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// 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 hasSideEffects(lhs) || hasSideEffects(rhs) {
continue // expressions may not be equal
}
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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