Bug #20917: redo/next in nested begin block causes wrong order of execution

• Status: Open
• Assignee: -
• Target version: -
• ruby -v: ruby 3.3.5 (2024-09-03 revision ef084cc8f4) [x86_64-darwin24]
• Backport: 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN

[hoshiumiarata (Arata Hoshiumi)]

It seems that redo/next in a nested begin block can cause the wrong order of execution.
For example:

for _ in [0]
  puts 0
  begin
    puts 1
    begin
      puts 2
      redo
    ensure
      puts 3
    end
  ensure
    puts 4
    break
  end
end

It prints:

0
1
2
3
4
3
4
=> nil

But I think it should print:

0
1
2
3
4
=> nil

Because execution order should be:

1. puts 0
2. puts 1
3. puts 2
4. redo
5. unwind to nested ensure block
6. puts 3
7. unwind to outer ensure block
8. puts 4
9. break
10. end of loop

Interestingly enough, if we add an empty rescue block before any of the ensure blocks, then the execution order is correct.

[Eregon (Benoit Daloze)]

Indeed, it seems like a bug, I think as well the "redo jump/unwind/exception" should run ensure's and get to the "break jump/unwind/exception" which should override the redo like when a Ruby exception overrides another.

FWIW, this is 0 1 2 3 4 on both TruffleRuby and JRuby.

[kddnewton (Kevin Newton)]

Agreed this is a bug. For additional context, this is the same on parse.y and prism.

[wanabe (_ wanabe)]

I simplified the script to make it easier to read in ISEQ.

1.times do
  begin
    redo
  ensure
  end
ensure
  puts 1
  break
end

$ ./miniruby -v --dump=insn a.rb
ruby 4.1.0dev (2026-08-30T06:52:45Z :detached: a889da909c) +PRISM [x86_64-linux]
== disasm: #<ISeq:<main>@a.rb:1 (1,0)-(9,3)>
== catch table
| catch type: break  st: 0000 ed: 0004 sp: 0000 cont: 0004
| == disasm: #<ISeq:block in <main>@a.rb:1 (1,8)-(9,3)>
| == catch table
| | catch type: ensure st: 0001 ed: 0001 sp: 0001 cont: 0014
| | == disasm: #<ISeq:ensure in block in <main>@a.rb:4 (4,2)-(5,5)>
| | local table (size: 1, argc: 0 [opts: 0, rest: -1, post: 0, block: -1, kw: -1@-1, kwrest: -1])
| | [ 1] "$!"@0
| | 0000 getlocal_WC_0                          "$!"@0                    (   4)
| | 0002 throw                                  0
| | catch type: ensure st: 0001 ed: 0013 sp: 0001 cont: 0014
| | catch type: ensure st: 0001 ed: 0001 sp: 0001 cont: 0023
| | == disasm: #<ISeq:ensure in block in <main>@a.rb:7 (7,2)-(8,7)>
| | local table (size: 1, argc: 0 [opts: 0, rest: -1, post: 0, block: -1, kw: -1@-1, kwrest: -1])
| | [ 1] "$!"@0
| | 0000 putself                                                          (   7)[Li]
| | 0001 putobject_INT2FIX_1_
| | 0002 opt_send_without_block                 <calldata!mid:puts, argc:1, FCALL|ARGS_SIMPLE>
| | 0004 pop
| | 0005 putnil                                                           (   8)[Li]
| | 0006 throw                                  2
| | 0008 pop
| | 0009 getlocal_WC_0                          "$!"@0                    (   6)
| | 0011 throw                                  0
| | catch type: ensure st: 0010 ed: 0014 sp: 0001 cont: 0023
| | catch type: redo   st: 0001 ed: 0023 sp: 0000 cont: 0001
| | catch type: next   st: 0001 ed: 0023 sp: 0000 cont: 0023
| |------------------------------------------------------------------------
| 0000 nop                                                              (   1)[Bc]
| 0001 putself                                                          (   7)[Li]
| 0002 putobject_INT2FIX_1_
| 0003 opt_send_without_block                 <calldata!mid:puts, argc:1, FCALL|ARGS_SIMPLE>
| 0005 pop
| 0006 putnil                                                           (   8)[Li]
| 0007 throw                                  2
| 0009 pop
| 0010 jump                                   1                         (   3)
| 0012 putnil
| 0013 nop
| 0014 putself                                                          (   7)[Li]
| 0015 putobject_INT2FIX_1_
| 0016 opt_send_without_block                 <calldata!mid:puts, argc:1, FCALL|ARGS_SIMPLE>
| 0018 pop
| 0019 putnil                                                           (   8)[Li]
| 0020 throw                                  2
| 0022 pop
| 0023 leave                                                            (   9)[Br]
|------------------------------------------------------------------------
0000 putobject_INT2FIX_1_                                             (   1)[Li]
0001 send                                   <calldata!mid:times, argc:0>, block in <main>
0004 leave

catch type: ensure st: 0001 ed: 0013 sp: 0001 cont: 0014 catches throw 2 but I guess it is unexpected.

