lexers: add one for groff

Generated from Pygments one, some filename extensions added.

Author: scop

Diff for: README.md

@@ -41,7 +41,7 @@ C | C, C#, C++, Caddyfile, Caddyfile Directives, Cap'n Proto, Cassandra CQL, Cey
 D | D, Dart, Diff, Django/Jinja, Docker, DTD, Dylan
 E | EBNF, Elixir, Elm, EmacsLisp, Erlang
 F | Factor, Fish, Forth, Fortran, FSharp
-G | GAS, GDScript, Genshi, Genshi HTML, Genshi Text, Gherkin, GLSL, Gnuplot, Go, Go HTML Template, Go Text Template, GraphQL, Groovy
+G | GAS, GDScript, Genshi, Genshi HTML, Genshi Text, Gherkin, GLSL, Gnuplot, Go, Go HTML Template, Go Text Template, GraphQL, Groff, Groovy
 H | Handlebars, Haskell, Haxe, HCL, Hexdump, HLB, HTML, HTTP, Hy
 I | Idris, Igor, INI, Io
 J | J, Java, JavaScript, JSON, Julia, Jungle

Diff for: lexers/g/groff.go

@@ -0,0 +1,47 @@
+package g
+
+import (
+	. "github.com/alecthomas/chroma" // nolint
+	"github.com/alecthomas/chroma/lexers/internal"
+)
+
+// Groff lexer.
+var Groff = internal.Register(MustNewLazyLexer(
+	&Config{
+		Name:      "Groff",
+		Aliases:   []string{"groff", "nroff", "man"},
+		Filenames: []string{"*.[1-9]", "*.1p", "*.3pm", "*.man"},
+		MimeTypes: []string{"application/x-troff", "text/troff"},
+	},
+	func() Rules {
+		return Rules{
+			"root": {
+				{`(\.)(\w+)`, ByGroups(Text, Keyword), Push("request")},
+				{`\.`, Punctuation, Push("request")},
+				{`[^\\\n]+`, Text, Push("textline")},
+				Default(Push("textline")),
+			},
+			"textline": {
+				Include("escapes"),
+				{`[^\\\n]+`, Text, nil},
+				{`\n`, Text, Pop(1)},
+			},
+			"escapes": {
+				{`\\"[^\n]*`, Comment, nil},
+				{`\\[fn]\w`, LiteralStringEscape, nil},
+				{`\\\(.{2}`, LiteralStringEscape, nil},
+				{`\\.\[.*\]`, LiteralStringEscape, nil},
+				{`\\.`, LiteralStringEscape, nil},
+				{`\\\n`, Text, Push("request")},
+			},
+			"request": {
+				{`\n`, Text, Pop(1)},
+				Include("escapes"),
+				{`"[^\n"]+"`, LiteralStringDouble, nil},
+				{`\d+`, LiteralNumber, nil},
+				{`\S+`, LiteralString, nil},
+				{`\s+`, Text, nil},
+			},
+		}
+	},
+))