feat: add file-length-limit rule

Author: alexandear

README.md

@@ -540,6 +540,7 @@ List of all available rules. The rules ported from `golint` are left unchanged a
 | [`enforce-repeated-arg-type-style`](./RULES_DESCRIPTIONS.md#enforce-repeated-arg-type-style) |  string (defaults to "any")  |  Enforces consistent style for repeated argument and/or return value types. |    no    |  no   |
 | [`max-control-nesting`](./RULES_DESCRIPTIONS.md#max-control-nesting) |  int (defaults to 5)  | Sets restriction for maximum nesting of control structures. |    no    |  no   |
 | [`comments-density`](./RULES_DESCRIPTIONS.md#comments-density) |  int (defaults to 0)  | Enforces a minimum comment / code relation |    no    |  no   |
+| [`file-length-limit`](./RULES_DESCRIPTIONS.md#file-length-limit) | map (optional)| Enforces a maximum number of lines per file |    no    |  no   |
 
 
 ## Configurable rules

RULES_DESCRIPTIONS.md

@@ -38,6 +38,7 @@ List of all available rules.
   - [errorf](#errorf)
   - [exported](#exported)
   - [file-header](#file-header)
+  - [file-length-limit](#file-length-limit)
   - [flag-parameter](#flag-parameter)
   - [function-length](#function-length)
   - [function-result-limit](#function-result-limit)
@@ -501,6 +502,23 @@ Example:
   arguments = ["This is the text that must appear at the top of source files."]
 ```
 
+## file-length-limit
+
+_Description_: This rule enforces a maximum number of lines per file, in order to aid in maintainability and reduce complexity.
+
+_Configuration_:
+
+* `max` (int) a maximum number of lines in a file (default 500)
+* `skipComments` (bool) ignore lines containing just comments
+* `skipBlankLines` (bool) ignore lines made up purely of whitespace
+
+Example:
+
+```toml
+[rule.file-length-limit]
+  arguments = [{max=100,skipComments=true,skipBlankLines=true}]
+```
+
 ## flag-parameter
 
 _Description_: If a function controls the flow of another by passing it information on what to do, both functions are said to be [control-coupled](https://en.wikipedia.org/wiki/Coupling_(computer_programming)#Procedural_programming).

config/config.go

@@ -96,6 +96,7 @@ var allRules = append([]lint.Rule{
 	&rule.EnforceSliceStyleRule{},
 	&rule.MaxControlNestingRule{},
 	&rule.CommentsDensityRule{},
+	&rule.FileLengthLimitRule{},
 }, defaultRules...)
 
 var allFormatters = []lint.Formatter{

rule/file-length-limit.go

@@ -0,0 +1,125 @@
+package rule
+
+import (
+	"bufio"
+	"bytes"
+	"fmt"
+	"go/ast"
+	"go/token"
+	"strings"
+	"sync"
+
+	"github.com/mgechev/revive/lint"
+)
+
+const defaultFileLengthLimitMax = 500
+
+// FileLengthLimitRule lints the number of lines in a file.
+type FileLengthLimitRule struct {
+	max            int
+	skipComments   bool
+	skipBlankLines bool
+	sync.Mutex
+}
+
+// Apply applies the rule to given file.
+func (r *FileLengthLimitRule) Apply(file *lint.File, arguments lint.Arguments) []lint.Failure {
+	r.configure(arguments)
+
+	all := 0
+	blank := 0
+	scanner := bufio.NewScanner(bytes.NewReader(file.Content()))
+	for scanner.Scan() {
+		all++
+		if len(scanner.Bytes()) == 0 {
+			blank++
+		}
+	}
+
+	if err := scanner.Err(); err != nil {
+		panic(err.Error())
+	}
+
+	lines := all
+	if r.skipComments {
+		lines -= countCommentLines(file.AST.Comments)
+	}
+
+	if r.skipBlankLines {
+		lines -= blank
+	}
+
+	if lines <= r.max {
+		return nil
+	}
+
+	return []lint.Failure{
+		{
+			Category:   "code-style",
+			Confidence: 1,
+			Position: lint.FailurePosition{
+				Start: token.Position{
+					Filename: file.Name,
+					Line:     all,
+				},
+			},
+			Failure: fmt.Sprintf("file length is %d lines, which exceeds the limit of %d", lines, r.max),
+		},
+	}
+}
+
