internal compiler error: unexpected panic using attributes

[qorost]

The compiler failed when using a self defined attribute (compiler plugin), the code is as below:

The source code to use it

#![feature(plugin)]
#![feature(custom_attribute)]
#![plugin(myplugin)]

#[check]
fn main() {
    let x = hello_AA!();
    println!("x.x = {}",x.x);
}

The source code of the plugin code (built successfully)

#![crate_type = "dylib"]
#![feature(plugin_registrar, quote, rustc_private,debug)]
#![feature(box_syntax, rustc_private)]

#![allow(dead_code)]
#![allow(unused_imports)]
extern crate syntax;
#[macro_use]
extern crate rustc;
extern crate rustc_plugin;
extern crate syntax_pos;

use syntax::ast::{self, StructField, Unsafety};
use syntax::codemap::DUMMY_SP;
use syntax::ext::base::*;
use syntax::ext::quote::rt::ToTokens;
use syntax::parse::{self, token};
use syntax::ptr::P;
use syntax::symbol::Symbol;
use syntax::tokenstream::TokenTree;
use syntax_pos::Span;
use rustc_plugin::Registry;


//for fold
use syntax::codemap::{BytePos, Spanned};
use std::fmt::{self, Display, Formatter};
use syntax::fold::{self, Folder};
use syntax::ext::build::AstBuilder;
use syntax::ast::{BinOpKind, Block, Expr, ExprKind, Item, ItemKind, Lit,
                  LitKind, Mac, MetaItem, MetaItemKind, NestedMetaItemKind,
                  Path, PathSegment, Stmt, StmtKind, UnOp,FnDecl};
use syntax::util::small_vector::SmallVector;

struct Refchecker<'a, 'cx: 'a> {
    cx: &'a mut ExtCtxt<'cx>,
    left: bool, //tell if the expr is in the left of the statment
}

impl<'a,'cx> Folder for Refchecker<'a, 'cx> {
}

#[plugin_registrar]
pub fn plugin_registrar(reg: &mut Registry) {
    #[cfg(feature = "debugmyplugin")]
    println!("DEBUG: IN the plugin_registrar expand_checkderef");
    reg.register_syntax_extension(
        Symbol::intern("check"),
        // FIXME (#22405): Replace `Box::new` with `box` here when/if possible.
        //MultiModifier(Box::new(expand_newcheckderef)));
        MultiModifier(Box::new(|cx: &mut ExtCtxt, _span: Span, mi: &MetaItem, a: Annotatable| {
           let mut checker = &mut Refchecker {
                cx: cx,
                left: false,
            };
            match a {
                Annotatable::Item(i) => Annotatable::Item (
                    checker.fold_item(i).expect_one("expected exactly one item")),
                Annotatable::TraitItem(i) => Annotatable::TraitItem (
                    i.map(|i| checker.fold_trait_item(i).expect_one("expected exactly one item"))),
                Annotatable::ImplItem(i) => Annotatable::ImplItem(
                    i.map(|i| checker.fold_impl_item(i).expect_one("expected exactly one item"))),
            }
        })));
}

The error mesage:

error: internal compiler error: unexpected panic

note: the compiler unexpectedly panicked. this is a bug.

note: we would appreciate a bug report: https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md#bug-reports

thread 'rustc' panicked at 'fold_mac disabled by default', /checkout/src/libsyntax/fold.rs:180
note: Run with `RUST_BACKTRACE=1` for a backtrace.

