Add a dune tools env command to add dev tools to PATH

The expected use-case is for the output of this command to be eval'd in
the user's shell. In order for a terminal-based editor to run the
ocamllsp dev tool, `eval $(dune tools env)` must be run in that terminal
before launching the editor.

Fixes #10964

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

Author: gridbugs

bin/tools/group.ml

@@ -33,4 +33,7 @@ end
 
 let doc = "Command group for wrapped tools."
 let info = Cmd.info ~doc "tools"
-let group = Cmd.group info [ Exec.group; Install.group; Which.group ]
+
+let group =
+  Cmd.group info [ Exec.group; Install.group; Which.group; Tools_common.env_command ]
+;;

bin/tools/tools_common.ml

@@ -1,10 +1,13 @@
 open! Import
 module Pkg_dev_tool = Dune_rules.Pkg_dev_tool
 
+let dev_tool_bin_dirs =
+  List.map Pkg_dev_tool.all ~f:(fun tool ->
+    Pkg_dev_tool.exe_path tool |> Path.Build.parent_exn |> Path.build)
+;;
+
 let add_dev_tools_to_path env =
-  List.fold_left Pkg_dev_tool.all ~init:env ~f:(fun acc tool ->
-    let dir = Pkg_dev_tool.exe_path tool |> Path.Build.parent_exn |> Path.build in
-    Env_path.cons acc ~dir)
+  List.fold_left dev_tool_bin_dirs ~init:env ~f:(fun acc dir -> Env_path.cons acc ~dir)
 ;;
 
 let dev_tool_exe_path dev_tool = Path.build @@ Pkg_dev_tool.exe_path dev_tool
@@ -134,3 +137,40 @@ let exec_command dev_tool =
   in
   Cmd.v info term
 ;;
+
+let env_command =
+  let term =
+    let+ builder = Common.Builder.term
+    and+ fish =
+      Arg.(
+        value
+        & flag
+        & info [ "fish" ] ~doc:"Print command for the fish shell raher than posix shells")
+    in
+    let _ = Common.init builder in
+    if fish
+    then (
+      let space_separated_dev_tool_paths =
+        List.map dev_tool_bin_dirs ~f:Path.to_string_maybe_quoted
+        |> String.concat ~sep:" "
+      in
+      print_endline (sprintf "fish_add_path --prepend %s" space_separated_dev_tool_paths))
+    else (
+      let initial_path = Env.get Env.initial Env_path.var in
+      let new_path =
+        List.fold_left dev_tool_bin_dirs ~init:initial_path ~f:(fun acc bin_dir ->
+          Some (Bin.cons_path bin_dir ~_PATH:acc))
+      in
+      match new_path with
+      | None -> ()
+      | Some new_path -> print_endline (sprintf "export %s=%s" Env_path.var new_path))
+  in
+  let info =
+    let doc =
+      "Print a command which can be eval'd to enter an environment where all dev tools \
+       are runnable as commands."
+    in
+    Cmd.info "env" ~doc
+  in
+  Cmd.v info term
+;;

bin/tools/tools_common.mli

@@ -13,3 +13,4 @@ val lock_build_and_run_dev_tool
 val which_command : Dune_pkg.Dev_tool.t -> unit Cmd.t
 val install_command : Dune_pkg.Dev_tool.t -> unit Cmd.t
 val exec_command : Dune_pkg.Dev_tool.t -> unit Cmd.t
+val env_command : unit Cmd.t

test/blackbox-tests/test-cases/pkg/ocamllsp/dev-tool-ocamllsp-basic.t

@@ -30,3 +30,9 @@ a lockdir containing an "ocaml" lockfile.
   - ocaml-lsp-server.0.0.1
        Running 'ocamllsp'
   hello from fake ocamllsp
+
+Make sure that after evaling the output of 'dune tools env', the first ocamllsp
+executable in PATH is the one installed by dune as a dev tool.
+  $ DUNE_CONFIG__LOCK_DEV_TOOL=enabled eval $(dune tools env)
+  $ which ocamllsp
+  $TESTCASE_ROOT/_build/_private/default/.dev-tool/ocaml-lsp-server/ocaml-lsp-server/target/bin/ocamllsp