pkg: command to check if project uses package management (ocaml#11997)

Some users have been using the presence of a lockdir to determine
whether a project indicates that package management should be used, for
example when a text editor checks whether ocamllsp should be invoked via
dune (as a dev tool) or from an opam switch. This is brittle, as dune
may change the way projects indicate they intend to use package
management in the future.

This change introduces a new command "dune pkg enabled" which
communicates via its exit status whether dune detects that a project
intends to use package management (a status of 0 indicates package
management is enabled). If/when dune changes how a project should
indicate that it should use package management, the implementation of
this command will be changed to match.

Signed-off-by: Stephen Sherratt <[email protected]>

Author: gridbugs

bin/pkg/pkg.ml

@@ -8,7 +8,12 @@ let man =
 ;;
 
 let subcommands =
-  [ Lock.command; Print_solver_env.command; Outdated.command; Validate_lock_dir.command ]
+  [ Lock.command
+  ; Print_solver_env.command
+  ; Outdated.command
+  ; Validate_lock_dir.command
+  ; Pkg_enabled.command
+  ]
 ;;
 
 let info name =

bin/pkg/pkg_common.ml

@@ -169,6 +169,8 @@ module Lock_dirs_arg = struct
     | All
     | Selected of Path.Source.t list
 
+  let all = All
+
   let term =
     Common.one_of
       (let+ arg =

bin/pkg/pkg_common.mli

@@ -62,6 +62,9 @@ module Lock_dirs_arg : sig
       [Lock_dirs_arg.lock_dirs_of_workspace]. *)
   type t
 
+  (** Select all lockdirs *)
+  val all : t
+
   (** [Lock_dirs_arg.term] is a command-line argument that can be used to
       specify the lock directories to consider. This can then be passed to
       [Lock_dirs_arg.lock_dirs_of_workspace].

bin/pkg/pkg_enabled.ml

@@ -0,0 +1,31 @@
+open Import
+
+let term =
+  let+ builder = Common.Builder.term in
+  let common, config = Common.init builder in
+  Scheduler.go_with_rpc_server ~common ~config (fun () ->
+    Memo.run
+    @@
+    let open Memo.O in
+    let+ workspace = Workspace.workspace () in
+    let lock_dir_paths =
+      Pkg_common.Lock_dirs_arg.lock_dirs_of_workspace
+        Pkg_common.Lock_dirs_arg.all
+        workspace
+    in
+    let any_lockdir_exists =
+      List.exists lock_dir_paths ~f:(fun lock_dir_path ->
+        Path.exists (Path.source lock_dir_path))
+    in
+    if any_lockdir_exists then () else exit 1)
+;;
+
+let info =
+  let doc =
+    "Check if the project indicates that dune's package management features should be \
+     enabled. Exits with 0 if package management is enabled and 1 otherwise."
+  in
+  Cmd.info "enabled" ~doc
+;;
+
+let command = Cmd.v info term

bin/pkg/pkg_enabled.mli

@@ -0,0 +1,3 @@
+open Import
+
+val command : unit Cmd.t

test/blackbox-tests/test-cases/pkg/pkg-enabled.t

@@ -0,0 +1,41 @@
+Exercise the "dune pkg enabled" command which checks whether package management
+should be used.
+
+  $ . ./helpers.sh
+
+  $ mkrepo
+
+  $ cat >dune-workspace <<EOF
+  > (lang dune 3.20)
+  > (lock_dir
+  >  (path dune.lock)
+  >  (repositories mock))
+  > (lock_dir
+  >  (path dune.other.lock)
+  >  (repositories mock))
+  > (repository
+  >  (name mock)
+  >  (url "file://$(pwd)/mock-opam-repository"))
+  > EOF
+
+  $ cat > dune-project <<EOF
+  > (lang dune 3.13)
+  > (package
+  >  (allow_empty)
+  >  (name foo))
+  > EOF
+
+When no lockdir is present pkg is not enabled:
+  $ dune pkg enabled
+  [1]
+
+When the default lockdir is present pkg is enabled:
+  $ dune pkg lock > /dev/null 2> /dev/null
+
+  $ dune pkg enabled
+
+  $ rm -r dune.lock
+
+When a non-default lockdir is present, pkg is still enabled:
+  $ dune pkg lock dune.other.lock > /dev/null 2> /dev/null
+  $ dune pkg enabled