checkers: add new checker stringsCompare (#1195)

Updates #1167

checkers/rules/rules.go

@@ -736,3 +736,20 @@ func dynamicFmtString(m dsl.Matcher) {
 		Suggest("errors.New($f($*args))").
 		Report(`use errors.New($f($*args)) or fmt.Errorf("%s", $f($*args)) instead`)
 }
+
+//doc:summary Detects strings.Compare usage
+//doc:tags    style experimental
+//doc:before  strings.Compare(x, y)
+//doc:after   x < y
+func stringsCompare(m dsl.Matcher) {
+	m.Match(`strings.Compare($s1, $s2) == 0`).
+		Suggest(`$s1 == $s2`)
+
+	m.Match(`strings.Compare($s1, $s2) == -1`,
+		`strings.Compare($s1, $s2) < 0`).
+		Suggest(`$s1 < $s2`)
+
+	m.Match(`strings.Compare($s1, $s2) == 1`,
+		`strings.Compare($s1, $s2) > 0`).
+		Suggest(`$s1 > $s2`)
+}

checkers/testdata/stringsCompare/negative_tests.go

@@ -0,0 +1,78 @@
+package checker_test
+
+import (
+	"bytes"
+	"strings"
+)
+
+type s []string
+
+func (s) Compare(x, y string) int {
+	if x < y {
+		return 1
+	}
+	return 0
+}
+
+func negative() {
+	bytes.Compare([]byte{}, []byte{})
+
+	strings := s{}
+	_ = strings.Compare("1", "3") == 0
+}
+
+func negative2() {
+	var a, b = "aaa", "bbb"
+	if a > b {
+		print(1)
+	}
+
+	if a == b {
+		print(0)
+	}
+
+	if a < b {
+		print(-1)
+	}
+
+	switch a > b {
+	case true:
+		print(1)
+	case false:
+		print(0, -1)
+	}
+}
+
+func negative3() {
+	if "aaa" > "bbb" {
+		print(1)
+	}
+
+	if "aaa" == "bbb" {
+		print(0)
+	}
+
+	if "aaa" < "bbb" {
+		print(-1)
+	}
+
+	switch "aaa" > "bbb" {
+	case true:
+		print(1)
+	case false:
+		print(0, -1)
+	}
+}
+
+func negative4() {
+	f, b := "aaa", "bbb"
+
+	_ = strings.Compare(f, b) > -100
+	_ = strings.Compare(f, b) < 100
+	_ = strings.Compare(f, b) >= -1
+	_ = strings.Compare(f, b) <= -1
+	_ = strings.Compare(f, b) >= 1
+	_ = strings.Compare(f, b) <= 1
+	_ = strings.Compare(f, b) >= 0
+	_ = strings.Compare(f, b) <= 0
+}

checkers/testdata/stringsCompare/positive_tests.go

@@ -0,0 +1,36 @@
+package checker_test
+
+import (
+	"strings"
+)
+
+func warning() {
+	f, b := "aaa", "bbb"
+
+	/*! suggestion: f == b */
+	if strings.Compare(f, b) == 0 {
+	}
+
+	/*! suggestion: f > b */
+	switch foo := strings.Compare(f, b) > 0; foo {
+	case true:
+		print(0)
+	case false:
+		print(1)
+	}
+
+	/*! suggestion: "s" < "ww" */
+	_ = strings.Compare("s", "ww") < 0
+	/*! suggestion: "s" == "ww" */
+	_ = strings.Compare("s", "ww") == 0
+	/*! suggestion: "s" > "ww" */
+	_ = strings.Compare("s", "ww") > 0
+
+	/*! suggestion: "s" > "ww" */
+	_ = strings.Compare("s", "ww") > 0
+
+	/*! suggestion: "s" > "ww" */
+	_ = strings.Compare("s", "ww") == 1
+	/*! suggestion: "s" < "ww" */
+	_ = strings.Compare("s", "ww") == -1
+}