Fix #10, don't highlight everything

Only highlight, if a highlighting rule exists. This will of course
still highlight everything, if the user so desires.

src/config/rule.rs

@@ -54,6 +54,10 @@ impl Rule {
         (all_adds_empty || any_add) && !any_sub
     }
 
+    pub fn is_non_empty_match(&self, meal: &MealComplete) -> bool {
+        !self.is_empty() && self.is_match(meal)
+    }
+
     pub fn joined(self, other: Self) -> Self {
         Self {
             name: self.name.joined(other.name),
@@ -61,9 +65,17 @@ impl Rule {
             category: self.category.joined(other.category),
         }
     }
+
+    pub fn is_empty(&self) -> bool {
+        self.name.is_empty() && self.tag.is_empty() && self.category.is_empty()
+    }
 }
 
 impl TagRule {
+    pub fn is_empty(&self) -> bool {
+        self.add.is_empty() && self.sub.is_empty()
+    }
+
     fn is_match_add(&self, meal: &MealComplete) -> bool {
         self.add.iter().any(|tag| meal.meta.tags.contains(tag))
     }
@@ -101,6 +113,10 @@ impl RegexRule {
         Self { add, sub }
     }
 
+    pub fn is_empty(&self) -> bool {
+        self.add.is_none() && self.sub.is_none()
+    }
+
     fn is_match_add(&self, meal: &MealComplete) -> bool {
         match self.add {
             Some(ref rset) => rset.is_match(&meal.meta.category),

src/meal/mod.rs

@@ -103,7 +103,7 @@ impl Meal {
                     for meal in meals {
                         let complete = meal.complete()?;
                         if filter.is_match(&complete) {
-                            let is_fav = favs.is_match(&complete);
+                            let is_fav = favs.is_non_empty_match(&complete);
                             println!("{}", *PRE);
                             complete.print(is_fav);
                             printed_at_least_one_meal = true;