|
| 1 | +// Copyright 2010 The Go Authors. All rights reserved. |
| 2 | +// Use of this source code is governed by a BSD-style |
| 3 | +// license that can be found in the LICENSE file. |
| 4 | + |
| 5 | +package imports |
| 6 | + |
| 7 | +import ( |
| 8 | + "go/ast" |
| 9 | + "go/token" |
| 10 | + "reflect" |
| 11 | +) |
| 12 | + |
| 13 | +type simplifier struct{} |
| 14 | + |
| 15 | +func (s simplifier) Visit(node ast.Node) ast.Visitor { |
| 16 | + switch n := node.(type) { |
| 17 | + case *ast.CompositeLit: |
| 18 | + // array, slice, and map composite literals may be simplified |
| 19 | + outer := n |
| 20 | + var keyType, eltType ast.Expr |
| 21 | + switch typ := outer.Type.(type) { |
| 22 | + case *ast.ArrayType: |
| 23 | + eltType = typ.Elt |
| 24 | + case *ast.MapType: |
| 25 | + keyType = typ.Key |
| 26 | + eltType = typ.Value |
| 27 | + } |
| 28 | + |
| 29 | + if eltType != nil { |
| 30 | + var ktyp reflect.Value |
| 31 | + if keyType != nil { |
| 32 | + ktyp = reflect.ValueOf(keyType) |
| 33 | + } |
| 34 | + typ := reflect.ValueOf(eltType) |
| 35 | + for i, x := range outer.Elts { |
| 36 | + px := &outer.Elts[i] |
| 37 | + // look at value of indexed/named elements |
| 38 | + if t, ok := x.(*ast.KeyValueExpr); ok { |
| 39 | + if keyType != nil { |
| 40 | + s.simplifyLiteral(ktyp, keyType, t.Key, &t.Key) |
| 41 | + } |
| 42 | + x = t.Value |
| 43 | + px = &t.Value |
| 44 | + } |
| 45 | + s.simplifyLiteral(typ, eltType, x, px) |
| 46 | + } |
| 47 | + // node was simplified - stop walk (there are no subnodes to simplify) |
| 48 | + return nil |
| 49 | + } |
| 50 | + |
| 51 | + case *ast.SliceExpr: |
| 52 | + // a slice expression of the form: s[a:len(s)] |
| 53 | + // can be simplified to: s[a:] |
| 54 | + // if s is "simple enough" (for now we only accept identifiers) |
| 55 | + // |
| 56 | + // Note: This may not be correct because len may have been redeclared in |
| 57 | + // the same package. However, this is extremely unlikely and so far |
| 58 | + // (April 2022, after years of supporting this rewrite feature) |
| 59 | + // has never come up, so let's keep it working as is (see also #15153). |
| 60 | + // |
| 61 | + // Also note that this code used to use go/ast's object tracking, |
| 62 | + // which was removed in exchange for go/parser.Mode.SkipObjectResolution. |
| 63 | + // False positives are extremely unlikely as described above, |
| 64 | + // and go/ast's object tracking is incomplete in any case. |
| 65 | + if n.Max != nil { |
| 66 | + // - 3-index slices always require the 2nd and 3rd index |
| 67 | + break |
| 68 | + } |
| 69 | + if s, _ := n.X.(*ast.Ident); s != nil { |
| 70 | + // the array/slice object is a single identifier |
| 71 | + if call, _ := n.High.(*ast.CallExpr); call != nil && len(call.Args) == 1 && !call.Ellipsis.IsValid() { |
| 72 | + // the high expression is a function call with a single argument |
| 73 | + if fun, _ := call.Fun.(*ast.Ident); fun != nil && fun.Name == "len" { |
| 74 | + // the function called is "len" |
| 75 | + if arg, _ := call.Args[0].(*ast.Ident); arg != nil && arg.Name == s.Name { |
| 76 | + // the len argument is the array/slice object |
| 77 | + n.High = nil |
| 78 | + } |
| 79 | + } |
