Detect bytes.Equal used to compare net.IP values

Updates gh-64

Idea-By: Filippo Valsorda <hi@filippo.io>
Idea-By: Dmitri Shuralyov <shurcooL@gmail.com>

README.md

@@ -67,6 +67,7 @@ The following things are currently checked by staticcheck:
 | SA1018     | `strings.Replace` called with n == 0, which does nothing                                                                                              |
 | SA1019     | Using a deprecated function, variable, constant or field                                                                                              |
 | SA1020     | Using an invalid `host:port` pair with a `net.Listen`-related function                                                                                |
+| SA1021     | Using bytes.Equal to compare two net.IP                                                                                                               |
 |            |                                                                                                                                                       |
 | **SA2???** | **Concurrency issues**                                                                                                                                |
 | SA2000     | `sync.WaitGroup.Add` called inside the goroutine, leading to a race condition                                                                         |

lint.go

@@ -110,6 +110,7 @@ func (c *Checker) Funcs() map[string]lint.Func {
 		"SA1018": c.CheckStringsReplaceZero,
 		"SA1019": c.CheckDeprecated,
 		"SA1020": c.CheckListenAddress,
+		"SA1021": c.CheckBytesEqualIP,
 
 		"SA2000": c.CheckWaitgroupAdd,
 		"SA2001": c.CheckEmptyCriticalSection,
@@ -2748,3 +2749,21 @@ var checkListenAddressRules = map[string]CallRule{
 func (c *Checker) CheckListenAddress(f *lint.File) {
 	c.checkCalls(f, checkListenAddressRules)
 }
+
+var checkBytesEqualIPRules = map[string]CallRule{
+	"bytes.Equal": CallRule{
+		[]ArgumentRule{
+			NotChangedTypeFrom{
+				argumentRule{
+					idx:     0,
+					Message: "use net.IP.Equal to compare net.IPs, not bytes.Equal",
+				},
+				"net.IP",
+			},
+		},
+	},
+}
+
+func (c *Checker) CheckBytesEqualIP(f *lint.File) {
+	c.checkCalls(f, checkBytesEqualIPRules)
+}

rules.go

@@ -330,3 +330,22 @@ func (hp ValidHostPort) Validate(v ssa.Value, fn *ssa.Function, c *Checker) erro
 	}
 	return nil
 }
+
+type NotChangedTypeFrom struct {
+	argumentRule
+	Type string
+}
+
+func (nt NotChangedTypeFrom) Validate(v ssa.Value, fn *ssa.Function, c *Checker) error {
+	change, ok := v.(*ssa.ChangeType)
+	if !ok {
+		return nil
+	}
+	if types.TypeString(change.X.Type(), nil) == nt.Type {
+		if nt.Message != "" {
+			return errors.New(nt.Message)
+		}
+		return fmt.Errorf("shouldn't use function with type %s", nt.Type)
+	}
+	return nil
+}

testdata/CheckBytesEqualIP.go

@@ -0,0 +1,19 @@
+package pkg
+
+import (
+	"bytes"
+	"net"
+)
+
+func fn() {
+	type T []byte
+	var i1, i2 net.IP
+	var b1, b2 []byte
+	var t1, t2 T
+
+	bytes.Equal(i1, i2) // MATCH /use net.IP.Equal to compare net.IPs, not bytes.Equal/
+	bytes.Equal(b1, b2)
+	bytes.Equal(t1, t2)
+
+	// bytes.Equal(i1, b1)
+}