From 8ba55264a985b435dfaa3730311e1ac4d0818521 Mon Sep 17 00:00:00 2001
From: Ali Caglayan <alizter@gmail.com>
Date: Tue, 23 Jun 2026 12:26:06 +0100
Subject: [PATCH 1/2] test(pkg): repro @doc-new crash on locked META-only lib
 (#15290)

Build @doc-new against a lock-dir package whose lib is exposed via a META
file only (no dune-package) and observe the as_outside_build_dir_exn crash
in Odoc_new.modules_of_dir.

Signed-off-by: Ali Caglayan <alizter@gmail.com>
---
 .../test-cases/pkg/doc-new-with-locked-lib.t  | 53 +++++++++++++++++++
 1 file changed, 53 insertions(+)
 create mode 100644 test/blackbox-tests/test-cases/pkg/doc-new-with-locked-lib.t

diff --git a/test/blackbox-tests/test-cases/pkg/doc-new-with-locked-lib.t b/test/blackbox-tests/test-cases/pkg/doc-new-with-locked-lib.t
new file mode 100644
index 00000000000..623a79234c3
--- /dev/null
+++ b/test/blackbox-tests/test-cases/pkg/doc-new-with-locked-lib.t
@@ -0,0 +1,53 @@
+Reproduction for https://github.com/ocaml/dune/issues/15290
+
+Building @doc-new with package management enabled crashes when a locked
+package installs a library via a META file (without a dune-package), because
+the odoc rules classify it as a "fallback" directory and try to read the
+cmti directory as if it were outside the build tree.
+
+  $ mkdir external_sources
+
+  $ cat >external_sources/META <<EOF
+  > version = "0.0.1"
+  > description = ""
+  > archive(byte) = "fakefmt.cma"
+  > EOF
+
+  $ touch external_sources/fakefmt.cma
+
+  $ cat >external_sources/fakefmt.install <<EOF
+  > lib: [
+  >  "META"
+  >  "fakefmt.cma"
+  > ]
+  > EOF
+
+  $ make_dune_project 3.25
+
+  $ cat > dune-workspace <<EOF
+  > (lang dune 3.25)
+  > (pkg enabled)
+  > EOF
+
+  $ make_lockdir
+  $ make_lockpkg fakefmt <<EOF
+  > (version 0.0.1)
+  > (source (copy $PWD/external_sources))
+  > EOF
+
+  $ cat > dune-project <<EOF
+  > (lang dune 3.25)
+  > (package (name foo) (depends fakefmt))
+  > EOF
+
+  $ cat > dune <<EOF
+  > (library
+  >  (public_name foo)
+  >  (libraries fakefmt))
+  > EOF
+
+  $ touch foo.ml
+
+  $ dune build @doc-new 2>&1 | grep "Internal error"
+  Internal error! Please report to https://github.com/ocaml/dune/issues,
+  [1]

From 0c83f2cfc1e34583bc63b8b89b2fcfcf707c0830 Mon Sep 17 00:00:00 2001
From: Ali Caglayan <alizter@gmail.com>
Date: Tue, 23 Jun 2026 12:33:02 +0100
Subject: [PATCH 2/2] fix(odoc): handle build-dir cmti paths in @doc-new
 fallback (#15290)

[Odoc_new.modules_of_dir] called [Fs_memo.dir_contents] via
[Path.as_outside_build_dir_exn], which crashes when the cmti
directory lives under [_build/_private/.../target/lib] - the case
for libraries installed by lock-dir packages.

Use [Fs.dir_contents] instead: it branches on build-vs-outside and
waits on [Build_system.build_dir] for inside-build paths, so the
locked package's install action finishes before we list its modules.

Signed-off-by: Ali Caglayan <alizter@gmail.com>
---
 src/dune_rules/odoc/odoc_new.ml                           | 5 ++---
 .../test-cases/pkg/doc-new-with-locked-lib.t              | 8 +++++---
 2 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/src/dune_rules/odoc/odoc_new.ml b/src/dune_rules/odoc/odoc_new.ml
index 04b4ed61403..98774e65537 100644
--- a/src/dune_rules/odoc/odoc_new.ml
+++ b/src/dune_rules/odoc/odoc_new.ml
@@ -1178,11 +1178,10 @@ let modules_of_dir d : (Module_name.t * (Path.t * [ `Cmti | `Cmt | `Cmi ])) list
     List.find_map extensions ~f:(fun (ext', ty) ->
       Option.some_if (Filename.Extension.equal ext ext') ty)
   in
-  Fs_memo.dir_contents (Path.as_outside_build_dir_exn d)
+  Fs.dir_contents d
   >>| function
   | Error _ -> []
-  | Ok dc ->
-    let list = Fs_memo.Dir_contents.to_list dc in
+  | Ok list ->
     List.filter_map list ~f:(fun (x, ty) ->
       match ty, Filename.extension x |> Filename.Extension.Or_empty.extension with
       | Unix.S_REG, Some ext when Option.is_some (ty_of_ext ext) ->
diff --git a/test/blackbox-tests/test-cases/pkg/doc-new-with-locked-lib.t b/test/blackbox-tests/test-cases/pkg/doc-new-with-locked-lib.t
index 623a79234c3..1f3e8f73499 100644
--- a/test/blackbox-tests/test-cases/pkg/doc-new-with-locked-lib.t
+++ b/test/blackbox-tests/test-cases/pkg/doc-new-with-locked-lib.t
@@ -48,6 +48,8 @@ cmti directory as if it were outside the build tree.
 
   $ touch foo.ml
 
-  $ dune build @doc-new 2>&1 | grep "Internal error"
-  Internal error! Please report to https://github.com/ocaml/dune/issues,
-  [1]
+  $ dune build @doc-new
+  File "fakefmt.mld", line 7, characters 0-11:
+  Warning: '{!modules ...}' should not be empty.
+  File "page-fakefmt.odoc":
+  Warning: Failed to lookup child page dummy