From 0404d6654828bebd20ab489124ed8d0a8c02838b Mon Sep 17 00:00:00 2001
From: SalvadorC <salvadorcavadini+github@gmail.com>
Date: Sat, 28 Jul 2018 07:38:39 +0200
Subject: [PATCH] unnecessary-stmt (new rule) (#45)

* simpler (new rule)

* simpler: checks unitary switches

* unnecessary-stmt (new rule)
---
 README.md                     |   1 +
 config.go                     |   1 +
 fixtures/unnecessary-stmt.go  |  49 ++++++++++++++++
 rule/unnecessary-stmt.go      | 107 ++++++++++++++++++++++++++++++++++
 test/unnecessary-stmt_test.go |  12 ++++
 5 files changed, 170 insertions(+)
 create mode 100644 fixtures/unnecessary-stmt.go
 create mode 100644 rule/unnecessary-stmt.go
 create mode 100644 test/unnecessary-stmt_test.go

diff --git a/README.md b/README.md
index 18246d1..6db1147 100644
--- a/README.md
+++ b/README.md
@@ -261,6 +261,7 @@ List of all available rules. The rules ported from `golint` are left unchanged a
 | `unreachable-code`    |  n/a   | Warns on unreachable code                                        |    no    |  no   |
 | `add-constant`        |  map   | Suggests using constant for magic numbers and string literals    |    no    |  no   |
 | `flag-parameter`      |  n/a   | Warns on boolean parameters that create a control coupling       |    no    |  no   |
+| `unnecessary-stmt`    |  n/a   | Suggests removing or simplifying unnecessary statements          |    no    |  no   |
 
 ## Available Formatters
 
diff --git a/config.go b/config.go
index 805b3b5..2379693 100644
--- a/config.go
+++ b/config.go
@@ -58,6 +58,7 @@ var allRules = append([]lint.Rule{
 	&rule.UnreachableCodeRule{},
 	&rule.AddConstantRule{},
 	&rule.FlagParamRule{},
+	&rule.UnnecessaryStmtRule{},
 }, defaultRules...)
 
 var allFormatters = []lint.Formatter{
diff --git a/fixtures/unnecessary-stmt.go b/fixtures/unnecessary-stmt.go
new file mode 100644
index 0000000..9969a8a
--- /dev/null
+++ b/fixtures/unnecessary-stmt.go
@@ -0,0 +1,49 @@
+package fixtures
+
+func foo(a, b, c, d int) {
+	switch n := node.(type) { // MATCH /switch with only one case can be replaced by an if-then/
+	case *ast.SwitchStmt:
+		caseSelector := func(n ast.Node) bool {
+			_, ok := n.(*ast.CaseClause)
+			return ok
+		}
+		cases := pick(n.Body, caseSelector, nil)
+		if len(cases) == 1 {
+			cs, ok := cases[0].(*ast.CaseClause)
+			if ok && len(cs.List) == 1 {
+				w.onFailure(lint.Failure{
+					Confidence: 1,
+					Node:       n,
+					Category:   "style",
+					Failure:    "switch can be replaced by an if-then",
+				})
+			}
+		}
+	}
+}
+
+func bar() {
+	a := 1
+
+	switch a {
+	case 1, 2:
+		a++
+	}
+
+loop:
+	for {
+		switch a {
+		case 1:
+			a++
+			println("one")
+			break // MATCH /omit unnecessary break at the end of case clause/
+		case 2:
+			println("two")
+			break loop
+		default:
+			println("default")
+		}
+	}
+
+	return // MATCH /omit unnecessary return statement/
+}
diff --git a/rule/unnecessary-stmt.go b/rule/unnecessary-stmt.go
new file mode 100644
index 0000000..50379bf
--- /dev/null
+++ b/rule/unnecessary-stmt.go
@@ -0,0 +1,107 @@
+package rule
+
+import (
+	"go/ast"
+	"go/token"
+
+	"github.com/mgechev/revive/lint"
+)
+
+// UnnecessaryStmtRule warns on unnecessary statements.
+type UnnecessaryStmtRule struct{}
+
+// Apply applies the rule to given file.
+func (r *UnnecessaryStmtRule) Apply(file *lint.File, arguments lint.Arguments) []lint.Failure {
+	var failures []lint.Failure
+	onFailure := func(failure lint.Failure) {
+		failures = append(failures, failure)
+	}
+
+	w := lintUnnecessaryStmtRule{onFailure}
+	ast.Walk(w, file.AST)
+	return failures
+}
+
+// Name returns the rule name.
+func (r *UnnecessaryStmtRule) Name() string {
+	return "unnecessary-stmt"
+}
+
+type lintUnnecessaryStmtRule struct {
+	onFailure func(lint.Failure)
+}
+
+func (w lintUnnecessaryStmtRule) Visit(node ast.Node) ast.Visitor {
+	switch n := node.(type) {
+	case *ast.FuncDecl:
+		if n.Body == nil || n.Type.Results != nil {
+			return w
+		}
+		stmts := n.Body.List
+		if len(stmts) == 0 {
+			return w
+		}
+
+		lastStmt := stmts[len(stmts)-1]
+		rs, ok := lastStmt.(*ast.ReturnStmt)
+		if !ok {
+			return w
+		}
+
+		if len(rs.Results) == 0 {
+			w.newFailure(lastStmt, "omit unnecessary return statement")
+		}
+
+	case *ast.SwitchStmt:
+		w.checkSwitchBody(n.Body)
+	case *ast.TypeSwitchStmt:
+		w.checkSwitchBody(n.Body)
+	case *ast.CaseClause:
+		if n.Body == nil {
+			return w
+		}
+		stmts := n.Body
+		if len(stmts) == 0 {
+			return w
+		}
+
+		lastStmt := stmts[len(stmts)-1]
+		rs, ok := lastStmt.(*ast.BranchStmt)
+		if !ok {
+			return w
+		}
+
+		if rs.Tok == token.BREAK && rs.Label == nil {
+			w.newFailure(lastStmt, "omit unnecessary break at the end of case clause")
+		}
+	}
+
+	return w
+}
+
+func (w lintUnnecessaryStmtRule) checkSwitchBody(b *ast.BlockStmt) {
+	cases := b.List
+	if len(cases) != 1 {
+		return
+	}
+
+	cc, ok := cases[0].(*ast.CaseClause)
+	if !ok {
+		return
+	}
+
+	if len(cc.List) > 1 { // skip cases with multiple expressions
+		return
+	}
+
+	w.newFailure(b, "switch with only one case can be replaced by an if-then")
+}
+
+func (w lintUnnecessaryStmtRule) newFailure(node ast.Node, msg string) {
+	w.onFailure(lint.Failure{
+		Confidence: 1,
+		Node:       node,
+		Category:   "style",
+		Failure:    msg,
+	})
+}
diff --git a/test/unnecessary-stmt_test.go b/test/unnecessary-stmt_test.go
new file mode 100644
index 0000000..577a8aa
--- /dev/null
+++ b/test/unnecessary-stmt_test.go
@@ -0,0 +1,12 @@
+package test
+
+import (
+	"testing"
+
+	"github.com/mgechev/revive/rule"
+)
+
+// TestUnnecessaryStmt rule.
+func TestUnnecessaryStmt(t *testing.T) {
+	testRule(t, "unnecessary-stmt", &rule.UnnecessaryStmtRule{})
+}