h2. Issues

While reviewing/researching #25634 (and in its extend, r16501 & r16502 for #25503), I noticed three issues with the implementation - both pre and post r16568:

@Redmine::SyntaxHighlighting::CodeRay.language_supported?@ includes internal CodeRay scanners (@default@, @debug@, @raydebug@ & @scanner@)¶

@Redmine::SyntaxHighlighting::CodeRay.language_supported?@ has multiple responsibilities:¶

retrieval of the array of supported languages symbols from CodeRay library¶

storing of a reference to the resulting array in a local variable¶

checking if the passed @language@ argument is included in the array referenced by the local variable and return the result¶

the array containing supported languages symbols is rebuild for every invocation of @Redmine::SyntaxHighlighting::CodeRay.language_supported?@, ie. for each and every pre-formatted, syntax-highlighted code block (this seems a uselessly CPU-intensive approach since the array's values won't change unless Redmine is restarted)¶

h2. Fixes/changes

I've applied the following four changes to solve each of the three issues:

• change 1 (0001-Remove-internal-CodeRay-scanners.patch): remove the four internal CodeRay scanners by subtracting a hard-coded array containing the symbols of these scanners ** It does not seem to be possible to do this in a more dynamical way.
• change 2 (0002-Pull-up-retrieve_supported_languages-private-class-m.patch): pull-up a new @Redmine::SyntaxHighlighting::CodeRay.retrieve_supported_languages@ private class method (that doesn't store the result)
• change 3 (0003-Use-stored-ref.-to-array-holding-supported-languages.patch): use a stored reference to the resulting array — retrieved by @Redmine::SyntaxHighlighting::CodeRay.retrieve_supported_languages@, holding the supported languages symbols — via a constant[1] ** I think there are two ways of solving this: storing a reference to the resulting array 1) in a memoized instance variable or 2) in a constant. After some benchmarking[1] I decided to go with the constant-storage approach as it seems a tiny bit faster than the memoized instance variable storage approach. Though, both approaches are ~360-400 times faster than the approaches where the array is rebuild on every invocation of @Redmine::SyntaxHighlighting::CodeRay.language_supported?@.
• change 4 (0004-Tests-for-Redmine-SyntaxHighlighting-CodeRay.retriev.patch): add test-coverage for @Redmine::SyntaxHighlighting::CodeRay.retrieve_supported_languages@ and remove obsolete @ApplicationHelperTest#test_syntax_highlight_by_coderay_alias@ (there's no need to test through @textilizable@)

This patch serial, against current source:/trunk@16580, is produced using @git format-patch@, which makes the individual patches apply-able using "@patch -p1 < 0001-...@".

h2. Environment

Environment:
  Redmine version                3.3.3.devel@r16580
  Ruby version                   2.3.3-p222 (2016-11-21) [x86_64-linux]
  Rails version                  4.2.8
  Environment                    production
  Database adapter               Mysql2
SCM:
  Subversion                     1.8.8
  Git                            1.9.1
  Filesystem                     
Redmine plugins:
  no plugin installed

h2. Footnotes

fn1. I passed the following benchmark script to @rails runner -e production@:

puts "####################"

puts "Using benchmark:"

puts "####################"


puts

require 'benchmark'

Benchmark.bmbm do |x|

x.report(".language_supported_core_pre_25634?")  { 100.times do Redmine::SyntaxHighlighting::CodeRay.language_supported_core_pre_25634?('ruby') end }

x.report(".language_supported_core?")            { 100.times do Redmine::SyntaxHighlighting::CodeRay.language_supported_core?('ruby') end }

x.report(".language_supported_core_ext?")        { 100.times do Redmine::SyntaxHighlighting::CodeRay.language_supported_core_ext?('ruby') end }

x.report(".language_supported_core_ext_split?")  { 100.times do Redmine::SyntaxHighlighting::CodeRay.language_supported_core_ext_split?('ruby') end }

x.report(".language_supported_ivar_ext_split?")  { 100.times do Redmine::SyntaxHighlighting::CodeRay.language_supported_ivar_ext_split?('ruby') end }

x.report(".language_supported_const_ext_split?") { 100.times do Redmine::SyntaxHighlighting::CodeRay.language_supported_const_ext_split?('ruby') end }

end

puts

puts "####################"

puts "Using benchmark/ips:"

puts "####################"

puts

require 'benchmark/ips'

Benchmark.ips do |x|

  # Configure the number of seconds used during

  # the warmup phase (default 2) and calculation phase (default 5)

  x.config(:time => 5, :warmup => 2)

x.report(".language_supported_core_pre_25634?")  { 100.times do Redmine::SyntaxHighlighting::CodeRay.language_supported_core_pre_25634?('ruby') end }

  x.report(".language_supported_core?")            { 100.times do Redmine::SyntaxHighlighting::CodeRay.language_supported_core?('ruby') end }

  x.report(".language_supported_core_ext?")        { 100.times do Redmine::SyntaxHighlighting::CodeRay.language_supported_core_ext?('ruby') end }

  x.report(".language_supported_core_ext_split?")  { 100.times do Redmine::SyntaxHighlighting::CodeRay.language_supported_core_ext_split?('ruby') end }

  x.report(".language_supported_ivar_ext_split?")  { 100.times do Redmine::SyntaxHighlighting::CodeRay.language_supported_ivar_ext_split?('ruby') end }

  x.report(".language_supported_const_ext_split?") { 100.times do Redmine::SyntaxHighlighting::CodeRay.language_supported_const_ext_split?('ruby') end }

# Compare the iterations per second of the various reports

  x.compare!

end

####################

Using benchmark:

####################


Rehearsal ------------------------------------------------------------------------

