Add test for [subdirs]

Signed-off-by: Rudi Grinberg <me@rgrinberg.com>

test/blackbox-tests/dune.inc

@@ -1836,6 +1836,14 @@
    test-cases/strict-package-deps
    (progn (run dune-cram run run.t) (diff? run.t run.t.corrected)))))
 
+(rule
+ (alias subdir-stanza)
+ (deps (package dune) (source_tree test-cases/subdir-stanza))
+ (action
+  (chdir
+   test-cases/subdir-stanza
+   (progn (run dune-cram run run.t) (diff? run.t run.t.corrected)))))
+
 (rule
  (alias subst)
  (deps (package dune) (source_tree test-cases/subst))
@@ -2607,6 +2615,7 @@
   (alias stale-artifact-removal)
   (alias stdlib-compilation)
   (alias strict-package-deps)
+  (alias subdir-stanza)
   (alias subst)
   (alias syntax-versioning)
   (alias target-dir-alias)
@@ -2864,6 +2873,7 @@
   (alias stale-artifact-removal)
   (alias stdlib-compilation)
   (alias strict-package-deps)
+  (alias subdir-stanza)
   (alias subst)
   (alias syntax-versioning)
   (alias target-dir-alias)

test/blackbox-tests/test-cases/subdir-stanza/run.t

@@ -0,0 +1,12 @@
+  $ echo "(lang dune 2.4)" > dune-project
+  $ cat >dune <<EOF
+  > (rule (with-stdout-to foo.txt (echo "bar")))
+  > (subdir
+  >  bar
+  >  (rule (with-stdout-to foo.txt (echo "bar"))))
+  > EOF
+  $ mkdir bar
+  $ touch bar/dune
+  $ dune build ./foo.txt ./bar/foo.txt
+  $ cat _build/default/foo.txt
+  bar