Can HLS deal, in a given IDE session, with files belonging to different projects? #4048

I manage my Haskell development via GHCup, so I use ghcup tui to install and update cabal/GHC/HLS (no Stack installed), and cabal to install libraries if I need them (e.g. cabal install --lib flow, if I needed to import Flow).

Assume I have two sibling directories as these,

.
├── dir1
│   ├── bar.cabal
│   ├── bar.hs
│   └── cabal.project
└── dir2
    ├── cabal.project
    ├── foo.cabal
    └── foo.hs

where foo.hs contains

import Data.Text
main :: IO ()
main = putStrLn "hello"

bar.hs contains

main :: IO ()
main = putStrLn "hello"

foo.cabal contains

cabal-version:       3.0
name:                foo
version:             0.1.0.0
executable foo
  main-is:             foo.hs
  build-depends:       base >= 4.13
                     , text

bar.cabal

cabal-version:       3.0
name:                bar
version:             0.1.0.0
executable bar
  main-is:             bar.hs
  build-depends:       base >= 4.13

and both cabal.project files contain

packages: .
with-compiler: ghc-9.4.8
package foo
  flags: +all_extensions

In Vim (I use YouCompleteMe plugin) I can verify that HLS is running in the project directory of the first of those two files to be open; indeed, if I opened Vim via vim -O dir1/bar.hs dir2/foo.hs (which opens bar.hs on the left and focuses it first, and foo.hs on the right) all is fine with bar.hs, but as soon as I moving to the other file, an error like the following is shown

Loading the module '/home/enrico/deleteme/deleteme/dir2/foo.hs' failed.

It may not be listed in your .cabal file!
Perhaps you need to add `foo` to other-modules or exposed-modules.

For more information, visit: https://cabal.readthedocs.io/en/3.4/developing-packages.html#modules-included-in-the-package

"././bar.hs" - Cabal {component = Just "bar:exe:bar"}

which seems to support my understanding that HLS has detected one project and got "stuck" on it.

If I delete the two cabal.project files, so the structure is

.
├── dir1
│   ├── bar.cabal
│   └── bar.hs
└── dir2
    ├── foo.cabal
    └── foo.hs

the issue does not occur, so I think the problem occurs when jumping across two projects.

Is this the case? Or, if the IDE that uses HLS is supposed to handle the scenario above, what information can I provide for you to help me understand what I'm doing wrong?

I've already spoken to YouCompleteMe devs, and they say that Vim+YCM seems to be sending the correct info to HLS, so I'm coming here to seek some help understanding what I'm doing wrong.

Here is a screencast: untitled - asciinema.org