+func (r *FileLengthLimitRule) configure(arguments lint.Arguments) {
+	r.Lock()
+	defer r.Unlock()
+
+	if len(arguments) == 0 {
+		r.max = defaultFileLengthLimitMax
+		return
+	}
+
+	argKV, ok := arguments[0].(map[string]any)
+	if !ok {
+		panic(fmt.Sprintf(`invalid argument to the "file-length-limit" rule. Expecting a k,v map, got %T`, arguments[0]))
+	}
+	for k, v := range argKV {
+		switch k {
+		case "max":
+			maxLines, ok := v.(int64)
+			if !ok || maxLines < 1 {
+				panic(fmt.Sprintf(`invalid configuration value for max lines in "file-length-limit" rule; need int64 but got %T`, arguments[0]))
+			}
+			r.max = int(maxLines)
+		case "skipComments":
+			skipComments, ok := v.(bool)
+			if !ok {
+				panic(fmt.Sprintf(`invalid configuration value for skip comments in "file-length-limit" rule; need bool but got %T`, arguments[1]))
+			}
+			r.skipComments = skipComments
+		case "skipBlankLines":
+			skipBlankLines, ok := v.(bool)
+			if !ok {
+				panic(fmt.Sprintf(`invalid configuration value for skip blank lines in "file-length-limit" rule; need bool but got %T`, arguments[2]))
+			}
+			r.skipBlankLines = skipBlankLines
+		}
+	}
+}
+
+func (*FileLengthLimitRule) Name() string {
+	return "file-length-limit"
+}
+
+func countCommentLines(comments []*ast.CommentGroup) int {
+	count := 0
+	for _, cg := range comments {
+		for _, comment := range cg.List {
+			switch comment.Text[1] {
+			case '/': // single-line comment
+				count++
+			case '*': // multi-line comment
+				count += strings.Count(comment.Text, "\n") + 1
+			}
+		}
+	}
+	return count
+}

test/file-length-limit_test.go

@@ -0,0 +1,26 @@
+package test
+
+import (
+	"testing"
+
+	"github.com/mgechev/revive/lint"
+	"github.com/mgechev/revive/rule"
+)
+
+func TestFileLengthLimit(t *testing.T) {
+	testRule(t, "file-length-limit-default", &rule.FileLengthLimitRule{}, &lint.RuleConfig{
+		Arguments: []any{},
+	})
+	testRule(t, "file-length-limit-9", &rule.FileLengthLimitRule{}, &lint.RuleConfig{
+		Arguments: []any{map[string]any{"max": int64(9)}},
+	})
+	testRule(t, "file-length-limit-7-skip-comments", &rule.FileLengthLimitRule{}, &lint.RuleConfig{
+		Arguments: []any{map[string]any{"max": int64(7), "skipComments": true}},
+	})
+	testRule(t, "file-length-limit-6-skip-blank", &rule.FileLengthLimitRule{}, &lint.RuleConfig{
+		Arguments: []any{map[string]any{"max": int64(6), "skipBlankLines": true}},
+	})
+	testRule(t, "file-length-limit-4-skip-comments-skip-blank", &rule.FileLengthLimitRule{}, &lint.RuleConfig{
+		Arguments: []any{map[string]any{"max": int64(4), "skipComments": true, "skipBlankLines": true}},
+	})
+}

testdata/file-length-limit-4-skip-comments-skip-blank.go

@@ -0,0 +1,10 @@
+package fixtures
+
+import "fmt"
+
+// Foo is a function.
+func Foo(a, b int) {
+	fmt.Println("Hello, world!")
+}
+
+// MATCH /file length is 5 lines, which exceeds the limit of 4/

testdata/file-length-limit-6-skip-blank.go

@@ -0,0 +1,10 @@
+package fixtures
+
+import "fmt"
+
+// Foo is a function.
+func Foo(a, b int) {
+	fmt.Println("Hello, world!")
+}
+
+// MATCH /file length is 7 lines, which exceeds the limit of 6/

testdata/file-length-limit-7-skip-comments.go

@@ -0,0 +1,20 @@
+package fixtures
+
+import "fmt"
+
+// Foo is a function.
+func Foo(a, b int) {
+	// This
+	/* is
+	a
+	*/
+	// a comment.
+	fmt.Println("Hello, world!")
+	/*
+		This is
+		multiline
+		comment.
+	*/
+}
+
+// MATCH /file length is 8 lines, which exceeds the limit of 7/

testdata/file-length-limit-9.go

@@ -0,0 +1,10 @@
+package fixtures
+
+import "fmt"
+
+// Foo is a function.
+func Foo(a, b int) {
+	fmt.Println("Hello, world!")
+}
+
+// MATCH /file length is 10 lines, which exceeds the limit of 9/