used for variables later.
+    // It will represent a single voter.
+    struct Voter {
+        uint weight; // weight is accumulated by delegation
+        bool voted;  // if true, that person already voted
+        address delegate; // person delegated to
+        uint vote;   // index of the voted proposal
+    }
+
+    // This is a type for a single proposal.
+    struct Proposal {
+        bytes32 name;   // short name (up to 32 bytes)
+        uint voteCount; // number of accumulated votes
+    }
+
+    address public chairperson;
+
+    // This declares a state variable that
+    // stores a `Voter` struct for each possible address.
+    mapping(address => Voter) public voters;
+
+    // A dynamically-sized array of `Proposal` structs.
+    Proposal[] public proposals;
+
+    /// Create a new ballot to choose one of `proposalNames`.
+    constructor(bytes32[] memory proposalNames) public {
+        chairperson = msg.sender;
+        voters[chairperson].weight = 1;
+
+        // For each of the provided proposal names,
+        // create a new proposal object and add it
+        // to the end of the array.
+        for (uint i = 0; i < proposalNames.length; i++) {
+            // `Proposal({...})` creates a temporary
+            // Proposal object and `proposals.push(...)`
+            // appends it to the end of `proposals`.
+            proposals.push(Proposal({
+                name: proposalNames[i],
+                voteCount: 0
+            }));
+        }
+    }
+
+    // Give `voter` the right to vote on this ballot.
+    // May only be called by `chairperson`.
+    function giveRightToVote(address voter) public {
+        // If the first argument of `require` evaluates
+        // to `false`, execution terminates and all
+        // changes to the state and to Ether balances
+        // are reverted.
+        // This used to consume all gas in old EVM versions, but
+        // not anymore.
+        // It is often a good idea to use `require` to check if
+        // functions are called correctly.
+        // As a second argument, you can also provide an
+        // explanation about what went wrong.
+        require(
+            msg.sender == chairperson,
+            "Only chairperson can give right to vote."
+        );
+        require(
+            !voters[voter].voted,
+            "The voter already voted."
+        );
+        require(voters[voter].weight == 0);
+        voters[voter].weight = 1;
+    }
+
+    /// Delegate your vote to the voter `to`.
+    function delegate(address to) public {
+        // assigns reference
+        Voter storage sender = voters[msg.sender];
+        require(!sender.voted, "You already voted.");
+
+        require(to != msg.sender, "Self-delegation is disallowed.");
+
+        // Forward the delegation as long as
+        // `to` also delegated.
+        // In general, such loops are very dangerous,
+        // because if they run too long, they might
+        // need more gas than is available in a block.
+        // In this case, the delegation will not be executed,
+        // but in other situations, such loops might
+        // cause a contract to get "stuck" completely.
+        while (voters[to].delegate != address(0)) {
+            to = voters[to].delegate;
+
+            // We found a loop in the delegation, not allowed.
+            require(to != msg.sender, "Found loop in delegation.");
+        }
+
+        // Since `sender` is a reference, this
+        // modifies `voters[msg.sender].voted`
+        sender.voted = true;
+        sender.delegate = to;
+        Voter storage delegate_ = voters[to];
+        if (delegate_.voted) {
+            // If the delegate already voted,
+            // directly add to the number of votes
+            proposals[delegate_.vote].voteCount += sender.weight;
+        } else {
+            // If the delegate did not vote yet,
+            // add to her weight.
+            delegate_.weight += sender.weight;
+        }
+    }
+
+    /// Give your vote (including votes delegated to you)
+    /// to proposal `proposals[proposal].name`.
+    function vote(uint proposal) public {
+        Voter storage sender = voters[msg.sender];
+        require(!sender.voted, "Already voted.");
+        sender.voted = true;
+        sender.vote = proposal;
+
+        // If `proposal` is out of the range of the array,
+        // this will throw automatically and revert all
+        // changes.
+        proposals[proposal].voteCount += sender.weight;
+    }
+
+    /// @dev Computes the winning proposal taking all
+    /// previous votes into account.
+    function winningProposal() public view
+            returns (uint winningProposal_)
+    {
+        uint winningVoteCount = 0;
+        for (uint p = 0; p < proposals.length; p++) {
+            if (proposals[p].voteCount > winningVoteCount) {
+                winningVoteCount = proposals[p].voteCount;
+                winningProposal_ = p;
+            }
+        }
+    }
+
+    // Calls winningProposal() function to get the index
+    // of the winner contained in the proposals array and then
+    // returns the name of the winner
+    function winnerName() public view
+            returns (bytes32 winnerName_)
+    {
+        winnerName_ = proposals[winningProposal()].name;
+    }
+}