solc：solidity的编译器

solidity编写的以太坊智能合约可通过命令行编译工具solc来进行编译，成为以太坊虚拟机中的代码。solc编译后最终部署到链上形成我们所见到的各种智能合约。

作为一个solidity命令行编译工具，我们来看看官网都怎么说solc。

solc的安装很简单：

npm install -g solc//或者npm install -g solc-cli//或者sudo apt-get install solc复制代码

安装完成后我们来看，solc --help，solc --help命令显示所有的solc命令选项。编译器可以生成各种输出，比如最终的二进制合约文件、语法树的汇编或者需要预计的要花费的gas等。solc --bin sourceFile.sol，可以编译后输出一个名为sourceFile.sol的智能合约文件。如果你想从solc获得更丰富的一些输出变量，你可以使用solc -o outputDirectory --bin --ast --asm sourceFile.sol。

你在部署之前可以用solc --optimize --bin sourceFile.sol优化一下。默认情况下solc编译器会帮你优化200次。你也可以设置 --runs=1，这样就按照最小化的方式进行编译，如果你希望多次交易不太在乎成本，那你可以设置成你想要的次数:)。

命令行编译器会自动读取需要导入的文件，也可以通过使用prefix = path来指定路径，例如：

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

这样编译器就会从指定目录github.com/ethereum/dapp-bin/下的/usr/local/lib/dapp-bin/目录开始搜索，如果没有找到文件，它将查看/usr/local/lib/fallback。solc将只读取你指定的这两个路径的，因此像import "/etc/passwd";必须要通过/=重新映射才起作用。如果有多个匹配，则选择具有最长公共前缀的进行匹配。

出于安全上的考虑，编译器限制了它可以访问的一些目录。在命令行中指定的源文件的路径（及其子目录）和命令行指定的路径外其他所有内容都会被拒绝。--allow-paths /sample/path,/another/sample/path来切换。

如果智能合约使用了，你会注意到字节码包含了__LibraryName______的子字符串。您可以使用solc作为链接器，这意味着它将在这些点为您插入库地址。

可以通过添加库--libraries "Math:0x12345678901234567890 Heap:0xabcdef0123456"到您的命令，以提供每个库的地址，或者使用文件中的说明字符串（每行一个库），并使用--libraries fileName运行solc。

如果用选项--link调用Solc，则所有输入文件都被解释为未链接的二进制文件（HEX编码），在上面给出的__LibraryName____格式中，将其链接到适当地址（如果从stdin读取输入，则将其写入stdout）。在这种情况下，除了库外，所有选项都被忽略（包括-o）。

如果用--standard-json调用SOLC，它就将标准的JSON输入（如下所述），并返回JSON输出。

#solc编译器输入输出JSON描述

这些JSON格式通过编译器API使用，可以通过SOLC获得。内容都是可以修改的，一些对象是可选的（如前所述），其目的是向后兼容。

编译器的API需要一个JSON格式的输入，然后以JSON格式输出编译结果。

注意不允许注释。下面示例中的注释，是官网为了学习者更好的理解标注的。

• 输入格式说明：

{  // 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" ]      }    }  }}复制代码

• 输出格式说明

{  // 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: ""        }      }    }  }}复制代码

• 错误类型说明：

1. JSONError：JSON错误，JSON输入不符合要求的格式，例如输入不是JSON对象，不支持语言，等等。
2. IOError：IO错误，IO和导入处理错误，如提供的源中的不可解析URL或hash不匹配。
3. ParserError：语法f分析错误，源代码不符合语言规则。
4. DocstringParsingError：文档解析错误，无法解析注释块中的NATSPEC标记。
5. SytRealError：语法错误，如continue在for循环之外使用。
6. DeclarationError：声明错误，无效、不可解析或冲突的标识符名称。例如未找到标识符
7. TypeError：类型错误，如无效类型转换、无效赋值等。
8. UnimplementedFeatureError：编译器不支持该特性，但希望在将来的版本中得到支持。
9. InternalCompilerError：编译器中触发内部错误，这应该作为一个问题来反馈。
10. Exception：例外，编译过程中未知的故障，这应该作为一个问题反馈。
11. CompilerError：编译错误，编译器堆栈的使用无效，这应该作为一个问题来反馈。
12. FatalError：致命错误，这应该作为一个问题来反馈。
13. Warning：警告并没有停止编译，但如果可能的话，应该加以处理。

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