feat: introduce env_vars alias for env-vars

doc/reference/dune/env.rst

@@ -30,6 +30,11 @@ Fields supported in ``<settings>`` are:
   variables to the environment where the build commands are executed and are
   used by ``dune exec``.
 
+- ``(env_vars (<var1> <val1>) .. (<varN> <valN>))`` is an alias for ``env-vars``.
+  It was introduced to stick to the underscore naming convention.
+
+  .. versionadded:: 3.18
+
 - ``(menhir_flags <flags>))`` specifies flags for Menhir stanzas. This flag was
   replaced by the ``(menhir)`` field (see below) starting in version 3.0 of the
   Menhir extension.

src/dune_rules/dune_env.ml

@@ -196,16 +196,25 @@ let inline_tests_field =
 ;;
 
 let env_vars_field =
-  field
-    "env-vars"
-    ~default:Env.empty
-    (Dune_lang.Syntax.since Stanza.syntax (1, 5)
-     >>> located (repeat (pair string string))
-     >>| fun (loc, pairs) ->
-     match Env.Map.of_list pairs with
-     | Ok vars -> Env.extend Env.empty ~vars
-     | Error (k, _, _) ->
-       User_error.raise ~loc [ Pp.textf "Variable %s is specified several times" k ])
+  let env_decoder =
+    located (repeat (pair string string))
+    >>| fun (loc, pairs) ->
+    match Env.Map.of_list pairs with
+    | Ok vars -> Env.extend Env.empty ~vars
+    | Error (k, _, _) ->
+      User_error.raise ~loc [ Pp.textf "Variable %s is specified several times" k ]
+  in
+  let+ env_vars_legacy =
+    field_o "env-vars" (Dune_lang.Syntax.since Stanza.syntax (1, 5) >>> env_decoder)
+  and+ env_vars =
+    field_o "env_vars" (Dune_lang.Syntax.since Stanza.syntax (3, 18) >>> env_decoder)
+  in
+  match env_vars_legacy, env_vars with
+  | None, None -> Env.empty
+  | Some env, None -> env
+  | None, Some env -> env
+  | Some _, Some _ ->
+    Code_error.raise "(env_vars) and (env-vars) are aliases and cannot both be present" []
 ;;
 
 let odoc_field =

test/blackbox-tests/test-cases/env/env_vars_alias.t

@@ -0,0 +1,19 @@
+Since Dune 3.18, we support `env_vars` as an alias for `env-vars` for naming
+consistency.
+
+  $ cat > dune-project << EOF
+  > (lang dune 3.18)
+  > EOF
+
+We check the rule is evaluated:
+
+  $ cat > dune << 'EOF'
+  > (env
+  >  (_   (env_vars (VAR default ))))
+  > (rule
+  >  (alias runtest)
+  >  (action (system "echo $VAR")))
+  > EOF
+
+  $ dune runtest
+  default