Add staticcheck tool

vendor/honnef.co/go/tools/staticcheck/sa1021/sa1021.go

@@ -0,0 +1,49 @@
+package sa1021
+
+import (
+	"go/types"
+
+	"honnef.co/go/tools/analysis/callcheck"
+	"honnef.co/go/tools/analysis/lint"
+	"honnef.co/go/tools/go/ir"
+	"honnef.co/go/tools/internal/passes/buildir"
+	"honnef.co/go/tools/knowledge"
+
+	"golang.org/x/tools/go/analysis"
+)
+
+var SCAnalyzer = lint.InitializeAnalyzer(&lint.Analyzer{
+	Analyzer: &analysis.Analyzer{
+		Name:     "SA1021",
+		Requires: []*analysis.Analyzer{buildir.Analyzer},
+		Run:      callcheck.Analyzer(rules),
+	},
+	Doc: &lint.RawDocumentation{
+		Title: `Using \'bytes.Equal\' to compare two \'net.IP\'`,
+		Text: `A \'net.IP\' stores an IPv4 or IPv6 address as a slice of bytes. The
+length of the slice for an IPv4 address, however, can be either 4 or
+16 bytes long, using different ways of representing IPv4 addresses. In
+order to correctly compare two \'net.IP\'s, the \'net.IP.Equal\' method should
+be used, as it takes both representations into account.`,
+		Since:    "2017.1",
+		Severity: lint.SeverityWarning,
+		MergeIf:  lint.MergeIfAny,
+	},
+})
+
+var Analyzer = SCAnalyzer.Analyzer
+
+var rules = map[string]callcheck.Check{
+	"bytes.Equal": func(call *callcheck.Call) {
+		if isConvertedFrom(call.Args[knowledge.Arg("bytes.Equal.a")].Value, "net.IP") &&
+			isConvertedFrom(call.Args[knowledge.Arg("bytes.Equal.b")].Value, "net.IP") {
+			call.Invalid("use net.IP.Equal to compare net.IPs, not bytes.Equal")
+		}
+	},
+}
+
+// ConvertedFrom reports whether value v was converted from type typ.
+func isConvertedFrom(v callcheck.Value, typ string) bool {
+	change, ok := v.Value.(*ir.ChangeType)
+	return ok && types.TypeString(types.Unalias(change.X.Type()), nil) == typ
+}