Add staticcheck tool

vendor/honnef.co/go/tools/staticcheck/sa6005/sa6005.go

@@ -0,0 +1,75 @@
+package sa6005
+
+import (
+	"go/ast"
+	"go/token"
+
+	"honnef.co/go/tools/analysis/code"
+	"honnef.co/go/tools/analysis/edit"
+	"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:     "SA6005",
+		Run:      run,
+		Requires: code.RequiredAnalyzers,
+	},
+	Doc: &lint.RawDocumentation{
+		Title: `Inefficient string comparison with \'strings.ToLower\' or \'strings.ToUpper\'`,
+		Text: `Converting two strings to the same case and comparing them like so
+
+    if strings.ToLower(s1) == strings.ToLower(s2) {
+        ...
+    }
+
+is significantly more expensive than comparing them with
+\'strings.EqualFold(s1, s2)\'. This is due to memory usage as well as
+computational complexity.
+
+\'strings.ToLower\' will have to allocate memory for the new strings, as
+well as convert both strings fully, even if they differ on the very
+first byte. strings.EqualFold, on the other hand, compares the strings
+one character at a time. It doesn't need to create two intermediate
+strings and can return as soon as the first non-matching character has
+been found.
+
+For a more in-depth explanation of this issue, see
+https://blog.digitalocean.com/how-to-efficiently-compare-strings-in-go/`,
+		Since:    "2019.2",
+		Severity: lint.SeverityWarning,
+		MergeIf:  lint.MergeIfAny,
+	},
+})
+
+var Analyzer = SCAnalyzer.Analyzer
+
+var (
+	checkToLowerToUpperComparisonQ = pattern.MustParse(`
+	(BinaryExpr
+		(CallExpr fun@(Symbol (Or "strings.ToLower" "strings.ToUpper")) [a])
+ 		tok@(Or "==" "!=")
+ 		(CallExpr fun [b]))`)
+	checkToLowerToUpperComparisonR = pattern.MustParse(`(CallExpr (SelectorExpr (Ident "strings") (Ident "EqualFold")) [a b])`)
+)
+
+func run(pass *analysis.Pass) (any, error) {
+	for node, m := range code.Matches(pass, checkToLowerToUpperComparisonQ) {
+		rn := pattern.NodeToAST(checkToLowerToUpperComparisonR.Root, m.State).(ast.Expr)
+		if m.State["tok"].(token.Token) == token.NEQ {
+			rn = &ast.UnaryExpr{
+				Op: token.NOT,
+				X:  rn,
+			}
+		}
+
+		report.Report(pass, node,
+			"should use strings.EqualFold instead",
+			report.Fixes(edit.Fix("Replace with strings.EqualFold", edit.ReplaceWithNode(pass.Fset, node, rn))))
+	}
+	return nil, nil
+}