Add dogsled linter. (#705)

Author: tpounds

Diff for: .golangci.example.yml

@@ -201,6 +201,9 @@ linters-settings:
       - NOTE
       - OPTIMIZE # marks code that should be optimized before merging
       - HACK # marks hack-arounds that should be removed before merging
+  dogsled:
+    # checks assignments with too many blank identifiers; default is 2
+    max-blank-identifiers: 2
 
 linters:
   enable:

Diff for: .golangci.yml

@@ -49,6 +49,7 @@ linters:
     - bodyclose
     - deadcode
     - depguard
+    # - dogsled - TODO: enable it when golangci.com will support it.
     - dupl
     - errcheck
     # - funlen - TODO: enable it when golangci.com will support it.

Diff for: README.md

@@ -195,6 +195,7 @@ $ golangci-lint help linters
 Disabled by default linters:
 bodyclose: checks whether HTTP response body is closed successfully [fast: false, auto-fix: false]
 depguard: Go linter that checks if package imports are in a list of acceptable packages [fast: true, auto-fix: false]
+dogsled: Checks assignments with too many blank identifiers (e.g. x, _, _, _, := f()) [fast: true, auto-fix: false]
 dupl: Tool for code clone detection [fast: true, auto-fix: false]
 funlen: Tool for detection of long functions [fast: true, auto-fix: false]
 gochecknoglobals: Checks that no globals are present in Go code [fast: true, auto-fix: false]
@@ -454,6 +455,7 @@ golangci-lint help linters
 - [misspell](https://github.com/client9/misspell) - Finds commonly misspelled English words in comments
 - [lll](https://github.com/walle/lll) - Reports long lines
 - [unparam](https://github.com/mvdan/unparam) - Reports unused function parameters
+- [dogsled](https://github.com/alexkohler/dogsled) - Checks assignments with too many blank identifiers (e.g. x, _, _, _, := f())
 - [nakedret](https://github.com/alexkohler/nakedret) - Finds naked returns in functions greater than a specified function length
 - [prealloc](https://github.com/alexkohler/prealloc) - Finds slice declarations that could potentially be preallocated
 - [scopelint](https://github.com/kyoh86/scopelint) - Scopelint checks for unpinned variables in go programs
@@ -783,6 +785,9 @@ linters-settings:
       - NOTE
       - OPTIMIZE # marks code that should be optimized before merging
       - HACK # marks hack-arounds that should be removed before merging
+  dogsled:
+    # checks assignments with too many blank identifiers; default is 2
+    max-blank-identifiers: 2
 
 linters:
   enable:
@@ -916,6 +921,7 @@ linters:
     - bodyclose
     - deadcode
     - depguard
+    # - dogsled - TODO: enable it when golangci.com will support it.
     - dupl
     - errcheck
     # - funlen - TODO: enable it when golangci.com will support it.

Diff for: pkg/config/config.go

@@ -178,6 +178,7 @@ type LintersSettings struct {
 	Errcheck ErrcheckSettings
 	Gocritic GocriticSettings
 	Godox    GodoxSettings
+	Dogsled  DogsledSettings
 }
 
 type GovetSettings struct {
@@ -234,6 +235,10 @@ type GodoxSettings struct {
 	Keywords []string
 }
 
+type DogsledSettings struct {
+	MaxBlankIdentifiers int `mapstructure:"max-blank-identifiers"`
+}
+
 var defaultLintersSettings = LintersSettings{
 	Lll: LllSettings{
 		LineLength: 120,
@@ -256,6 +261,9 @@ var defaultLintersSettings = LintersSettings{
 	Godox: GodoxSettings{
 		Keywords: []string{},
 	},
+	Dogsled: DogsledSettings{
+		MaxBlankIdentifiers: 2,
+	},
 }
 
 type Linters struct {

Diff for: pkg/golinters/dogsled.go

@@ -0,0 +1,79 @@
+package golinters
+
+import (
+	"context"
+	"fmt"
+	"go/ast"
+	"go/token"
+
+	"github.com/golangci/golangci-lint/pkg/lint/linter"
+	"github.com/golangci/golangci-lint/pkg/result"
+)
+
+type Dogsled struct{}
+
+func (Dogsled) Name() string {
+	return "dogsled"
+}
+
+func (Dogsled) Desc() string {
+	return "Checks assignments with too many blank identifiers (e.g. x, _, _, _, := f())"
+}
+
+func (d Dogsled) Run(ctx context.Context, lintCtx *linter.Context) ([]result.Issue, error) {
+
+	var res []result.Issue
+	for _, f := range lintCtx.ASTCache.GetAllValidFiles() {
+		v := returnsVisitor{
+			maxBlanks: lintCtx.Settings().Dogsled.MaxBlankIdentifiers,
+			f:         f.Fset,
+		}
+		ast.Walk(&v, f.F)
+		res = append(res, v.issues...)
+	}
+
+	return res, nil
+}
+
+type returnsVisitor struct {
+	f         *token.FileSet
+	maxBlanks int
+	issues    []result.Issue
+}
+
+func (v *returnsVisitor) Visit(node ast.Node) ast.Visitor {
+	funcDecl, ok := node.(*ast.FuncDecl)
+	if !ok {
+		return v
+	}
+	if funcDecl.Body == nil {
+		return v
+	}
+
+	for _, expr := range funcDecl.Body.List {
+		assgnStmt, ok := expr.(*ast.AssignStmt)
+		if !ok {
+			continue
+		}
+
+		numBlank := 0
+		for _, left := range assgnStmt.Lhs {
+			ident, ok := left.(*ast.Ident)
+			if !ok {
+				continue
+			}
+			if ident.Name == "_" {
+				numBlank++
+			}
+		}
+
+		if numBlank > v.maxBlanks {
+			v.issues = append(v.issues, result.Issue{
+				FromLinter: Dogsled{}.Name(),
+				Text:       fmt.Sprintf("declaration has %v blank identifiers", numBlank),
+				Pos:        v.f.Position(assgnStmt.Pos()),
+			})
+		}
+	}
+	return v
+}

Diff for: pkg/lint/lintersdb/manager.go

@@ -215,6 +215,10 @@ func (m Manager) GetAllSupportedLinterConfigs() []*linter.Config {
 			WithLoadDepsTypeInfo().
 			WithSSA().
 			WithURL("https://github.com/mvdan/unparam"),
+		linter.NewConfig(golinters.Dogsled{}).
+			WithPresets(linter.PresetStyle).
+			WithSpeed(10).
+			WithURL("https://github.com/alexkohler/dogsled"),
 		linter.NewConfig(golinters.Nakedret{}).
 			WithPresets(linter.PresetComplexity).
 			WithSpeed(10).

Diff for: test/testdata/dogsled.go

@@ -0,0 +1,25 @@
+//args: -Edogsled
+package testdata
+
+func Dogsled() {
+	_ = ret1()
+	_, _ = ret2()
+	_, _, _ = ret3()    // ERROR "declaration has 3 blank identifiers"
+	_, _, _, _ = ret4() // ERROR "declaration has 4 blank identifiers"
+}
+
+func ret1() (a int) {
+	return 1
+}
+
+func ret2() (a, b int) {
+	return 1, 2
+}
+
+func ret3() (a, b, c int) {
+	return 1, 2, 3
+}
+
+func ret4() (a, b, c, d int) {
+	return 1, 2, 3, 4
+}

Diff for: third_party/dogsled/LICENSE

@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2018 Alex Kohler
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.