Add BibTeX lexer (rouge-ruby#1360)

This commit adds a lexer for BibTeX.

Co-authored-by: Alex Liheng Wang <alw1@GS17003.SP.CS.CMU.EDU>
Co-authored-by: Michael Camilleri <mike@inqk.net>

lib/rouge/demos/bibtex

@@ -0,0 +1,12 @@
+@article{Witten:1988hf,
+      author         = "Witten, Edward",
+      title          = "{Quantum Field Theory and the Jones Polynomial}",
+      journal        = "Commun. Math. Phys.",
+      volume         = "121",
+      year           = "1989",
+      pages          = "351-399",
+      doi            = "10.1007/BF01217730",
+      note           = "[,233(1988)]",
+      reportNumber   = "IASSNS-HEP-88-33",
+      SLACcitation   = "%%CITATION = CMPHA,121,351;%%"
+}

lib/rouge/lexers/bibtex.rb

@@ -0,0 +1,115 @@
+# -*- coding: utf-8 -*- #
+# frozen_string_literal: true
+
+# Regular expressions based on https://github.com/SaswatPadhi/prismjs-bibtex
+# and https://github.com/alecthomas/chroma/blob/master/lexers/b/bibtex.go
+
+module Rouge
+  module Lexers
+    class BibTeX < RegexLexer
+      title 'BibTeX'
+      desc "BibTeX"
+      tag 'bibtex'
+      aliases 'bib'
+      filenames '*.bib'
+
+      valid_punctuation = Regexp.quote("@!$&.\\:;<>?[]^`|~*/+-")
+      valid_name = /[a-z_#{valid_punctuation}][\w#{valid_punctuation}]*/io
+
+      state :root do
+        mixin :whitespace
+
+        rule %r/@(#{valid_name})/o do |m|
+          match = m[1].downcase
+
+          if match == "comment"
+            token Comment
+          elsif match == "preamble"
+            token Name::Class
+            push :closing_brace
+            push :value
+            push :opening_brace
+          elsif match == "string"
+            token Name::Class
+            push :closing_brace
+            push :field
+            push :opening_brace
+          else
+            token Name::Class
+            push :closing_brace
+            push :command_body
+            push :opening_brace
+          end
+        end
+
+        rule %r/.+/, Comment
+      end
+
+      state :opening_brace do
+        mixin :whitespace
+        rule %r/[{(]/, Punctuation, :pop!
+      end
+
+      state :closing_brace do
+        mixin :whitespace
+        rule %r/[})]/, Punctuation, :pop!
+      end
+
+      state :command_body do
+        mixin :whitespace
+        rule %r/[^\s\,\}]+/ do
+          token Name::Label
+          pop!
+          push :fields
+        end
+      end
+
+      state :fields do
+        mixin :whitespace
+        rule %r/,/, Punctuation, :field
+        rule(//) { pop! }
+      end
+
+      state :field do
+        mixin :whitespace
+        rule valid_name do
+          token Name::Attribute
+          push :value
+          push :equal_sign
+        end
+        rule(//) { pop! }
+      end
+
+      state :equal_sign do
+        mixin :whitespace
+        rule %r/=/, Punctuation, :pop!
+      end
+
+      state :value do
+        mixin :whitespace
+        rule valid_name, Name::Variable
+        rule %r/"/, Literal::String, :quoted_string
+        rule %r/\{/, Literal::String, :braced_string
+        rule %r/\d+/, Literal::Number
+        rule %r/#/, Punctuation
+        rule(//) { pop! }
+      end
+
+      state :quoted_string do
+        rule %r/\{/, Literal::String, :braced_string
+        rule %r/"/, Literal::String, :pop!
+        rule %r/[^\{\"]+/, Literal::String
+      end
+
+      state :braced_string do
+        rule %r/\{/, Literal::String, :braced_string
+        rule %r/\}/, Literal::String, :pop!
+        rule %r/[^\{\}]+/, Literal::String
+      end
+
+      state :whitespace do
+        rule %r/\s+/, Text
+      end
+    end
+  end
+end

spec/lexers/bibtex_spec.rb

@@ -0,0 +1,15 @@
+# -*- coding: utf-8 -*- #
+# frozen_string_literal: true
+
+describe Rouge::Lexers::BibTeX do
+  let(:subject) { Rouge::Lexers::BibTeX.new }
+
+  describe 'guessing' do
+    include Support::Guessing
+
+    it 'guesses by filename' do
+      assert_guess :filename => 'foo.bib'
+    end
+  end
+end
+

spec/visual/samples/bibtex

@@ -0,0 +1,68 @@
+%%% Bibtex comment
+
+@inproceedings{DBLP:conf/pldi/PadhiSM16,
+  author    = {Saswat Padhi and
+               Rahul Sharma and
+               Todd D. Millstein},
+  title     = {Data-driven precondition inference with learned features},
+  booktitle = {Proceedings of the 37th {ACM} {SIGPLAN} Conference on Programming
+               Language Design and Implementation, {PLDI} 2016, Santa Barbara, CA,
+               USA, June 13-17, 2016},
+  pages     = {42--56},
+  year      = {2016},
+  crossref  = {DBLP:conf/pldi/2016},
+  url       = {https://doi.org/10.1145/2908080.2908099},
+  doi       = {10.1145/2908080.2908099},
+  timestamp = {Tue, 06 Nov 2018 16:59:30 +0100},
+  biburl    = {https://dblp.org/rec/bib/conf/pldi/PadhiSM16},
+  bibsource = {dblp computer science bibliography, https://dblp.org}
+}
+
+@article{article,
+  author  = {Peter Adams},
+  title   = {The title of the work},
+  journal = {The name of the journal},
+  year    = 1993,
+  number  = 2,
+  pages   = {201-213},
+  month   = 7,
+  note    = {An optional note},
+  volume  = 4
+}
+
+@MISC{WEBSITE:1,
+  HOWPUBLISHED = "\url{http://example.com}",
+  AUTHOR = "Intel",
+  TITLE = "Example Website",
+  MONTH = "Dec",
+  YEAR = "1988",
+  NOTE = "Accessed on 2012-11-11"
+}
+
+@STRING(PRL="Phys. Rev. Lett.")
+@STRING(RMP="Rev. Mod. Phys.")
+
+@ARTICLE{klitzing:nobel,
+   AUTHOR="Klaus von Klitzing",
+   TITLE="The Quantised Hall Effect",
+   JOURNAL=RMP,
+   VOLUME=58,
+   PAGES=519,
+   YEAR=1986
+}
+
+@preamble{ "\newcommand{\mytext}{Last accessed:}" }
+
+@ARTICLE{knuth:1974,
+  author = {Knuth, Donald E.},
+  title = {{C}omputer {P}rogramming as an {A}rt},
+  journal = {Communications of the ACM},
+  year = {1974},
+  volume = {17},
+  pages = {667--673},
+  number = {12},
+  month = {December },
+  address = {New York, NY, USA},
+  publisher = {ACM Press},
+  note = {\mytext{} 09/20/12}
+}