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cmd/gofmt: make gofmt -s simplify slices in presence of dot-imports
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>
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@ -10,11 +10,9 @@ import (
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"reflect"
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)
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type simplifier struct {
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hasDotImport bool // package file contains: import . "some/import/path"
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}
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type simplifier struct{}
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func (s *simplifier) Visit(node ast.Node) ast.Visitor {
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func (s simplifier) Visit(node ast.Node) ast.Visitor {
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switch n := node.(type) {
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case *ast.CompositeLit:
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// array, slice, and map composite literals may be simplified
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@ -68,10 +66,13 @@ func (s *simplifier) Visit(node ast.Node) ast.Visitor {
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// a slice expression of the form: s[a:len(s)]
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// can be simplified to: s[a:]
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// if s is "simple enough" (for now we only accept identifiers)
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if n.Max != nil || s.hasDotImport {
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//
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// Note: This may not be correct because len may have been redeclared in another
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// file belonging to the same package. However, this is extremely unlikely
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// and so far (April 2016, after years of supporting this rewrite feature)
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// has never come up, so let's keep it working as is (see also #15153).
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if n.Max != nil {
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// - 3-index slices always require the 2nd and 3rd index
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// - if dot imports are present, we cannot be certain that an
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// unresolved "len" identifier refers to the predefined len()
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break
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}
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if s, _ := n.X.(*ast.Ident); s != nil && s.Obj != nil {
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@ -118,20 +119,11 @@ func isBlank(x ast.Expr) bool {
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}
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func simplify(f *ast.File) {
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var s simplifier
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// determine if f contains dot imports
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for _, imp := range f.Imports {
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if imp.Name != nil && imp.Name.Name == "." {
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s.hasDotImport = true
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break
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}
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}
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// remove empty declarations such as "const ()", etc
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removeEmptyDeclGroups(f)
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ast.Walk(&s, f)
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var s simplifier
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ast.Walk(s, f)
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}
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func removeEmptyDeclGroups(f *ast.File) {
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63
src/cmd/gofmt/testdata/slices2.golden
vendored
63
src/cmd/gofmt/testdata/slices2.golden
vendored
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@ -1,63 +0,0 @@
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//gofmt -s
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// Test cases for slice expression simplification.
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// Because of a dot import, these slices must remain untouched.
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package p
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import . "math"
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var (
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a [10]byte
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b [20]float32
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s []int
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t struct {
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s []byte
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}
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_ = a[0:]
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_ = a[1:10]
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_ = a[2:len(a)]
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_ = a[3:(len(a))]
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_ = a[len(a) : len(a)-1]
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_ = a[0:len(b)]
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_ = a[:]
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_ = a[:10]
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_ = a[:len(a)]
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_ = a[:(len(a))]
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_ = a[:len(a)-1]
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_ = a[:len(b)]
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_ = s[0:]
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_ = s[1:10]
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_ = s[2:len(s)]
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_ = s[3:(len(s))]
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_ = s[len(a) : len(s)-1]
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_ = s[0:len(b)]
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_ = s[:]
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_ = s[:10]
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_ = s[:len(s)]
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_ = s[:(len(s))]
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_ = s[:len(s)-1]
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_ = s[:len(b)]
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_ = t.s[0:]
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_ = t.s[1:10]
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_ = t.s[2:len(t.s)]
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_ = t.s[3:(len(t.s))]
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_ = t.s[len(a) : len(t.s)-1]
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_ = t.s[0:len(b)]
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_ = t.s[:]
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_ = t.s[:10]
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_ = t.s[:len(t.s)]
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_ = t.s[:(len(t.s))]
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_ = t.s[:len(t.s)-1]
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_ = t.s[:len(b)]
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)
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func _() {
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s := s[0:len(s)]
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_ = s
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}
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63
src/cmd/gofmt/testdata/slices2.input
vendored
63
src/cmd/gofmt/testdata/slices2.input
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@ -1,63 +0,0 @@
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//gofmt -s
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// Test cases for slice expression simplification.
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// Because of a dot import, these slices must remain untouched.
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package p
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import . "math"
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var (
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a [10]byte
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b [20]float32
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s []int
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t struct {
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s []byte
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}
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_ = a[0:]
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_ = a[1:10]
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_ = a[2:len(a)]
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_ = a[3:(len(a))]
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_ = a[len(a) : len(a)-1]
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_ = a[0:len(b)]
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_ = a[:]
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_ = a[:10]
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_ = a[:len(a)]
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_ = a[:(len(a))]
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_ = a[:len(a)-1]
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_ = a[:len(b)]
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_ = s[0:]
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_ = s[1:10]
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_ = s[2:len(s)]
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_ = s[3:(len(s))]
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_ = s[len(a) : len(s)-1]
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_ = s[0:len(b)]
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_ = s[:]
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_ = s[:10]
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_ = s[:len(s)]
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_ = s[:(len(s))]
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_ = s[:len(s)-1]
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_ = s[:len(b)]
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_ = t.s[0:]
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_ = t.s[1:10]
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_ = t.s[2:len(t.s)]
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_ = t.s[3:(len(t.s))]
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_ = t.s[len(a) : len(t.s)-1]
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_ = t.s[0:len(b)]
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_ = t.s[:]
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_ = t.s[:10]
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_ = t.s[:len(t.s)]
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_ = t.s[:(len(t.s))]
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_ = t.s[:len(t.s)-1]
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_ = t.s[:len(b)]
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)
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func _() {
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s := s[0:len(s)]
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_ = s
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}
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