test(pkg): reproduce #11405

Signed-off-by: Rudi Grinberg <[email protected]>

<!-- ps-id: 6f68050b-a79c-4ee2-989c-75502462ab58 -->

test/blackbox-tests/test-cases/pkg/findlib-meta-optional-directory.t

@@ -0,0 +1,44 @@
+Demonstrate the handling of findlib directories that don't exist
+
+Reproduces #11405
+
+  $ . ./helpers.sh
+
+  $ mkdir external_sources
+
+  $ cat >external_sources/META <<EOF
+  > package "sub" (
+  >   directory = "sub"
+  >   version = "0.0.1"
+  >   exists_if = "sub.cma"
+  > )
+  > EOF
+
+  $ cat >external_sources/mypkg.install <<EOF
+  > lib: [
+  >  "META"
+  > ]
+  > EOF
+
+  $ cat >dune-project <<EOF
+  > (lang dune 3.17)
+  > EOF
+
+  $ mkdir dune.lock
+
+  $ cat >dune.lock/lock.dune <<EOF
+  > (lang package 0.1)
+  > EOF
+
+  $ cat >dune.lock/mypkg.pkg <<EOF
+  > (version 0.0.1)
+  > (source (copy $PWD/external_sources))
+  > EOF
+
+  $ cat >dune <<EOF
+  > (executable
+  >  (libraries mypkg.sub)
+  >  (name foo))
+  > EOF
+
+  $ dune build foo.exe