Re: [Caml-list] Test coverage of generated lexers/parsers

[Gabriel Scherer <gabriel.scherer@gmail.com>]

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This is an interesting question and, as far as I know, there is no good
solution using existing versions of the interacting tools.

Below very simple patch that will add (*BISECT-IGNORE*) in front of every
line of code generated by Menhir, except those written by the programmer
(the "strecthes" in Menhir-speak). It applies cleanly on top of the latest
released Menhir archive,
  http://gallium.inria.fr/~fpottier/menhir/menhir-20160303.tar.gz

The patch as-is is obviously a hack: it would need to be a configuration
option when running menhir, and hard-coding Bisect (or bisect_ppx)'s syntax
into Menhir is not elegant. One could try to have a configuration option to
let users write a fixed string (or comment) at the beginning of each
generated code line, but I'm not sure whether François Pottier (in cc:)
would consider this is elegant enough. François, would you comment on
whether this is a direction that seems acceptable to you?

(Bisect support ignoring entire regions at once by using
(*BISECT-IGNORE-BEGIN*) and (*BISECT-IGNORE-END*); we could try to
implement that instead of a per-line change, but I suspect that it would be
slightly harder to implement (you have to hook the beginning of input, end
of input, and around each user-code insertion) for no real gain.)

Toggling code-coverage semantics by inserting comments is not a very nice
interface (although rather logical when you think of the level of
generality required), so it's a bit frustrating that parser generators
would have to play at this level. It would be better to have a more
structured, unified interface supported by all the code-coverage tools, but
to my knowledge no such thing exists.


From d595ba5149a314c56623e1735af7678f5f62d525 Mon Sep 17 00:00:00 2001
From: Gabriel Scherer <gabriel.scherer@gmail.com>
Date: Sun, 6 Mar 2016 17:43:14 -0500
Subject: [PATCH] output (*BISECT-IGNORE*) in front of each
 non-programmer-written line

EXPERIMENTAL PATCH: this should of course be turned into an explicit option
---
 src/printer.ml | 1 +
 1 file changed, 1 insertion(+)

diff --git a/src/printer.ml b/src/printer.ml
index ea978bc..714bb08 100644
--- a/src/printer.ml
+++ b/src/printer.ml
@@ -46,6 +46,7 @@ let rawnl f =

 let nl f =
   rawnl f;
+  output_string f "(*BISECT-IGNORE*)";
   output_substring f whitespace 0 !indentation

 let indent ofs producer f x =
-- 
2.5.0



On Sun, Mar 6, 2016 at 2:53 PM, Vincent Jacques <vincent@vincent-jacques.net
> wrote:

> Hello,
>
> Does somebody have experience measuring test coverage of generated
> lexers/parsers?
>
> I'm using ocamllex/ocamlyacc [1] (but I can switch to Menhir [2]) to
> generate a lexer/parser. In my tests, I simply check that some input
> strings give the ASTs I expect.
>
> I usually use Bisect [3] to make sure that my tests cover the code I
> intended to cover, but in that configuration, Bisect is lost between the
> .mll/.mly files and the generated .ml files and produces useless reports.
>
> How would you measure test coverage in that case?
>
> Thanks,
>
> [1] http://caml.inria.fr/pub/docs/manual-ocaml/lexyacc.html
> [2] http://gallium.inria.fr/~fpottier/menhir/
> [3] http://bisect.x9c.fr/
> --
> Vincent Jacques
> http://vincent-jacques.net
>
> "S'il n'y a pas de solution, c'est qu'il n'y a pas de problème"
>             Devise Shadock
>

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From d595ba5149a314c56623e1735af7678f5f62d525 Mon Sep 17 00:00:00 2001
From: Gabriel Scherer <gabriel.scherer@gmail.com>
Date: Sun, 6 Mar 2016 17:43:14 -0500
Subject: [PATCH] output (*BISECT-IGNORE*) in front of each
 non-programmer-written line

EXPERIMENTAL PATCH: this should of course be turned into an explicit option
---
 src/printer.ml | 1 +
 1 file changed, 1 insertion(+)

diff --git a/src/printer.ml b/src/printer.ml
index ea978bc..714bb08 100644
--- a/src/printer.ml
+++ b/src/printer.ml
@@ -46,6 +46,7 @@ let rawnl f =
 
 let nl f =
   rawnl f;
+  output_string f "(*BISECT-IGNORE*)";
   output_substring f whitespace 0 !indentation
 
 let indent ofs producer f x =
-- 
2.5.0