+++ /dev/null
-// Copyright 2013 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-// Package unreachable defines an Analyzer that checks for unreachable code.
-package unreachable
-
-// TODO(adonovan): use the new cfg package, which is more precise.
-
-import (
- "go/ast"
- "go/token"
- "log"
-
- "golang.org/x/tools/go/analysis"
- "golang.org/x/tools/go/analysis/passes/inspect"
- "golang.org/x/tools/go/ast/inspector"
-)
-
-const Doc = `check for unreachable code
-
-The unreachable analyzer finds statements that execution can never reach
-because they are preceded by an return statement, a call to panic, an
-infinite loop, or similar constructs.`
-
-var Analyzer = &analysis.Analyzer{
- Name: "unreachable",
- Doc: Doc,
- Requires: []*analysis.Analyzer{inspect.Analyzer},
- RunDespiteErrors: true,
- Run: run,
-}
-
-func run(pass *analysis.Pass) (interface{}, error) {
- inspect := pass.ResultOf[inspect.Analyzer].(*inspector.Inspector)
-
- nodeFilter := []ast.Node{
- (*ast.FuncDecl)(nil),
- (*ast.FuncLit)(nil),
- }
- inspect.Preorder(nodeFilter, func(n ast.Node) {
- var body *ast.BlockStmt
- switch n := n.(type) {
- case *ast.FuncDecl:
- body = n.Body
- case *ast.FuncLit:
- body = n.Body
- }
- if body == nil {
- return
- }
- d := &deadState{
- pass: pass,
- hasBreak: make(map[ast.Stmt]bool),
- hasGoto: make(map[string]bool),
- labels: make(map[string]ast.Stmt),
- }
- d.findLabels(body)
- d.reachable = true
- d.findDead(body)
- })
- return nil, nil
-}
-
-type deadState struct {
- pass *analysis.Pass
- hasBreak map[ast.Stmt]bool
- hasGoto map[string]bool
- labels map[string]ast.Stmt
- breakTarget ast.Stmt
-
- reachable bool
-}
-
-// findLabels gathers information about the labels defined and used by stmt
-// and about which statements break, whether a label is involved or not.
-func (d *deadState) findLabels(stmt ast.Stmt) {
- switch x := stmt.(type) {
- default:
- log.Fatalf("%s: internal error in findLabels: unexpected statement %T", d.pass.Fset.Position(x.Pos()), x)
-
- case *ast.AssignStmt,
- *ast.BadStmt,
- *ast.DeclStmt,
- *ast.DeferStmt,
- *ast.EmptyStmt,
- *ast.ExprStmt,
- *ast.GoStmt,
- *ast.IncDecStmt,
- *ast.ReturnStmt,
- *ast.SendStmt:
- // no statements inside
-
- case *ast.BlockStmt:
- for _, stmt := range x.List {
- d.findLabels(stmt)
- }
-
- case *ast.BranchStmt:
- switch x.Tok {
- case token.GOTO:
- if x.Label != nil {
- d.hasGoto[x.Label.Name] = true
- }
-
- case token.BREAK:
- stmt := d.breakTarget
- if x.Label != nil {
- stmt = d.labels[x.Label.Name]
- }
- if stmt != nil {
- d.hasBreak[stmt] = true
- }
- }
-
- case *ast.IfStmt:
- d.findLabels(x.Body)
- if x.Else != nil {
- d.findLabels(x.Else)
- }
-
- case *ast.LabeledStmt:
- d.labels[x.Label.Name] = x.Stmt
- d.findLabels(x.Stmt)
-
- // These cases are all the same, but the x.Body only works
- // when the specific type of x is known, so the cases cannot
- // be merged.
- case *ast.ForStmt:
- outer := d.breakTarget
- d.breakTarget = x
- d.findLabels(x.Body)
- d.breakTarget = outer
-
- case *ast.RangeStmt:
- outer := d.breakTarget
- d.breakTarget = x
- d.findLabels(x.Body)
- d.breakTarget = outer
-
- case *ast.SelectStmt:
- outer := d.breakTarget
- d.breakTarget = x
- d.findLabels(x.Body)
- d.breakTarget = outer
-
- case *ast.SwitchStmt:
- outer := d.breakTarget
- d.breakTarget = x
- d.findLabels(x.Body)
- d.breakTarget = outer
-
- case *ast.TypeSwitchStmt:
- outer := d.breakTarget
- d.breakTarget = x
- d.findLabels(x.Body)
- d.breakTarget = outer
-
- case *ast.CommClause:
- for _, stmt := range x.Body {
- d.findLabels(stmt)
- }
-
- case *ast.CaseClause:
- for _, stmt := range x.Body {
- d.findLabels(stmt)
- }
- }
-}
-
-// findDead walks the statement looking for dead code.
