#249 Add explicit info logger to avoid writing info logs to stderr (#313)

* Add explicit info logger to avoid writing info logs to stderr

* Add a loaderOption for the logLevel and logging to different logLevels

* Fix tsc compile error

* Add a new loaderOption to specify the info logging output.

* Change documentation text according to review advise

* Doing uppercase on loaderOptions logLevel just once

* Bugfix the default value of logLevel must be string

Author: ThYpHo0n

README.md

@@ -139,6 +139,16 @@ different dependencies in your application will be lost. You should also
 set the `isolatedModules` TypeScript option if you plan to ever make use
 of this.
 
+##### logInfoToStdOut *(boolean) (default=false)*
+
+This is important if you read from stdout or stderr and for proper error handling.
+The default value ensures that you can read from stdout e.g. via pipes or you use webpack -j to generate json output.
+
+##### logLevel *(string) (default=info)*
+
+Can be `info`, `warn` or `error` which limits the log output to the specified log level.
+Beware of the fact that errors are written to stderr and everything else is written to stderr (or stdout if logInfoToStdOut is true).
+
 ##### silent *(boolean) (default=false)*
 
 If true, no console.log messages will be emitted. Note that most error

index.ts

@@ -15,7 +15,8 @@ var Console = require('console').Console;
 var semver = require('semver')
 require('colors');
 
-const console = new Console(process.stderr);
+const stderrConsole = new Console(process.stderr);
+const stdoutConsole = new Console(process.stdout);
 
 var pushArray = function(arr, toPush) {
     Array.prototype.splice.apply(arr, [0, 0].concat(toPush));
@@ -25,8 +26,16 @@ function hasOwnProperty(obj, property) {
     return Object.prototype.hasOwnProperty.call(obj, property)
 }
 
+enum LogLevel {
+    INFO = 1,
+    WARN = 2,
+    ERROR = 3
+}
+
 interface LoaderOptions {
     silent: boolean;
+    logLevel: string;
+    logInfoToStdOut: boolean;
     instance: string;
     compiler: string;
     configFileName: string;
@@ -149,8 +158,34 @@ function findConfigFile(compiler: typeof typescript, searchPath: string, configF
 function ensureTypeScriptInstance(loaderOptions: LoaderOptions, loader: any): { instance?: TSInstance, error?: WebpackError } {
 
     function log(...messages: string[]): void {
+        logToConsole(stdoutConsole, messages);
+    }
+
+    function logToConsole(logConsole:any, messages: string[]): void {
         if (!loaderOptions.silent) {
-            console.log.apply(console, messages);
+            console.log.apply(logConsole, messages);
+        }
+    }
+
+    function logInfo(...messages: string[]): void {
+        if (LogLevel[loaderOptions.logLevel] <= LogLevel.INFO) {
+            if(loaderOptions.logInfoToStdOut) {
+                logToConsole(stdoutConsole, messages);
+            } else {
+                logToConsole(stderrConsole, messages);
+            }
+        }
+    }
+
+    function logError(...messages: string[]): void {
+        if (LogLevel[loaderOptions.logLevel] <= LogLevel.ERROR) {
+            logToConsole(stderrConsole, messages);
+        }
+    }
+
+    function logWarning(...messages: string[]): void {
+        if (LogLevel[loaderOptions.logLevel] <= LogLevel.WARN) {
+            logToConsole(stderrConsole, messages);
         }
     }
 
@@ -180,11 +215,11 @@ function ensureTypeScriptInstance(loaderOptions: LoaderOptions, loader: any): {
             compilerCompatible = true;
         }
         else {
-            log(`${motd}. This version is incompatible with ts-loader. Please upgrade to the latest version of TypeScript.`.red);
+            logError(`${motd}. This version is incompatible with ts-loader. Please upgrade to the latest version of TypeScript.`.red);
         }
     }
     else {
-        log(`${motd}. This version may or may not be compatible with ts-loader.`.yellow);
+        logWarning(`${motd}. This version may or may not be compatible with ts-loader.`.yellow);
     }
 
     var files = <TSFiles>{};
@@ -211,8 +246,8 @@ function ensureTypeScriptInstance(loaderOptions: LoaderOptions, loader: any): {
         error?: typescript.Diagnostic;
     };
     if (configFilePath) {
-        if (compilerCompatible) log(`${motd} and ${configFilePath}`.green)
-        else log(`ts-loader: Using config file at ${configFilePath}`.green)
+        if (compilerCompatible) logInfo(`${motd} and ${configFilePath}`.green)
+        else logInfo(`ts-loader: Using config file at ${configFilePath}`.green)
 
         // HACK: relies on the fact that passing an extra argument won't break
         // the old API that has a single parameter
@@ -227,7 +262,7 @@ function ensureTypeScriptInstance(loaderOptions: LoaderOptions, loader: any): {
         }
     }
     else {
-        if (compilerCompatible) log(motd.green)
+        if (compilerCompatible) logInfo(motd.green)
 
         configFile = {
             config: {
@@ -556,13 +591,16 @@ function loader(contents) {
 
     var options = objectAssign<LoaderOptions>({}, {
         silent: false,
+        logLevel: 'INFO',
+        logInfoToStdOut: false,
         instance: 'default',
         compiler: 'typescript',
         configFileName: 'tsconfig.json',
         transpileOnly: false,
         compilerOptions: {}
     }, configFileOptions, queryOptions);
     options.ignoreDiagnostics = arrify(options.ignoreDiagnostics).map(Number);
+    options.logLevel = options.logLevel.toUpperCase();
 
     // differentiate the TypeScript instance based on the webpack instance
     var webpackIndex = webpackInstances.indexOf(this._compiler);