src

qf1002.go (3441B)

---

 package qf1002
 
 import (
 	"fmt"
 	"go/ast"
 	"go/token"
 	"strings"
 
 	"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/go/ast/astutil"
 
 	"golang.org/x/tools/go/analysis"
 	"golang.org/x/tools/go/analysis/passes/inspect"
 )
 
 var SCAnalyzer = lint.InitializeAnalyzer(&lint.Analyzer{
 	Analyzer: &analysis.Analyzer{
 		Name:     "QF1002",
 		Run:      run,
 		Requires: []*analysis.Analyzer{inspect.Analyzer},
 	},
 	Doc: &lint.RawDocumentation{
 		Title: "Convert untagged switch to tagged switch",
 		Text: `
 An untagged switch that compares a single variable against a series of
 values can be replaced with a tagged switch.`,
 		Before: `
 switch {
 case x == 1 || x == 2, x == 3:
     ...
 case x == 4:
     ...
 default:
     ...
 }`,
 
 		After: `
 switch x {
 case 1, 2, 3:
     ...
 case 4:
     ...
 default:
     ...
 }`,
 		Since:    "2021.1",
 		Severity: lint.SeverityHint,
 	},
 })
 
 var Analyzer = SCAnalyzer.Analyzer
 
 func run(pass *analysis.Pass) (any, error) {
 	fn := func(node ast.Node) {
 		swtch := node.(*ast.SwitchStmt)
 		if swtch.Tag != nil || len(swtch.Body.List) == 0 {
 			return
 		}
 
 		pairs := make([][]*ast.BinaryExpr, len(swtch.Body.List))
 		for i, stmt := range swtch.Body.List {
 			stmt := stmt.(*ast.CaseClause)
 			for _, cond := range stmt.List {
 				if !findSwitchPairs(pass, cond, &pairs[i]) {
 					return
 				}
 			}
 		}
 
 		var x ast.Expr
 		for _, pair := range pairs {
 			if len(pair) == 0 {
 				continue
 			}
 			if x == nil {
 				x = pair[0].X
 			} else {
 				if !astutil.Equal(x, pair[0].X) {
 					return
 				}
 			}
 		}
 		if x == nil {
 			// the switch only has a default case
 			if len(pairs) > 1 {
 				panic("found more than one case clause with no pairs")
 			}
 			return
 		}
 
 		edits := make([]analysis.TextEdit, 0, len(swtch.Body.List)+1)
 		for i, stmt := range swtch.Body.List {
 			stmt := stmt.(*ast.CaseClause)
 			if stmt.List == nil {
 				continue
 			}
 
 			var values []string
 			for _, binexpr := range pairs[i] {
 				y := binexpr.Y
 				if p, ok := y.(*ast.ParenExpr); ok {
 					y = p.X
 				}
 				values = append(values, report.Render(pass, y))
 			}
 
 			edits = append(edits, edit.ReplaceWithString(edit.Range{stmt.List[0].Pos(), stmt.Colon}, strings.Join(values, ", ")))
 		}
 		pos := swtch.Body.Lbrace
 		edits = append(edits, edit.ReplaceWithString(edit.Range{pos, pos}, " "+report.Render(pass, x)))
 		report.Report(pass, swtch, fmt.Sprintf("could use tagged switch on %s", report.Render(pass, x)),
 			report.Fixes(edit.Fix("Replace with tagged switch", edits...)),
 			report.ShortRange())
 	}
 
 	code.Preorder(pass, fn, (*ast.SwitchStmt)(nil))
 	return nil, nil
 }
 
 func findSwitchPairs(pass *analysis.Pass, expr ast.Expr, pairs *[]*ast.BinaryExpr) bool {
 	binexpr, ok := ast.Unparen(expr).(*ast.BinaryExpr)
 	if !ok {
 		return false
 	}
 	switch binexpr.Op {
 	case token.EQL:
 		if code.MayHaveSideEffects(pass, binexpr.X, nil) || code.MayHaveSideEffects(pass, binexpr.Y, nil) {
 			return false
 		}
 		// syntactic identity should suffice. we do not allow side
 		// effects in the case clauses, so there should be no way for
 		// values to change.
 		if len(*pairs) > 0 && !astutil.Equal(binexpr.X, (*pairs)[0].X) {
 			return false
 		}
 		*pairs = append(*pairs, binexpr)
 		return true
 	case token.LOR:
 		return findSwitchPairs(pass, binexpr.X, pairs) && findSwitchPairs(pass, binexpr.Y, pairs)
 	default:
 		return false
 	}
 }