Add 'opam install -u' to allow upgrades

there was no command to upgrade-or-install a package, which was annoying when developping
(the package may be already installed, or have previously failed).

The workaround was to use 'opam reinstall', which is not equivalent

src/client/opamClient.ml

@@ -1437,7 +1437,7 @@ module API = struct
       full_orphans,
       orphan_versions
 
-  let install_t ?ask atoms add_to_roots deps_only t =
+  let install_t ?ask atoms add_to_roots ~deps_only ~upgrade t =
     log "INSTALL %a" (slog OpamFormula.string_of_atoms) atoms;
     let names = OpamPackage.Name.Set.of_list (List.rev_map fst atoms) in
 
@@ -1454,10 +1454,11 @@ module API = struct
           if OpamPackage.Set.mem nv t.installed then
             match add_to_roots with
             | None ->
-              OpamConsole.note
-                "Package %s is already installed (current version is %s)."
-                (OpamPackage.Name.to_string (OpamPackage.name nv))
-                (OpamPackage.Version.to_string (OpamPackage.version nv));
+              if not upgrade then
+                OpamConsole.note
+                  "Package %s is already installed (current version is %s)."
+                  (OpamPackage.Name.to_string (OpamPackage.name nv))
+                  (OpamPackage.Version.to_string (OpamPackage.version nv));
               t
             | Some true ->
               if OpamPackage.Set.mem nv t.installed_roots then
@@ -1499,16 +1500,23 @@ module API = struct
 
     OpamSolution.check_availability t (Lazy.force t.available_packages) atoms;
 
-    if pkg_new <> [] then (
+    let wish_upgrade =
+      if upgrade then List.filter (fun at -> not (List.mem at pkg_new)) atoms
+      else [] in
+
+    if pkg_new <> [] || wish_upgrade <> [] then (
 
       let request =
         preprocessed_request t full_orphans orphan_versions
-          ~wish_install:atoms ();
+          ~wish_install:atoms ~wish_upgrade ();
       in
       let action =
-        if add_to_roots = Some false || deps_only then
-          Install OpamPackage.Name.Set.empty
-        else Install names in
+        if wish_upgrade <> [] then Upgrade (OpamPackage.Set.of_list pkg_skip)
+        (* Fixme: the above won't properly handle setting as a root *)
+        else match add_to_roots, deps_only with
+          | Some false, _ | None, true ->
+            Install OpamPackage.Name.Set.empty
+          | _ -> Install names in
       let solution =
         OpamSolution.resolve t action
           ~orphans:(full_orphans ++ orphan_versions)
@@ -1530,11 +1538,11 @@ module API = struct
       OpamSolution.check_solution t solution
     )
 
-  let install names add_to_roots deps_only =
+  let install names add_to_roots ~deps_only ~upgrade =
     with_switch_backup "install" @@ fun t ->
     let atoms = OpamSolution.sanitize_atom_list ~permissive:true t names in
     let t = update_dev_packages_t atoms t in
-    install_t atoms add_to_roots deps_only t
+    install_t atoms add_to_roots ~deps_only ~upgrade t
 
   let remove_t ?ask ~autoremove ~force atoms t =
     log "REMOVE autoremove:%b %a" autoremove
@@ -1679,9 +1687,12 @@ module API = struct
         OpamConsole.msg "%s needs to be %sinstalled.\n"
           (OpamPackage.Name.to_string name)
           (if OpamPackage.has_name t.installed name then "re" else "");
-        if OpamPackage.Set.mem nv t.installed
-        then reinstall_t ~ask:true [name, Some (`Eq,v)] t (* same version *)
-        else install_t ~ask:true [name, Some (`Eq,v)] None false t (* != version or new *)
+        if OpamPackage.Set.mem nv t.installed then
+          reinstall_t ~ask:true [name, Some (`Eq,v)] t (* same version *)
+        else
+          install_t ~ask:true [name, Some (`Eq,v)] None
+            ~deps_only:false ~upgrade:false t
+          (* != version or new *)
       | None ->
         try
           let nv = OpamPackage.max_version t.installed name in
@@ -1829,8 +1840,8 @@ module SafeAPI = struct
   let info ~fields ~raw_opam ~where regexps =
     read_lock (fun () -> API.info ~fields ~raw_opam ~where regexps)
 
-  let install names add_to_roots deps_only =
-    switch_lock (fun () -> API.install names add_to_roots deps_only)
+  let install names add_to_roots ~deps_only ~upgrade =
+    switch_lock (fun () -> API.install names add_to_roots ~deps_only ~upgrade)
 
   let reinstall names =
     switch_lock (fun () -> API.reinstall names)

src/client/opamClient.mli

@@ -47,7 +47,8 @@ module API: sig
   (** Install the given list of packages. Second argument, if not None, specifies
       that given packages should be added or removed from the roots.
       Third argument installs all dependencies but not the packages themselves *)
-  val install: atom list -> bool option -> bool -> unit
+  val install:
+    atom list -> bool option -> deps_only:bool -> upgrade:bool -> unit
 
   (** Reinstall the given set of packages. *)
   val reinstall: atom list -> unit

src/client/opamMain.ml

@@ -632,13 +632,18 @@ let install =
     Arg.(value & flag & info ["deps-only"]
            ~doc:"Install all its dependencies, but don't actually install the \
                  package.") in
-  let install global_options build_options add_to_roots deps_only atoms =
+  let upgrade =
+    Arg.(value & flag & info ["u";"upgrade"]
+           ~doc:"Upgrade the packages if already installed, rather than \
+                 ignoring them") in
+  let install
+      global_options build_options add_to_roots deps_only upgrade atoms =
     apply_global_options global_options;
     apply_build_options build_options;
-    Client.install atoms add_to_roots deps_only
+    Client.install atoms add_to_roots ~deps_only ~upgrade
   in
   Term.(pure install $global_options $build_options
-        $add_to_roots $deps_only $nonempty_atom_list),
+        $add_to_roots $deps_only $upgrade $nonempty_atom_list),
   term_info "install" ~doc ~man
 
 (* REMOVE *)
@@ -1453,7 +1458,7 @@ let check_and_run_external_commands () =
           (OpamRepositoryConfig.init ();
            OpamSolverConfig.init ();
            OpamClientConfig.init ();
-           Client.install [pkgname,None] None false;
+           Client.install [pkgname,None] None ~deps_only:false ~upgrade:false;
            OpamConsole.header_msg "Carrying on to \"%s\""
              (String.concat " " (Array.to_list Sys.argv));
            OpamConsole.msg "\n";