| 80 | + } |
| 81 | + } |
| 82 | + // Note: We could also simplify slice expressions of the form s[0:b] to s[:b] |
| 83 | + // but we leave them as is since sometimes we want to be very explicit |
| 84 | + // about the lower bound. |
| 85 | + // An example where the 0 helps: |
| 86 | + // x, y, z := b[0:2], b[2:4], b[4:6] |
| 87 | + // An example where it does not: |
| 88 | + // x, y := b[:n], b[n:] |
| 89 | + |
| 90 | + case *ast.RangeStmt: |
| 91 | + // - a range of the form: for x, _ = range v {...} |
| 92 | + // can be simplified to: for x = range v {...} |
| 93 | + // - a range of the form: for _ = range v {...} |
| 94 | + // can be simplified to: for range v {...} |
| 95 | + if isBlank(n.Value) { |
| 96 | + n.Value = nil |
| 97 | + } |
| 98 | + if isBlank(n.Key) && n.Value == nil { |
| 99 | + n.Key = nil |
| 100 | + } |
| 101 | + } |
| 102 | + |
| 103 | + return s |
| 104 | +} |
| 105 | + |
| 106 | +func (s simplifier) simplifyLiteral(typ reflect.Value, astType, x ast.Expr, px *ast.Expr) { |
| 107 | + ast.Walk(s, x) // simplify x |
| 108 | + |
| 109 | + // if the element is a composite literal and its literal type |
| 110 | + // matches the outer literal's element type exactly, the inner |
| 111 | + // literal type may be omitted |
| 112 | + if inner, ok := x.(*ast.CompositeLit); ok { |
| 113 | + if match(nil, typ, reflect.ValueOf(inner.Type)) { |
| 114 | + inner.Type = nil |
| 115 | + } |
| 116 | + } |
| 117 | + // if the outer literal's element type is a pointer type *T |
| 118 | + // and the element is & of a composite literal of type T, |
| 119 | + // the inner &T may be omitted. |
| 120 | + if ptr, ok := astType.(*ast.StarExpr); ok { |
| 121 | + if addr, ok := x.(*ast.UnaryExpr); ok && addr.Op == token.AND { |
| 122 | + if inner, ok := addr.X.(*ast.CompositeLit); ok { |
| 123 | + if match(nil, reflect.ValueOf(ptr.X), reflect.ValueOf(inner.Type)) { |
| 124 | + inner.Type = nil // drop T |
| 125 | + *px = inner // drop & |
| 126 | + } |
| 127 | + } |
| 128 | + } |
| 129 | + } |
| 130 | +} |
| 131 | + |
| 132 | +func isBlank(x ast.Expr) bool { |
| 133 | + ident, ok := x.(*ast.Ident) |
| 134 | + return ok && ident.Name == "_" |
| 135 | +} |
| 136 | + |
| 137 | +func simplify(f *ast.File) { |
| 138 | + // remove empty declarations such as "const ()", etc |
| 139 | + removeEmptyDeclGroups(f) |
| 140 | + |
| 141 | + var s simplifier |
| 142 | + ast.Walk(s, f) |
| 143 | +} |
| 144 | + |
| 145 | +func removeEmptyDeclGroups(f *ast.File) { |
| 146 | + i := 0 |
| 147 | + for _, d := range f.Decls { |
| 148 | + if g, ok := d.(*ast.GenDecl); !ok || !isEmpty(f, g) { |
| 149 | + f.Decls[i] = d |
| 150 | + i++ |
| 151 | + } |
| 152 | + } |
| 153 | + f.Decls = f.Decls[:i] |
| 154 | +} |
| 155 | + |
| 156 | +func isEmpty(f *ast.File, g *ast.GenDecl) bool { |
| 157 | + if g.Doc != nil || g.Specs != nil { |
| 158 | + return false |
| 159 | + } |
| 160 | + |
| 161 | + for _, c := range f.Comments { |
| 162 | + // if there is a comment in the declaration, it is not considered empty |
| 163 | + if g.Pos() <= c.Pos() && c.End() <= g.End() { |
| 164 | + return false |
| 165 | + } |
| 166 | + } |
| 167 | + |
| 168 | + return true |
| 169 | +} |
0 commit comments