-// If d.reachable is false on entry, stmt itself is dead.
-// When findDead returns, d.reachable tells whether the
-// statement following stmt is reachable.
-func (d *deadState) findDead(stmt ast.Stmt) {
- // Is this a labeled goto target?
- // If so, assume it is reachable due to the goto.
- // This is slightly conservative, in that we don't
- // check that the goto is reachable, so
- // L: goto L
- // will not provoke a warning.
- // But it's good enough.
- if x, isLabel := stmt.(*ast.LabeledStmt); isLabel && d.hasGoto[x.Label.Name] {
- d.reachable = true
- }
-
- if !d.reachable {
- switch stmt.(type) {
- case *ast.EmptyStmt:
- // do not warn about unreachable empty statements
- default:
- d.pass.Report(analysis.Diagnostic{
- Pos: stmt.Pos(),
- End: stmt.End(),
- Message: "unreachable code",
- SuggestedFixes: []analysis.SuggestedFix{{
- Message: "Remove",
- TextEdits: []analysis.TextEdit{{
- Pos: stmt.Pos(),
- End: stmt.End(),
- }},
- }},
- })
- d.reachable = true // silence error about next statement
- }
- }
-
- switch x := stmt.(type) {
- default:
- log.Fatalf("%s: internal error in findDead: unexpected statement %T", d.pass.Fset.Position(x.Pos()), x)
-
- case *ast.AssignStmt,
- *ast.BadStmt,
- *ast.DeclStmt,
- *ast.DeferStmt,
- *ast.EmptyStmt,
- *ast.GoStmt,
- *ast.IncDecStmt,
- *ast.SendStmt:
- // no control flow
-
- case *ast.BlockStmt:
- for _, stmt := range x.List {
- d.findDead(stmt)
- }
-
- case *ast.BranchStmt:
- switch x.Tok {
- case token.BREAK, token.GOTO, token.FALLTHROUGH:
- d.reachable = false
- case token.CONTINUE:
- // NOTE: We accept "continue" statements as terminating.
- // They are not necessary in the spec definition of terminating,
- // because a continue statement cannot be the final statement
- // before a return. But for the more general problem of syntactically
- // identifying dead code, continue redirects control flow just
- // like the other terminating statements.
- d.reachable = false
- }
-
- case *ast.ExprStmt:
- // Call to panic?
- call, ok := x.X.(*ast.CallExpr)
- if ok {
- name, ok := call.Fun.(*ast.Ident)
- if ok && name.Name == "panic" && name.Obj == nil {
- d.reachable = false
- }
- }
-
- case *ast.ForStmt:
- d.findDead(x.Body)
- d.reachable = x.Cond != nil || d.hasBreak[x]
-
- case *ast.IfStmt:
- d.findDead(x.Body)
- if x.Else != nil {
- r := d.reachable
- d.reachable = true
- d.findDead(x.Else)
- d.reachable = d.reachable || r
- } else {
- // might not have executed if statement
- d.reachable = true
- }
-
- case *ast.LabeledStmt:
- d.findDead(x.Stmt)
-
- case *ast.RangeStmt:
- d.findDead(x.Body)
- d.reachable = true
-
- case *ast.ReturnStmt:
- d.reachable = false
-
- case *ast.SelectStmt:
- // NOTE: Unlike switch and type switch below, we don't care
- // whether a select has a default, because a select without a
- // default blocks until one of the cases can run. That's different
- // from a switch without a default, which behaves like it has
- // a default with an empty body.
- anyReachable := false
- for _, comm := range x.Body.List {
- d.reachable = true
- for _, stmt := range comm.(*ast.CommClause).Body {
- d.findDead(stmt)
- }
- anyReachable = anyReachable || d.reachable
- }
- d.reachable = anyReachable || d.hasBreak[x]
-
- case *ast.SwitchStmt:
- anyReachable := false
- hasDefault := false
- for _, cas := range x.Body.List {
- cc := cas.(*ast.CaseClause)
- if cc.List == nil {
- hasDefault = true
- }
- d.reachable = true
- for _, stmt := range cc.Body {
- d.findDead(stmt)
- }
- anyReachable = anyReachable || d.reachable
- }
- d.reachable = anyReachable || d.hasBreak[x] || !hasDefault
-
- case *ast.TypeSwitchStmt:
- anyReachable := false
- hasDefault := false
- for _, cas := range x.Body.List {
- cc := cas.(*ast.CaseClause)
- if cc.List == nil {
- hasDefault = true
- }
- d.reachable = true
- for _, stmt := range cc.Body {
- d.findDead(stmt)
- }
- anyReachable = anyReachable || d.reachable
- }
- d.reachable = anyReachable || d.hasBreak[x] || !hasDefault
- }
-}
projects / dotfiles / .git / blobdiff