solc：solidity的編譯器

solidity編寫的以太坊智慧合約可通過命令列編譯工具solc來進行編譯，成為以太坊虛擬機器中的程式碼。solc編譯後最終部署到鏈上形成我們所見到的各種智慧合約。

作為一個solidity命令列編譯工具，我們來看看官網都怎麼說solc。

solc的安裝很簡單：

npm install -g solc
//或者
npm install -g solc-cli
//或者
sudo apt-get install solc

安裝完成後我們來看，solc --help，solc –help命令顯示所有的solc命令選項。編譯器可以生成各種輸出，比如最終的二進位制合約檔案、語法樹的彙編或者需要預計的要花費的gas等。solc --bin sourceFile.sol

你在部署以太坊智慧合約之前可以用solc --optimize --bin sourceFile.sol優化一下。預設情況下solc編譯器會幫你優化200次。你也可以設定 --runs=1，這樣就按照最小化的方式進行編譯，如果你希望多次交易不太在乎成本，那你可以設定成你想要的次數:)。

命令列編譯器會自動讀取需要匯入的檔案，也可以通過使用prefix = path

solc github.com/ethereum/dapp-bin/=/usr/local/lib/dapp-bin/ =/usr/local/lib/fallback file.sol

這樣編譯器就會從指定目錄github.com/ethereum/dapp-bin/下的/usr/local/lib/dapp-bin/目錄開始搜尋，如果沒有找到檔案，它將檢視/usr/local/lib/fallback。solc將只讀取你指定的這兩個路徑的，因此像import "/etc/passwd";必須要通過/=重新對映才起作用。如果有多個匹配，則選擇具有最長公共字首的進行匹配。

出於安全上的考慮，編譯器限制了它可以訪問的一些目錄。在命令列中指定的原始檔的路徑（及其子目錄）和命令列指定的路徑外其他所有內容都會被拒絕。--allow-paths /sample/path,/another/sample/path

如果智慧合約使用了libraries，你會注意到位元組碼包含了__LibraryName______的子字串。您可以使用solc作為連結器，這意味著它將在這些點為您插入庫地址。

可以通過新增庫--libraries "Math:0x12345678901234567890 Heap:0xabcdef0123456"到您的命令，以提供每個庫的地址，或者使用檔案中的說明字串（每行一個庫），並使用--libraries fileName執行solc。

如果用選項--link呼叫Solc，則所有輸入檔案都被解釋為未連結的二進位制檔案（HEX編碼），在上面給出的__LibraryName____格式中，將其連結到適當地址（如果從stdin讀取輸入，則將其寫入stdout）。在這種情況下，除了庫外，所有選項都被忽略（包括-o）。

