Optimize preparation of options for Rouge

[ashmaroli]

Summary

• Replace array allocation [span_opts, block_opts] for every method call with serial calls to an extracted module method.
• Replace use of Hash#update and a static {:wrap=>false} with a direct mutation via Hash#[]= to avoid allocating {:wrap=>false} on every method call.
• Since hash.keys allocates an array even for empty hashes, add a guard-clause.

Benchmark

(on Ruby 2.4, Windows)

highlighter options:  {:default_lang=>"plaintext", :guess_lang=>true}
Warming up --------------------------------------
     master     6.134k i/100ms
   proposed     7.358k i/100ms
Calculating -------------------------------------
     master     70.786k (A± 4.1%) i/s -    355.772k in   5.034089s
   proposed     89.577k (A± 4.7%) i/s -    448.838k in   5.021782s

Comparison:
   proposed:    89577.2 i/s
     master:    70786.3 i/s - 1.27x  slower

highlighter options:  {:default_lang=>"plaintext", :guess_lang=>true, :span=>{"foo"=>"bar"}, :block=>{"lorem"=>"ipsum"}}
Warming up --------------------------------------
     master     3.521k i/100ms
   proposed     3.737k i/100ms
Calculating -------------------------------------
     master     40.721k (A± 5.2%) i/s -    204.218k in   5.028392s
   proposed     43.369k (A± 8.7%) i/s -    216.746k in   5.030135s

Comparison:
   proposed:    43369.5 i/s
     master:    40720.8 i/s - same-ish: difference falls within error

Memory profiles

highlighter options:  {:default_lang=>"plaintext", :guess_lang=>true}

memory-profile with master code through 1000 iterations

Total allocated: 1.24 MB (12000 objects)
Total retained:  576.00 B (3 objects)

memory-profile with proposed code through 1000 iterations

Total allocated: 848.00 kB (6000 objects)
Total retained:  576.00 B (3 objects)

highlighter options:  {:default_lang=>"plaintext", :guess_lang=>true, :span=>{"foo"=>"bar"}, :block=>{"lorem"=>"ipsum"}}

memory-profile with master code through 1000 iterations

Total allocated: 1.72 MB (14006 objects)
Total retained:  736.00 B (7 objects)

memory-profile with proposed code through 1000 iterations

Total allocated: 1.49 MB (12006 objects)
Total retained:  736.00 B (7 objects)

[gettalong]

Thank you!