Do not run ocamldep on single module buildables

CHANGES.md

@@ -34,6 +34,9 @@ Unreleased
   native, dynlink) are disabled. Previously, dune would generate all archives
   for regardless of settings. (#3829, @rgrinberg)
 
+- Do no run ocamldep to for single module executables & libraries. The
+  dependency graph for such artifacts is trivial (#3847, @rgrinberg)
+
 2.7.1 (2/09/2020)
 -----------------
 

src/dune_rules/dep_rules.ml

@@ -102,8 +102,14 @@ let rec deps_of cctx ~ml_kind (m : Modules.Sourced_module.t) =
       | Intf -> deps_of cctx ~ml_kind (Imported_from_vlib m)
       | Impl -> deps_of cctx ~ml_kind (Normal m) )
 
+let for_module cctx module_ =
+  Ml_kind.Dict.of_func (fun ~ml_kind -> deps_of cctx ~ml_kind (Normal module_))
+
 let rules cctx ~modules =
-  let dir = Compilation_context.dir cctx in
-  Ml_kind.Dict.of_func (fun ~ml_kind ->
-      let per_module = Modules.obj_map modules ~f:(deps_of cctx ~ml_kind) in
-      Dep_graph.make ~dir ~per_module)
+  match Modules.as_singleton modules with
+  | Some m -> Dep_graph.Ml_kind.dummy m
+  | None ->
+    let dir = Compilation_context.dir cctx in
+    Ml_kind.Dict.of_func (fun ~ml_kind ->
+        let per_module = Modules.obj_map modules ~f:(deps_of cctx ~ml_kind) in
+        Dep_graph.make ~dir ~per_module)

src/dune_rules/dep_rules.mli

@@ -1,5 +1,8 @@
 (** Get dependencies for a set of modules using either ocamldep or ocamlobjinfo *)
 open! Dune_engine
 
+val for_module :
+  Compilation_context.t -> Module.t -> Module.t list Build.t Ml_kind.Dict.t
+
 val rules :
   Compilation_context.t -> modules:Modules.t -> Dep_graph.t Ml_kind.Dict.t

src/dune_rules/menhir.ml

@@ -193,21 +193,15 @@ module Run (P : PARAMS) : sig end = struct
       in
       Module.of_source ~visibility:Public ~kind:Impl source
     in
-    let modules =
-      (* The following incantation allows the mock [.ml] file to be preprocessed
-         by the user-specified [ppx] rewriters. *)
-      let mock_module =
-        Preprocessing.pp_module_as
-          (Compilation_context.preprocessing cctx)
-          name mock_module ~lint:false
-      in
-      Modules.singleton_exe mock_module
+    let mock_module =
+      Preprocessing.pp_module_as
+        (Compilation_context.preprocessing cctx)
+        name mock_module ~lint:false
     in
-    let dep_graphs = Dep_rules.rules cctx ~modules in
     let cctx = Compilation_context.without_bin_annot cctx in
-    Modules.iter_no_vlib modules ~f:(fun m ->
-        Module_compilation.ocamlc_i ~dep_graphs cctx m
-          ~output:(inferred_mli base));
+    let deps = Dep_rules.for_module cctx mock_module in
+    Module_compilation.ocamlc_i ~deps cctx mock_module
+      ~output:(inferred_mli base);
     (* 3. A second invocation of Menhir reads the inferred [.mli] file. *)
     rule
       (menhir

src/dune_rules/module_compilation.ml

@@ -234,18 +234,17 @@ let build_module ~dep_graphs ?(precompiled_cmi = false) cctx m =
            SC.add_rules sctx ~dir
              (Jsoo_rules.build_cm cctx ~js_of_ocaml ~src ~target))
 
