Add a "default" alias defined as follow:

- if "default" is specified by the user explicitely, use this
  definition
- otherwise assume the following definition:

  (alias
   (name default)
   (deps (alias_rec install)))

Signed-off-by: Jeremie Dimino <jeremie@dimino.org>

CHANGES.md

@@ -95,6 +95,13 @@ next
 
 - Version `dune-workspace` and `~/.config/dune/config` files (#..., @diml)
 
+- Add the ability to build an alias non-recursively from the command
+  line by writing `@@alias` (#926, @diml)
+
+- Add a special `default` alias that defaults to `(alias_rec install)`
+  when not defined by the user and make `@@default` be the default
+  target (#926, @diml)
+
 1.0+beta20 (10/04/2018)
 -----------------------
 

bin/main.ml

@@ -26,6 +26,7 @@ type common =
   ; (* Original arguments for the external-lib-deps hint *)
     orig_args             : string list
   ; config                : Config.t
+  ; default_target        : string
   }
 
 let prefix_target common s = common.target_prefix ^ s
@@ -234,6 +235,7 @@ let common =
          ignore_promoted_rules,
          config_file,
          profile,
+         default_target,
          orig)
         x
         display
@@ -296,6 +298,7 @@ let common =
     ; x
     ; config
     ; build_dir
+    ; default_target
     }
   in
   let docs = copts_sect in
@@ -484,6 +487,20 @@ let common =
       in
       Term.(ret (const merge $ config_file $ no_config))
     in
+    let default_target_default =
+      match Which_program.t with
+      | Dune     -> "@@default"
+      | Jbuilder -> "@install"
+    in
+    let default_target =
+      Arg.(value
+           & opt (some string) None
+           & info ["default-target"] ~docs ~docv:"TARGET"
+               ~doc:(sprintf
+                       {|Set the default target that when none is specified to
+                         $(b,dune build). It defaults to %s.|}
+                       default_target_default))
+    in
     let for_release = "for-release-of-packages" in
     let frop =
       Arg.(value
@@ -496,33 +513,37 @@ let common =
                       packages as well as getting reproducible builds.|})
     in
     let merge root only_packages ignore_promoted_rules
-          (config_file_opt, config_file) profile release =
+          (config_file_opt, config_file) profile default_target release =
       let fail opt = incompatible ("-p/--" ^ for_release) opt in
       match release, root, only_packages, ignore_promoted_rules,
-            profile, config_file_opt with
-      | Some _, Some _, _, _, _, _ -> fail "--root"
-      | Some _, _, Some _, _, _, _ -> fail "--only-packages"
-      | Some _, _, _, true  , _, _ -> fail "--ignore-promoted-rules"
-      | Some _, _, _, _, Some _, _ -> fail "--profile"
-      | Some _, _, _, _, _, Some s -> fail s
-      | Some pkgs, None, None, false, None, None ->
+            profile, default_target, config_file_opt with
+      | Some _, Some _, _, _, _, _, _ -> fail "--root"
+      | Some _, _, Some _, _, _, _, _ -> fail "--only-packages"
+      | Some _, _, _, true  , _, _, _ -> fail "--ignore-promoted-rules"
+      | Some _, _, _, _, Some _, _, _ -> fail "--profile"
+      | Some _, _, _, _, _, Some s, _ -> fail s
+      | Some _, _, _, _, _, _, Some _ -> fail "--default-target"
+      | Some pkgs, None, None, false, None, None, None ->
         `Ok (Some ".",
              Some pkgs,
              true,
              No_config,
              Some "release",
+             "@install",
              ["-p"; pkgs]
             )
-      | None, _, _, _, _, _ ->
+      | None, _, _, _, _, _, _ ->
         `Ok (root,
              only_packages,
              ignore_promoted_rules,
              config_file,
              profile,
+             Option.value default_target ~default:default_target_default,
              List.concat
                [ dump_opt "--root" root
                ; dump_opt "--only-packages" only_packages
                ; dump_opt "--profile" profile
+               ; dump_opt "--default-target" default_target
                ; if ignore_promoted_rules then
                    ["--ignore-promoted-rules"]
                  else
@@ -540,6 +561,7 @@ let common =
                $ ignore_promoted_rules
                $ config_file
                $ profile
+               $ default_target
                $ frop))
   in
   let x =
@@ -771,9 +793,14 @@ let build_targets =
       (Main.setup ~log common >>= fun setup ->
        let targets = resolve_targets_exn ~log common setup targets in
        do_build setup targets) in
+  let default_target =
+    match Which_program.t with
+    | Dune     -> "@@default"
+    | Jbuilder -> "@install"
+  in
   ( Term.(const go
           $ common
-          $ Arg.(value & pos_all string ["@install"] name_))
+          $ Arg.(value & pos_all string [default_target] name_))
   , Term.info "build" ~doc ~man)
 
 let runtest =

doc/jbuild.rst

@@ -531,6 +531,8 @@ menhir
 A ``menhir`` stanza is available to support the menhir_ parser generator. See
 the :ref:`menhir-main` section for details.
 
