Add staticcheck tool

vendor/honnef.co/go/tools/staticcheck/sa4021/sa4021.go

@@ -0,0 +1,36 @@
+package sa4021
+
+import (
+	"honnef.co/go/tools/analysis/code"
+	"honnef.co/go/tools/analysis/facts/generated"
+	"honnef.co/go/tools/analysis/lint"
+	"honnef.co/go/tools/analysis/report"
+	"honnef.co/go/tools/pattern"
+
+	"golang.org/x/tools/go/analysis"
+)
+
+var SCAnalyzer = lint.InitializeAnalyzer(&lint.Analyzer{
+	Analyzer: &analysis.Analyzer{
+		Name:     "SA4021",
+		Run:      run,
+		Requires: append([]*analysis.Analyzer{generated.Analyzer}, code.RequiredAnalyzers...),
+	},
+	Doc: &lint.RawDocumentation{
+		Title:    `\"x = append(y)\" is equivalent to \"x = y\"`,
+		Since:    "2019.2",
+		Severity: lint.SeverityWarning,
+		MergeIf:  lint.MergeIfAny,
+	},
+})
+
+var Analyzer = SCAnalyzer.Analyzer
+
+var checkSingleArgAppendQ = pattern.MustParse(`(CallExpr (Builtin "append") [_])`)
+
+func run(pass *analysis.Pass) (any, error) {
+	for node := range code.Matches(pass, checkSingleArgAppendQ) {
+		report.Report(pass, node, "x = append(y) is equivalent to x = y", report.FilterGenerated())
+	}
+	return nil, nil
+}