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Source file src/cmd/vet/assign.go

Documentation: cmd/vet

  // 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.
  
  /*
  This file contains the code to check for useless assignments.
  */
  
  package main
  
  import (
  	"go/ast"
  	"go/token"
  	"reflect"
  )
  
  func init() {
  	register("assign",
  		"check for useless assignments",
  		checkAssignStmt,
  		assignStmt)
  }
  
  // TODO: should also check for assignments to struct fields inside methods
  // that are on T instead of *T.
  
  // checkAssignStmt checks for assignments of the form "<expr> = <expr>".
  // These are almost always useless, and even when they aren't they are usually a mistake.
  func checkAssignStmt(f *File, node ast.Node) {
  	stmt := node.(*ast.AssignStmt)
  	if stmt.Tok != token.ASSIGN {
  		return // ignore :=
  	}
  	if len(stmt.Lhs) != len(stmt.Rhs) {
  		// If LHS and RHS have different cardinality, they can't be the same.
  		return
  	}
  	for i, lhs := range stmt.Lhs {
  		rhs := stmt.Rhs[i]
  		if reflect.TypeOf(lhs) != reflect.TypeOf(rhs) {
  			continue // short-circuit the heavy-weight gofmt check
  		}
  		le := f.gofmt(lhs)
  		re := f.gofmt(rhs)
  		if le == re {
  			f.Badf(stmt.Pos(), "self-assignment of %s to %s", re, le)
  		}
  	}
  }
  

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