我正在尝试在Go语言中进行一些元编程，想要使用go/ast包。
下面是创建AST的代码片段：
// Create an AST
fooFn := &ast.FuncDecl{
Name: &ast.Ident{Name: "foofn"},
Body: &ast.BlockStmt{
List: []ast.Stmt{&ast.ExprStmt{
X: &ast.CallExpr{
Fun: &ast.Ident{Name: "println"},
Args: []ast.Expr{
&ast.BasicLit{Kind: token.INT, Value: "42"},
},
},
}},
},
}
f := &ast.File{
Name: &ast.Ident{Name: "foopackage"},
Decls: []ast.Decl{fooFn},
Scope: &ast.Scope{
Objects: map[string]*ast.Object{
"Foo": &ast.Object{
Kind: ast.Fun,
Name: "Foo",
Decl: fooFn,
},
},
},
}
请参见完整代码，链接为http://play.golang.org/p/zTJdnqVx__，该代码应生成以下输出：
panic: runtime error: invalid memory address or nil pointer dereference
[signal 0xb code=0xffffffff addr=0x0 pc=0x773ae]
goroutine 16 [running]:
runtime.panic(0x18b5a0, 0x24c8af)
/tmp/sandbox/go/src/pkg/runtime/panic.c:279 +0x120
go/ast.(*FuncType).Pos(0x0, 0x1c827eb4, 0xfefd02b8, 0x10422360)
/tmp/sandbox/go/src/pkg/go/ast/ast.go:446 +0x2e
go/ast.(*FuncDecl).Pos(0x10422360, 0x10422360, 0x47, 0xfeee1cb0)
/tmp/sandbox/go/src/pkg/go/ast/ast.go:933 +0x40
go/printer.(*printer).declList(0x10402840, 0x1040e108, 0x1, 0x1)
/tmp/sandbox/go/src/pkg/go/printer/nodes.go:1587 +0x180
go/printer.(*printer).file(0x10402840, 0x10442080)
/tmp/sandbox/go/src/pkg/go/printer/nodes.go:1597 +0x1e0
go/printer.(*printer).printNode(0x10402840, 0x184ba0, 0x10442080, 0x104223c0, 0x0, 0x0)
/tmp/sandbox/go/src/pkg/go/printer/printer.go:1087 +0xa40
go/printer.(*Config).fprint(0xfeee1e90, 0xfefd02d8, 0x10426180, 0x104181b0, 0x184ba0, 0x10442080, 0x104223c0, 0xfefd02d8, 0x0, 0x0)
/tmp/sandbox/go/src/pkg/go/printer/printer.go:1226 +0xc0
go/printer.(*Config).Fprint(0xfeee1e90, 0xfefd02d8, 0x10426180, 0x104181b0, 0x184ba0, 0x10442080, 0x0, 0x0)
/tmp/sandbox/go/src/pkg/go/printer/printer.go:1284 +0xa0
main.main()
/tmpfs/gosandbox-eb231fa6_4e4e43ec_79a6f993_ce4170ce_07ee185b/prog.go:46 +0x8c0
编辑：这里是可工作版本，FuncDelc.Type已设置并且Scope已删除（因为我只需要源代码缓冲区）：