-let ocamlc_i ?(flags = []) ~dep_graphs cctx (m : Module.t) ~output =
+let ocamlc_i ?(flags = []) ~deps cctx (m : Module.t) ~output =
   let sctx = CC.super_context cctx in
   let obj_dir = CC.obj_dir cctx in
   let dir = CC.dir cctx in
   let ctx = SC.context sctx in
   let src = Option.value_exn (Module.file m ~ml_kind:Impl) in
-  let dep_graph = Ml_kind.Dict.get dep_graphs Impl in
   let sandbox = Compilation_context.sandbox cctx in
   let cm_deps =
     Build.dyn_paths_unit
       (let open Build.O in
-      let+ deps = Dep_graph.deps_of dep_graph m in
+      let+ deps = Ml_kind.Dict.get deps Impl in
       List.concat_map deps ~f:(fun m ->
           [ Path.build (Obj_dir.Module.cm_file_exn obj_dir m ~kind:Cmi) ]))
   in

src/dune_rules/module_compilation.mli

@@ -13,7 +13,7 @@ val build_module :
 
 val ocamlc_i :
      ?flags:string list
-  -> dep_graphs:Dep_graph.Ml_kind.t
+  -> deps:Module.t list Build.t Ml_kind.Dict.t
   -> Compilation_context.t
   -> Module.t
   -> output:Path.Build.t

src/dune_rules/modules.ml

@@ -763,6 +763,10 @@ let is_empty = function
   | Unwrapped w -> Module_name.Map.is_empty w
   | Wrapped w -> Wrapped.empty w
 
+let as_singleton = function
+  | Singleton m -> Some m
+  | _ -> None
+
 let source_dirs =
   fold_user_written ~init:Path.Set.empty ~f:(fun m acc ->
       Module.sources m

src/dune_rules/modules.mli

@@ -100,4 +100,6 @@ val relocate_alias_module : t -> src_dir:Path.t -> t
 
 val is_empty : t -> bool
 
+val as_singleton : t -> Module.t option
+
 val source_dirs : t -> Path.Set.t

test/blackbox-tests/test-cases/all-alias.t/run.t

@@ -12,7 +12,6 @@
 
   $ dune build --display short --root private-lib @all
   Entering directory 'private-lib'
-      ocamldep .bar.objs/bar.ml.d
         ocamlc .bar.objs/byte/bar.{cmi,cmo,cmt}
       ocamlopt .bar.objs/native/bar.{cmx,o}
         ocamlc bar.cma

test/blackbox-tests/test-cases/byte-code-only.t/run.t

@@ -1,16 +1,13 @@
   $ env ORIG_PATH="$PATH" PATH="$PWD/ocaml-bin:$PATH" dune build @all --display short
-      ocamldep bin/.toto.eobjs/toto.ml.d
-      ocamldep src/.foo.objs/foo.ml.d
-        ocamlc build-info/.build_info.objs/byte/build_info.{cmi,cmo,cmt}
-      ocamldep build-info/.build_info.objs/build_info_data.mli.d
-      ocamldep bin-with-build-info/.print_version.eobjs/print_version.ml.d
         ocamlc bin/.toto.eobjs/byte/dune__exe__Toto.{cmi,cmo,cmt}
         ocamlc src/.foo.objs/byte/foo.{cmi,cmo,cmt}
-        ocamlc build-info/build_info.cma
-        ocamlc build-info/.build_info.objs/byte/build_info__Build_info_data.{cmi,cmti}
+        ocamlc build-info/.build_info.objs/byte/build_info.{cmi,cmo,cmt}
+      ocamldep build-info/.build_info.objs/build_info_data.mli.d
         ocamlc bin/toto.exe
         ocamlc bin/toto.bc
         ocamlc src/foo.cma
+        ocamlc build-info/build_info.cma
+        ocamlc build-info/.build_info.objs/byte/build_info__Build_info_data.{cmi,cmti}
         ocamlc bin-with-build-info/.print_version.eobjs/byte/build_info__Build_info_data.{cmo,cmt}
         ocamlc bin-with-build-info/.print_version.eobjs/byte/dune__exe__Print_version.{cmi,cmo,cmt}
         ocamlc bin-with-build-info/print_version.bc

test/blackbox-tests/test-cases/cross-compilation.t/run.t

@@ -1,10 +1,8 @@
   $ env OCAMLFIND_CONF=$PWD/etc/findlib.conf dune build --display short -x foo file @install --promote-install-files
-      ocamldep lib/.p.objs/p.ml.d [default.foo]
-      ocamldep bin/.blah.eobjs/blah.ml.d [default.foo]
-      ocamldep lib/.p.objs/p.ml.d
-      ocamldep bin/.blah.eobjs/blah.ml.d
         ocamlc lib/.p.objs/byte/p.{cmi,cmo,cmt} [default.foo]
+      ocamldep bin/.blah.eobjs/blah.ml.d [default.foo]
         ocamlc lib/.p.objs/byte/p.{cmi,cmo,cmt}
+      ocamldep bin/.blah.eobjs/blah.ml.d
       ocamlopt lib/.p.objs/native/p.{cmx,o} [default.foo]
         ocamlc lib/p.cma [default.foo]
       ocamlopt lib/.p.objs/native/p.{cmx,o}

