fix(jsii): color codes are logged to logfiles (#3284)

When the output is not a terminal, color codes get in the way. They
lead to unreadable logging like this:

```
monocdk: ^[[96mlib/aws-apigateway/lib/domain-name.ts^[[0m:^[[93m114^[[0m:^[[93m19^[[0m - ^[[93mwarning^[[0m^[[90m JSII5019: ^[[0mThe property name "domainName" conflicts with the declaring class "DomainName". This will result in renaming the class to "_DomainName" in C#. Consider renaming "domainName".
monocdk: �[7m114�[0m   public readonly domainName: string;
monocdk: �[7m   �[0m �[93m                  ~~~~~~~~~~�[0m
```

Don't output color codes if we detect the output is not a TTY.



---

By submitting this pull request, I confirm that my contribution is made under the terms of the [Apache 2.0 license].

[Apache 2.0 license]: https://www.apache.org/licenses/LICENSE-2.0

packages/jsii/bin/jsii.ts

@@ -2,6 +2,7 @@ import '@jsii/check-node/run';
 
 import * as log4js from 'log4js';
 import * as path from 'path';
+import * as util from 'util';
 import * as yargs from 'yargs';
 
 import { Compiler } from '../lib/compiler';
@@ -132,15 +133,26 @@ const warningTypes = Object.keys(enabledWarnings);
 });
 
 function _configureLog4js(verbosity: number) {
+  const stderrColor = !!process.stderr.isTTY;
+  const stdoutColor = !!process.stdout.isTTY;
+
+  log4js.addLayout('passThroughNoColor', () => {
+    return (loggingEvent) => stripAnsi(util.format(...loggingEvent.data));
+  });
+
   log4js.configure({
     appenders: {
       console: {
         type: 'stderr',
-        layout: { type: 'colored' },
+        layout: { type: stderrColor ? 'colored' : 'basic' },
       },
       [utils.DIAGNOSTICS]: {
         type: 'stdout',
-        layout: { type: 'messagePassThrough' },
+        layout: {
+          type: stdoutColor
+            ? 'messagePassThrough'
+            : ('passThroughNoColor' as any),
+        },
       },
     },
     categories: {
@@ -168,3 +180,11 @@ function _configureLog4js(verbosity: number) {
     }
   }
 }
+
+const ANSI_REGEX =
+  // eslint-disable-next-line no-control-regex
+  /[\u001b\u009b][[()#;?]*(?:[0-9]{1,4}(?:;[0-9]{0,4})*)?[0-9A-ORZcf-nqry=><]/g;
+
+function stripAnsi(x: string): string {
+  return x.replace(ANSI_REGEX, '');
+}