Add support for custom solc versions (#11)

* Add support for custom solc versions

If the required version of solc isn't currently in use solc will
[1](download the required version of itself). Normally you can pass
"version" in the the truffle config to trigger this behavior but our
truffle version field is already filled with a path to our custom solc
compiler. Instead we pass the enviroment variable `SOLC_VERSION` which
triggers it.

Truffle expects `compile` to be synchronous so we can't do anything
asynchronous in that function. To get around this we use `execSync` which
executes synchronously.

[1]: https://github.com/ethereum/solc-js/blob/5c1280ca2c73dfba58bad21849b16eb1fa5618e5/README.md#using-a-legacy-version

packages/solc-transpiler/package.json

@@ -31,6 +31,7 @@
   "dependencies": {
     "@eth-optimism/core-utils": "~0.0.1-alpha.7",
     "@eth-optimism/rollup-dev-tools": "~0.0.1-alpha.7",
+    "require-from-string": "^2.0.2",
     "solc": "^0.5.12"
   },
   "devDependencies": {

packages/solc-transpiler/src/compiler.ts

@@ -17,6 +17,8 @@ import {
   remove0x,
 } from '@eth-optimism/core-utils'
 import * as solc from 'solc'
+import { execSync } from 'child_process'
+import * as requireFromString from 'require-from-string'
 
 const log: Logger = getLogger('solc-transpiler')
 
@@ -36,14 +38,15 @@ interface TranspilationOutput {
  * @returns The Solc output as a string.
  */
 export const compile = (configJsonString: string, callbacks?: any): string => {
+  const compiler = getCompiler(process.env.SOLC_VERSION)
   log.debug(`Trying to transpile with config: ${configJsonString}`)
   let json: any
   try {
     json = JSON.parse(configJsonString)
   } catch (e) {
     log.debug(`Cannot parse JSON: ${JSON.stringify(e)}`)
     // todo: populate some errors
-    return solc.compile(configJsonString)
+    return compiler.compile(configJsonString)
   }
 
   const inputErrors: string = getInputErrors(json)
@@ -53,8 +56,8 @@ export const compile = (configJsonString: string, callbacks?: any): string => {
 
   const solcConfig: string = getSolcConfig(json)
   const resString = !!callbacks
-    ? solc.compile(solcConfig, callbacks)
-    : solc.compile(solcConfig)
+    ? compiler.compile(solcConfig, callbacks)
+    : compiler.compile(solcConfig)
 
   const res = JSON.parse(resString)
   if (
@@ -110,6 +113,64 @@ export const compile = (configJsonString: string, callbacks?: any): string => {
   return formatOutput(res, json)
 }
 
+/**
+ * Gets the requested version of the solc module. solc-js provides downloadable
+ * versions of itself which can be downloaded and used to compile contracts that
+ * require different compiler versions. This function must be synchronous so it
+ * can be used in the compilation process which is also synchronous. To achieve
+ * this we construct a string of JavaScript which downloads the latest version
+ * of solc and run that code using `execSync`
+ *
+ * @param versionString The requested version of solc
+ * @returns The requested version of the `solc` module or the latest version
+ */
+const getCompiler = (versionString: string): typeof solc => {
+  if (!versionString) {
+    return solc
+  }
+
+  const getCompilerString = `
+    function httpsRequest(params, postData) {
+      return new Promise(function(resolve, reject) {
+          var req = https.request(params, function(res) {
+              var body = [];
+              res.on("data", function(chunk) {
+                  body.push(chunk);
+              });
+              res.on("end", function() {
+                  try {
+                      body = Buffer.concat(body).toString();
+                  } catch(e) {
+                      reject(e);
+                  }
+                  resolve(body);
+              });
+          });
+          req.on("error", function(err) {
+              reject(err);
+          });
+          req.end();
+      });
+    }
+
+    async function getSolcVersion(versionString) {
+      const listUrl = "https://ethereum.github.io/solc-bin/bin/list.json";
+      const {releases} = JSON.parse(await httpsRequest(listUrl))
+      const solcUrl = "https://ethereum.github.io/solc-bin/bin/" + releases[versionString];
+      return await httpsRequest(solcUrl);
+    }
+
+    (async () => {
+      await process.stdout.write(await getSolcVersion("${versionString}"));
+    })();
+    `
+  return solc.setupMethods(
+    requireFromString(
+      execSync(`${process.argv[0]} -e '${getCompilerString}'`).toString()
+    )
+  )
+}
+
 const getExecutionManagerAddress = (configObject: any): string => {
   return (
     configObject.settings.executionManagerAddress ||

yarn.lock

@@ -8906,7 +8906,7 @@ require-directory@^2.1.1:
   resolved "https://registry.yarnpkg.com/require-directory/-/require-directory-2.1.1.tgz#8c64ad5fd30dab1c976e2344ffe7f792a6a6df42"
   integrity sha1-jGStX9MNqxyXbiNE/+f3kqam30I=
 
-require-from-string@^2.0.0:
+require-from-string@^2.0.0, require-from-string@^2.0.2:
   version "2.0.2"
   resolved "https://registry.yarnpkg.com/require-from-string/-/require-from-string-2.0.2.tgz#89a7fdd938261267318eafe14f9c32e598c36909"
   integrity sha512-Xf0nWe6RseziFMu+Ap9biiUbmplq6S9/p+7w7YXP/JBHhrUDDUhwa+vANyubuqfZWTveU//DYVGsDG7RKL/vEw==