test/blackbox-tests/test-cases/dune-init.t/run.t

@@ -354,7 +354,6 @@ Can init and build a new library project
 
   $ dune runtest --root test_lib_proj --display short
   Entering directory 'test_lib_proj'
-      ocamldep test/.test_lib_proj.eobjs/test_lib_proj.ml.d
         ocamlc test/.test_lib_proj.eobjs/byte/dune__exe__Test_lib_proj.{cmi,cmo,cmt}
       ocamlopt test/.test_lib_proj.eobjs/native/dune__exe__Test_lib_proj.{cmx,o}
       ocamlopt test/test_lib_proj.exe

test/blackbox-tests/test-cases/dune-ppx-driver-system.t/run.t

@@ -98,9 +98,6 @@ Test that going through the -ppx option of the compiler works
 
   $ dune build --root driver-tests test_ppx_staged.cma
   Entering directory 'driver-tests'
-      ocamldep .test_ppx_staged.objs/test_ppx_staged.ml.d
-  tool name: ocamldep
-  args:--as-ppx -arg1 -arg2 -arg3=Oreo -foo bar Snickerdoodle --cookie france="Petit Beurre" --cookie italy="Biscotti" --cookie library-name="test_ppx_staged"
         ocamlc .test_ppx_staged.objs/byte/test_ppx_staged.{cmi,cmo,cmt}
   tool name: ocamlc
   args:--as-ppx -arg1 -arg2 -arg3=Oreo -foo bar Snickerdoodle --cookie france="Petit Beurre" --cookie italy="Biscotti" --cookie library-name="test_ppx_staged"

test/blackbox-tests/test-cases/installable-dup-private-libs.t/run.t

@@ -1,6 +1,4 @@
   $ dune build @install --display short
-      ocamldep a1/.a.objs/a.ml.d
-      ocamldep a2/.a.objs/a.ml.d
         ocamlc a1/.a.objs/byte/a.{cmi,cmo,cmt}
         ocamlc a2/.a.objs/byte/a.{cmi,cmo,cmt}
       ocamlopt a1/.a.objs/native/a.{cmx,o}

test/blackbox-tests/test-cases/intf-only.t/run.t

@@ -5,7 +5,6 @@ Successes:
       ocamldep .foo.objs/foo.ml.d
         ocamlc .foo.objs/byte/foo__.{cmi,cmo,cmt}
       ocamldep .foo.objs/intf.mli.d
-      ocamldep test/.bar.objs/bar.ml.d
       ocamlopt .foo.objs/native/foo__.{cmx,o}
         ocamlc .foo.objs/byte/foo__Intf.{cmi,cmti}
         ocamlc .foo.objs/byte/foo.{cmi,cmo,cmt}

test/blackbox-tests/test-cases/jsoo/explicit-js-mode-anon.t/run.t

@@ -3,7 +3,6 @@ Anonymous projects have explicit_js_mode enabled
   $ dune build --display short @all
   Info: Creating file dune-project with this contents:
   | (lang dune 2.8)
-      ocamldep .foo.objs/foo.ml.d
         ocamlc .foo.objs/byte/foo.{cmi,cmo,cmt}
       ocamlopt .foo.objs/native/foo.{cmx,o}
         ocamlc foo.cma

test/blackbox-tests/test-cases/menhir/general.t/run.t

@@ -1,5 +1,19 @@
 Build and run a source file that requires a menhir parser.
 
