src

qf1003.go (5312B)

---

 package qf1003
 
 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:     "QF1003",
 		Run:      run,
 		Requires: []*analysis.Analyzer{inspect.Analyzer},
 	},
 	Doc: &lint.RawDocumentation{
 		Title: "Convert if/else-if chain to tagged switch",
 		Text: `
 A series of if/else-if checks comparing the same variable against
 values can be replaced with a tagged switch.`,
 		Before: `
 if x == 1 || x == 2 {
     ...
 } else if x == 3 {
     ...
 } else {
     ...
 }`,
 
 		After: `
 switch x {
 case 1, 2:
     ...
 case 3:
     ...
 default:
     ...
 }`,
 		Since:    "2021.1",
 		Severity: lint.SeverityInfo,
 	},
 })
 
 var Analyzer = SCAnalyzer.Analyzer
 
 func run(pass *analysis.Pass) (any, error) {
 nodeLoop:
 	for c := range code.Cursor(pass).Preorder((*ast.IfStmt)(nil)) {
 		node := c.Node()
 		if _, ok := c.Parent().Node().(*ast.IfStmt); ok {
 			// this if statement is part of an if-else chain
 			continue
 		}
 		ifstmt := node.(*ast.IfStmt)
 
 		m := map[ast.Expr][]*ast.BinaryExpr{}
 		for item := ifstmt; item != nil; {
 			if item.Init != nil {
 				continue nodeLoop
 			}
 			if item.Body == nil {
 				continue nodeLoop
 			}
 
 			skip := false
 			ast.Inspect(item.Body, func(node ast.Node) bool {
 				if branch, ok := node.(*ast.BranchStmt); ok && branch.Tok != token.GOTO {
 					skip = true
 					return false
 				}
 				return true
 			})
 			if skip {
 				continue nodeLoop
 			}
 
 			var pairs []*ast.BinaryExpr
 			if !findSwitchPairs(pass, item.Cond, &pairs) {
 				continue nodeLoop
 			}
 			m[item.Cond] = pairs
 			switch els := item.Else.(type) {
 			case *ast.IfStmt:
 				item = els
 			case *ast.BlockStmt, nil:
 				item = nil
 			default:
 				panic(fmt.Sprintf("unreachable: %T", els))
 			}
 		}
 
 		var x ast.Expr
 		for _, pair := range m {
 			if len(pair) == 0 {
 				continue
 			}
 			if x == nil {
 				x = pair[0].X
 			} else {
 				if !astutil.Equal(x, pair[0].X) {
 					continue nodeLoop
 				}
 			}
 		}
 		if x == nil {
 			// shouldn't happen
 			continue nodeLoop
 		}
 
 		// We require at least two 'if' to make this suggestion, to
 		// avoid clutter in the editor.
 		if len(m) < 2 {
 			continue nodeLoop
 		}
 
 		// Note that we insert the switch statement as the first text edit instead of the last one so that gopls has an
 		// easier time converting it to an LSP-conforming edit.
 		//
 		// Specifically:
 		// > Text edits ranges must never overlap, that means no part of the original
 		// > document must be manipulated by more than one edit. However, it is
 		// > possible that multiple edits have the same start position: multiple
 		// > inserts, or any number of inserts followed by a single remove or replace
 		// > edit. If multiple inserts have the same position, the order in the array
 		// > defines the order in which the inserted strings appear in the resulting
 		// > text.
 		//
 		// See https://go.dev/issue/63930
 		//
 		// FIXME this edit forces the first case to begin in column 0 because we ignore indentation. try to fix that.
 		edits := []analysis.TextEdit{edit.ReplaceWithString(edit.Range{ifstmt.If, ifstmt.If}, fmt.Sprintf("switch %s {\n", report.Render(pass, x)))}
 		for item := ifstmt; item != nil; {
 			var end token.Pos
 			if item.Else != nil {
 				end = item.Else.Pos()
 			} else {
 				// delete up to but not including the closing brace.
 				end = item.Body.Rbrace
 			}
 
 			var conds []string
 			for _, cond := range m[item.Cond] {
 				y := cond.Y
 				if p, ok := y.(*ast.ParenExpr); ok {
 					y = p.X
 				}
 				conds = append(conds, report.Render(pass, y))
 			}
 			sconds := strings.Join(conds, ", ")
 			edits = append(edits,
 				edit.ReplaceWithString(edit.Range{item.If, item.Body.Lbrace + 1}, "case "+sconds+":"),
 				edit.Delete(edit.Range{item.Body.Rbrace, end}))
 
 			switch els := item.Else.(type) {
 			case *ast.IfStmt:
 				item = els
 			case *ast.BlockStmt:
 				edits = append(edits, edit.ReplaceWithString(edit.Range{els.Lbrace, els.Lbrace + 1}, "default:"))
 				item = nil
 			case nil:
 				item = nil
 			default:
 				panic(fmt.Sprintf("unreachable: %T", els))
 			}
 		}
 		report.Report(pass, ifstmt, fmt.Sprintf("could use tagged switch on %s", report.Render(pass, x)),
 			report.Fixes(edit.Fix("Replace with tagged switch", edits...)),
 			report.ShortRange())
 	}
 	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
 	}
 }