backtrace

thread 'rustc' panicked at 'fold_mac disabled by default', /checkout/src/libsyntax/fold.rs:180
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
stack backtrace:
   0: syntax::fold::Folder::fold_mac
             at ./<panic macros>:3
   1: syntax::fold::noop_fold_expr
             at /checkout/src/libsyntax/fold.rs:1256
   2: syntax::fold::Folder::fold_expr::{{closure}}
             at /checkout/src/libsyntax/fold.rs:112
   3: <syntax::ptr::P<T>>::map
             at /checkout/src/libsyntax/ptr.rs:88
   4: syntax::fold::Folder::fold_expr
             at /checkout/src/libsyntax/fold.rs:112
   5: syntax::fold::noop_fold_local::{{closure}}::{{closure}}
             at /checkout/src/libsyntax/fold.rs:482
   6: <core::option::Option<T>>::map
             at /checkout/src/libcore/option.rs:392
   7: syntax::fold::noop_fold_local::{{closure}}
             at /checkout/src/libsyntax/fold.rs:482
   8: <syntax::ptr::P<T>>::map
             at /checkout/src/libsyntax/ptr.rs:88
   9: syntax::fold::noop_fold_local
             at /checkout/src/libsyntax/fold.rs:478
  10: syntax::fold::Folder::fold_local
             at /checkout/src/libsyntax/fold.rs:176
  11: syntax::fold::noop_fold_stmt_kind
             at /checkout/src/libsyntax/fold.rs:1299
  12: syntax::fold::noop_fold_stmt
             at /checkout/src/libsyntax/fold.rs:1292
  13: syntax::fold::Folder::fold_stmt
             at /checkout/src/libsyntax/fold.rs:100
  14: syntax::fold::noop_fold_block::{{closure}}::{{closure}}
             at /checkout/src/libsyntax/fold.rs:844
  15: <collections::vec::Vec<T> as syntax::util::move_map::MoveMap<T>>::move_flat_map
             at /checkout/src/libsyntax/util/move_map.rs:40
  16: syntax::fold::noop_fold_block::{{closure}}
             at /checkout/src/libsyntax/fold.rs:844
  17: <syntax::ptr::P<T>>::map
             at /checkout/src/libsyntax/ptr.rs:88
  18: syntax::fold::noop_fold_block
             at /checkout/src/libsyntax/fold.rs:842
  19: syntax::fold::Folder::fold_block
             at /checkout/src/libsyntax/fold.rs:96
  20: syntax::fold::noop_fold_item_kind
             at /checkout/src/libsyntax/fold.rs:865
  21: syntax::fold::Folder::fold_item_kind
             at /checkout/src/libsyntax/fold.rs:80
  22: syntax::fold::noop_fold_item_simple
             at /checkout/src/libsyntax/fold.rs:1013
  23: syntax::fold::Folder::fold_item_simple
             at /checkout/src/libsyntax/fold.rs:72
  24: syntax::fold::noop_fold_item::{{closure}}
             at /checkout/src/libsyntax/fold.rs:1002
  25: <syntax::ptr::P<T>>::map
             at /checkout/src/libsyntax/ptr.rs:88
  26: syntax::fold::noop_fold_item
             at /checkout/src/libsyntax/fold.rs:1002
  27: syntax::fold::Folder::fold_item
             at /checkout/src/libsyntax/fold.rs:68
  28: myplugin::plugin_registrar::{{closure}}
             at ./myplugin/src/lib.rs:83
  29: <F as syntax::ext::base::MultiItemModifier>::expand
             at /checkout/src/libsyntax/ext/base.rs:143
  30: syntax::ext::expand::MacroExpander::expand_invoc
  31: syntax::ext::expand::MacroExpander::expand
  32: syntax::ext::expand::MacroExpander::expand_crate
  33: rustc_driver::driver::phase_2_configure_and_expand::{{closure}}
  34: rustc_driver::driver::phase_2_configure_and_expand
  35: rustc_driver::driver::compile_input
  36: rustc_driver::run_compiler
  37: std::panicking::try::do_call
  38: __rust_maybe_catch_panic
             at /checkout/src/libpanic_unwind/lib.rs:98
  39: <F as alloc::boxed::FnBox<A>>::call_box
  40: std::sys::imp::thread::Thread::new::thread_start
             at /checkout/src/liballoc/boxed.rs:650
             at /checkout/src/libstd/sys_common/thread.rs:21
             at /checkout/src/libstd/sys/unix/thread.rs:84
  41: start_thread
  42: clone

error: Could not compile `macro_compiler_conflicts`.

Running on:
rustc 1.18.0-nightly (c58c928 2017-04-11)

System

No LSB modules are available.
Distributor ID:	Ubuntu
Description:	Ubuntu 16.04.2 LTS
Release:	16.04
Codename:	xenial

[sinkuu]

This is intended behavior of syntax::fold::Folder. fold_mac method has to be overridden when used on an AST before macro expansion.

rust/src/libsyntax/fold.rs

Lines 183 to 190 in a7d98c7

	fn fold_mac(&mut self, _mac: Mac) -> Mac {
	panic!("fold_mac disabled by default");
	// NB: see note about macros above.
	// if you really want a folder that
	// works on macros, use this
	// definition in your trait impl:
	// fold::noop_fold_mac(_mac, self)
	}

[cjgillot]

Syntactic plugins have been removed by #66647.