如果用--standard-json呼叫SOLC，它就將標準的JSON輸入（如下所述），並返回JSON輸出。

solc編譯器輸入輸出JSON描述

這些JSON格式通過編譯器API使用，可以通過SOLC獲得。內容都是可以修改的，一些物件是可選的（如前所述），其目的是向後相容。

編譯器的API需要一個JSON格式的輸入，然後以JSON格式輸出編譯結果。

注意不允許註釋。下面示例中的註釋，是官網為了學習者更好的理解標註的。

• 輸入格式說明：

{
  // Required: Source code language, such as "Solidity", "serpent", "lll", "assembly", etc.
  language: "Solidity",
  // Required
  sources:
  {
    // The keys here are the "global" names of the source files,
    // imports can use other files via remappings (see below).
    "myFile.sol":
    {
      // Optional: keccak256 hash of the source file
      // It is used to verify the retrieved content if imported via URLs.
      "keccak256": "0x123...",
      // Required (unless "content" is used, see below): URL(s) to the source file.
      // URL(s) should be imported in this order and the result checked against the
      // keccak256 hash (if available). If the hash doesn't match or none of the
      // URL(s) result in success, an error should be raised.
      "urls":
      [
        "bzzr://56ab...",
        "ipfs://Qma...",
        "file:///tmp/path/to/file.sol"
      ]
    },
    "mortal":
    {
      // Optional: keccak256 hash of the source file
      "keccak256": "0x234...",
      // Required (unless "urls" is used): literal contents of the source file
      "content": "contract mortal is owned { function kill() { if (msg.sender == owner) selfdestruct(owner); } }"
    }
  },
  // Optional
  settings:
  {
    // Optional: Sorted list of remappings
    remappings: [ ":g/dir" ],
    // Optional: Optimizer settings
    optimizer: {
      // disabled by default
      enabled: true,
      // Optimize for how many times you intend to run the code.
      // Lower values will optimize more for initial deployment cost, higher values will optimize more for high-frequency usage.
      runs: 200
    },
    evmVersion: "byzantium", // Version of the EVM to compile for. Affects type checking and code generation. Can be homestead, tangerineWhistle, spuriousDragon, byzantium or constantinople
    // Metadata settings (optional)
    metadata: {
      // Use only literal content and not URLs (false by default)
      useLiteralContent: true
    },
    // Addresses of the libraries. If not all libraries are given here, it can result in unlinked objects whose output data is different.
    libraries: {
      // The top level key is the the name of the source file where the library is used.
      // If remappings are used, this source file should match the global path after remappings were applied.
      // If this key is an empty string, that refers to a global level.
      "myFile.sol": {
        "MyLib": "0x123123..."
      }
    }
    // The following can be used to select desired outputs.
    // If this field is omitted, then the compiler loads and does type checking, but will not generate any outputs apart from errors.
    // The first level key is the file name and the second is the contract name, where empty contract name refers to the file itself,
    // while the star refers to all of the contracts.
    //
    // The available output types are as follows:
    //   abi - ABI
    //   ast - AST of all source files
    //   legacyAST - legacy AST of all source files
    //   devdoc - Developer documentation (natspec)
    //   userdoc - User documentation (natspec)
    //   metadata - Metadata
    //   ir - New assembly format before desugaring
    //   evm.assembly - New assembly format after desugaring
    //   evm.legacyAssembly - Old-style assembly format in JSON
    //   evm.bytecode.object - Bytecode object
    //   evm.bytecode.opcodes - Opcodes list
    //   evm.bytecode.sourceMap - Source mapping (useful for debugging)
    //   evm.bytecode.linkReferences - Link references (if unlinked object)
    //   evm.deployedBytecode* - Deployed bytecode (has the same options as evm.bytecode)
    //   evm.methodIdentifiers - The list of function hashes
    //   evm.gasEstimates - Function gas estimates
    //   ewasm.wast - eWASM S-expressions format (not supported atm)
    //   ewasm.wasm - eWASM binary format (not supported atm)
    //
    // Note that using a using `evm`, `evm.bytecode`, `ewasm`, etc. will select every
    // target part of that output. Additionally, `*` can be used as a wildcard to request everything.
    //
    outputSelection: {
      // Enable the metadata and bytecode outputs of every single contract.
      "*": {
        "*": [ "metadata", "evm.bytecode" ]
      },
      // Enable the abi and opcodes output of MyContract defined in file def.
      "def": {
        "MyContract": [ "abi", "evm.bytecode.opcodes" ]
      },
      // Enable the source map output of every single contract.
      "*": {
        "*": [ "evm.bytecode.sourceMap" ]
      },
      // Enable the legacy AST output of every single file.
      "*": {
        "": [ "legacyAST" ]
      }
    }
  }
}