.language_supported_core_pre_25634?    0.010000   0.010000   0.020000 (  0.017590)

.language_supported_core?              0.010000   0.000000   0.010000 (  0.018621)

.language_supported_core_ext?          0.020000   0.010000   0.030000 (  0.018680)

.language_supported_core_ext_split?    0.010000   0.000000   0.010000 (  0.018822)

.language_supported_ivar_ext_split?    0.000000   0.000000   0.000000 (  0.000302)

.language_supported_const_ext_split?   0.000000   0.000000   0.000000 (  0.000069)

--------------------------------------------------------------- total: 0.070000sec
                                       user     system      total        real

.language_supported_core_pre_25634?    0.030000   0.000000   0.030000 (  0.025548)

.language_supported_core?              0.010000   0.000000   0.010000 (  0.018236)

.language_supported_core_ext?          0.020000   0.000000   0.020000 (  0.018472)

.language_supported_core_ext_split?    0.020000   0.000000   0.020000 (  0.018835)

.language_supported_ivar_ext_split?    0.000000   0.000000   0.000000 (  0.000068)

.language_supported_const_ext_split?   0.000000   0.000000   0.000000 (  0.000049)

####################

Using benchmark/ips:

####################

Warming up --------------------------------------

.language_supported_core_pre_25634?

                         5.000  i/100ms

.language_supported_core?

                         5.000  i/100ms

.language_supported_core_ext?

                         4.000  i/100ms

.language_supported_core_ext_split?

                         4.000  i/100ms

.language_supported_ivar_ext_split?

                         1.763k i/100ms

.language_supported_const_ext_split?

                         2.084k i/100ms

Calculating -------------------------------------

.language_supported_core_pre_25634?

                         53.819  (± 5.6%) i/s -    270.000  in   5.035559s

.language_supported_core?

                         53.027  (± 5.7%) i/s -    265.000  in   5.015003s

.language_supported_core_ext?

                         50.711  (± 5.9%) i/s -    256.000  in   5.071990s

.language_supported_core_ext_split?

                         49.493  (± 8.1%) i/s -    248.000  in   5.055206s

.language_supported_ivar_ext_split?

                         17.443k (±10.2%) i/s -     86.387k in   5.011711s

.language_supported_const_ext_split?

                         19.710k (±11.7%) i/s -     97.948k in   5.045098s

Comparison:

.language_supported_const_ext_split?:  19710.5 i/s

.language_supported_ivar_ext_split?:   17443.3 i/s - same-ish: difference falls within error

.language_supported_core_pre_25634?:      53.8 i/s - 366.23x  slower

.language_supported_core?:                53.0 i/s - 371.71x  slower

.language_supported_core_ext?:            50.7 i/s - 388.68x  slower

.language_supported_core_ext_split?:      49.5 i/s - 398.24x  slower

fn2. including six different implementations looking like:
|. Nr. |. Method |. Description |. Abbreviated implementation code |
| 1. | @Redmine::SyntaxHighlighting::CodeRay.language_supported_core_pre_25634?@ | state of trunk, pre #25634 | View abbreviated implementation...View abbreviated implementation...

      class << self
        ...

        def language_supported_core_pre_25634?(language)
          ::CodeRay::Scanners.list.include?(language.to_s.downcase.to_sym)
        rescue
          false
        end
      end

      class << self
        ...

        def language_supported_core?(language)
          supported_languages =
            ::CodeRay::Scanners.list +
            ::CodeRay::Scanners.plugin_hash.keys.map(&:to_sym)
          supported_languages.include?(language.to_s.downcase.to_sym)
        rescue
          false
        end
      end

      class << self
        ...

        def language_supported_core_ext?(language)
          supported_languages =
            ::CodeRay::Scanners.list +
            ::CodeRay::Scanners.plugin_hash.keys.map(&:to_sym) -
            %w(debug default raydebug scanner).map(&:to_sym)
          supported_languages.include?(language.to_s.downcase.to_sym)
        rescue
          false
        end
      end

      def self.retrieve_supported_languages
        ::CodeRay::Scanners.list +
        # Add CodeRay scanner aliases
        ::CodeRay::Scanners.plugin_hash.keys.map(&:to_sym) -
        # Remove internal CodeRay scanners
        %w(debug default raydebug scanner).map(&:to_sym)
      end
      private_class_method :retrieve_supported_languages

      class << self
        ...

        def language_supported_core_ext_split?(language)
          supported_languages = retrieve_supported_languages
          supported_languages.include?(language.to_s.downcase.to_sym)
        rescue
          false
        end
      end

      def self.retrieve_supported_languages
        ::CodeRay::Scanners.list +
        # Add CodeRay scanner aliases
        ::CodeRay::Scanners.plugin_hash.keys.map(&:to_sym) -
        # Remove internal CodeRay scanners
        %w(debug default raydebug scanner).map(&:to_sym)
      end
      private_class_method :retrieve_supported_languages

      class << self
        ...

        def language_supported_ivar_ext_split?(language)
          @supported_languages ||= retrieve_supported_languages
          @supported_languages.include?(language.to_s.downcase.to_sym)
        rescue
          false
        end

      def self.retrieve_supported_languages
        ::CodeRay::Scanners.list +
        # Add CodeRay scanner aliases
        ::CodeRay::Scanners.plugin_hash.keys.map(&:to_sym) -
        # Remove internal CodeRay scanners
        %w(debug default raydebug scanner).map(&:to_sym)
      end
      private_class_method :retrieve_supported_languages

      SUPPORTED_LANGUAGES = retrieve_supported_languages

      class << self
        ...

        def language_supported_const_ext_split?(language)
          SUPPORTED_LANGUAGES.include?(language.to_s.downcase.to_sym)
        rescue
          false
        end