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// 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:
fmt.Fprintf(buf, "(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:
WriteExpr(buf, x.Type)
buf.WriteByte('{')
if len(x.Elts) > 0 {
buf.WriteString("…")
}
buf.WriteByte('}')
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)
}
}