Add iface linter (#4871)

Co-authored-by: Fernandez Ludovic <ldez@users.noreply.github.com>

Author: uudashr

.golangci.next.reference.yml

@@ -63,6 +63,7 @@ linters:
     - gosmopolitan
     - govet
     - grouper
+    - iface
     - importas
     - inamedparam
     - ineffassign
@@ -178,6 +179,7 @@ linters:
     - gosmopolitan
     - govet
     - grouper
+    - ifcae
     - importas
     - inamedparam
     - ineffassign
@@ -1928,6 +1930,20 @@ linters-settings:
     # Default: false
     var-require-grouping: true
 
+  iface:
+    # List of analyzers.
+    # Default: ["identical"]
+    enable:
+      - identical # Identifies interfaces in the same package that have identical method sets.
+      - unused # Identifies interfaces that are not used anywhere in the same package where the interface is defined.
+      - opaque # Identifies functions that return interfaces, but the actual returned value is always a single concrete implementation.
+    settings:
+      unused:
+        # List of packages path to exclude from the check.
+        # Default: []
+        exclude:
+          - github.com/example/log
+
   importas:
     # Do not allow unaliased imports of aliased packages.
     # Default: false

go.mod

@@ -116,6 +116,7 @@ require (
 	github.com/ultraware/funlen v0.1.0
 	github.com/ultraware/whitespace v0.1.1
 	github.com/uudashr/gocognit v1.1.3
+	github.com/uudashr/iface v1.2.0
 	github.com/valyala/quicktemplate v1.8.0
 	github.com/xen0n/gosmopolitan v1.2.2
 	github.com/yagipy/maintidx v1.0.0

go.sum

@@ -295,6 +295,13 @@
         "waitgroup-by-value"
       ]
     },
+    "iface-analyzers": {
+      "enum": [
+        "identical",
+        "unused",
+        "opaque"
+      ]
+    },
     "linters": {
       "$comment": "anyOf with enum is used to allow auto completion of non-custom linters",
       "description": "Linters usable.",
@@ -356,6 +363,7 @@
             "gosmopolitan",
             "govet",
             "grouper",
+            "iface",
             "ifshort",
             "importas",
             "inamedparam",
@@ -1922,6 +1930,37 @@
             }
           }
         },
+        "iface": {
+          "type": "object",
+          "additionalProperties": false,
+          "properties": {
+            "enable": {
+              "description": "Enable analyzers by name.",
+              "type": "array",
+              "items": {
+                "$ref": "#/definitions/iface-analyzers"
+              }
+            },
+            "settings": {
+              "type": "object",
+              "additionalProperties": false,
+              "properties": {
+                "unused": {
+                  "type": "object",
+                  "additionalProperties": false,
+                  "properties": {
+                    "exclude": {
+                      "type": "array",
+                      "items": {
+                        "type": "string"
+                      }
+                    }
+                  }
+                }
+              }
+            }
+          }
+        },
         "importas": {
           "type": "object",
           "additionalProperties": false,

jsonschema/golangci.next.jsonschema.json

@@ -237,6 +237,7 @@ type LintersSettings struct {
 	Gosmopolitan    GosmopolitanSettings
 	Govet           GovetSettings
 	Grouper         GrouperSettings
+	Iface           IfaceSettings
 	ImportAs        ImportAsSettings
 	Inamedparam     INamedParamSettings
 	InterfaceBloat  InterfaceBloatSettings
@@ -656,6 +657,11 @@ type GrouperSettings struct {
 	VarRequireGrouping        bool `mapstructure:"var-require-grouping"`
 }
 
+type IfaceSettings struct {
+	Enable   []string                  `mapstructure:"enable"`
+	Settings map[string]map[string]any `mapstructure:"settings"`
+}
+
 type ImportAsSettings struct {
 	Alias          []ImportAsAlias
 	NoUnaliased    bool `mapstructure:"no-unaliased"`

