--- /dev/null
+// Copyright 2010 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.
+
+package main
+
+import (
+ "go/ast"
+ "go/token"
+ "reflect"
+)
+
+type simplifier struct{}
+
+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
+ outer := n
+ var keyType, eltType ast.Expr
+ switch typ := outer.Type.(type) {
+ case *ast.ArrayType:
+ eltType = typ.Elt
+ case *ast.MapType:
+ keyType = typ.Key
+ eltType = typ.Value
+ }
+
+ if eltType != nil {
+ var ktyp reflect.Value
+ if keyType != nil {
+ ktyp = reflect.ValueOf(keyType)
+ }
+ typ := reflect.ValueOf(eltType)
+ for i, x := range outer.Elts {
+ px := &outer.Elts[i]
+ // look at value of indexed/named elements
+ if t, ok := x.(*ast.KeyValueExpr); ok {
+ if keyType != nil {
+ s.simplifyLiteral(ktyp, keyType, t.Key, &t.Key)
+ }
+ x = t.Value
+ px = &t.Value
+ }
+ s.simplifyLiteral(typ, eltType, x, px)
+ }
+ // node was simplified - stop walk (there are no subnodes to simplify)
+ return nil
+ }
+
+ case *ast.SliceExpr:
+ // 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)
+ //
+ // 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
+ break
+ }
+ if s, _ := n.X.(*ast.Ident); s != nil && s.Obj != nil {
+ // the array/slice object is a single, resolved identifier
+ if call, _ := n.High.(*ast.CallExpr); call != nil && len(call.Args) == 1 && !call.Ellipsis.IsValid() {
+ // the high expression is a function call with a single argument
+ if fun, _ := call.Fun.(*ast.Ident); fun != nil && fun.Name == "len" && fun.Obj == nil {
+ // the function called is "len" and it is not locally defined; and
+ // because we don't have dot imports, it must be the predefined len()
+ if arg, _ := call.Args[0].(*ast.Ident); arg != nil && arg.Obj == s.Obj {
+ // the len argument is the array/slice object
+ n.High = nil
+ }
+ }
+ }
+ }
+ // Note: We could also simplify slice expressions of the form s[0:b] to s[:b]
+ // but we leave them as is since sometimes we want to be very explicit
+ // about the lower bound.
+ // An example where the 0 helps:
+ // x, y, z := b[0:2], b[2:4], b[4:6]
+ // An example where it does not:
+ // x, y := b[:n], b[n:]
+
+ case *ast.RangeStmt:
+ // - a range of the form: for x, _ = range v {...}
+ // can be simplified to: for x = range v {...}
+ // - a range of the form: for _ = range v {...}
+ // can be simplified to: for range v {...}
+ if isBlank(n.Value) {
+ n.Value = nil
+ }
+ if isBlank(n.Key) && n.Value == nil {
+ n.Key = nil
+ }
+ }
+
+ return s
+}
+
+func (s simplifier) simplifyLiteral(typ reflect.Value, astType, x ast.Expr, px *ast.Expr) {
+ ast.Walk(s, x) // simplify x
+
+ // if the element is a composite literal and its literal type
+ // matches the outer literal's element type exactly, the inner
+ // literal type may be omitted
+ if inner, ok := x.(*ast.CompositeLit); ok {
+ if match(nil, typ, reflect.ValueOf(inner.Type)) {
+ inner.Type = nil
+ }
+ }
+ // if the outer literal's element type is a pointer type *T
+ // and the element is & of a composite literal of type T,
+ // the inner &T may be omitted.
+ if ptr, ok := astType.(*ast.StarExpr); ok {
+ if addr, ok := x.(*ast.UnaryExpr); ok && addr.Op == token.AND {
+ if inner, ok := addr.X.(*ast.CompositeLit); ok {
+ if match(nil, reflect.ValueOf(ptr.X), reflect.ValueOf(inner.Type)) {
+ inner.Type = nil // drop T
+ *px = inner // drop &
+ }
+ }
+ }
+ }
+}
+
+func isBlank(x ast.Expr) bool {
+ ident, ok := x.(*ast.Ident)
+ return ok && ident.Name == "_"
+}
+
+func simplify(f *ast.File) {
+ // remove empty declarations such as "const ()", etc
+ removeEmptyDeclGroups(f)
+
+ var s simplifier
+ ast.Walk(s, f)
+}
+
+func removeEmptyDeclGroups(f *ast.File) {
+ i := 0
+ for _, d := range f.Decls {
+ if g, ok := d.(*ast.GenDecl); !ok || !isEmpty(f, g) {
+ f.Decls[i] = d
+ i++
+ }
+ }
+ f.Decls = f.Decls[:i]
+}
+
+func isEmpty(f *ast.File, g *ast.GenDecl) bool {
+ if g.Doc != nil || g.Specs != nil {
+ return false
+ }
+
+ for _, c := range f.Comments {
+ // if there is a comment in the declaration, it is not considered empty
+ if g.Pos() <= c.Pos() && c.End() <= g.End() {
+ return false
+ }
+ }
+
+ return true
+}
projects / dotfiles / .git / blobdiff