test: exhibit a bug when promoting directories

test/blackbox-tests/test-cases/promote/deep-subdir.t/dune

@@ -0,0 +1,7 @@
+(rule
+ (deps
+  (source_tree deep))
+ (targets (dir deep_copied))
+ (mode promote)
+ (action
+  (run cp -r deep deep_copied)))

test/blackbox-tests/test-cases/promote/deep-subdir.t/dune-project

@@ -0,0 +1,3 @@
+(lang dune 3.0)
+
+(using directory-targets 0.1)

test/blackbox-tests/test-cases/promote/deep-subdir.t/run.t

@@ -0,0 +1,43 @@
+Tests for promoting directory targets
+-------------------------------------
+
+Let's create the directory structure we are going to promote (as a copy on
+another dir):
+
+  $ mkdir -p deep/a/
+  $ touch deep/a/deep_file
+  $ touch deep/base_file
+
+Let's try this:
+
+  $ dune build deep_copied
+
+This one works. Now, let's add a layer between base_file and deep_file:
+
+  $ rm -rf deep
+  $ mkdir -p deep/a/b/
+  $ touch deep/a/b/deep_file
+  $ touch deep/base_file
+
+  $ dune build deep_copied
+  File "dune", lines 1-7, characters 0-121:
+  1 | (rule
+  2 |  (deps
+  3 |   (source_tree deep))
+  4 |  (targets (dir deep_copied))
+  5 |  (mode promote)
+  6 |  (action
+  7 |   (run cp -r deep deep_copied)))
+  Error: Cannot promote files to "deep_copied/a/b".
+  Reason: opendir(deep_copied/a/b): No such file or directory
+  -> required by _build/default/deep_copied
+  [1]
+
+It does not work! Note that the `base_file` is required. For instance, move it
+to `a/`, or remove it, and it works:
+
+  $ mv deep/base_file deep/a/
+  $ dune build deep_copied
+
+  $ rm deep/a/base_file
+  $ dune build deep_copied