Add C lexer (#815)

lexers/c.go

@@ -0,0 +1,37 @@
+package lexers
+
+import (
+	"regexp"
+
+	. "github.com/alecthomas/chroma/v2" // nolint
+)
+
+var (
+	cAnalyserIncludeRe = regexp.MustCompile(`(?m)^\s*#include [<"]`)
+	cAnalyserIfdefRe   = regexp.MustCompile(`(?m)^\s*#ifn?def `)
+)
+
+// C lexer.
+var C = Register(MustNewXMLLexer(
+	embedded,
+	"embedded/c.xml",
+).SetConfig(
+	&Config{
+		Name:      "C",
+		Aliases:   []string{"c"},
+		Filenames: []string{"*.c", "*.h", "*.idc", "*.x[bp]m"},
+		MimeTypes: []string{"text/x-chdr", "text/x-csrc", "image/x-xbitmap", "image/x-xpixmap"},
+		EnsureNL:  true,
+		Priority:  0.1,
+	},
+).SetAnalyser(func(text string) float32 {
+	if cAnalyserIncludeRe.MatchString(text) {
+		return 0.1
+	}
+
+	if cAnalyserIfdefRe.MatchString(text) {
+		return 0.1
+	}
+
+	return 0
+}))

lexers/c_test.go

@@ -0,0 +1,44 @@
+package lexers_test
+
+import (
+	"io/ioutil"
+	"testing"
+
+	"github.com/alecthomas/chroma/v2"
+	"github.com/alecthomas/chroma/v2/lexers"
+
+	"github.com/alecthomas/assert/v2"
+)
+
+func TestC_AnalyseText(t *testing.T) {
+	tests := map[string]struct {
+		Filepath string
+		Expected float32
+	}{
+		"include": {
+			Filepath: "testdata/c_include.c",
+			Expected: 0.1,
+		},
+		"ifdef": {
+			Filepath: "testdata/c_ifdef.c",
+			Expected: 0.1,
+		},
+		"ifndef": {
+			Filepath: "testdata/c_ifndef.c",
+			Expected: 0.1,
+		},
+	}
+
+	for name, test := range tests {
+		test := test
+		t.Run(name, func(t *testing.T) {
+			data, err := ioutil.ReadFile(test.Filepath)
+			assert.NoError(t, err)
+
+			analyser, ok := lexers.C.(chroma.Analyser)
+			assert.True(t, ok)
+
+			assert.Equal(t, test.Expected, analyser.AnalyseText(string(data)))
+		})
+	}
+}

lexers/testdata/c_ifdef.c

@@ -0,0 +1,2 @@
+
+#ifdef DEBUG

lexers/testdata/c_ifndef.c

@@ -0,0 +1,2 @@
+
+#ifndef DEBUG

lexers/testdata/c_include.c

@@ -0,0 +1,2 @@
+
+#include <stdio.h>