.config/coc/extensions/coc-go-data/tools/pkg/mod/golang.org/x/tools@v0.0.0-20201028153306-37f0764111ff/go/analysis/passes/assign/assign.go

   1 // Copyright 2013 The Go Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style
   3 // license that can be found in the LICENSE file.
   4
   5 // Package assign defines an Analyzer that detects useless assignments.
   6 package assign
   7
   8 // TODO(adonovan): check also for assignments to struct fields inside
   9 // methods that are on T instead of *T.
  10
  11 import (
  12         "fmt"
  13         "go/ast"
  14         "go/token"
  15         "reflect"
  16
  17         "golang.org/x/tools/go/analysis"
  18         "golang.org/x/tools/go/analysis/passes/inspect"
  19         "golang.org/x/tools/go/analysis/passes/internal/analysisutil"
  20         "golang.org/x/tools/go/ast/inspector"
  21 )
  22
  23 const Doc = `check for useless assignments
  24
  25 This checker reports assignments of the form x = x or a[i] = a[i].
  26 These are almost always useless, and even when they aren't they are
  27 usually a mistake.`
  28
  29 var Analyzer = &analysis.Analyzer{
  30         Name:     "assign",
  31         Doc:      Doc,
  32         Requires: []*analysis.Analyzer{inspect.Analyzer},
  33         Run:      run,
  34 }
  35
  36 func run(pass *analysis.Pass) (interface{}, error) {
  37         inspect := pass.ResultOf[inspect.Analyzer].(*inspector.Inspector)
  38
  39         nodeFilter := []ast.Node{
  40                 (*ast.AssignStmt)(nil),
  41         }
  42         inspect.Preorder(nodeFilter, func(n ast.Node) {
  43                 stmt := n.(*ast.AssignStmt)
  44                 if stmt.Tok != token.ASSIGN {
  45                         return // ignore :=
  46                 }
  47                 if len(stmt.Lhs) != len(stmt.Rhs) {
  48                         // If LHS and RHS have different cardinality, they can't be the same.
  49                         return
  50                 }
  51                 for i, lhs := range stmt.Lhs {
  52                         rhs := stmt.Rhs[i]
  53                         if analysisutil.HasSideEffects(pass.TypesInfo, lhs) ||
  54                                 analysisutil.HasSideEffects(pass.TypesInfo, rhs) {
  55                                 continue // expressions may not be equal
  56                         }
  57                         if reflect.TypeOf(lhs) != reflect.TypeOf(rhs) {
  58                                 continue // short-circuit the heavy-weight gofmt check
  59                         }
  60                         le := analysisutil.Format(pass.Fset, lhs)
  61                         re := analysisutil.Format(pass.Fset, rhs)
  62                         if le == re {
  63                                 pass.Report(analysis.Diagnostic{
  64                                         Pos: stmt.Pos(), Message: fmt.Sprintf("self-assignment of %s to %s", re, le),
  65                                         SuggestedFixes: []analysis.SuggestedFix{
  66                                                 {Message: "Remove", TextEdits: []analysis.TextEdit{
  67                                                         {Pos: stmt.Pos(), End: stmt.End(), NewText: []byte{}},
  68                                                 }},
  69                                         },
  70                                 })
  71                         }
  72                 }
  73         })
  74
  75         return nil, nil
  76 }