Display an error when no installable mode is found

If an executable is only available as a shared object for example,
Dune cannot install it. In that case, it displays an error message.
However, it is still possible to build a private one explicitly.

Signed-off-by: Etienne Millon <etienne@cryptosense.com>

src/jbuild.ml

@@ -879,8 +879,16 @@ module Executables = struct
       ; buildable
       }
     in
+    let has_public_name =
+      List.exists ~f:Option.is_some public_names
+    in
     let to_install =
       match Link_mode.Set.best_install_mode t.modes with
+      | None when has_public_name ->
+        Loc.fail
+          buildable.loc
+          "No installable mode found for %s."
+          (if multi then "these executables" else "this executable")
       | None -> []
       | Some mode ->
         let ext =

test/blackbox-tests/dune.inc

@@ -372,6 +372,15 @@
      (run ${exe:cram.exe} -skip-versions 4.02.3 -test run.t)
      (diff? run.t run.t.corrected))))))
 
+(alias
+ ((name no-installable-mode)
+  (deps
+   ((package dune) (files_recursively_in test-cases/no-installable-mode)))
+  (action
+   (chdir
+    test-cases/no-installable-mode
+    (progn (run ${exe:cram.exe} -test run.t) (diff? run.t run.t.corrected))))))
+
 (alias
  ((name null-dep)
   (deps ((package dune) (files_recursively_in test-cases/null-dep)))
@@ -579,6 +588,7 @@
     (alias meta-gen)
     (alias misc)
     (alias multiple-private-libs)
+    (alias no-installable-mode)
     (alias null-dep)
     (alias ocaml-syntax)
     (alias ocamldep-multi-stanzas)
@@ -639,6 +649,7 @@
     (alias merlin-tests)
     (alias meta-gen)
     (alias misc)
+    (alias no-installable-mode)
     (alias null-dep)
     (alias ocaml-syntax)
     (alias ocamldep-multi-stanzas)

test/blackbox-tests/test-cases/no-installable-mode/private/jbuild

@@ -0,0 +1,8 @@
+(jbuild_version 1)
+
+(executable
+  (
+   (name myprivatelib)
+   (modes (shared_object))
+   )
+  )

test/blackbox-tests/test-cases/no-installable-mode/public/jbuild

@@ -0,0 +1,9 @@
+(jbuild_version 1)
+
+(executable
+  (
+   (name mylib)
+   (public_name mylib)
+   (modes (shared_object))
+   )
+  )

test/blackbox-tests/test-cases/no-installable-mode/run.t

@@ -0,0 +1,16 @@
+When a public executable is built in shared_object mode, a specific error
+message is displayed:
+
+  $ dune build --root=public --display=short
+  File "jbuild", line 4, characters 2-74:
+  Error: No installable mode found for this executable.
+  [1]
+
+However, it is possible to build a private one explicitly.
+
+  $ dune build --root=private --display=short myprivatelib.so
+  Entering directory 'private'
+      ocamldep myprivatelib.ml.d
+        ocamlc .myprivatelib.eobjs/myprivatelib.{cmi,cmo,cmt}
+      ocamlopt .myprivatelib.eobjs/myprivatelib.{cmx,o}
+      ocamlopt myprivatelib$ext_dll