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