Relative paths in (paths are absolutized inside the build directory

Signed-off-by: François Bobot <francois.bobot@cea.fr>

doc/usage.rst

@@ -504,7 +504,7 @@ context or can be the description of an opam switch, as follows:
   ``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 workspace root, see :ref:`finding-root`.
+  interpreted with respect to the context build directory.
 
 
 If environment variables, such as ``PATH``, are modified in the `dune-workspace`

src/context.ml

@@ -530,7 +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
@@ -549,7 +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
@@ -650,7 +656,9 @@ let instantiate_context env (workspace : Workspace.t)
       (Env_nodes.extra_env
          ~profile:(Workspace.Context.profile context) env_nodes)
   in
-  let env = extend_paths ~env (Workspace.Context.paths context) 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 = _ } ->

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