6 files changed, 31 insertions, 15 deletions
diff --git a/lib/logger/errors.rb b/lib/logger/errors.rb
index e8925e14ac..88581793f0 100644
--- a/lib/logger/errors.rb
+++ b/lib/logger/errors.rb
@@ -1,7 +1,7 @@
 # frozen_string_literal: true
 
-# not used after 1.2.7. just for compat.
 class Logger
+  # not used after 1.2.7. just for compat.
   class Error < RuntimeError # :nodoc:
   end
   class ShiftingError < Error # :nodoc:
diff --git a/lib/logger/formatter.rb b/lib/logger/formatter.rb
index 6a135b6fab..c634dbf34d 100644
--- a/lib/logger/formatter.rb
+++ b/lib/logger/formatter.rb
@@ -3,7 +3,8 @@
 class Logger
   # Default formatter for log messages.
   class Formatter
-    Format = "%s, [%s#%d] %5s -- %s: %s\n"
+    Format = "%.1s, [%s #%d] %5s -- %s: %s\n"
+    DatetimeFormat = "%Y-%m-%dT%H:%M:%S.%6N"
 
     attr_accessor :datetime_format
 
@@ -12,14 +13,13 @@ class Logger
     end
 
     def call(severity, time, progname, msg)
-      Format % [severity[0..0], format_datetime(time), Process.pid, severity, progname,
-        msg2str(msg)]
+      sprintf(Format, severity, format_datetime(time), Process.pid, severity, progname, msg2str(msg))
     end
 
   private
 
     def format_datetime(time)
-      time.strftime(@datetime_format || "%Y-%m-%dT%H:%M:%S.%6N ")
+      time.strftime(@datetime_format || DatetimeFormat)
     end
 
     def msg2str(msg)
diff --git a/lib/logger/log_device.rb b/lib/logger/log_device.rb
index 96d77b7b6a..84277a2656 100644
--- a/lib/logger/log_device.rb
+++ b/lib/logger/log_device.rb
@@ -79,8 +79,10 @@ class Logger
     def set_dev(log)
       if log.respond_to?(:write) and log.respond_to?(:close)
         @dev = log
-        if log.respond_to?(:path)
-          @filename = log.path
+        if log.respond_to?(:path) and path = log.path
+          if File.exist?(path)
+            @filename = path
+          end
         end
       else
         @dev = open_logfile(log)
@@ -135,7 +137,7 @@ class Logger
       end
     end
 
-    if /mswin|mingw|cygwin/ =~ RUBY_PLATFORM
+    if /mswin|mingw|cygwin/ =~ RbConfig::CONFIG['host_os']
       def lock_shift_log
         yield
       end
diff --git a/lib/logger/logger.gemspec b/lib/logger/logger.gemspec
index ccd4e70db7..5e8232e4ab 100644
--- a/lib/logger/logger.gemspec
+++ b/lib/logger/logger.gemspec
@@ -18,10 +18,5 @@ Gem::Specification.new do |spec|
   spec.files         = Dir.glob("lib/**/*.rb") + ["logger.gemspec"]
   spec.require_paths = ["lib"]
 
-  spec.required_ruby_version = ">= 2.3.0"
-
-  spec.add_development_dependency "bundler", ">= 0"
-  spec.add_development_dependency "rake", ">= 12.3.3"
-  spec.add_development_dependency "test-unit"
-  spec.add_development_dependency "rdoc"
+  spec.required_ruby_version = ">= 2.5.0"
 end
diff --git a/lib/logger/severity.rb b/lib/logger/severity.rb
index b38afb7d22..e96fb0d320 100644
--- a/lib/logger/severity.rb
+++ b/lib/logger/severity.rb
@@ -15,5 +15,24 @@ class Logger
     FATAL = 4
     # An unknown message that should always be logged.
     UNKNOWN = 5
+
+    LEVELS = {
+      "debug" => DEBUG,
+      "info" => INFO,
+      "warn" => WARN,
+      "error" => ERROR,
+      "fatal" => FATAL,
+      "unknown" => UNKNOWN,
+    }
+    private_constant :LEVELS
+
+    def self.coerce(severity)
+      if severity.is_a?(Integer)
+        severity
+      else
+        key = severity.to_s.downcase
+        LEVELS[key] || raise(ArgumentError, "invalid log level: #{severity}")
+      end
+    end
   end
 end
diff --git a/lib/logger/version.rb b/lib/logger/version.rb
index e0f71830d2..202b6e4fba 100644
--- a/lib/logger/version.rb
+++ b/lib/logger/version.rb
@@ -1,5 +1,5 @@
 # frozen_string_literal: true
 
 class Logger
-  VERSION = "1.4.3"
+  VERSION = "1.6.0"
 end