| // 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 implements printing of expressions. |
| |
| package types |
| |
| import ( |
| "bytes" |
| "fmt" |
| "go/ast" |
| "go/internal/typeparams" |
| ) |
| |
| // ExprString returns the (possibly shortened) string representation for x. |
| // Shortened representations are suitable for user interfaces but may not |
| // necessarily follow Go syntax. |
| func ExprString(x ast.Expr) string { |
| var buf bytes.Buffer |
| WriteExpr(&buf, x) |
| return buf.String() |
| } |
| |
| // WriteExpr writes the (possibly shortened) string representation for x to buf. |
| // Shortened representations are suitable for user interfaces but may not |
| // necessarily follow Go syntax. |
| func WriteExpr(buf *bytes.Buffer, x ast.Expr) { |
| // The AST preserves source-level parentheses so there is |
| // no need to introduce them here to correct for different |
| // operator precedences. (This assumes that the AST was |
| // generated by a Go parser.) |
| |
| switch x := x.(type) { |
| default: |
| buf.WriteString(fmt.Sprintf("(ast: %T)", x)) // nil, ast.BadExpr, ast.KeyValueExpr |
| |
| case *ast.Ident: |
| buf.WriteString(x.Name) |
| |
| case *ast.Ellipsis: |
| buf.WriteString("...") |
| if x.Elt != nil { |
| WriteExpr(buf, x.Elt) |
| } |
| |
| case *ast.BasicLit: |
| buf.WriteString(x.Value) |
| |
| case *ast.FuncLit: |
| buf.WriteByte('(') |
| WriteExpr(buf, x.Type) |
| buf.WriteString(" literal)") // shortened |
| |
| case *ast.CompositeLit: |
| buf.WriteByte('(') |
| WriteExpr(buf, x.Type) |
| buf.WriteString(" literal)") // shortened |
| |
| case *ast.ParenExpr: |
| buf.WriteByte('(') |
| WriteExpr(buf, x.X) |
| buf.WriteByte(')') |
| |
| case *ast.SelectorExpr: |
| WriteExpr(buf, x.X) |
| buf.WriteByte('.') |
| buf.WriteString(x.Sel.Name) |
| |
| case *ast.IndexExpr, *ast.IndexListExpr: |
| ix := typeparams.UnpackIndexExpr(x) |
| WriteExpr(buf, ix.X) |
| buf.WriteByte('[') |
| writeExprList(buf, ix.Indices) |
| buf.WriteByte(']') |
| |
| case *ast.SliceExpr: |
| WriteExpr(buf, x.X) |
| buf.WriteByte('[') |
| if x.Low != nil { |
| WriteExpr(buf, x.Low) |
| } |
| buf.WriteByte(':') |
| if x.High != nil { |
| WriteExpr(buf, x.High) |
| } |
| if x.Slice3 { |
| buf.WriteByte(':') |
| if x.Max != nil { |
| WriteExpr(buf, x.Max) |
| } |
| } |
| buf.WriteByte(']') |
| |
| case *ast.TypeAssertExpr: |
| WriteExpr(buf, x.X) |
| buf.WriteString(".(") |
| WriteExpr(buf, x.Type) |
| buf.WriteByte(')') |
| |
| case *ast.CallExpr: |
| WriteExpr(buf, x.Fun) |
| buf.WriteByte('(') |
| writeExprList(buf, x.Args) |
| if x.Ellipsis.IsValid() { |
| buf.WriteString("...") |
| } |
| buf.WriteByte(')') |
| |
| case *ast.StarExpr: |
| buf.WriteByte('*') |
| WriteExpr(buf, x.X) |
| |
| case *ast.UnaryExpr: |
| buf.WriteString(x.Op.String()) |
| WriteExpr(buf, x.X) |
| |
| case *ast.BinaryExpr: |
| WriteExpr(buf, x.X) |
| buf.WriteByte(' ') |
| buf.WriteString(x.Op.String()) |
| buf.WriteByte(' ') |
| WriteExpr(buf, x.Y) |
| |
| case *ast.ArrayType: |
| buf.WriteByte('[') |
| if x.Len != nil { |
| WriteExpr(buf, x.Len) |
| } |
| buf.WriteByte(']') |
| WriteExpr(buf, x.Elt) |
| |
| case *ast.StructType: |
| buf.WriteString("struct{") |
| writeFieldList(buf, x.Fields.List, "; ", false) |
| buf.WriteByte('}') |
| |
| case *ast.FuncType: |
| buf.WriteString("func") |
| writeSigExpr(buf, x) |
| |
| case *ast.InterfaceType: |
| buf.WriteString("interface{") |
| writeFieldList(buf, x.Methods.List, "; ", true) |
| buf.WriteByte('}') |
| |
| case *ast.MapType: |
| buf.WriteString("map[") |
| WriteExpr(buf, x.Key) |
| buf.WriteByte(']') |
| WriteExpr(buf, x.Value) |
| |
| case *ast.ChanType: |
| var s string |
| switch x.Dir { |
| case ast.SEND: |
| s = "chan<- " |
| case ast.RECV: |
| s = "<-chan " |
| default: |
| s = "chan " |
| } |
| buf.WriteString(s) |
| WriteExpr(buf, x.Value) |
| } |
| } |
| |
| func writeSigExpr(buf *bytes.Buffer, sig *ast.FuncType) { |
| buf.WriteByte('(') |
| writeFieldList(buf, sig.Params.List, ", ", false) |
| buf.WriteByte(')') |
| |
| res := sig.Results |
| n := res.NumFields() |
| if n == 0 { |
| // no result |
| return |
| } |
| |
| buf.WriteByte(' ') |
| if n == 1 && len(res.List[0].Names) == 0 { |
| // single unnamed result |
| WriteExpr(buf, res.List[0].Type) |
| return |
| } |
| |
| // multiple or named result(s) |
| buf.WriteByte('(') |
| writeFieldList(buf, res.List, ", ", false) |
| buf.WriteByte(')') |
| } |
| |
| func writeFieldList(buf *bytes.Buffer, list []*ast.Field, sep string, iface bool) { |
| for i, f := range list { |
| if i > 0 { |
| buf.WriteString(sep) |
| } |
| |
| // field list names |
| writeIdentList(buf, f.Names) |
| |
| // types of interface methods consist of signatures only |
| if sig, _ := f.Type.(*ast.FuncType); sig != nil && iface { |
| writeSigExpr(buf, sig) |
| continue |
| } |
| |
| // named fields are separated with a blank from the field type |
| if len(f.Names) > 0 { |
| buf.WriteByte(' ') |
| } |
| |
| WriteExpr(buf, f.Type) |
| |
| // ignore tag |
| } |
| } |
| |
| func writeIdentList(buf *bytes.Buffer, list []*ast.Ident) { |
| for i, x := range list { |
| if i > 0 { |
| buf.WriteString(", ") |
| } |
| buf.WriteString(x.Name) |
| } |
| } |
| |
| func writeExprList(buf *bytes.Buffer, list []ast.Expr) { |
| for i, x := range list { |
| if i > 0 { |
| buf.WriteString(", ") |
| } |
| WriteExpr(buf, x) |
| } |
| } |