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cmd/gofmt: make gofmt -s simplify slices in presence of dot-imports

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A dot-import cannot possibly introduce a `len` function since that
function would not be exported (it's lowercase). Furthermore, the
existing code already (incorrectly) assumed that there was no other
`len` function in another file of the package. Since this has been
an ok assumption for years, let's leave it, but remove the dot-import
restriction.

Fixes #15153.

Change-Id: I18fbb27acc5a5668833b4b4aead0cca540862b52
Reviewed-on: https://go-review.googlesource.com/21613
Reviewed-by: Alan Donovan <adonovan@google.com>
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
This commit is contained in:
Robert Griesemer 2016-04-06 10:49:12 -07:00
parent d7ddee78dd
commit ff7ba773f4
3 changed files with 10 additions and 144 deletions
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28
src/cmd/gofmt/simplify.go
View file

@ -10,11 +10,9 @@ import (
"reflect"
)
type simplifier struct {
hasDotImport bool // package file contains: import . "some/import/path"
}
type simplifier struct{}
func (s *simplifier) Visit(node ast.Node) ast.Visitor {
func (s simplifier) Visit(node ast.Node) ast.Visitor {
switch n := node.(type) {
case *ast.CompositeLit:
// array, slice, and map composite literals may be simplified
@ -68,10 +66,13 @@ func (s *simplifier) Visit(node ast.Node) ast.Visitor {
// a slice expression of the form: s[a:len(s)]
// can be simplified to: s[a:]
// if s is "simple enough" (for now we only accept identifiers)
if n.Max != nil || s.hasDotImport {
//
// Note: This may not be correct because len may have been redeclared in another
// file belonging to the same package. However, this is extremely unlikely
// and so far (April 2016, after years of supporting this rewrite feature)
// has never come up, so let's keep it working as is (see also #15153).
if n.Max != nil {
// - 3-index slices always require the 2nd and 3rd index
// - if dot imports are present, we cannot be certain that an
// unresolved "len" identifier refers to the predefined len()
break
}
if s, _ := n.X.(*ast.Ident); s != nil && s.Obj != nil {
@ -118,20 +119,11 @@ func isBlank(x ast.Expr) bool {
}
func simplify(f *ast.File) {
var s simplifier
// determine if f contains dot imports
for _, imp := range f.Imports {
if imp.Name != nil && imp.Name.Name == "." {
s.hasDotImport = true
break
}
}
// remove empty declarations such as "const ()", etc
removeEmptyDeclGroups(f)
ast.Walk(&s, f)
var s simplifier
ast.Walk(s, f)
}
func removeEmptyDeclGroups(f *ast.File) {

63
src/cmd/gofmt/testdata/slices2.golden vendored
View file

@ -1,63 +0,0 @@
//gofmt -s
// Test cases for slice expression simplification.
// Because of a dot import, these slices must remain untouched.
package p
import . "math"
var (
a [10]byte
b [20]float32
s []int
t struct {
s []byte
}
_ = a[0:]
_ = a[1:10]
_ = a[2:len(a)]
_ = a[3:(len(a))]
_ = a[len(a) : len(a)-1]
_ = a[0:len(b)]
_ = a[:]
_ = a[:10]
_ = a[:len(a)]
_ = a[:(len(a))]
_ = a[:len(a)-1]
_ = a[:len(b)]
_ = s[0:]
_ = s[1:10]
_ = s[2:len(s)]
_ = s[3:(len(s))]
_ = s[len(a) : len(s)-1]
_ = s[0:len(b)]
_ = s[:]
_ = s[:10]
_ = s[:len(s)]
_ = s[:(len(s))]
_ = s[:len(s)-1]
_ = s[:len(b)]
_ = t.s[0:]
_ = t.s[1:10]
_ = t.s[2:len(t.s)]
_ = t.s[3:(len(t.s))]
_ = t.s[len(a) : len(t.s)-1]
_ = t.s[0:len(b)]
_ = t.s[:]
_ = t.s[:10]
_ = t.s[:len(t.s)]
_ = t.s[:(len(t.s))]
_ = t.s[:len(t.s)-1]
_ = t.s[:len(b)]
)
func _() {
s := s[0:len(s)]
_ = s
}

63
src/cmd/gofmt/testdata/slices2.input vendored
View file

@ -1,63 +0,0 @@
//gofmt -s
// Test cases for slice expression simplification.
// Because of a dot import, these slices must remain untouched.
package p
import . "math"
var (
a [10]byte
b [20]float32
s []int
t struct {
s []byte
}
_ = a[0:]
_ = a[1:10]
_ = a[2:len(a)]
_ = a[3:(len(a))]
_ = a[len(a) : len(a)-1]
_ = a[0:len(b)]
_ = a[:]
_ = a[:10]
_ = a[:len(a)]
_ = a[:(len(a))]
_ = a[:len(a)-1]
_ = a[:len(b)]
_ = s[0:]
_ = s[1:10]
_ = s[2:len(s)]
_ = s[3:(len(s))]
_ = s[len(a) : len(s)-1]
_ = s[0:len(b)]
_ = s[:]
_ = s[:10]
_ = s[:len(s)]
_ = s[:(len(s))]
_ = s[:len(s)-1]
_ = s[:len(b)]
_ = t.s[0:]
_ = t.s[1:10]
_ = t.s[2:len(t.s)]
_ = t.s[3:(len(t.s))]
_ = t.s[len(a) : len(t.s)-1]
_ = t.s[0:len(b)]
_ = t.s[:]
_ = t.s[:10]
_ = t.s[:len(t.s)]
_ = t.s[:(len(t.s))]
_ = t.s[:len(t.s)-1]
_ = t.s[:len(b)]
)
func _() {
s := s[0:len(s)]
_ = s
}