• 輸出格式說明

{
  // Optional: not present if no errors/warnings were encountered
  errors: [
    {
      // Optional: Location within the source file.
      sourceLocation: {
        file: "sourceFile.sol",
        start: 0,
        end: 100
      ],
      // Mandatory: Error type, such as "TypeError", "InternalCompilerError", "Exception", etc.
      // See below for complete list of types.
      type: "TypeError",
      // Mandatory: Component where the error originated, such as "general", "ewasm", etc.
      component: "general",
      // Mandatory ("error" or "warning")
      severity: "error",
      // Mandatory
      message: "Invalid keyword"
      // Optional: the message formatted with source location
      formattedMessage: "sourceFile.sol:100: Invalid keyword"
    }
  ],
  // This contains the file-level outputs. In can be limited/filtered by the outputSelection settings.
  sources: {
    "sourceFile.sol": {
      // Identifier (used in source maps)
      id: 1,
      // The AST object
      ast: {},
      // The legacy AST object
      legacyAST: {}
    }
  },
  // This contains the contract-level outputs. It can be limited/filtered by the outputSelection settings.
  contracts: {
    "sourceFile.sol": {
      // If the language used has no contract names, this field should equal to an empty string.
      "ContractName": {
        // The Ethereum Contract ABI. If empty, it is represented as an empty array.
        // See https://github.com/ethereum/wiki/wiki/Ethereum-Contract-ABI
        abi: [],
        // See the Metadata Output documentation (serialised JSON string)
        metadata: "{...}",
        // User documentation (natspec)
        userdoc: {},
        // Developer documentation (natspec)
        devdoc: {},
        // Intermediate representation (string)
        ir: "",
        // EVM-related outputs
        evm: {
          // Assembly (string)
          assembly: "",
          // Old-style assembly (object)
          legacyAssembly: {},
          // Bytecode and related details.
          bytecode: {
            // The bytecode as a hex string.
            object: "00fe",
            // Opcodes list (string)
            opcodes: "",
            // The source mapping as a string. See the source mapping definition.
            sourceMap: "",
            // If given, this is an unlinked object.
            linkReferences: {
              "libraryFile.sol": {
                // Byte offsets into the bytecode. Linking replaces the 20 bytes located there.
                "Library1": [
                  { start: 0, length: 20 },
                  { start: 200, length: 20 }
                ]
              }
            }
          },
          // The same layout as above.
          deployedBytecode: { },
          // The list of function hashes
          methodIdentifiers: {
            "delegate(address)": "5c19a95c"
          },
          // Function gas estimates
          gasEstimates: {
            creation: {
              codeDepositCost: "420000",
              executionCost: "infinite",
              totalCost: "infinite"
            },
            external: {
              "delegate(address)": "25000"
            },
            internal: {
              "heavyLifting()": "infinite"
            }
          }
        },
        // eWASM related outputs
        ewasm: {
          // S-expressions format
          wast: "",
          // Binary format (hex string)
          wasm: ""
        }
      }
    }
  }
}

• 錯誤型別說明：
  
  1. JSONError：JSON錯誤，JSON輸入不符合要求的格式，例如輸入不是JSON物件，不支援語言，等等。
  2. IOError：IO錯誤，IO和匯入處理錯誤，如提供的源中的不可解析URL或hash不匹配。
  3. ParserError：語法f分析錯誤，原始碼不符合語言規則。
  4. DocstringParsingError：文件解析錯誤，無法解析註釋塊中的NATSPEC標記。
  5. SytRealError：語法錯誤，如continue在for迴圈之外使用。
  6. DeclarationError：宣告錯誤，無效、不可解析或衝突的識別符號名稱。例如未找到識別符號
  7. TypeError：型別錯誤，如無效型別轉換、無效賦值等。
  8. UnimplementedFeatureError：編譯器不支援該特性，但希望在將來的版本中得到支援。
  9. InternalCompilerError：編譯器中觸發內部錯誤，這應該作為一個問題來反饋。
  10. Exception：例外，編譯過程中未知的故障，這應該作為一個問題反饋。
  11. CompilerError：編譯錯誤，編譯器堆疊的使用無效，這應該作為一個問題來反饋。
  12. FatalError：致命錯誤，這應該作為一個問題來反饋。
  13. Warning：警告並沒有停止編譯，但如果可能的話，應該加以處理。

原文請訪問：solc

如果你希望馬上開始學習以太坊DApp開發，推薦訪問一個線上教程：
* 以太坊智慧合約，主要介紹智慧合約與dapp應用開發，適合入門。
* 以太坊開發，主要是介紹使用node.js、mongodb、區塊鏈、ipfs實現去中心化電商DApp實戰，適合進階。