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// Copyright 2015 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 unusedresult defines an analyzer that checks for unused
// results of calls to certain pure functions.
package unusedresult
import (
"go/ast"
"go/token"
"go/types"
"sort"
"strings"
"golang.org/x/tools/go/analysis"
"golang.org/x/tools/go/analysis/passes/inspect"
"golang.org/x/tools/go/analysis/passes/internal/analysisutil"
"golang.org/x/tools/go/ast/inspector"
)
// TODO(adonovan): make this analysis modular: export a mustUseResult
// fact for each function that tail-calls one of the functions that we
// check, and check those functions too.
const Doc = `check for unused results of calls to some functions
Some functions like fmt.Errorf return a result and have no side effects,
so it is always a mistake to discard the result. This analyzer reports
calls to certain functions in which the result of the call is ignored.
The set of functions may be controlled using flags.`
var Analyzer = &analysis.Analyzer{
Name: "unusedresult",
Doc: Doc,
Requires: []*analysis.Analyzer{inspect.Analyzer},
Run: run,
}
// flags
var funcs, stringMethods stringSetFlag
func init() {
// TODO(adonovan): provide a comment syntax to allow users to
// add their functions to this set using facts.
funcs.Set("errors.New,fmt.Errorf,fmt.Sprintf,fmt.Sprint,sort.Reverse,context.WithValue,context.WithCancel,context.WithDeadline,context.WithTimeout")
Analyzer.Flags.Var(&funcs, "funcs",
"comma-separated list of functions whose results must be used")
stringMethods.Set("Error,String")
Analyzer.Flags.Var(&stringMethods, "stringmethods",
"comma-separated list of names of methods of type func() string whose results must be used")
}
func run(pass *analysis.Pass) (interface{}, error) {
inspect := pass.ResultOf[inspect.Analyzer].(*inspector.Inspector)
nodeFilter := []ast.Node{
(*ast.ExprStmt)(nil),
}
inspect.Preorder(nodeFilter, func(n ast.Node) {
call, ok := analysisutil.Unparen(n.(*ast.ExprStmt).X).(*ast.CallExpr)
if !ok {
return // not a call statement
}
fun := analysisutil.Unparen(call.Fun)
if pass.TypesInfo.Types[fun].IsType() {
return // a conversion, not a call
}
selector, ok := fun.(*ast.SelectorExpr)
if !ok {
return // neither a method call nor a qualified ident
}
sel, ok := pass.TypesInfo.Selections[selector]
if ok && sel.Kind() == types.MethodVal {
// method (e.g. foo.String())
obj := sel.Obj().(*types.Func)
sig := sel.Type().(*types.Signature)
if types.Identical(sig, sigNoArgsStringResult) {
if stringMethods[obj.Name()] {
pass.Reportf(call.Lparen, "result of (%s).%s call not used",
sig.Recv().Type(), obj.Name())
}
}
} else if !ok {
// package-qualified function (e.g. fmt.Errorf)
obj := pass.TypesInfo.Uses[selector.Sel]
if obj, ok := obj.(*types.Func); ok {
qname := obj.Pkg().Path() + "." + obj.Name()
if funcs[qname] {
pass.Reportf(call.Lparen, "result of %v call not used", qname)
}
}
}
})
return nil, nil
}
// func() string
var sigNoArgsStringResult = types.NewSignature(nil, nil,
types.NewTuple(types.NewVar(token.NoPos, nil, "", types.Typ[types.String])),
false)
type stringSetFlag map[string]bool
func (ss *stringSetFlag) String() string {
var items []string
for item := range *ss {
items = append(items, item)
}
sort.Strings(items)
return strings.Join(items, ",")
}
func (ss *stringSetFlag) Set(s string) error {
m := make(map[string]bool) // clobber previous value
if s != "" {
for _, name := range strings.Split(s, ",") {
if name == "" {
continue // TODO: report error? proceed?
}
m[name] = true
}
}
*ss = m
return nil
}
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