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// Copyright 2020 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 unusedparams defines an analyzer that checks for unused
// parameters of functions.
package unusedparams
import (
"fmt"
"go/ast"
"go/types"
"strings"
"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 unused parameters of functions
The unusedparams analyzer checks functions to see if there are
any parameters that are not being used.
To reduce false positives it ignores:
- methods
- parameters that do not have a name or are underscored
- functions in test files
- functions with empty bodies or those with just a return stmt`
var Analyzer = &analysis.Analyzer{
Name: "unusedparams",
Doc: Doc,
Requires: []*analysis.Analyzer{inspect.Analyzer},
Run: run,
}
type paramData struct {
field *ast.Field
ident *ast.Ident
typObj types.Object
}
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 fieldList *ast.FieldList
var body *ast.BlockStmt
// Get the fieldList and body from the function node.
switch f := n.(type) {
case *ast.FuncDecl:
fieldList, body = f.Type.Params, f.Body
// TODO(golang/go#36602): add better handling for methods, if we enable methods
// we will get false positives if a struct is potentially implementing
// an interface.
if f.Recv != nil {
return
}
// Ignore functions in _test.go files to reduce false positives.
if file := pass.Fset.File(n.Pos()); file != nil && strings.HasSuffix(file.Name(), "_test.go") {
return
}
case *ast.FuncLit:
fieldList, body = f.Type.Params, f.Body
}
// If there are no arguments or the function is empty, then return.
if fieldList.NumFields() == 0 || len(body.List) == 0 {
return
}
switch expr := body.List[0].(type) {
case *ast.ReturnStmt:
// Ignore functions that only contain a return statement to reduce false positives.
return
case *ast.ExprStmt:
callExpr, ok := expr.X.(*ast.CallExpr)
if !ok || len(body.List) > 1 {
break
}
// Ignore functions that only contain a panic statement to reduce false positives.
if fun, ok := callExpr.Fun.(*ast.Ident); ok && fun.Name == "panic" {
return
}
}
// Get the useful data from each field.
params := make(map[string]*paramData)
unused := make(map[*paramData]bool)
for _, f := range fieldList.List {
for _, i := range f.Names {
if i.Name == "_" {
continue
}
params[i.Name] = ¶mData{
field: f,
ident: i,
typObj: pass.TypesInfo.ObjectOf(i),
}
unused[params[i.Name]] = true
}
}
// Traverse through the body of the function and
// check to see which parameters are unused.
ast.Inspect(body, func(node ast.Node) bool {
n, ok := node.(*ast.Ident)
if !ok {
return true
}
param, ok := params[n.Name]
if !ok {
return false
}
if nObj := pass.TypesInfo.ObjectOf(n); nObj != param.typObj {
return false
}
delete(unused, param)
return false
})
// Create the reports for the unused parameters.
for u := range unused {
start, end := u.field.Pos(), u.field.End()
if len(u.field.Names) > 1 {
start, end = u.ident.Pos(), u.ident.End()
}
// TODO(golang/go#36602): Add suggested fixes to automatically
// remove the unused parameter. To start, just remove it from the
// function declaration. Later, remove it from every use of this
// function.
pass.Report(analysis.Diagnostic{
Pos: start,
End: end,
Message: fmt.Sprintf("potentially unused parameter: '%s'", u.ident.Name),
})
}
})
return nil, nil
}
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