+  $ cat >dune-project <<EOF
+  > (lang dune 1.0)
+  > (using menhir 1.0)
+  > EOF
+
+  $ dune build ./src/test.exe --debug-dependency-path
+  $ ls _build/default/src/test.exe
+  _build/default/src/test.exe
+
+  $ cat >dune-project <<EOF
+  > (lang dune 2.0)
+  > (using menhir 2.0)
+  > EOF
+
   $ dune build ./src/test.exe --debug-dependency-path
   $ ls _build/default/src/test.exe
   _build/default/src/test.exe

test/blackbox-tests/test-cases/ocaml-dep-single-exe.t

@@ -0,0 +1,17 @@
+When creating single module libraries & executables, running ocamldep isn't
+necessary.
+
+  $ cat >dune-project <<EOF
+  > (lang dune 2.8)
+  > EOF
+  $ cat >dune <<EOF
+  > (executable (name foo))
+  > EOF
+  $ cat >foo.ml <<EOF
+  > print_endline "hello world"
+  > EOF
+  $ dune exec ./foo.exe
+  hello world
+
+We check to see if ocamldep artifacts have been created:
+  $ find _build/default -name "*.all-deps" -or -name "*.d"

test/blackbox-tests/test-cases/ocamldep-error-check.t

@@ -0,0 +1,74 @@
+Dune uses ocamldep to prevent a module from depending on itself.
+
+  $ cat >dune-project <<EOF
+  > (lang dune 2.8)
+  > (wrapped_executables false)
+  > EOF
+
+  $ mkdir lib
+  $ cat >lib/dune <<EOF
+  > (library
+  >  (name foo))
+  > EOF
+  $ cat >lib/bar.ml <<EOF
+  > Foo.bar
+  > EOF
+  $ dune build @all
+  Error: Module Bar in directory _build/default/lib depends on Foo.
+  This doesn't make sense to me.
+
+  Foo is the main module of the library and is the only module exposed outside
+  of the library. Consequently, it should be the one depending on all the other
+  modules in the library.
+  [1]
+
+  $ rm lib/bar.ml
+
+This check doesn't apply to single module libraries:
+
+  $ cat >lib/foo.ml <<EOF
+  > let x = Foo.x
+  > EOF
+  $ dune build @all
+  File "lib/foo.ml", line 1, characters 8-13:
+  1 | let x = Foo.x
+              ^^^^^
+  Error: Unbound module Foo
+  [1]
+  $ rm lib/foo.ml
+
+However, we'll demonstrate that this check isn't applicable to executables:
+
+  $ cat >lib/bar.ml <<EOF
+  > let run () = print_endline "Hello World"
+  > EOF
+
+  $ mkdir exe
+  $ cat >exe/dune <<EOF
+  > (executable
+  >  (name foo)
+  >  (libraries foo))
+  > EOF
+  $ cat >exe/foo.ml <<EOF
+  > Foo.Bar.run ();;
+  > EOF
+
+Although we get slightly different behavior if warpping is on or off:
+
+  $ cat >dune-project <<EOF
+  > (lang dune 2.8)
+  > (wrapped_executables false)
+  > EOF
+  $ dune exec ./exe/foo.exe
+  File "exe/foo.ml", line 1, characters 0-11:
+  1 | Foo.Bar.run ();;
+      ^^^^^^^^^^^
+  Error: Unbound module Foo
+  [1]
+
+  $ cat >dune-project <<EOF
+  > (lang dune 2.8)
+  > (wrapped_executables true)
+  > EOF
+  $ dune exec ./exe/foo.exe
+  Hello World

test/blackbox-tests/test-cases/odoc/multiple-private-libs.t/run.t

@@ -2,8 +2,6 @@ This test checks that there is no clash when two private libraries have the same
 
   $ dune build --display short @doc-private
           odoc _doc/_html/highlight.pack.js,_doc/_html/odoc.css
-      ocamldep a/.test.objs/test.ml.d
-      ocamldep b/.test.objs/test.ml.d
         ocamlc a/.test.objs/byte/test.{cmi,cmo,cmt}
         ocamlc b/.test.objs/byte/test.{cmi,cmo,cmt}
           odoc a/.test.objs/byte/test.odoc

