[fix] [directory targets] Fix promotion of directory targets in some …

…cases

When the promoted directory has sub-directories with only other
sub-directories inside, the map will miss that directory and it will
not be properly re-created, failing at children creation time.

I am not sure I fully follow the logic here (cc: @rleshchinskiy), for
example, I did have trouble making a testcase fail without using `npm`
to generate a large directory.

Regression in b1c339b / #9407

Signed-off-by: Emilio Jesus Gallego Arias <e+git@x80.org>

doc/changes/xxxxx.md

@@ -0,0 +1,3 @@
+- Fix promotion of directory targets when the promoted directory has
+  sub-directories with only other sub-directories inside; regression
+  in b1c339b / #9407 (@ejgallego, closes #10609)

src/dune_targets/dune_targets.ml

@@ -243,9 +243,7 @@ module Produced = struct
                 acc_filenames, Path.Local.Map.union_exn acc_dirs dir
               | _ -> Error (Unsupported_file (Path.Build.relative dir filename, kind)))
         in
-        if not (Filename.Map.is_empty filenames)
-        then Path.Local.Map.add_exn dirs local filenames
-        else dirs
+        Path.Local.Map.add_exn dirs local filenames
     in
     let directory root dirname =
       let open Result.O in

test/blackbox-tests/test-cases/directory-targets/github10609/run.t

@@ -0,0 +1,28 @@
+We test that a directory target with only other subdirs can be
+properly promoted.
+
+  $ cat > dune-project <<EOF
+  > (lang dune 3.16)
+  > (using directory-targets 0.1)
+  > EOF
+
+  $ cat > dune <<EOF
+  > (rule
+  >  (targets (dir node_modules))
+  >  (mode (promote (until-clean)))
+  >  (action (system "mkdir -p node_modules/@clusterws/cws && mkdir -p node_modules/@clusterws/cws/build && mkdir -p node_modules/@clusterws/cws/dist && mkdir -p node_modules/@clusterws/cws/src && touch node_modules/@clusterws/cws/foo.txt && touch node_modules/@clusterws/cws/bar.txt")))
+  > EOF
+
+  $ dune build node_modules
+  $ ls _build/default/node_modules/@clusterws/cws
+  bar.txt
+  build
+  dist
+  foo.txt
+  src
+  $ ls node_modules/@clusterws/cws
+  bar.txt
+  build
+  dist
+  foo.txt
+  src

test/blackbox-tests/test-cases/directory-targets/main.t

@@ -57,8 +57,8 @@ Error message when the matching directory target is empty.
   2 |   (deps (sandbox always))
   3 |   (targets (dir output))
   4 |   (action (bash "mkdir output")))
-  Error: Rule produced directory "output" that contains no files nor non-empty
-  subdirectories
+  Error: This rule defines a directory target "output" that matches the
+  requested path "output/x" but the rule's action didn't produce it
   [1]
 
 Error message when the matching directory target doesn't contain a requested path.