checkers: refactor and fix hexLiteral checker (go-critic#789)

Also renamed it from hexLiterals to hexLiteral.

Fixes go-critic#780

Signed-off-by: Iskander Sharipov <[email protected]>

checkers/hexLiteral_checker.go

@@ -0,0 +1,60 @@
+package checkers
+
+import (
+	"go/ast"
+	"go/token"
+	"strings"
+
+	"github.com/go-lintpack/lintpack"
+	"github.com/go-lintpack/lintpack/astwalk"
+	"github.com/go-toolsmith/astcast"
+)
+
+func init() {
+	var info lintpack.CheckerInfo
+	info.Name = "hexLiteral"
+	info.Tags = []string{"style", "experimental"}
+	info.Summary = ""
+	info.Before = `
+x := 0X12
+y := 0xfF`
+	info.After = `
+x := 0x12
+// (A)
+y := 0xff
+// (B)
+y := 0xFF`
+
+	collection.AddChecker(&info, func(ctx *lintpack.CheckerContext) lintpack.FileWalker {
+		return astwalk.WalkerForExpr(&hexLiteralChecker{ctx: ctx})
+	})
+}
+
+type hexLiteralChecker struct {
+	astwalk.WalkHandler
+	ctx *lintpack.CheckerContext
+}
+
+func (c *hexLiteralChecker) warn0X(lit *ast.BasicLit) {
+	suggest := "0x" + lit.Value[len("0X"):]
+	c.ctx.Warn(lit, "prefer 0x over 0X, s/%s/%s/", lit.Value, suggest)
+}
+
+func (c *hexLiteralChecker) warnMixedDigits(lit *ast.BasicLit) {
+	c.ctx.Warn(lit, "don't mix hex literal letter digits casing")
+}
+
+func (c *hexLiteralChecker) VisitExpr(expr ast.Expr) {
+	lit := astcast.ToBasicLit(expr)
+	if lit.Kind != token.INT || len(lit.Value) < 3 {
+		return
+	}
+	if strings.HasPrefix(lit.Value, "0X") {
+		c.warn0X(lit)
+		return
+	}
+	digits := lit.Value[len("0x"):]
+	if strings.ToLower(digits) != digits && strings.ToUpper(digits) != digits {
+		c.warnMixedDigits(lit)
+	}
+}

checkers/testdata/hexLiteral/negative_tests.go

@@ -0,0 +1,23 @@
+package checker_test
+
+func negatives() {
+	_ = 0xFF
+	_ = 0xff
+	_ = "0xfF"
+}
+
+func noLetters() {
+	_ = 0x11
+	_ = 0x0
+}
+
+func digitsAndLetters() {
+	_ = 0x1aa
+	_ = 0x1AA
+}
+
+func decimals() {
+	_ = 1
+	_ = 10
+	_ = 12345
+}

checkers/testdata/hexLiteral/positive_tests.go

@@ -0,0 +1,23 @@
+package checker_test
+
+func bad0X() {
+	/*! prefer 0x over 0X, s/0X12/0x12/ */
+	_ = 0X12
+	/*! prefer 0x over 0X, s/0XEE/0xEE/ */
+	_ = 0XEE
+	/*! prefer 0x over 0X, s/0Xaa/0xaa/ */
+	_ = 0Xaa
+}
+
+func mixedLetterDigits() {
+	/*! don't mix hex literal letter digits casing */
+	_ = 0xfF
+	/*! don't mix hex literal letter digits casing */
+	_ = 0xFf
+	/*! don't mix hex literal letter digits casing */
+	_ = 0x11f0F
+	/*! don't mix hex literal letter digits casing */
+	_ = 0xff11FF
+	/*! don't mix hex literal letter digits casing */
+	_ = 0xabcdE
+}