Re: Project out of sources compilation

[Eli Zaretskii <eliz@gnu.org>]

> Date: Sun, 17 Mar 2024 08:22:56 +0100
> From: Ergus <spacibba@aol.com>
> 
> >> 1. Out of sources compilation.
> >> 
> >> Most of projects now prefer to do out-of sources compilation. Either to
> >> keep source code clean or to keep multiple compilations at the same time
> >> (i.e Debug/Release/win32)
> >> 
> >> The project.el package has already some compilation commands, but they
> >> assume that the compilation will be executed in the project's
> >> root... which is not true most of the time.
> >> 
> >> Maybe we may add an extra custom variable that could be specified in the
> >> dir-locals.el in order specify where the compilation command must be
> >> executed.
> >> 
> >> Some more heuristics here is possible, but I would settle for at least
> >> something simpler.
> >
> >project.el has just one, very simple command, where the only thing that it does it switch to the root first. How will you customize it? With a hook, where the user would write a function "determine a directory for compilation"? They might as well define a new command - or redefine this one. Or just an option with relative directory name?
> >
> 
> IMO the only thing we need is probably a variable/custom like project-build-dir. The user can define it in the dir-locals and the project command will use it if defined/ else use project-root. Maybe the backend could initialize it.
> 
> Alternatively (and not totally exclusive) project.el could define a project-build-dir function that project backends could optionally redefine (i.e I use a plist as project id in gags-mode and getting any stored property from there is very easy with a command). By default it will be an alias for project-root in the VC backend.

Maybe I'm missing something, but isn't the build tree just one more
tree that is part of the project?  If so, can't you use
project-external-roots to add this tree to the project?  I thought
this was the mechanism to add trees to a project as included in the
original design of project.el and its support in Emacs?

> There is also some need for a 'bin' dir, that is, where the final executable will reside, useful to execute and debug with tools like gud and independent from 'build'...  For example in a python project this may be the project root OR where the file with __main__ resides, but a python project usually won't specify a build dir. But let's go for one thing at a time.

Likewise here.

Or what am I missing?