lint: add elseif checker v1 (#80)

Fixes #77

cmd/kfulint/lint_test.go

@@ -43,6 +43,7 @@ var tests = []*struct {
 	{"parenthesis"},
 	{"param-duplication"},
 	{"underef"},
+	{"elseif"},
 	{"big-copy"},
 	{"long-chain"},
 }

cmd/kfulint/testdata/elseif/checker_tests.go

@@ -0,0 +1,66 @@
+package checker_test
+
+func noWarnings() {
+	cond1 := true
+	cond2 := true
+
+	if cond1 {
+	}
+
+	if cond1 {
+	} else {
+	}
+
+	if cond1 {
+	} else if cond2 {
+	}
+}
+
+func suggestSwitch() {
+	cond1 := true
+	cond2 := true
+	cond3 := true
+
+	///: should rewrite if-else to switch statement
+	if cond1 {
+	} else if cond2 {
+	} else {
+	}
+
+	///: should rewrite if-else to switch statement
+	if cond1 {
+	} else if cond2 {
+	} else if cond3 {
+	}
+
+	///: should rewrite if-else to switch statement
+	if cond1 {
+	} else if cond2 {
+	} else if cond3 {
+	} else {
+	}
+
+	///: should rewrite if-else to switch statement
+	if cond1 {
+	} else if cond2 {
+		if cond3 {
+		}
+	} else {
+		// Assume that top if-else statement warning is enough.
+		if cond1 {
+		} else if cond2 {
+		} else {
+		}
+	}
+}
+
+func describeInt(x int) string {
+	///: should rewrite if-else to switch statement
+	if x == 0 {
+		return "zero"
+	} else if x < 0 {
+		return "negative"
+	} else {
+		return "positive"
+	}
+}

lint/elseif_checker.go

@@ -0,0 +1,68 @@
+package lint
+
+import (
+	"fmt"
+	"go/ast"
+)
+
+type elseifChecker struct {
+	ctx *Context
+
+	rootStmt ast.Stmt
+}
+
+func newElseifChecker(ctx *Context) Checker {
+	return &elseifChecker{ctx: ctx}
+}
+
+// Check finds repeated if-else statements and suggests to replace
+// them with switch statement.
+//
+// Features
+//
+// Permits single else or else-if; repeated else-if or else + else-if
+// will trigger suggestion to use switch statement.
+func (c *elseifChecker) Check(f *ast.File) {
+	ast.Inspect(f, func(x ast.Node) bool {
+		if stmt, ok := x.(*ast.IfStmt); ok {
+			c.rootStmt = stmt
+			return !c.checkIfStmt(stmt)
+		}
+		return true
+	})
+}
+
+func (c *elseifChecker) checkIfStmt(stmt *ast.IfStmt) bool {
+	const minThreshold = 2
+	if c.countIfelseLen(stmt) >= minThreshold {
+		c.warn()
+		return true
+	}
+	return false
+}
+
+func (c *elseifChecker) countIfelseLen(stmt *ast.IfStmt) int {
+	count := 0
+	for {
+		switch e := stmt.Else.(type) {
+		case *ast.IfStmt:
+			// Else if.
+			stmt = e
+			count++
+		case *ast.BlockStmt:
+			// Else branch.
+			return count + 1
+		default:
+			// No else or else if.
+			return count
+		}
+	}
+}
+
+func (c *elseifChecker) warn() {
+	c.ctx.addWarning(Warning{
+		Kind: "elseif",
+		Node: c.rootStmt,
+		Text: fmt.Sprintf("should rewrite if-else to switch statement"),
+	})
+}

lint/lint.go

@@ -63,6 +63,7 @@ var checkers = map[string]func(c *Context) Checker{
 	"parenthesis":       newParenthesisChecker,
 	"underef":           newUnderefChecker,
 	"param-duplication": newParamDuplicationChecker,
+	"elseif":            newElseifChecker,
 	"big-copy":          newBigCopyChecker,
 	"long-chain":        newLongChainChecker,
 }