Improve silent mode (#20)

* Make activity() respect silent mode

* Make progress() respect silent mode

* Disable activity and progress in CI environment

* Update readme with text about silent mode

README.md

@@ -4,7 +4,9 @@ An elegant console reporter, borrowed from [Yarn](https://yarnpkg.com).
 
 ## Introduction
 
-Pretty console output makes developers happy and Yarn is doing a nice job. Yurnalist takes the internal console reporter code from Yarn and makes it available for use in other Node.js applications.
+Pretty console output makes developers happy and Yarn is doing a nice job.
+Yurnalist takes the internal console reporter code from Yarn and makes it
+available for use in other Node.js applications.
 
 The current version is based on code from Yarn v1.13.0.
 
@@ -80,7 +82,9 @@ Node >= 4
 
 ## Examples
 
-Examples showing different API functions are found in [/examples](/examples). You can run them directly with node >= 7.6 (because of async/await syntax). For older versions you could use the `--harmony` flag, or otherwise Babel.
+Examples showing different API functions are found in [/examples](/examples).
+You can run them directly with node >= 7.6 (because of async/await syntax). For
+older versions you could use the `--harmony` flag, or otherwise Babel.
 
 To run the activity example:
 
@@ -90,7 +94,9 @@ node examples/activity.js
 
 ## Configuration
 
-A normal import gives you a reporter instance configured with defaults for easy use. If you want something else you can call `createReporter(options)` to give you an instance with different options.
+A normal import gives you a reporter instance configured with defaults for easy
+use. If you want something else you can call `createReporter(options)` to give
+you an instance with different options.
 
 ### Options
 
@@ -126,11 +132,26 @@ const defaults = {
 }
 ```
 
-The peekMemoryCounter is disabled by default. If you enable it, you'll have to call `reporter.close()` to stop its running timer. Otherwise your program will not exit. The memory counter can be used to display in the footer data.
+The peekMemoryCounter is disabled by default. If you enable it, you'll have to
+call `reporter.close()` to stop its running timer. Otherwise your program will
+not exit. The memory counter can be used to display in the footer data.
+
+## Silent Mode and CI
+
+Silent mode can be set via the options passed to createReporter. It disables
+output for various functions like `info`, `list`, `activity` and `progress`. The
+output from `warning` and `error` messages is not silenced.
+
+Silent mode can also be enabled with the `YURNALIST_SILENT` environment
+variable.
+
+In CI environments the output from `activity` and `progress` is disabled.
 
 ## API
 
-The API still needs some documentation, but most methods are straightforward. In the meantime you can also look at the [examples](./examples) and possibly even the [tests](./__tests__).
+The API still needs some documentation, but most methods are straightforward. In
+the meantime you can also look at the [examples](./examples) and possibly even
+the [tests](./__tests__).
 
 The following functions are available:
 
@@ -142,10 +163,10 @@ The following functions are available:
 
 Pretty-prints the `thing`.
 
-### list(key: string, items: Array<string>, hints?: Object) 
+### list(key: string, items: Array<string>, hints?: Object)
 
-Generates a list of the provided items. Turns into a definition 
-list if `hints` are provided. Note that the `key` is not used.
+Generates a list of the provided items. Turns into a definition list if `hints`
+are provided. Note that the `key` is not used.
 
 Example of a simple list:
 
@@ -184,7 +205,7 @@ report.list('dunno', someList, hints);
 ```
 generates
 ```
-info My grocery list 
+info My grocery list
     - bananas
       for baking
    - tulips
@@ -214,13 +235,18 @@ info My grocery list
 
 ## Language
 
-Yarn uses a language file for certain messages. For example if you try to skip a required question, or when you pick an invalid item from a select. This language file is not yet exposed in the Yurnalist API. The only supported language is English, as it is in Yarn at the moment.
+Yarn uses a language file for certain messages. For example if you try to skip a
+required question, or when you pick an invalid item from a select. This language
+file is not yet exposed in the Yurnalist API. The only supported language is
+English, as it is in Yarn at the moment.
 
-I plan to make this configurable so that you can define your own messages in your own language .
+I plan to make this configurable so that you can define your own messages in
+your own language .
 
 ## Emojis
 
-You can use Emojis in your output. Yurnalist should disable them if they are not allowed in the application environment.
+You can use Emojis in your output. Yurnalist should disable them if they are not
+allowed in the application environment.
 
 Check:
 
@@ -229,4 +255,6 @@ Check:
 
 ## Credits
 
-Of course ❤️ and credits to all the contributers of [Yarn](https://yarnpkg.com). The ease with which I was able to extract this module from their codebase is proving some awesome engineering skills.
+Of course ❤️ and credits to all the contributers of [Yarn](https://yarnpkg.com).
+The ease with which I was able to extract this module from their codebase is
+proving some awesome engineering skills.

src/reporters/console/console-reporter.js

@@ -19,6 +19,7 @@ import {clearLine} from './util.js';
 import {removeSuffix} from '../../util/misc.js';
 import {sortTrees, recurseTree, getFormattedOutput} from './helpers/tree-helper.js';
 import inquirer from 'inquirer';
+import isCI from 'is-ci';
 
 const {inspect} = require('util');
 const readline = require('readline');
@@ -321,7 +322,7 @@ export default class ConsoleReporter extends BaseReporter {
   }
 
   activity(): ReporterSpinner {
-    if (!this.isTTY) {
+    if (!this.isTTY || this.isSilent || isCI) {
       return {
         tick() {},
         end() {},
@@ -411,7 +412,7 @@ export default class ConsoleReporter extends BaseReporter {
       };
     }
 
-    if (!this.isTTY) {
+    if (!this.isTTY || this.isSilent || isCI) {
       return function() {
         // TODO what should the behaviour here be? we could buffer progress messages maybe
       };