Fix the priority order for environment variables between workspace and context

doc/usage.rst

@@ -501,13 +501,15 @@ context or can be the description of an opam switch, as follows:
   are meant to be executed on the host machine, such as preprocessors.
 
 - ``(paths (<var1> <val1>) .. (<varN> <valN>))`` allows to set the value of any
-  ``PATH``-like variables in this context. If ``PATH`` itself is modified in
-  this way, its value will be used to resolve binaries in the workspace,
-  including finding the compiler and related tools. These variables will also be
-  passed as part of the environment to any program launched by ``dune``. For
-  each variable, the value is specified using the :ref:`ordered-set-language`.
-  Relative paths are interpreted with respect to the workspace root, see
-  :ref:`finding-root`.
+  ``PATH``-like variables in this context. These variables are passed as part of
+  the environment to any program launched by ``dune``. For each variable, the
+  value is specified using the :ref:`ordered-set-language`. Relative paths are
+  interpreted with respect to the context build directory.
+
+
+If environment variables, such as ``PATH``, are modified in the `dune-workspace`
+through `env-vars` or `paths`, its value will be used to resolve binaries in the
+workspace, including finding the compiler and related tools.
 
 Both ``(default ...)`` and ``(opam ...)`` accept a ``targets`` field in order to
 setup cross compilation. See :ref:`advanced-cross-compilation` for more

src/context.ml

@@ -29,8 +29,8 @@ module Env_nodes = struct
 
   let extra_env ~profile env_nodes =
     Env.extend_env
-      (Dune_env.Stanza.find env_nodes.context ~profile).env_vars
       (Dune_env.Stanza.find env_nodes.workspace ~profile).env_vars
+      (Dune_env.Stanza.find env_nodes.context ~profile).env_vars
 end
 
 type t =
@@ -407,7 +407,6 @@ let create ~(kind : Kind.t) ~path ~env ~env_nodes ~name ~merlin ~targets
         Option.value ~default:Env.empty
           (Option.map findlib_config ~f:Findlib.Config.env)
       )
-    |> Env.extend_env (Env_nodes.extra_env ~profile env_nodes)
     in
     let stdlib_dir = Path.of_string (Ocaml_config.standard_library ocfg) in
     let natdynlink_supported = Ocaml_config.natdynlink_supported ocfg in
@@ -531,7 +530,7 @@ let create ~(kind : Kind.t) ~path ~env ~env_nodes ~name ~merlin ~targets
   in
   native :: List.filter_opt others
 
-let extend_paths t ~env =
+let extend_paths t ~env ~build_dir =
   let module Eval =
     Ordered_set_lang.Make(String)
       (struct
@@ -550,7 +549,13 @@ let extend_paths t ~env =
   in
   let vars =
     let to_absolute_filename s =
-      Path.of_string s |> Path.to_absolute_filename in
+      if Filename.is_relative s then
+        Path.Build.relative build_dir s
+        |> Path.build
+        |> Path.to_absolute_filename
+      else
+        s
+    in
     let sep = String.make 1 Bin.path_sep in
     let env = Env.Map.of_list_exn t in
     let f l = String.concat ~sep (List.map ~f:to_absolute_filename l) in
@@ -646,9 +651,17 @@ let instantiate_context env (workspace : Workspace.t)
     ; workspace = workspace.env
     }
   in
+  let env =
+    Env.extend_env env
+      (Env_nodes.extra_env
+         ~profile:(Workspace.Context.profile context) env_nodes)
+  in
+  let build_dir =
+    Path.Build.relative Path.Build.root (Workspace.Context.name context) in
+  let env = extend_paths ~env ~build_dir (Workspace.Context.paths context) in
   match context with
   | Default { targets; name; host_context = _; profile; env = _
-            ; toolchain ; paths; loc = _ } ->
+            ; toolchain ; paths = _; loc = _ } ->
     let merlin =
       workspace.merlin_context = Some (Workspace.Context.name context)
     in
@@ -657,13 +670,11 @@ let instantiate_context env (workspace : Workspace.t)
       | Some _ -> toolchain
       | None -> Env.get env "OCAMLFIND_TOOLCHAIN"
     in
-    let env = extend_paths ~env paths in
     default ~env ~env_nodes ~profile ~targets ~name ~merlin ~host_context
       ~host_toolchain
   | Opam { base = { targets; name; host_context = _; profile; env = _
-                  ; toolchain; paths; loc = _ }
+                  ; toolchain; paths = _; loc = _ }
          ; switch; root; merlin } ->
-    let env = extend_paths ~env paths in
     create_for_opam ~root ~env_nodes ~env ~profile ~switch ~name ~merlin
       ~targets ~host_context ~host_toolchain:toolchain
 

src/stdune/env.mli

@@ -23,6 +23,7 @@ val get : t -> Var.t -> string option
 val extend : t -> vars:string Map.t -> t
 
 val extend_env : t -> t -> t
+(** [extend_env x y] gives priority to the values of y *)
 
 val add : t -> var:Var.t -> value:string -> t
 

src/workspace.ml

@@ -168,6 +168,14 @@ module Context = struct
     | Default x -> x.targets
     | Opam    x -> x.base.targets
 
+  let profile = function
+    | Default x -> x.profile
+    | Opam    x -> x.base.profile
+
+  let paths = function
+    | Default x -> x.paths
+    | Opam    x -> x.base.paths
+
   let all_names t =
     let n = name t in
     n :: List.filter_map (targets t) ~f:(function

src/workspace.mli

@@ -42,6 +42,9 @@ module Context : sig
 
   val env : t -> Dune_env.Stanza.t
 
+  val profile : t -> string
+  val paths : t -> (string * Ordered_set_lang.t) list
+
   val host_context : t -> string option
 end
 

test/blackbox-tests/test-cases/env-variables/run.t

@@ -20,7 +20,7 @@ used.
   $ dune exec --root precedence ./printenv.exe VARIABLE_FROM_BOTH
   Entering directory 'precedence'
   Entering directory 'precedence'
-  VARIABLE_FROM_BOTH=from_workspace
+  VARIABLE_FROM_BOTH=from_context
 
 When a variable is repeated, an error message is displayed:
 

test/blackbox-tests/test-cases/workspace-paths/bin/dune

@@ -1,3 +1,3 @@
 (executable
  (name hello)
- (promote (until-clean)))
+)

test/blackbox-tests/test-cases/workspace-paths/run.t

@@ -1,6 +1,8 @@
-  $ dune build
+  $ dune build bin/hello.exe
+
+  $ dune build @default
          hello alias default
-  Hello: $TESTCASE_ROOT/a:/c
+  Hello: $TESTCASE_ROOT/_build/default/a:/c
 
   $ mkdir sub
   $ cat > sub/dune-workspace <<EOF