Add ifshort linter (#1587)

Author: esimonov

Diff for: .golangci.example.yml

@@ -293,6 +293,12 @@ linters-settings:
     packages-with-error-message:
       # specify an error message to output when a blacklisted package is used
       - github.com/sirupsen/logrus: "logging is allowed only by logutils.Log"
+  ifshort:
+    # Maximum length of variable declaration measured in number of lines, after which linter won't suggest using short syntax. 
+    # Has higher priority than max-decl-chars.
+    max-decl-lines: 1
+    # Maximum length of variable declaration measured in number of characters, after which linter won't suggest using short syntax.
+    max-decl-chars: 30
   lll:
     # max line length, lines longer will be reported. Default is 120.
     # '\t' is counted as 1 character by default, and can be changed with the tab-width option

Diff for: go.mod

@@ -11,6 +11,7 @@ require (
 	github.com/bombsimon/wsl/v3 v3.1.0
 	github.com/daixiang0/gci v0.2.8
 	github.com/denis-tingajkin/go-header v0.4.2
+	github.com/esimonov/ifshort v1.0.0
 	github.com/fatih/color v1.10.0
 	github.com/go-critic/go-critic v0.5.3
 	github.com/go-xmlfmt/xmlfmt v0.0.0-20191208150333-d5b6f63a941b

Diff for: go.sum

@@ -270,6 +270,7 @@ type LintersSettings struct {
 	Makezero    MakezeroSettings
 	Thelper     ThelperSettings
 	Forbidigo   ForbidigoSettings
+	Ifshort     IfshortSettings
 	Predeclared PredeclaredSettings
 
 	Custom map[string]CustomLinterSettings
@@ -408,6 +409,11 @@ type ThelperSettings struct {
 	} `mapstructure:"benchmark"`
 }
 
+type IfshortSettings struct {
+	MaxDeclLines int `mapstructure:"max-decl-lines"`
+	MaxDeclChars int `mapstructure:"max-decl-chars"`
+}
+
 type ForbidigoSettings struct {
 	Forbid []string `mapstructure:"forbid"`
 }

Diff for: pkg/config/config.go

@@ -0,0 +1,17 @@
+package golinters
+
+import (
+	"github.com/esimonov/ifshort/pkg/analyzer"
+	"golang.org/x/tools/go/analysis"
+
+	"github.com/golangci/golangci-lint/pkg/golinters/goanalysis"
+)
+
+func NewIfshort() *goanalysis.Linter {
+	return goanalysis.NewLinter(
+		"ifshort",
+		"Checks that your code uses short syntax for if-statements whenever possible",
+		[]*analysis.Analyzer{analyzer.Analyzer},
+		nil,
+	).WithLoadMode(goanalysis.LoadModeSyntax)
+}

Diff for: pkg/golinters/ifshort.go

@@ -344,6 +344,9 @@ func (m Manager) GetAllSupportedLinterConfigs() []*linter.Config {
 		linter.NewConfig(golinters.NewForbidigo()).
 			WithPresets(linter.PresetStyle).
 			WithURL("https://github.com/ashanbrown/forbidigo"),
+		linter.NewConfig(golinters.NewIfshort()).
+			WithPresets(linter.PresetStyle).
+			WithURL("https://github.com/esimonov/ifshort"),
 		linter.NewConfig(golinters.NewPredeclared(predeclaredCfg)).
 			WithPresets(linter.PresetStyle).
 			WithURL("https://github.com/nishanths/predeclared"),

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

@@ -0,0 +1,11 @@
+//args: -Eifshort
+package testdata
+
+func DontUseShortSyntaxWhenPossible() {
+	getValue := func() interface{} { return nil }
+
+	v := getValue() // ERROR "variable 'v' is only used in the if-statement .*"
+	if v != nil {
+		return
+	}
+}