--- /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