pkg/config/linters_settings.go

@@ -0,0 +1,57 @@
+package iface
+
+import (
+	"slices"
+
+	"github.com/uudashr/iface/identical"
+	"github.com/uudashr/iface/opaque"
+	"github.com/uudashr/iface/unused"
+	"golang.org/x/tools/go/analysis"
+
+	"github.com/golangci/golangci-lint/pkg/config"
+	"github.com/golangci/golangci-lint/pkg/goanalysis"
+)
+
+func New(settings *config.IfaceSettings) *goanalysis.Linter {
+	var conf map[string]map[string]any
+	if settings != nil {
+		conf = settings.Settings
+	}
+
+	return goanalysis.NewLinter(
+		"iface",
+		"Detect the incorrect use of interfaces, helping developers avoid interface pollution.",
+		analyzersFromSettings(settings),
+		conf,
+	).WithLoadMode(goanalysis.LoadModeTypesInfo)
+}
+
+func analyzersFromSettings(settings *config.IfaceSettings) []*analysis.Analyzer {
+	allAnalyzers := map[string]*analysis.Analyzer{
+		"identical": identical.Analyzer,
+		"unused":    unused.Analyzer,
+		"opaque":    opaque.Analyzer,
+	}
+
+	if settings == nil || len(settings.Enable) == 0 {
+		// Default enable `identical` analyzer only
+		return []*analysis.Analyzer{identical.Analyzer}
+	}
+
+	var analyzers []*analysis.Analyzer
+	for _, name := range uniqueNames(settings.Enable) {
+		if _, ok := allAnalyzers[name]; !ok {
+			// skip unknown analyzer
+			continue
+		}
+
+		analyzers = append(analyzers, allAnalyzers[name])
+	}
+
+	return analyzers
+}
+
+func uniqueNames(names []string) []string {
+	slices.Sort(names)
+	return slices.Compact(names)
+}

pkg/golinters/iface/iface.go

@@ -0,0 +1,11 @@
+package iface
+
+import (
+	"testing"
+
+	"github.com/golangci/golangci-lint/test/testshared/integration"
+)
+
+func TestFromTestdata(t *testing.T) {
+	integration.RunTestdata(t)
+}

pkg/golinters/iface/iface_integration_test.go

@@ -0,0 +1,68 @@
+//golangcitest:args -Eiface
+//golangcitest:config_path testdata/iface_all.yml
+package testdata
+
+import "fmt"
+
+// identical
+
+type Pinger interface { // want "identical: interface Pinger contains identical methods or type constraints from another interface, causing redundancy"
+	Ping() error
+}
+
+type Healthcheck interface { // want "identical: interface Healthcheck contains identical methods or type constraints from another interface, causing redundancy"
+	Ping() error
+}
+
+// opaque
+
+type Server interface {
+	Serve() error
+}
+
+type server struct {
+	addr string
+}
+
+func (s server) Serve() error {
+	return nil
+}
+
+func NewServer(addr string) Server { // want "opaque: NewServer function return Server interface at the 1st result, abstract a single concrete implementation of \\*server"
+	return &server{addr: addr}
+}
+
+// unused
+
+type User struct {
+	ID   string
+	Name string
+}
+
+type UserRepository interface { // want "unused: interface UserRepository is declared but not used within the package"
+	UserOf(id string) (*User, error)
+}
+
+type UserRepositorySQL struct {
+}
+
+func (r *UserRepositorySQL) UserOf(id string) (*User, error) {
+	return nil, nil
+}
+
+type Granter interface {
+	Grant(permission string) error
+}
+
+func AllowAll(g Granter) error {
+	return g.Grant("all")
+}
+
+type Allower interface {
+	Allow(permission string) error
+}
+
+func Allow(x any) {
+	_ = x.(Allower)
+	fmt.Println("allow")
+}

pkg/golinters/iface/testdata/iface_all.go

@@ -0,0 +1,6 @@
+linters-settings:
+  iface:
+    enable:
+      - unused
+      - identical
+      - opaque

pkg/golinters/iface/testdata/iface_all.yml

@@ -0,0 +1,67 @@
+//golangcitest:args -Eiface
+package testdata
+
+import "fmt"
+
+// identical
+
+type Pinger interface { // want "identical: interface Pinger contains identical methods or type constraints from another interface, causing redundancy"
+	Ping() error
+}
+
+type Healthcheck interface { // want "identical: interface Healthcheck contains identical methods or type constraints from another interface, causing redundancy"
+	Ping() error
+}
+
+// opaque
+
+type Server interface {
+	Serve() error
+}
+
+type server struct {
+	addr string
+}
+
+func (s server) Serve() error {
+	return nil
+}
+
+func NewServer(addr string) Server {
+	return &server{addr: addr}
+}
+
+// unused
+
+type User struct {
+	ID   string
+	Name string
+}
+
+type UserRepository interface {
+	UserOf(id string) (*User, error)
+}
+
+type UserRepositorySQL struct {
+}
+
+func (r *UserRepositorySQL) UserOf(id string) (*User, error) {
+	return nil, nil
+}
+
+type Granter interface {
+	Grant(permission string) error
+}
+
+func AllowAll(g Granter) error {
+	return g.Grant("all")
+}
+
+type Allower interface {
+	Allow(permission string) error
+}
+
+func Allow(x any) {
+	_ = x.(Allower)
+	fmt.Println("allow")
+}