(public_name -) different behaviour between executable and executables

[maiste]

Expected Behavior

Hi, dear dune maintainers,
While working with executable and executables I noticed a difference in behaviour with the stanza (public_name -) and (public_names - -).
As described in the documentation, they should work the same way:

The executables stanza is the same as the executable stanza except that it’s used to describe several executables sharing the same configuration, so the plural executables stanza is used to represent more than one executable.

Actual Behavior

IIUC, the two executables descriptions should work the same way as one is just a contraction of the other one:

 (executable
   (public_name -)
   (name example_1)
   (modules example_1)
   (package dune-example))

 (executable
   (public_name -)
   (name example_2)
   (modules example_2)
   (package dune-example))

 (executables
   (public_names - -)
   (names example_1 example_2)
   (package dune-example))

Whereas 2. works without any issue and the - name is taken as ignored this field, 1. raised the following error:

Error: Multiple rules generated for _build/install/default/bin/-:
- examples/dune:3
- examples/dune:9
-> required by _build/default/dune-example.install
-> required by alias all
-> required by alias default

Reproduction

The reproduction steps are:

git clone https://github.com/maiste/dune-example.git
cd dune-example
dune build .

Specifications

• Version of dune (output of dune --version): 3.2.0
• Version of ocaml (output of ocamlc --version): 4.14.0
• Operating system (distribution and version): Ubuntu 20.04 / EndeavourOS Linux

[nojb]

one is just a contraction of the other one

Orthogonal to the issue described here, but note that this is not actually correct: executables allow sharing modules between the different executables, while this is not possible if you replace it by multiple executable stanzas. Probably a good idea to fix the documentation to point this out.

raised the following error:

This is probaly because using - in a single-executable stanza doesn't make a lot of sense: you may as well just supress the public_name field altogether. On the other hand, it may be a good idea to implement the same behaviour as for executables just for the sake of uniformity.

[maiste]

Orthogonal to the issue described here, but note that this is not actually correct: executables allow sharing modules between the different executables, while this is not possible if you replace it by multiple executable stanzas. Probably a good idea to fix the documentation to point this out.

Apart from the possibility of sharing modules between executables, are they acting in the same way or is there other difference?

This is probably because using - in a single-executable stanza doesn't make a lot of sense: you may as well just supress the public_name field altogether. On the other hand, it may be a good idea to implement the same behaviour as for executables just for the sake of uniformity.

I agree that we should be able to remove this (public_name -). However, it needed to be used in case of some examples... This is the only hack I found to bypass the problem mentioned in ocaml/dune#5621.
By the same behaviour, do you that if (public_names - - -) look like this, it should raise an error?

[nojb]

By the same behaviour, do you that if (public_names - - -) look like this, it should raise an error?

No, I mean that any - in the public name fields (either in executable or executables stanzas) should be ignored.

[emillon]

@maiste now that this behaviour has been documented in #7505, is there anything that is left to be done on this issue?

[Alizter]

@emillon It seems to me like executable and executables have their public_name's validated differently.

[maiste]

There was indeed two issues in this issue:

• The problem with the documentation which was fixed in the PR you mentioned.
• The inconsistent behaviour of - which is still an issue.

[emillon]

Ok, I see. The alternatives are:

1. make (public_name -) equivalent to no public name (consistent with public_names in executables)
2. disallow (public_name -) in singular (executable) stanza

(Both solutions prevent the creation of an executable named - but that's still possible with a manual install stanza.)

I don't like adding equivalent forms ((public_name -) equivalent to no field at all), but this is already the case in the plural form. So that's an argument for solution 1. We can then forbid (public_name -) and (public_names) where all names are - in a future step if necessary.

Does that sound good to you?

[maiste]

Yes, I agree with this proposition 👍

[emillon]

Implemented in #7576 .