Adapt the behavior of dune subst for dune projects

[ghost]

Projects are better defined with dune, so we don't need the automatic project name detection jbuilder was doing and can simply read the dune-project file. Additionally, since dune subst is only meant to be called from opam files, this PR simplify this command a bit so that it doesn't looks up the root of the workspace. This fix #954 which was due to users often forgetting to pass "-p" name to the dune subst invocation.

[emillon]

If there is no dune-project file, one will be created automatically. What part takes care of this? Will it run and do the right thing if dune subst is run in a project without a dune-project file?

[ghost]

It's done in File_tree.load: whenever we encounter a dune file, we make sure the dune-project file exists and create it if not. dune subst doesn't call File_tree.load, so this won't happen. Additionally, the dune-project file that's automatically created doesn't have a name field, so dune subst would still fail on such a file. The name must be set explicitly by the user.

[rgrinberg]

Could you harmonize this error message with the one on line 180? Also I wonder if it makes sense to include the package names.

[ghost]

What do you have in mind for this error message?

[rgrinberg]

Looking at this again, the error on line 180 is slightly different. So ignore that comment. Everything looks fine. Though it might still be useful to include package_names in the error for convenience.

[rgrinberg]

Btw, I notice that subst doesn't really have a test suite at the moment. @diml would you mind adding some general tests for it? Otherwise I can just create a ticket and we can do it at another time.

[ghost]

Sure, I added a test

[rgrinberg]

Looking at this again, the error on line 180 is slightly different. So ignore that comment. Everything looks fine. Though it might still be useful to include package_names in the error for convenience.

[rgrinberg]

PS, the tests still need to pass:

File "test/blackbox-tests/test-cases/subst/file.ml", line 2, characters 15-30:
Error: variable "authors" not found in opam file

[ghost]

Ah, it's because ./boot --subst tries to edit the tests as well... I fixed that.

[ghost]

Though it might still be useful to include package_names in the error for convenience.

Yh, I'm not sure how to word the error message. The name comes from the dune-project file, not from the command line. So the problem is either that:

• the (name ...) field is wrong
• the <package>.opam file has the wrong name

[ghost]

I'm merging for now, we can improve this message in another PR