feat: filter -I flags per-module to match dependency filtering

When per-module dependency filtering determines which libraries a module
actually references, also restrict the -I/-H flags to only include
directories for those libraries. Previously, hidden deps were filtered
but -I flags included all libraries, allowing accidental compilation
success on clean builds while incremental rebuilds could fail.

This also improves caching: adding a new dependency no longer invalidates
the compilation cache for unrelated modules.

Both build_cm and ocamlc_i now compute -I flags and hidden deps together
from the filtered library set.

Signed-off-by: Robin Bate Boerop <me@robinbb.com>

Author: robinbb

src/dune_rules/module_compilation.ml

@@ -14,14 +14,17 @@ let all_libs cctx =
   d @ h
 ;;
 
-let filtered_lib_deps ~cctx ~obj_dir ~ml_kind ~for_ ~dep_graph ~opaque ~cm_kind ~mode m =
+(* Compute the filtered set of libraries that a module actually references.
+   Returns the library list, which callers use for both -I flags and hidden
+   deps. Falls back to all [libs] when virtual implementations are present. *)
+let filtered_libs_for_module ~cctx ~obj_dir ~ml_kind ~for_ ~dep_graph ~mode m =
   let open Action_builder.O in
   let* libs = Resolve.Memo.read (all_libs cctx) in
   let has_virtual_impl =
     List.exists libs ~f:(fun lib -> Option.is_some (Lib.implements lib))
   in
   if has_virtual_impl
-  then Action_builder.return ((), Lib_file_deps.deps_of_entries ~opaque ~cm_kind libs)
+  then Action_builder.return libs
   else
     let* lib_index = Resolve.Memo.read (Compilation_context.lib_index cctx) in
     let* raw_deps_m = Ocamldep.read_immediate_deps_raw_of ~obj_dir ~ml_kind ~for_ m in
@@ -67,8 +70,7 @@ let filtered_lib_deps ~cctx ~obj_dir ~ml_kind ~for_ ~dep_graph ~opaque ~cm_kind
     let libs_set = Table.create (module Lib) (List.length libs) in
     List.iter libs ~f:(fun lib -> Table.set libs_set lib ());
     let+ closed = Resolve.Memo.read (Lib.closure filtered_libs ~linking:false ~for_) in
-    let all_libs = List.filter closed ~f:(Table.mem libs_set) in
-    (), Lib_file_deps.deps_of_entries ~opaque ~cm_kind all_libs
+    List.filter closed ~f:(Table.mem libs_set)
 ;;
 
