Add jbuilder exec

CHANGES.org

@@ -19,6 +19,8 @@
   + =install=
   + =uninstall=
   + =installed-libraries=
+  + =exec=: execute a command in an environment similar to what you
+    would get after =jbuilder install=
 
 - Added support for aliases
   (#7, Rudi Grinberg)

bin/main.ml

@@ -449,6 +449,60 @@ let install_uninstall ~what =
 let install   = install_uninstall ~what:"install"
 let uninstall = install_uninstall ~what:"uninstall"
 
+let exec =
+  let doc =
+    "Execute a command in a similar environment as if installation was performed."
+  in
+  let man =
+    [ `S "DESCRIPTION"
+    ; `P {|$(b,jbuilder exec -- COMMAND) should behave in the same way as if you do:|}
+    ; `Pre "  \\$ jbuilder install\n\
+           \  \\$ COMMAND"
+    ; `P {|In particular if you run $(b,jbuilder exec ocaml), you will have access
+           to the libraries defined in the workspace using your usual directives
+           ($(b,#require) for instance)|}
+    ; `Blocks help_secs
+    ]
+  in
+  let go common context prog args =
+    set_common common;
+    Future.Scheduler.go ~log:(create_log ())
+      (Main.setup common >>= fun setup ->
+       let context =
+         match List.find setup.contexts ~f:(fun c -> c.name = context) with
+         | Some ctx -> ctx
+         | None ->
+           Format.eprintf "@{<Error>Error@}: Context %S not found!@." context;
+           die ""
+       in
+       match Context.which context prog with
+       | None ->
+         Format.eprintf "@{<Error>Error@}: Program %S not found!@." prog;
+         die ""
+       | Some real_prog ->
+         let real_prog = Path.to_string real_prog     in
+         let env       = Context.env_for_exec context in
+         if Sys.win32 then
+           Future.run ~env Strict real_prog (prog :: args)
+         else
+           Unix.execve real_prog (Array.of_list (prog :: args)) env
+      )
+  in
+  ( Term.(const go
+          $ common
+          $ Arg.(value
+                 & opt string "default"
+                 & info ["context"] ~docv:"CONTEXT"
+                     ~doc:{|Run the command in this build context.|}
+                )
+          $ Arg.(required
+                 & pos 0 (some string) None (Arg.info [] ~docv:"PROG"))
+          $ Arg.(value
+                 & pos_right 0 string [] (Arg.info [] ~docv:"ARGS"))
+         )
+  , Term.info "exec" ~doc ~man)
+
+
 let all =
   [ installed_libraries
   ; build_package
@@ -457,6 +511,7 @@ let all =
   ; runtest
   ; install
   ; uninstall
+  ; exec
   ]
 
 let default =

src/context.ml

@@ -323,3 +323,24 @@ let install_prefix t =
   opam_config_var t "prefix" >>| function
   | Some x -> Path.absolute x
   | None   -> Path.parent t.ocaml_bin
+
+
+(* CR-someday jdimino: maybe we should just do this for [t.env] directly? *)
+let env_for_exec t =
+  let sep = if Sys.win32 then ';' else ':' in
+  let cwd = Sys.getcwd () in
+  let extend_var var v =
+    let v = Filename.concat cwd (Path.to_string v) in
+    match get_env t.env var with
+    | None -> (var, v)
+    | Some prev -> (var, sprintf "%s%c%s" v sep prev)
+  in
+  let vars =
+    [ extend_var "CAML_LD_LIBRARY_PATH" (Config.local_install_dir ~context:t.name)
+    ; extend_var "OCAMLPATH"            (Path.relative
+                                           (Config.local_install_dir ~context:t.name)
+                                           "lib")
+    ; extend_var "PATH"                 (Config.local_install_bin_dir ~context:t.name)
+    ]
+  in
+  extend_env ~env:t.env ~vars:(String_map.of_alist_exn vars)

src/context.mli

@@ -127,3 +127,5 @@ val extend_env : vars:string String_map.t -> env:string array -> string array
 val opam_config_var : t -> string -> string option Future.t
 
 val install_prefix : t -> Path.t Future.t
+
+val env_for_exec : t -> string array