ocaml · rgrinberg · Apr 22, 2022 · Apr 22, 2022
diff --git a/CHANGES.md b/CHANGES.md
@@ -1,6 +1,8 @@
 3.2.0 (Unreleased)
 -----------------
 
+- Add `not` to boolean expressions (#5610, fix #5503, @rgrinberg)
+
 - Allow to specify `--prefix` via the environment variable
   `DUNE_INSTALL_PREFIX` (#5589, @vapourismo)
 

diff --git a/doc/concepts.rst b/doc/concepts.rst
@@ -73,6 +73,7 @@ Dune can evaluate. Here's a semi-formal specification of the language:
    expr := (and <expr>+)
          | (or <expr>+)
          | (<op> <template> <template>)
+         | (not <expr>)
          | <template>
 
 After an expression is evaluated, it must be exactly the string ``true`` or

diff --git a/src/dune_rules/blang.ml b/src/dune_rules/blang.ml
@@ -29,6 +29,7 @@ end
 
 type t =
   | Const of bool
+  | Not of t
   | Expr of String_with_vars.t
   | And of t list
   | Or of t list
@@ -50,6 +51,7 @@ let rec eval t ~dir ~f =
         [ Pp.text "This value must be either true or false" ])
   | And xs -> Memo.List.map xs ~f:(eval ~f ~dir) >>| List.for_all ~f:Fun.id
   | Or xs -> Memo.List.map xs ~f:(eval ~f ~dir) >>| List.exists ~f:Fun.id
+  | Not t -> eval t ~f ~dir >>| not
   | Compare (op, x, y) ->
     let+ x = String_with_vars.expand x ~mode:Many ~dir ~f
     and+ y = String_with_vars.expand y ~mode:Many ~dir ~f in
@@ -59,6 +61,7 @@ let rec to_dyn =
   let open Dyn in
   function
   | Const b -> variant "Const" [ bool b ]
+  | Not t -> variant "Not" [ to_dyn t ]
   | Expr e -> variant "Expr" [ String_with_vars.to_dyn e ]
   | And t -> variant "And" (List.map ~f:to_dyn t)
   | Or t -> variant "Or" (List.map ~f:to_dyn t)
@@ -83,6 +86,9 @@ let decode_gen decode_string =
         sum ~force_parens:true
           (("or", repeat t >>| fun x -> Or x)
           :: ("and", repeat t >>| fun x -> And x)
+          :: ( "not"
+             , Dune_lang.Syntax.since Stanza.syntax (3, 2) >>> t >>| fun x ->
+               Not x )
           :: ops)
         <|> let+ v = decode_string in
             Expr v)

diff --git a/src/dune_rules/blang.mli b/src/dune_rules/blang.mli
@@ -14,6 +14,7 @@ end
 
 type t =
   | Const of bool
+  | Not of t
   | Expr of String_with_vars.t
   | And of t list
   | Or of t list

diff --git a/test/blackbox-tests/test-cases/enabled_if-exec.t/run.t b/test/blackbox-tests/test-cases/enabled_if-exec.t/run.t
@@ -86,3 +86,20 @@ For dune >= 2.7 context_name allowed
   $ dune exec ./foo.exe --root var_context_name
   Entering directory 'var_context_name'
   bar
+
+For dune >= 3.2, negating expressions is allowed
+  $ mkdir negated
+  $ cat > negated/dune-project <<EOF
+  > (lang dune 3.2)
+  > EOF
+  $ cat > negated/dune <<EOF
+  > (executable
+  >  (name foo)
+  >  (enabled_if (not false)))
+  > EOF
+  $ cat > negated/foo.ml <<EOF
+  > print_endline "runs";;
+  > EOF
+  $ dune exec ./foo.exe --root negated
+  Entering directory 'negated'
+  runs