 (* Arguments for the compiler to prevent it from being too clever.
@@ -391,34 +393,50 @@ let build_cm
      && Module.has m ~ml_kind
      && not (Virtual_rules.is_implementation (Compilation_context.implements cctx))
    in
-   (* Fallback lib deps: when per-module filtering is not possible, depend
-      on all .cmi/.cmx files from all required libraries. *)
-   let lib_cm_deps_args =
-     if skip_lib_deps || can_filter
-     then Command.Args.empty
-     else
-       (let open Resolve.Memo.O in
-        let+ libs = all_libs cctx in
-        Command.Args.Hidden_deps (Lib_file_deps.deps_of_entries ~opaque ~cm_kind libs))
-       |> Resolve.Memo.args
-       |> Command.Args.memo
-   in
-   (* Dynamic lib deps: used when per-module filtering is possible. *)
-   let lib_cm_deps_filtered =
-     if not can_filter
-     then Action_builder.return ()
+   (* Per-module library deps and includes. When filtering is possible, both
+      hidden deps and -I flags are restricted to the libraries the module
+      actually references. Otherwise, fall back to all required libraries. *)
+   let lib_deps_and_includes =
+     if skip_lib_deps
+     then Action_builder.return (Command.Args.empty, Command.Args.empty)
+     else if can_filter
+     then
+       let open Action_builder.O in
+       let+ filtered =
+         filtered_libs_for_module ~cctx ~obj_dir ~ml_kind ~for_ ~dep_graph ~mode m
+       in
+       let project = Compilation_context.scope cctx |> Scope.project in
+       let lib_config = (Compilation_context.ocaml cctx).lib_config in
+       let includes =
+         Lib_flags.L.include_flags
+           ~project
+           ~direct_libs:filtered
+           ~hidden_libs:[]
+           (Lib_mode.of_cm_kind cm_kind)
+           lib_config
+       in
+       let deps =
+         Command.Args.Hidden_deps
+           (Lib_file_deps.deps_of_entries ~opaque ~cm_kind filtered)
+       in
+       includes, deps
      else
-       Action_builder.dyn_deps
-         (filtered_lib_deps
-            ~cctx
-            ~obj_dir
-            ~ml_kind
-            ~for_
-            ~dep_graph
-            ~opaque
-            ~cm_kind
-            ~mode
-            m)
+       let open Action_builder.O in
+       let+ libs = Resolve.Memo.read (all_libs cctx) in
+       let project = Compilation_context.scope cctx |> Scope.project in
+       let lib_config = (Compilation_context.ocaml cctx).lib_config in
+       let includes =
+         Lib_flags.L.include_flags
+           ~project
+           ~direct_libs:libs
+           ~hidden_libs:[]
+           (Lib_mode.of_cm_kind cm_kind)
+           lib_config
+       in
+       let deps =
+         Command.Args.Hidden_deps (Lib_file_deps.deps_of_entries ~opaque ~cm_kind libs)
+       in
+       includes, deps
    in
    let other_cm_files =
      let dep_graph = Ml_kind.Dict.get (Compilation_context.dep_graphs cctx) ml_kind in
@@ -538,7 +556,6 @@ let build_cm
      ?loc:(Compilation_context.loc cctx)
      (let open Action_builder.With_targets.O in
       Action_builder.with_no_targets other_cm_files
-      >>> Action_builder.with_no_targets lib_cm_deps_filtered
       >>> Command.run
             ~dir:(Path.build (Context.build_dir ctx))
             compiler
@@ -547,9 +564,9 @@ let build_cm
             ; cmt_args
             ; cms_args
             ; Command.Args.S obj_dirs
-            ; Command.Args.as_any
-                (Lib_mode.Cm_kind.Map.get (Compilation_context.includes cctx) cm_kind)
-            ; Command.Args.as_any lib_cm_deps_args
+            ; Dyn
+                (Action_builder.map lib_deps_and_includes ~f:(fun (includes, deps) ->
+                   Command.Args.S [ includes; deps ]))
             ; extra_args
             ; As as_parameter_arg
             ; as_argument_for
@@ -655,7 +672,7 @@ let ocamlc_i ~deps cctx (m : Module.t) ~output =
        List.concat_map deps ~f:(fun m ->
          [ Path.build (Obj_dir.Module.cm_file_exn obj_dir m ~kind:(Ocaml Cmi)) ]))
   in
-  let lib_cm_deps =
+  let lib_deps_and_includes =
     let opaque = Compilation_context.opaque cctx in
     let for_ = Compilation_context.for_ cctx in
     let ml_kind = Ml_kind.Impl in
@@ -669,24 +686,35 @@ let ocamlc_i ~deps cctx (m : Module.t) ~output =
       && Module.has m ~ml_kind
       && not (Virtual_rules.is_implementation (Compilation_context.implements cctx))
     in
-    if can_filter
-    then
-      Action_builder.dyn_deps
-        (filtered_lib_deps
-           ~cctx
-           ~obj_dir
-           ~ml_kind
-           ~for_
-           ~dep_graph
-           ~opaque
-           ~cm_kind:(Ocaml Cmo)
-           ~mode:(Ocaml Byte)
-           m)
-    else
-      Action_builder.dyn_deps
-        (let open Action_builder.O in
-         let+ libs = Resolve.Memo.read (all_libs cctx) in
-         (), Lib_file_deps.deps_of_entries ~opaque ~cm_kind:(Ocaml Cmo) libs)
+    let open Action_builder.O in
+    let+ libs =
+      if can_filter
+      then
+        filtered_libs_for_module
+          ~cctx
+          ~obj_dir
+          ~ml_kind
+          ~for_
+          ~dep_graph
+          ~mode:(Ocaml Byte)
+          m
+      else Resolve.Memo.read (all_libs cctx)
+    in
+    let project = Compilation_context.scope cctx |> Scope.project in
+    let lib_config = (Compilation_context.ocaml cctx).lib_config in
+    let includes =
+      Lib_flags.L.include_flags
+        ~project
+        ~direct_libs:libs
+        ~hidden_libs:[]
+        (Ocaml Byte)
+        lib_config
+    in
+    let deps =
+      Command.Args.Hidden_deps
+        (Lib_file_deps.deps_of_entries ~opaque ~cm_kind:(Ocaml Cmo) libs)
+    in
+    includes, deps
   in
   let ocaml_flags = Ocaml_flags.get (Compilation_context.flags cctx) (Ocaml Byte) in
   let modules = Compilation_context.modules cctx in
@@ -698,18 +726,16 @@ let ocamlc_i ~deps cctx (m : Module.t) ~output =
        ~file_targets:[ output ]
        (let open Action_builder.With_targets.O in
         Action_builder.with_no_targets cm_deps
-        >>> Action_builder.with_no_targets lib_cm_deps
         >>> Command.run
               (Ok ocaml.ocamlc)
               ~dir:(Path.build (Context.build_dir ctx))
               ~stdout_to:output
               [ Command.Args.dyn ocaml_flags
               ; A "-I"
               ; Path (Path.build (Obj_dir.byte_dir obj_dir))
-              ; Command.Args.as_any
-                  (Lib_mode.Cm_kind.Map.get
-                     (Compilation_context.includes cctx)
-                     (Ocaml Cmo))
+              ; Dyn
+                  (Action_builder.map lib_deps_and_includes ~f:(fun (includes, deps) ->
+                     Command.Args.S [ includes; deps ]))
               ; opens modules m
               ; A "-short-paths"
               ; A "-i"

test/blackbox-tests/test-cases/per-module-lib-deps/filtered-includes.t

@@ -57,7 +57,7 @@ module's own obj dir):
 
   $ extract_includes () {
   >   dune rules "$1" 2>&1 | tr -s '() \n' '\n' | \
-  >     awk '/^-I$/{getline; print}' | grep -v '\.main\.' | sort -u
+  >     awk '/^-I$/{getline; print}' | grep -v '\.main\.' | sort -u || true
   > }
 
 The module uses_mylib references Mylib, so its -I flags should include