logging/filter: Use std::string_view in ParseFilterString()

Allows avoiding constructing std::string instances, since this only
reads an arbitrary sequence of characters.

We can also make ParseFilterRule() internal, since it doesn't depend on
any private instance state of Filter

src/common/logging/filter.cpp

@@ -8,39 +8,9 @@
 #include "common/string_util.h"
 
 namespace Log {
-
-Filter::Filter(Level default_level) {
-    ResetAll(default_level);
-}
-
-void Filter::ResetAll(Level level) {
-    class_levels.fill(level);
-}
-
-void Filter::SetClassLevel(Class log_class, Level level) {
-    class_levels[static_cast<size_t>(log_class)] = level;
-}
-
-void Filter::ParseFilterString(const std::string& filter_str) {
-    auto clause_begin = filter_str.cbegin();
-    while (clause_begin != filter_str.cend()) {
-        auto clause_end = std::find(clause_begin, filter_str.cend(), ' ');
-
-        // If clause isn't empty
-        if (clause_end != clause_begin) {
-            ParseFilterRule(clause_begin, clause_end);
-        }
-
-        if (clause_end != filter_str.cend()) {
-            // Skip over the whitespace
-            ++clause_end;
-        }
-        clause_begin = clause_end;
-    }
-}
-
+namespace {
 template <typename It>
-static Level GetLevelByName(const It begin, const It end) {
+Level GetLevelByName(const It begin, const It end) {
     for (u8 i = 0; i < static_cast<u8>(Level::Count); ++i) {
         const char* level_name = GetLevelName(static_cast<Level>(i));
         if (Common::ComparePartialString(begin, end, level_name)) {
@@ -51,7 +21,7 @@ static Level GetLevelByName(const It begin, const It end) {
 }
 
 template <typename It>
-static Class GetClassByName(const It begin, const It end) {
+Class GetClassByName(const It begin, const It end) {
     for (ClassType i = 0; i < static_cast<ClassType>(Class::Count); ++i) {
         const char* level_name = GetLogClassName(static_cast<Class>(i));
         if (Common::ComparePartialString(begin, end, level_name)) {
@@ -61,8 +31,8 @@ static Class GetClassByName(const It begin, const It end) {
     return Class::Count;
 }
 
-bool Filter::ParseFilterRule(const std::string::const_iterator begin,
-                             const std::string::const_iterator end) {
+template <typename Iterator>
+bool ParseFilterRule(Filter& instance, Iterator begin, Iterator end) {
     auto level_separator = std::find(begin, end, ':');
     if (level_separator == end) {
         LOG_ERROR(Log, "Invalid log filter. Must specify a log level after `:`: {}",
@@ -77,7 +47,7 @@ bool Filter::ParseFilterRule(const std::string::const_iterator begin,
     }
 
     if (Common::ComparePartialString(begin, level_separator, "*")) {
-        ResetAll(level);
+        instance.ResetAll(level);
         return true;
     }
 
@@ -87,9 +57,40 @@ bool Filter::ParseFilterRule(const std::string::const_iterator begin,
         return false;
     }
 
-    SetClassLevel(log_class, level);
+    instance.SetClassLevel(log_class, level);
     return true;
 }
+} // Anonymous namespace
+
+Filter::Filter(Level default_level) {
+    ResetAll(default_level);
+}
+
+void Filter::ResetAll(Level level) {
+    class_levels.fill(level);
+}
+
+void Filter::SetClassLevel(Class log_class, Level level) {
+    class_levels[static_cast<size_t>(log_class)] = level;
+}
+
+void Filter::ParseFilterString(std::string_view filter_view) {
+    auto clause_begin = filter_view.cbegin();
+    while (clause_begin != filter_view.cend()) {
+        auto clause_end = std::find(clause_begin, filter_view.cend(), ' ');
+
+        // If clause isn't empty
+        if (clause_end != clause_begin) {
+            ParseFilterRule(*this, clause_begin, clause_end);
+        }
+
+        if (clause_end != filter_view.cend()) {
+            // Skip over the whitespace
+            ++clause_end;
+        }
+        clause_begin = clause_end;
+    }
+}
 
 bool Filter::CheckMessage(Class log_class, Level level) const {
     return static_cast<u8>(level) >= static_cast<u8>(class_levels[static_cast<size_t>(log_class)]);

src/common/logging/filter.h

@@ -6,7 +6,7 @@
 
 #include <array>
 #include <cstddef>
-#include <string>
+#include <string_view>
 #include "common/logging/log.h"
 
 namespace Log {
@@ -40,9 +40,7 @@ public:
      *  - `Service:Info` -- Sets the level of Service to Info.
      *  - `Service.FS:Trace` -- Sets the level of the Service.FS class to Trace.
      */
-    void ParseFilterString(const std::string& filter_str);
-    bool ParseFilterRule(const std::string::const_iterator start,
-                         const std::string::const_iterator end);
+    void ParseFilterString(std::string_view filter_view);
 
     /// Matches class/level combination against the filter, returning true if it passed.
     bool CheckMessage(Class log_class, Level level) const;