For example, if I make a change like this, it seems like it would work in this case, but I can't tell if there are any side effects.
(To be honest, Gemini AI wrote this code for me, so I don't really understand what it means.)

diff --git a/compile.c b/compile.c
index 2ff207928a5..d92770e9b63 100644
--- a/compile.c
+++ b/compile.c
@@ -6675,7 +6675,13 @@ add_ensure_iseq(LINK_ANCHOR *const ret, rb_iseq_t *iseq, int is_return)
             LABEL *lend = NEW_LABEL(0);
             INIT_ANCHOR(ensure_part);
 
-            add_ensure_range(iseq, enlp->erange, lstart, lend);
+            struct iseq_compile_data_ensure_node_stack *e = prev_enlp;
+            while (e) {
+                if (e->erange != NULL) {
+                    add_ensure_range(iseq, e->erange, lstart, lend);
+                }
+                e = e->prev;
+            }
 
             ISEQ_COMPILE_DATA(iseq)->ensure_node_stack = enlp->prev;
             ADD_LABEL(ensure_part, lstart);
diff --git a/prism_compile.c b/prism_compile.c
index 69e7d535491..9402395ace5 100644
--- a/prism_compile.c
+++ b/prism_compile.c
@@ -4751,7 +4751,13 @@ pm_add_ensure_iseq(LINK_ANCHOR *const ret, rb_iseq_t *iseq, int is_return, pm_sc
             LABEL *lstart = NEW_LABEL(0);
             LABEL *lend = NEW_LABEL(0);
 
-            add_ensure_range(iseq, enlp->erange, lstart, lend);
+            struct iseq_compile_data_ensure_node_stack *e = prev_enlp;
+            while (e) {
+                if (e->erange != NULL) {
+                    add_ensure_range(iseq, e->erange, lstart, lend);
+                }
+                e = e->prev;
+            }
 
             ISEQ_COMPILE_DATA(iseq)->ensure_node_stack = enlp->prev;
             PUSH_LABEL(ensure_part, lstart);

$ make -j miniruby 2>&1 >/dev/null && ./miniruby a.rb && ./miniruby -v --dump=insn a.rb
1
ruby 4.1.0dev (2026-08-30T06:52:45Z :detached: a889da909c) +PRISM [x86_64-linux]
== disasm: #<ISeq:<main>@a.rb:1 (1,0)-(9,3)>
== catch table
| catch type: break  st: 0000 ed: 0004 sp: 0000 cont: 0004
| == disasm: #<ISeq:block in <main>@a.rb:1 (1,8)-(9,3)>
| == catch table
| | catch type: ensure st: 0001 ed: 0001 sp: 0001 cont: 0014
| | == disasm: #<ISeq:ensure in block in <main>@a.rb:4 (4,2)-(5,5)>
| | local table (size: 1, argc: 0 [opts: 0, rest: -1, post: 0, block: -1, kw: -1@-1, kwrest: -1])
| | [ 1] "$!"@0
| | 0000 getlocal_WC_0                          "$!"@0                    (   4)
| | 0002 throw                                  0
| | catch type: ensure st: 0001 ed: 0001 sp: 0001 cont: 0014
| | catch type: ensure st: 0010 ed: 0013 sp: 0001 cont: 0014
| | catch type: ensure st: 0001 ed: 0001 sp: 0001 cont: 0023
| | == disasm: #<ISeq:ensure in block in <main>@a.rb:7 (7,2)-(8,7)>
| | local table (size: 1, argc: 0 [opts: 0, rest: -1, post: 0, block: -1, kw: -1@-1, kwrest: -1])
| | [ 1] "$!"@0
| | 0000 putself                                                          (   7)[Li]
| | 0001 putobject_INT2FIX_1_
| | 0002 opt_send_without_block                 <calldata!mid:puts, argc:1, FCALL|ARGS_SIMPLE>
| | 0004 pop
| | 0005 putnil                                                           (   8)[Li]
| | 0006 throw                                  2
| | 0008 pop
| | 0009 getlocal_WC_0                          "$!"@0                    (   6)
| | 0011 throw                                  0
| | catch type: ensure st: 0001 ed: 0001 sp: 0001 cont: 0023
| | catch type: ensure st: 0010 ed: 0014 sp: 0001 cont: 0023
| | catch type: redo   st: 0001 ed: 0023 sp: 0000 cont: 0001
| | catch type: next   st: 0001 ed: 0023 sp: 0000 cont: 0023
| |------------------------------------------------------------------------
| 0000 nop                                                              (   1)[Bc]
| 0001 putself                                                          (   7)[Li]
| 0002 putobject_INT2FIX_1_
| 0003 opt_send_without_block                 <calldata!mid:puts, argc:1, FCALL|ARGS_SIMPLE>
| 0005 pop
| 0006 putnil                                                           (   8)[Li]
| 0007 throw                                  2
| 0009 pop
| 0010 jump                                   1                         (   3)
| 0012 putnil
| 0013 nop
| 0014 putself                                                          (   7)[Li]
| 0015 putobject_INT2FIX_1_
| 0016 opt_send_without_block                 <calldata!mid:puts, argc:1, FCALL|ARGS_SIMPLE>
| 0018 pop
| 0019 putnil                                                           (   8)[Li]
| 0020 throw                                  2
| 0022 pop
| 0023 leave                                                            (   9)[Br]
|------------------------------------------------------------------------
0000 putobject_INT2FIX_1_                                             (   1)[Li]
0001 send                                   <calldata!mid:times, argc:0>, block in <main>
0004 leave