0004328: Handling of nil nodes is suboptimal

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Date Submitted

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0004328

OCaml

Camlp4

public

2007-06-23 03:42

2010-04-29 14:26

Reporter

cstork

Assigned To

ertai

Priority

normal

Severity

minor

Reproducibility

always

Status

closed

Resolution

fixed

Platform

OS Version

Product Version

3.10.0

Target Version

Fixed in Version

3.10+dev

Summary

0004328: Handling of nil nodes is suboptimal

Description

If I try to pretty print

  <:str_item< type $t$; ... >>

where t could potentially be a nil node, ie, <:ctyp<>>, then camlp4r produces a stack overflow.

Two suggestions:

1) CleanAst.ml could easily turn such empty str_item nodes into <:str_item<>>. Attached is a simple patch that achieves this for this case. If there's interest I'd extend this patch to cover more useful cases. This has the potential to make writing camlp4 extensions more pleasant.

2) camlp4 shouldn't simply crash on nil nodes, but produce a meaningful error message. In case that such a nil node is not pretty printed but dump'ed the error message is

  Assertion failed, file "camlp4/Camlp4/Struct/Camlp4Ast2OCamlAst.ml",
  line 792, char 11

which is a bit more helpful.

Additional Information

To reproduce:

$ echo << DONE
open Camlp4.PreCast.Syntax;
EXTEND Gram
GLOBAL: str_item;
str_item: [[ "type_Nil" -> <:str_item< type $ <:ctyp<>> $ >> ]];
END;
DONE > pa_type_Nil.ml
$ ocamlc -c -pp camlp4rf -I +camlp4 pa_type_Nil.ml
$ echo "type_Nil;" > type_Nil.ml
$ camlp4r pa_type_Nil.cmo type_Nil.ml
type (((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((...
Camlp4: Uncaught exception: Stack_overflow

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No tags attached.

Attached Files

CleanAst.patch [^] (981 bytes) 2007-06-23 03:42 [Show Content] [Hide Content]

Index: camlp4/Camlp4/Struct/CleanAst.ml
===================================================================
RCS file: /caml/ocaml/camlp4/Camlp4/Struct/CleanAst.ml,v
retrieving revision 1.3.4.2
diff -u -r1.3.4.2 CleanAst.ml
--- camlp4/Camlp4/Struct/CleanAst.ml	31 May 2007 15:30:21 -0000	1.3.4.2
+++ camlp4/Camlp4/Struct/CleanAst.ml	23 Jun 2007 01:39:23 -0000
@@ -100,12 +100,15 @@
       match super#sig_item sg with
       [ <:sig_item< $ <:sig_item<>> $; $sg$ >> |
         <:sig_item< $sg$; $ <:sig_item<>> $ >> -> sg
+      | <:sig_item@loc< type $ <:ctyp<>> $ >> ->  <:sig_item@loc<>>
       | sg -> sg ];
 
     method str_item st =
       match super#str_item st with
       [ <:str_item< $ <:str_item<>> $; $st$ >> |
         <:str_item< $st$; $ <:str_item<>> $ >> -> st
+      | <:str_item@loc< type $ <:ctyp<>> $ >> ->  <:str_item@loc<>>
+      | <:str_item@loc< value $rec:_$ $ <:binding<>> $ >> ->  <:str_item@loc<>>
       | st -> st ];
 
     method module_type mt =

Relationships

Notes
(0004336) ertai (developer) 2007-11-21 17:29	Thanks for your report. That's fixed in CVS.

Issue History
Date Modified	Username	Field	Change
2007-06-23 03:42	cstork	New Issue
2007-06-23 03:42	cstork	File Added: CleanAst.patch
2007-11-10 15:10	xleroy	Status	new => assigned
2007-11-10 15:10	xleroy	Assigned To	=> ertai
2007-11-21 17:29	ertai	Note Added: 0004336
2007-11-21 17:29	ertai	Status	assigned => resolved
2007-11-21 17:29	ertai	Resolution	open => fixed
2007-11-21 17:29	ertai	Fixed in Version	=> 3.10+dev
2010-04-29 14:26	xleroy	Status	resolved => closed