test/blackbox-tests/test-cases/plugin-mode.t/run.t

@@ -80,33 +80,27 @@ Testsuite for (mode plugin).
   > EOF
 
   $ dune build --display short @all 2>&1 | dune_cmd sanitize
-      ocamldep $ext_lib.eobjs/a.ml.d
-      ocamldep foo/.foo.objs/foo.ml.d
-      ocamldep .b.eobjs/b.ml.d
-      ocamldep foo/.bar.objs/bar.ml.d
-      ocamldep main/.main.eobjs/main.ml.d
-      ocamldep main2/.main.eobjs/main.ml.d
         ocamlc foo/.foo.objs/byte/foo.{cmi,cmo,cmt}
         ocamlc main2/.main.eobjs/byte/dune__exe__Main.{cmi,cmo,cmt}
-      ocamlopt foo/.foo.objs/native/foo.{cmx,o}
-        ocamlc foo/.bar.objs/byte/bar.{cmi,cmo,cmt}
         ocamlc $ext_lib.eobjs/byte/dune__exe__A.{cmi,cmo,cmt}
+        ocamlc foo/.bar.objs/byte/bar.{cmi,cmo,cmt}
+      ocamlopt foo/.foo.objs/native/foo.{cmx,o}
         ocamlc foo/foo.cma
       ocamlopt main2/.main.eobjs/native/dune__exe__Main.{cmx,o}
-      ocamlopt foo/foo.{a,cmxa}
+      ocamlopt $ext_lib.eobjs/native/dune__exe__A.{cmx,o}
       ocamlopt foo/.bar.objs/native/bar.{cmx,o}
         ocamlc foo/bar.cma
-      ocamlopt $ext_lib.eobjs/native/dune__exe__A.{cmx,o}
+      ocamlopt foo/foo.{a,cmxa}
       ocamlopt main2/main.exe
+      ocamlopt a.cmxs
+      ocamlopt foo/bar.{a,cmxa}
+      ocamlopt a.exe
         ocamlc .b.eobjs/byte/dune__exe__B.{cmi,cmo,cmt}
       ocamlopt foo/foo.cmxs
         ocamlc main/.main.eobjs/byte/dune__exe__Main.{cmi,cmo,cmt}
-      ocamlopt foo/bar.{a,cmxa}
-      ocamlopt a.cmxs
-      ocamlopt a.exe
+      ocamlopt foo/bar.cmxs
       ocamlopt .b.eobjs/native/dune__exe__B.{cmx,o}
       ocamlopt main/.main.eobjs/native/dune__exe__Main.{cmx,o}
-      ocamlopt foo/bar.cmxs
       ocamlopt b.cmxs
       ocamlopt main/main.exe
 

test/blackbox-tests/test-cases/private-public-overlap.t/run.t

@@ -17,7 +17,6 @@ On the other hand, public libraries may have private preprocessors
       ocamlopt ppx_internal.{a,cmxa}
       ocamlopt .ppx/be26d3600214af2fa78c2c9ef25e9069/ppx.exe
            ppx mylib.pp.ml
-      ocamldep .mylib.objs/mylib.pp.ml.d
         ocamlc .mylib.objs/byte/mylib.{cmi,cmo,cmt}
       ocamlopt .mylib.objs/native/mylib.{cmx,o}
         ocamlc mylib.cma

test/blackbox-tests/test-cases/variables-for-artifacts.t/run.t

@@ -19,12 +19,10 @@ prefixed and unprefixed modules are built.
   $ ./sdune clean
   $ ./sdune build --display short @t1
       ocamldep .a1.objs/a.ml.d
-      ocamldep .b.eobjs/b.ml.d
-      ocamldep .c1.objs/c.ml.d
-      ocamldep .c2.objs/d.ml.d
-        ocamlc .a1.objs/byte/a1.{cmi,cmo,cmt}
         ocamlc .b.eobjs/byte/dune__exe__B.{cmi,cmo,cmt}
         ocamlc .c1.objs/byte/c.{cmi,cmo,cmt}
+      ocamldep .c2.objs/d.ml.d
+        ocamlc .a1.objs/byte/a1.{cmi,cmo,cmt}
         ocamlc .c2.objs/byte/c2.{cmi,cmo,cmt}
         ocamlc .a1.objs/byte/a1__A.{cmi,cmo,cmt}
         ocamlc .c2.objs/byte/c2__D.{cmi,cmo,cmt}
@@ -182,7 +180,6 @@ public library defined in a subdirectory.
 
   $ ./sdune clean
   $ ./sdune build --display short @t10
-      ocamldep .c1.objs/c.ml.d
         ocamlc .c1.objs/byte/c.{cmi,cmo,cmt}
         ocamlc c1.cma