From 1ed3ac921af9284fd9a31a02487a4e8277f246d8 Mon Sep 17 00:00:00 2001
From: Robin Bate Boerop <me@robinbb.com>
Date: Thu, 30 Apr 2026 16:35:37 -0700
Subject: [PATCH] test: regression guard for cross-lib reads of single-module
 leaf libs

Adds [test-cases/per-module-lib-deps/no-ocamldep-leaf-lib.t]. Documents that a multi-module consumer of a single-module leaf library builds without error today.

Companion to the other observational baselines under [test-cases/per-module-lib-deps/]: each pins a structural shape that an inter-library filter must respect.

Signed-off-by: Robin Bate Boerop <me@robinbb.com>
---
 .../no-ocamldep-leaf-lib.t                    | 41 +++++++++++++++++++
 1 file changed, 41 insertions(+)
 create mode 100644 test/blackbox-tests/test-cases/per-module-lib-deps/no-ocamldep-leaf-lib.t

diff --git a/test/blackbox-tests/test-cases/per-module-lib-deps/no-ocamldep-leaf-lib.t b/test/blackbox-tests/test-cases/per-module-lib-deps/no-ocamldep-leaf-lib.t
new file mode 100644
index 00000000000..28412a899cf
--- /dev/null
+++ b/test/blackbox-tests/test-cases/per-module-lib-deps/no-ocamldep-leaf-lib.t
@@ -0,0 +1,41 @@
+A multi-module consumer of a single-module leaf library builds
+without error.
+
+  $ cat > dune-project <<EOF
+  > (lang dune 3.23)
+  > EOF
+
+[leaf]: unwrapped, single-module, no library dependencies. This is
+exactly the shape that triggers the no-ocamldep fast path:
+
+  $ mkdir leaf
+  $ cat > leaf/dune <<EOF
+  > (library (name leaf) (wrapped false))
+  > EOF
+  $ cat > leaf/mod_leaf.ml <<EOF
+  > let v = 1
+  > EOF
+  $ cat > leaf/mod_leaf.mli <<EOF
+  > val v : int
+  > EOF
+
+[consumer]: multi-module library that depends on [leaf] and
+references [Mod_leaf] from one of its modules. The consumer is
+multi-module (so it doesn't itself hit the no-ocamldep fast path);
+what we're probing is whether anything tries to read [leaf]'s
+ocamldep:
+
+  $ mkdir consumer
+  $ cat > consumer/dune <<EOF
+  > (library (name consumer) (wrapped false) (libraries leaf))
+  > EOF
+  $ cat > consumer/c.ml <<EOF
+  > let _ = Mod_leaf.v
+  > EOF
+  $ cat > consumer/d.ml <<EOF
+  > let _ = ()
+  > EOF
+
+Build must succeed:
+
+  $ dune build @check