feat: add 'each .. of ..' syntax to support all iterable objects (inc…

…luding Arrays) (pugjs#3179)

index.js

@@ -971,6 +971,39 @@ Lexer.prototype = {
     }
   },
 
+  /**
+   * EachOf.
+   */
+
+  eachOf: function() {
+    var captures;
+    if (captures = /^(?:each|for) (.*) of *([^\n]+)/.exec(this.input)) {
+      this.consume(captures[0].length);
+      var tok = this.tok('eachOf', captures[1]);
+      tok.value = captures[1];
+      this.incrementColumn(captures[0].length - captures[2].length);
+      this.assertExpression(captures[2])
+      tok.code = captures[2];
+      this.incrementColumn(captures[2].length);
+      this.tokens.push(this.tokEnd(tok));
+
+      if (!(/^[a-zA-Z_$][\w$]*$/.test(tok.value.trim()) || /^\[ *[a-zA-Z_$][\w$]* *\, *[a-zA-Z_$][\w$]* *\]$/.test(tok.value.trim()))) {
+        this.error(
+          'MALFORMED_EACH_OF_LVAL',
+          'The value variable for each must either be a valid identifier (e.g. `item`) or a pair of identifiers in square brackets (e.g. `[key, value]`).'
+        );
+      }
+
+      return true;
+    }
+    if (captures = /^- *(?:each|for) +([a-zA-Z_$][\w$]*)(?: *, *([a-zA-Z_$][\w$]*))? +of +([^\n]+)/.exec(this.input)) {
+      this.error(
+        'MALFORMED_EACH',
+        'Pug each and for should not be prefixed with a dash ("-"). They are pug keywords and not part of JavaScript.'
+      );
+    }
+  },
+
   /**
    * Code.
    */
@@ -1485,6 +1518,7 @@ Lexer.prototype = {
       || this.callLexerFunction('mixin')
       || this.callLexerFunction('call')
       || this.callLexerFunction('conditional')
+      || this.callLexerFunction('eachOf')
       || this.callLexerFunction('each')
       || this.callLexerFunction('while')
       || this.callLexerFunction('tag')

test/check-lexer-functions.test.js

@@ -23,6 +23,7 @@ var lexerFunctions = {
   doctype: true,
   dot: true,
   each: true,
+  eachOf: true,
   eos: true,
   endInterpolation: true,
   extends: true,