New rule: line-length-limit (mgechev#86)

* New rule: line-length-limit

* simplify the panic message of rule line-length-limit

* Refactors `line-length-limit` rule, use private `check` method instead of `Visit`

README.md

@@ -277,6 +277,7 @@ List of all available rules. The rules ported from `golint` are left unchanged a
 | `waitgroup-by-value`  |  n/a   | Warns on functions taking sync.WaitGroup as a by-value parameter |    no    |  no   |
 | `atomic`              |  n/a   | Check for common mistaken usages of the `sync/atomic` package    |    no    |  no   |
 | `empty-lines`   | n/a | Warns when there are heading or trailing newlines in a block              |    no    |  no   |
+| `line-lenght-limit`   | int    | Specifies the maximum number of characters in a line             |    no    |  no   |
 
 ## Configurable rules
 
@@ -410,4 +411,3 @@ Currently, type checking is enabled by default. If you want to run the linter wi
 ## License
 
 MIT
-

config.go

@@ -71,6 +71,7 @@ var allRules = append([]lint.Rule{
 	&rule.WaitGroupByValueRule{},
 	&rule.AtomicRule{},
 	&rule.EmptyLinesRule{},
+	&rule.LineLengthLimitRule{},
 }, defaultRules...)
 
 var allFormatters = []lint.Formatter{

fixtures/line-length-limit.go

@@ -0,0 +1,7 @@
+package fixtures
+
+import "fmt"
+
+func foo(a, b int) {
+	fmt.Printf("single line characters out of limit") // MATCH /line is 105 characters, out of limit 100/
+}

rule/line-length-limit.go

@@ -0,0 +1,85 @@
+package rule
+
+import (
+	"bufio"
+	"bytes"
+	"fmt"
+	"go/token"
+	"strings"
+	"unicode/utf8"
+
+	"github.com/mgechev/revive/lint"
+)
+
+// LineLengthLimitRule lints given else constructs.
+type LineLengthLimitRule struct{}
+
+// Apply applies the rule to given file.
+func (r *LineLengthLimitRule) Apply(file *lint.File, arguments lint.Arguments) []lint.Failure {
+	if len(arguments) != 1 {
+		panic(`invalid configuration for "line-length-limit"`)
+	}
+
+	max, ok := arguments[0].(int64) // Alt. non panicking version
+	if !ok || max < 0 {
+		panic(`invalid value passed as argument number to the "line-length-limit" rule`)
+	}
+
+	var failures []lint.Failure
+	checker := lintLineLengthNum{
+		max:  int(max),
+		file: file,
+		onFailure: func(failure lint.Failure) {
+			failures = append(failures, failure)
+		},
+	}
+
+	checker.check()
+
+	return failures
+}
+
+// Name returns the rule name.
+func (r *LineLengthLimitRule) Name() string {
+	return "line-length-limit"
+}
+
+type lintLineLengthNum struct {
+	max       int
+	file      *lint.File
+	onFailure func(lint.Failure)
+}
+
+func (r lintLineLengthNum) check() {
+	f := bytes.NewReader(r.file.Content())
+	spaces := strings.Repeat(" ", 4) // tab width = 4
+	l := 1
+	s := bufio.NewScanner(f)
+	for s.Scan() {
+		t := s.Text()
+		t = strings.Replace(t, "\t", spaces, -1)
+		c := utf8.RuneCountInString(t)
+		if c > r.max {
+			r.onFailure(lint.Failure{
+				Category: "code-style",
+				Position: lint.FailurePosition{
+					// Offset not set; it is non-trivial, and doesn't appear to be needed.
+					Start: token.Position{
+						Filename: r.file.Name,
+						Line:     l,
+						Column:   0,
+					},
+					End: token.Position{
+						Filename: r.file.Name,
+						Line:     l,
+						Column:   c,
+					},
+				},
+				Confidence: 1,
+				Failure:    fmt.Sprintf("line is %d characters, out of limit %d", c, r.max),
+				URL:        "",
+			})
+		}
+		l++
+	}
+}

test/line-length-limit_test.go

@@ -0,0 +1,14 @@
+package test
+
+import (
+	"testing"
+
+	"github.com/mgechev/revive/lint"
+	"github.com/mgechev/revive/rule"
+)
+
+func TestLineLengthLimit(t *testing.T) {
+	testRule(t, "line-length-limit", &rule.LineLengthLimitRule{}, &lint.RuleConfig{
+		Arguments: []interface{}{int64(100)},
+	})
+}

untyped.toml

@@ -16,3 +16,6 @@
 [rule.range-val-in-closure]
 [rule.waitgroup-by-value]
 [rule.atomic]
+[rule.empty-lines]
+[rule.line-length-limit]
+    arguments = [200]