Make (public_name -) equivalent to no public name (#7576)

* Make (public_name -) equivalent to no public name

Fixes #5852

This brings consistency with `(public_names)` in `(executables)`: a
plural stanza with only `-` in `(public_names)` installs nothing.

Signed-off-by: Etienne Millon <me@emillon.org>

CHANGES.md

@@ -156,6 +156,10 @@ Unreleased
 - Handle "Too many links" errors when using Dune cache on Windows.  The fix in
   3.7.0 for this same issue was not effective due to a typo. (#7472, @nojb)
 
+- In `(executable)`, `(public_name -)` is now equivalent to no `(public_name)`.
+  This is consistent with how `(executables)` handles this field.
+  (#7576 , fixes #5852, @emillon)
+
 3.7.0 (2023-02-17)
 ------------------
 

doc/stanzas/executable.rst

@@ -54,6 +54,9 @@ files for executables. See `executables_implicit_empty_intf`_.
        (section bin)
        (files (<name>.exe as <public-name>)))
 
+  As a special case, ``(public_name -)`` is the same as if the field was
+  absent.
+
 .. _shared-exe-fields:
 
 - ``(package <package>)`` if there is a ``(public_name ...)`` field, this

src/dune_rules/dune_file.ml

@@ -1103,17 +1103,19 @@ module Executables = struct
 
     let has_public_name t = Option.is_some t.public
 
-    let public_name =
+    let public_name ~dash_is_none =
       located string >>| fun (loc, s) ->
       ( loc
       , match s with
-        | "-" -> None
+        | "-" -> if dash_is_none then None else Some s
         | s -> Some s )
 
     let multi_fields =
       map_validate
         (let+ names = field_o "names" (repeat1 (located string))
-         and+ pub_names = field_o "public_names" (repeat1 public_name) in
+         and+ pub_names =
+           field_o "public_names" (repeat1 (public_name ~dash_is_none:true))
+         in
          (names, pub_names))
         ~f:(fun (names, public_names) ->
           match (names, public_names) with
@@ -1130,10 +1132,12 @@ module Executables = struct
           | names, public_names -> Ok (names, public_names))
 
     let single_fields =
+      let* dune_syntax = Dune_lang.Syntax.get_exn Stanza.syntax in
+      let dash_is_none = dune_syntax >= (3, 8) in
       let+ name = field_o "name" (located string)
-      and+ public_name = field_o "public_name" (located string) in
+      and+ public_name = field_o "public_name" (public_name ~dash_is_none) in
       ( Option.map name ~f:List.singleton
-      , Option.map public_name ~f:(fun (loc, s) -> [ (loc, Some s) ]) )
+      , Option.map public_name ~f:List.singleton )
 
     let pluralize s ~multi = if multi then s ^ "s" else s
 

test/blackbox-tests/test-cases/public-name-empty.t

@@ -0,0 +1,40 @@
+This test is about the semantics of `(public_name -)`.
+
+  $ set_ver() {
+  > cat > dune-project << EOF
+  > (lang dune $1)
+  > (package
+  >  (name e)
+  >  (allow_empty))
+  > EOF
+  > }
+  $ cat > dune << EOF
+  > (executable
+  >  (public_name -)
+  >  (name e))
+  > EOF
+  $ touch e.ml
+
+In 3.7, this declares a public name of "-":
+
+  $ set_ver 3.7
+  $ dune build @install
+  $ cat _build/default/e.install
+  lib: [
+    "_build/install/default/lib/e/META"
+    "_build/install/default/lib/e/dune-package"
+  ]
+  bin: [
+    "_build/install/default/bin/-"
+  ]
+
+In 3.8, this is equivalent to no `(public_name)` field, consistently with what
+happens with `(executables)`.
+
+  $ set_ver 3.8
+  $ dune build @install
+  $ cat _build/default/e.install
+  lib: [
+    "_build/install/default/lib/e/META"
+    "_build/install/default/lib/e/dune-package"
+  ]