+.. _alias-stanza:
+
 alias
 -----
 

doc/terminology.rst

@@ -50,6 +50,9 @@ Terminology
    alias in all children directories recursively. Jbuilder defines the
    following standard aliases:
 
+   -  ``default`` which is the alias build by default when no targets
+      are specified on the command line. See :ref:`default-alias` for
+      details
    -  ``runtest`` which runs user defined tests
    -  ``install`` which depends on everything that should be installed
    -  ``doc``     which depends on the generated HTML

doc/usage.rst

@@ -68,8 +68,9 @@ directory as this is normally the case.
 Interpretation of targets
 =========================
 
-This section describes how ``jbuilder`` interprets the targets given on
-the command line.
+This section describes how ``dune`` interprets the targets given on
+the command line. When no targets are specified, ``dune`` builds the
+``default`` alias, see :ref:`default-alias` for more details.
 
 Resolution
 ----------
@@ -128,6 +129,31 @@ You can also build an alias non-recursively by using ``@@`` instead of
 
    dune build @@runtest
 
+.. _default-alias:
+
+Default alias
+-------------
+
+When no targets are given to ``dune build``, it builds the special
+``default`` alias. Effectively ``dune build`` is equivalent to:
+
+.. code::
+
+   dune build @@default
+
+When a directory doesn't explicitly define what the ``default`` alias
+means via an :ref:`alias-stanza` stanza, the following implicit
+definition is assumed:
+
+.. code::
+
+   (alias
+    (name default)
+    (deps (alias_rec install)))
+
+Which means that by default ``dune build`` will build everything that
+is installable.
+
 Finding external libraries
 ==========================
 
@@ -214,7 +240,7 @@ follows:
     build: [["dune" "build" "-p" name "-j" jobs]]
 
 ``-p pkg`` is a shorthand for ``--root . --only-packages pkg --profile
-release``. ``-p`` is the short version of
+release --default-target @install``. ``-p`` is the short version of
 ``--for-release-of-packages``.
 
 This has the following effects:
@@ -224,6 +250,7 @@ This has the following effects:
 -  it sets the root to prevent jbuilder from looking it up
 -  it sets the build profile to ``release``
 -  it uses whatever concurrency option opam provides
+-  it sets the default target to ``@install`` rather than ``@@default``
 
 Note that ``name`` and ``jobs`` are variables expanded by opam. ``name``
 expands to the package name and ``jobs`` to the number of jobs available

src/build_system.ml

@@ -271,7 +271,7 @@ module Alias0 = struct
       stamp_file (make ~dir name)))
 
   let is_standard = function
-    | "runtest" | "install" | "doc" | "doc-private" | "lint" -> true
+    | "runtest" | "install" | "doc" | "doc-private" | "lint" | "default" -> true
     | _ -> false
 
   open Build.O
@@ -318,7 +318,7 @@ module Alias0 = struct
            It is not defined in %s or any of its descendants."
         name (Path.to_string_maybe_quoted src_dir)
 
-  let default     = make "DEFAULT"
+  let default     = make "default"
   let runtest     = make "runtest"
   let install     = make "install"
   let doc         = make "doc"
@@ -914,7 +914,28 @@ and load_dir_step2_exn t ~dir ~collector ~lazy_generators =
   let alias_dir = Path.append (Path.relative alias_dir context_name) sub_dir in
   let alias_rules, alias_stamp_files =
     let open Build.O in
-    String.Map.foldi collector.aliases ~init:([], Path.Set.empty)
+    let aliases = collector.aliases in
+    let aliases =
+      if String.Map.mem collector.aliases "default" then
+        aliases
+      else
+        match Path.extract_build_context_dir dir with
+        | None -> aliases
+        | Some (_, src_dir) ->
+          match File_tree.find_dir t.file_tree src_dir with
+          | None -> aliases
+          | Some _ ->
+            String.Map.add aliases "default"
+              { deps = Path.Set.empty
+              ; dyn_deps =
+                  Alias0.dep_rec (Alias0.install ~dir) ~loc:Loc.none
+                    ~file_tree:t.file_tree
+                  >>>
+                  Build.return Path.Set.empty
+              ; actions = []
+              }
+    in
+    String.Map.foldi aliases ~init:([], Path.Set.empty)
       ~f:(fun name { Dir_status. deps; dyn_deps; actions } (rules, alias_stamp_files) ->
         let base_path = Path.relative alias_dir name in
         let rules, deps =