4 files changed, 68 insertions, 4 deletions

diff --git a/packages/sol-compiler/src/cli.ts b/packages/sol-compiler/src/cli.ts
index 0a9db6e05..18cc68aaf 100644
--- a/packages/sol-compiler/src/cli.ts
+++ b/packages/sol-compiler/src/cli.ts
@@ -25,6 +25,10 @@ const SEPARATOR = ',';
             type: 'string',
             description: 'comma separated list of contracts to compile',
         })
+        .option('watch', {
+            alias: 'w',
+            default: false,
+        })
         .help().argv;
     const contracts = _.isUndefined(argv.contracts)
         ? undefined
@@ -37,7 +41,11 @@ const SEPARATOR = ',';
         contracts,
     };
     const compiler = new Compiler(opts);
-    await compiler.compileAsync();
+    if (argv.watch) {
+        await compiler.watchAsync();
+    } else {
+        await compiler.compileAsync();
+    }
 })().catch(err => {
     logUtils.log(err);
     process.exit(1);
diff --git a/packages/sol-compiler/src/compiler.ts b/packages/sol-compiler/src/compiler.ts
index 45cbf527b..17a1ce563 100644
--- a/packages/sol-compiler/src/compiler.ts
+++ b/packages/sol-compiler/src/compiler.ts
@@ -6,13 +6,17 @@ import {
     NPMResolver,
     RelativeFSResolver,
     Resolver,
+    SpyResolver,
     URLResolver,
 } from '@0x/sol-resolver';
 import { logUtils } from '@0x/utils';
+import chalk from 'chalk';
+import * as chokidar from 'chokidar';
 import { CompilerOptions, ContractArtifact, ContractVersionData, StandardOutput } from 'ethereum-types';
 import * as fs from 'fs';
 import * as _ from 'lodash';
 import * as path from 'path';
+import * as pluralize from 'pluralize';
 import * as semver from 'semver';
 import solc = require('solc');
 
@@ -30,6 +34,7 @@ import {
 } from './utils/compiler';
 import { constants } from './utils/constants';
 import { fsWrapper } from './utils/fs_wrapper';
+import { CompilationError } from './utils/types';
 import { utils } from './utils/utils';
 
 type TYPE_ALL_FILES_IDENTIFIER = '*';
@@ -129,6 +134,43 @@ export class Compiler {
         const promisedOutputs = this._compileContractsAsync(this._getContractNamesToCompile(), false);
         return promisedOutputs;
     }
+    public async watchAsync(): Promise<void> {
+        console.clear(); // tslint:disable-line:no-console
+        logWithTime('Starting compilation in watch mode...');
+        const watcher = chokidar.watch('^$', { ignored: /(^|[\/\\])\../ });
+        const onFileChangedAsync = async () => {
+            watcher.unwatch('*'); // Stop watching
+            try {
+                await this.compileAsync();
+                logWithTime('Found 0 errors. Watching for file changes.');
+            } catch (err) {
+                if (err.typeName === 'CompilationError') {
+                    logWithTime(`Found ${err.errorsCount} ${pluralize('error', err.errorsCount)}. Watching for file changes.`);
+                } else {
+                    logWithTime('Found errors. Watching for file changes.');
+                }
+            }
+
+            const pathsToWatch = this._getPathsToWatch();
+            watcher.add(pathsToWatch);
+        };
+        await onFileChangedAsync();
+        watcher.on('change', (changedFilePath: string) => {
+            console.clear(); // tslint:disable-line:no-console
+            logWithTime('File change detected. Starting incremental compilation...');
+            onFileChangedAsync();
+        });
+    }
+    private _getPathsToWatch(): string[] {
+        const contractNames = this._getContractNamesToCompile();
+        const spyResolver = new SpyResolver(this._resolver);
+        for (const contractName of contractNames) {
+            const contractSource = spyResolver.resolve(contractName);
+            getSourceTreeHash(spyResolver, contractSource.path);
+        }
+        const pathsToWatch = _.uniq(spyResolver.resolvedContractSources.map(cs => cs.absolutePath));
+        return pathsToWatch;
+    }
     private _getContractNamesToCompile(): string[] {
         let contractNamesToCompile;
         if (this._specifiedContracts === ALL_CONTRACTS_IDENTIFIER) {
@@ -298,3 +340,7 @@ export class Compiler {
         logUtils.warn(`${contractName} artifact saved!`);
     }
 }
+
+function logWithTime(arg: string): void {
+    logUtils.log(`[${chalk.gray(new Date().toLocaleTimeString())}] ${arg}`);
+}
diff --git a/packages/sol-compiler/src/utils/compiler.ts b/packages/sol-compiler/src/utils/compiler.ts
index 034f72f8d..486d8bedd 100644
--- a/packages/sol-compiler/src/utils/compiler.ts
+++ b/packages/sol-compiler/src/utils/compiler.ts
@@ -12,6 +12,7 @@ import { binPaths } from '../solc/bin_paths';
 
 import { constants } from './constants';
 import { fsWrapper } from './fs_wrapper';
+import { CompilationError } from './types';
 
 /**
  * Gets contract data on network or returns if an artifact does not exist.
@@ -147,13 +148,13 @@ function printCompilationErrorsAndWarnings(solcErrors: solc.SolcError[]): void {
     if (!_.isEmpty(errors)) {
         errors.forEach(error => {
             const normalizedErrMsg = getNormalizedErrMsg(error.formattedMessage || error.message);
-            logUtils.warn(chalk.red(normalizedErrMsg));
+            logUtils.log(chalk.red('error'), normalizedErrMsg);
         });
-        throw new Error('Compilation errors encountered');
+        throw new CompilationError(errors.length);
     } else {
         warnings.forEach(warning => {
             const normalizedWarningMsg = getNormalizedErrMsg(warning.formattedMessage || warning.message);
-            logUtils.warn(chalk.yellow(normalizedWarningMsg));
+            logUtils.log(chalk.yellow('warning'), normalizedWarningMsg);
         });
     }
 }
diff --git a/packages/sol-compiler/src/utils/types.ts b/packages/sol-compiler/src/utils/types.ts
index b211cfcbc..64328899d 100644
--- a/packages/sol-compiler/src/utils/types.ts
+++ b/packages/sol-compiler/src/utils/types.ts
@@ -29,3 +29,12 @@ export interface Token {
 }
 
 export type DoneCallback = (err?: Error) => void;
+
+export class CompilationError extends Error {
+    public errorsCount: number;
+    public typeName = 'CompilationError';
+    constructor(errorsCount: number) {
+        super('Compilation errors encountered');
+        this.errorsCount = errorsCount;
+    }
+}