refs #76: enhance filtering by tags.

* support multiple tags, e.g. `list -t google -t tree`
* tested with 'company' plugin 2017.12.18

Signed-off-by: Eric Wang <skygragon@gmail.com>

Author: skygragon

lib/commands/list.js

@@ -30,10 +30,10 @@ var cmd = {
       default:  false,
       describe: 'Show problems statistics'
     },
-    tag: {
+    tags: {
       alias:    't',
-      type:     'string',
-      default:  '',
+      type:     'array',
+      default:  [],
       describe: 'Filter problems by tags'
     }
   }
@@ -70,6 +70,12 @@ var QUERY_HANDLERS = {
   S: _.negate(byStarred)
 };
 
+function hasTag(o, tag) {
+  return _.isArray(o) && _.some(o, function(x) {
+    return x.indexOf(tag.toLowerCase()) !== -1;
+  });
+}
+
 cmd.handler = function(argv) {
   session.argv = argv;
   core.getProblems(function(e, problems) {
@@ -86,15 +92,14 @@ cmd.handler = function(argv) {
       });
     }
 
-    if (argv.tag) {
-      var tag = argv.tag.toLowerCase();
+    argv.tags.forEach(function(tag) {
       // TODO: fill company/tags in problems
-      problems = _.filter(problems, function(x) {
-        return x.category === tag ||
-          (_.isArray(x.companies) && x.companies.indexOf(tag) !== -1) ||
-          (_.isArray(x.tags) && x.tags.indexOf(tag) !== -1);
+      problems = _.filter(problems, function(p) {
+        return p.category === tag ||
+          hasTag(p.companies, tag) ||
+          hasTag(p.tags, tag);
       });
-    }
+    });
 
     var word = String(argv.keyword).toLowerCase();
     if (word) {