Add a (env) dependency

src/build_system.ml

@@ -1284,9 +1284,19 @@ let update_universe t =
   make_local_dirs t (Path.Set.singleton Path.build_dir);
   Io.write_file universe_file (Dsexp.to_string ~syntax:Dune (Dsexp.To_sexp.int n))
 
+let env_file = Path.relative Path.build_dir ".env"
+
+let update_env_file env =
+  Marshal.to_string env []
+  |> Digest.string
+  |> Digest.to_hex
+  |> Io.write_file env_file
+
 let do_build t ~request =
   entry_point t ~f:(fun () ->
     update_universe t;
+    let env_context = Option.value_exn @@ String.Map.find t.contexts "default" in
+    update_env_file env_context.env;
     eval_request t ~request ~process_target:(wait_for_file ~loc:None t))
 
 module Ir_set = Set.Make(Internal_rule)

src/build_system.mli

@@ -195,6 +195,9 @@ val do_build
 (** File for the [(universe)] dependency. *)
 val universe_file : Path.t
 
+(** File for the [(env)] dependency. *)
+val env_file : Path.t
+
 val is_target : t -> Path.t -> bool
 
 (** Return all the library dependencies (as written by the user)

src/dune_file.ml

@@ -308,6 +308,7 @@ module Dep_conf = struct
     | Source_tree of String_with_vars.t
     | Package of String_with_vars.t
     | Universe
+    | Env
 
   let remove_locs = function
     | File sw -> File (String_with_vars.remove_locs sw)
@@ -317,6 +318,7 @@ module Dep_conf = struct
     | Source_tree sw -> Source_tree (String_with_vars.remove_locs sw)
     | Package sw -> Package (String_with_vars.remove_locs sw)
     | Universe -> Universe
+    | Env -> Env
 
   let dparse =
     let dparse =
@@ -337,6 +339,7 @@ module Dep_conf = struct
           (let%map () = Syntax.since Stanza.syntax (1, 0)
            and x = sw in
            Source_tree x)
+        ; "env", return Env
         ]
     in
     if_list
@@ -365,6 +368,8 @@ module Dep_conf = struct
            ; String_with_vars.dgen t]
     | Universe ->
       Dsexp.unsafe_atom_of_string "universe"
+    | Env ->
+      Dsexp.unsafe_atom_of_string "env"
 
   let to_sexp t = Dsexp.to_sexp (dgen t)
 end

src/dune_file.mli

@@ -119,6 +119,7 @@ module Dep_conf : sig
     | Source_tree of String_with_vars.t
     | Package of String_with_vars.t
     | Universe
+    | Env
 
   val remove_locs : t -> t
 

src/super_context.ml

@@ -768,6 +768,9 @@ module Deps = struct
     | Universe ->
       Build.path Build_system.universe_file
       >>^ fun () -> []
+    | Env ->
+      Build.path Build_system.env_file
+      >>^ fun () -> []
 
   let interpret t ~scope ~dir l =
     List.map l ~f:(dep t ~scope ~dir)

test/blackbox-tests/dune.inc

@@ -159,6 +159,14 @@
    test-cases/env
    (progn (run %{exe:cram.exe} -test run.t) (diff? run.t run.t.corrected)))))
 
+(alias
+ (name env-tracking)
+ (deps (package dune) (source_tree test-cases/env-tracking))
+ (action
+  (chdir
+   test-cases/env-tracking
+   (progn (run %{exe:cram.exe} -test run.t) (diff? run.t run.t.corrected)))))
+
 (alias
  (name envs-and-contexts)
  (deps (package dune) (source_tree test-cases/envs-and-contexts))
@@ -843,6 +851,7 @@
   (alias dune-project-edition)
   (alias dup-fields)
   (alias env)
+  (alias env-tracking)
   (alias exclude-missing-module)
   (alias exec-cmd)
   (alias exec-missing)
@@ -945,6 +954,7 @@
   (alias dune-project-edition)
   (alias dup-fields)
   (alias env)
+  (alias env-tracking)
   (alias exclude-missing-module)
   (alias exec-cmd)
   (alias exec-missing)

test/blackbox-tests/test-cases/env-tracking/a.ml

@@ -0,0 +1,6 @@
+let var k =
+  match Sys.getenv k with
+  | v -> Printf.sprintf "%s = %S" k v
+  | exception Not_found -> Printf.sprintf "%s is not set" k
+
+let () = print_endline @@ var "X"

test/blackbox-tests/test-cases/env-tracking/dune

@@ -0,0 +1,14 @@
+(executable
+ (name a)
+)
+
+(alias
+ (name without_dep)
+ (action (run ./a.exe))
+)
+
+(alias
+ (name with_dep)
+ (deps (env))
+ (action (run ./a.exe))
+)

test/blackbox-tests/test-cases/env-tracking/dune-project

@@ -0,0 +1 @@
+(lang dune 1.1)

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

@@ -0,0 +1,15 @@
+Aliases without a (env) dependency are not rebuilt when the environment changes:
+
+  $ dune build @without_dep
+             a alias without_dep
+  X is not set
+  $ X=x dune build @without_dep
+
+But if there is a dependency, the alias gets rebuilt:
+
+  $ dune build @with_dep
+             a alias with_dep
+  X is not set
+  $ X=x dune build @with_dep
+             a alias with_dep
+  X = "x"