refactor: FilterParser (#4925)

* Make explainIllType anonymous/static
* Comment constructor

src/controllers/filters/lang/FilterParser.cpp

@@ -9,7 +9,9 @@
 #include "controllers/filters/lang/Filter.hpp"
 #include "controllers/filters/lang/Types.hpp"
 
-namespace chatterino::filters {
+namespace {
+
+using namespace chatterino::filters;
 
 QString explainIllType(const IllTyped &ill)
 {
@@ -18,6 +20,10 @@ QString explainIllType(const IllTyped &ill)
         .arg(ill.expr->filterString());
 }
 
+}  // namespace
+
+namespace chatterino::filters {
+
 FilterParser::FilterParser(const QString &text)
     : text_(text)
     , tokenizer_(Tokenizer(text))

src/controllers/filters/lang/FilterParser.hpp

@@ -9,6 +9,9 @@ namespace chatterino::filters {
 class FilterParser
 {
 public:
+    /**
+     * Take input text & attempt to parse it into a filter
+     **/
     FilterParser(const QString &text);
 
     bool valid() const;