2 files changed, 34 insertions, 16 deletions

diff --git a/packages/abi-gen/src/index.ts b/packages/abi-gen/src/index.ts
index 47f2c404b..753bb2cce 100644
--- a/packages/abi-gen/src/index.ts
+++ b/packages/abi-gen/src/index.ts
@@ -3,16 +3,12 @@
 import { abiUtils, logUtils } from '@0xproject/utils';
 import chalk from 'chalk';
 import { AbiDefinition, ConstructorAbi, EventAbi, MethodAbi } from 'ethereum-types';
-import * as fs from 'fs';
 import { sync as globSync } from 'glob';
 import * as Handlebars from 'handlebars';
 import * as _ from 'lodash';
 import * as mkdirp from 'mkdirp';
-import * as rimraf from 'rimraf';
 import * as yargs from 'yargs';
 
-import toSnakeCase = require('to-snake-case');
-
 import { ContextData, ContractsBackend, ParamKind } from './types';
 import { utils } from './utils';
 
@@ -71,16 +67,6 @@ function registerPartials(partialsGlob: string): void {
     }
 }
 
-function writeOutputFile(name: string, renderedTsCode: string): void {
-    let fileName = toSnakeCase(name);
-    // HACK: Snake case doesn't make a lot of sense for abbreviated names but we can't reliably detect abbreviations
-    // so we special-case the abbreviations we use.
-    fileName = fileName.replace('z_r_x', 'zrx').replace('e_r_c', 'erc');
-    const filePath = `${args.output}/${fileName}.ts`;
-    fs.writeFileSync(filePath, renderedTsCode);
-    logUtils.log(`Created: ${chalk.bold(filePath)}`);
-}
-
 Handlebars.registerHelper('parameterType', utils.solTypeToTsType.bind(utils, ParamKind.Input, args.backend));
 Handlebars.registerHelper('returnType', utils.solTypeToTsType.bind(utils, ParamKind.Output, args.backend));
 if (args.partials) {
@@ -97,7 +83,6 @@ if (_.isEmpty(abiFileNames)) {
     process.exit(1);
 } else {
     logUtils.log(`Found ${chalk.green(`${abiFileNames.length}`)} ${chalk.bold('ABI')} files`);
-    rimraf.sync(args.output);
     mkdirp.sync(args.output);
 }
 for (const abiFileName of abiFileNames) {
@@ -120,6 +105,14 @@ for (const abiFileName of abiFileNames) {
         process.exit(1);
     }
 
+    const outFileName = utils.makeOutputFileName(namedContent.name);
+    const outFilePath = `${args.output}/${outFileName}.ts`;
+
+    if (utils.isOutputFileUpToDate(abiFileName, outFilePath)) {
+        logUtils.log(`Aready up to date: ${chalk.bold(outFilePath)}`);
+        continue;
+    }
+
     let ctor = ABI.find((abi: AbiDefinition) => abi.type === ABI_TYPE_CONSTRUCTOR) as ConstructorAbi;
     if (_.isUndefined(ctor)) {
         ctor = utils.getEmptyConstructor(); // The constructor exists, but it's implicit in JSON's ABI definition
@@ -154,5 +147,6 @@ for (const abiFileName of abiFileNames) {
         events: eventAbis,
     };
     const renderedTsCode = template(contextData);
-    writeOutputFile(namedContent.name, renderedTsCode);
+    utils.writeOutputFile(outFilePath, renderedTsCode);
+    logUtils.log(`Created: ${chalk.bold(outFilePath)}`);
 }
diff --git a/packages/abi-gen/src/utils.ts b/packages/abi-gen/src/utils.ts
index 66390174c..56b996ce3 100644
--- a/packages/abi-gen/src/utils.ts
+++ b/packages/abi-gen/src/utils.ts
@@ -2,6 +2,7 @@ import { AbiType, ConstructorAbi, DataItem } from 'ethereum-types';
 import * as fs from 'fs';
 import * as _ from 'lodash';
 import * as path from 'path';
+import toSnakeCase = require('to-snake-case');
 
 import { ContractsBackend, ParamKind } from './types';
 
@@ -92,4 +93,27 @@ export const utils = {
             inputs: [],
         };
     },
+    makeOutputFileName(name: string): string {
+        let fileName = toSnakeCase(name);
+        // HACK: Snake case doesn't make a lot of sense for abbreviated names but we can't reliably detect abbreviations
+        // so we special-case the abbreviations we use.
+        fileName = fileName.replace('z_r_x', 'zrx').replace('e_r_c', 'erc');
+        return fileName;
+    },
+    writeOutputFile(filePath: string, renderedTsCode: string): void {
+        fs.writeFileSync(filePath, renderedTsCode);
+    },
+    isOutputFileUpToDate(abiFile: string, outputFile: string): boolean {
+        const abiFileModTimeMs = fs.statSync(abiFile).mtimeMs;
+        try {
+            const outFileModTimeMs = fs.statSync(outputFile).mtimeMs;
+            return outFileModTimeMs > abiFileModTimeMs;
+        } catch (err) {
+            if (err.code === 'ENOENT') {
+                return false;
+            } else {
+                throw err;
+            }
+        }
+    },
 };