Improve logging API

Adds multiple variable support and the ability to set statement level logging semantics.

This breaks that logger API, cleaning up the manner in which enums are set, but the other behaviors are backwards compatible.

Fixes #956

lib/handlebars/helpers/log.js

@@ -1,6 +1,19 @@
 export default function(instance) {
-  instance.registerHelper('log', function(message, options) {
-    let level = options.data && options.data.level != null ? parseInt(options.data.level, 10) : 1;
-    instance.log(level, message);
+  instance.registerHelper('log', function(/* message, options */) {
+    let args = [undefined],
+        options = arguments[arguments.length - 1];
+    for (let i = 0; i < arguments.length - 1; i++) {
+      args.push(arguments[i]);
+    }
+
+    let level = 1;
+    if (options.hash.level != null) {
+      level = options.hash.level;
+    } else if (options.data && options.data.level != null) {
+      level = options.data.level;
+    }
+    args[0] = level;
+
+    instance.log(... args);
   });
 }

lib/handlebars/logger.js

@@ -1,18 +1,31 @@
 let logger = {
-  methodMap: { 0: 'debug', 1: 'info', 2: 'warn', 3: 'error' },
+  methodMap: ['debug', 'info', 'warn', 'error'],
+  level: 'info',
 
-  // State enum
-  DEBUG: 0,
-  INFO: 1,
-  WARN: 2,
-  ERROR: 3,
-  level: 1,
+  // Maps a given level value to the `methodMap` indexes above.
+  lookupLevel: function(level) {
+    if (typeof level === 'string') {
+      let levelMap = logger.methodMap.indexOf(level.toLowerCase());
+      if (levelMap >= 0) {
+        level = levelMap;
+      } else {
+        level = parseInt(level, 10);
+      }
+    }
+
+    return level;
+  },
 
   // Can be overridden in the host environment
-  log: function(level, message) {
-    if (typeof console !== 'undefined' && logger.level <= level) {
+  log: function(level, ...message) {
+    level = logger.lookupLevel(level);
+
+    if (typeof console !== 'undefined' && logger.lookupLevel(logger.level) <= level) {
       let method = logger.methodMap[level];
-      (console[method] || console.log).call(console, message);    // eslint-disable-line no-console
+      if (!console[method]) {   // eslint-disable-line no-console
+        method = 'log';
+      }
+      console[method](...message);    // eslint-disable-line no-console
     }
   }
 };