Record the module after a qualified free path in the AST header

changes/qualified-own-namespace-dependency.fix.md

@@ -0,0 +1,2 @@
+- Make a module reached only as `Namespace.Module` from inside its own
+  namespace a dependency, so it builds first and its changes rebuild the user.

compiler/ml/depend.ml

@@ -65,7 +65,14 @@ let add_names s =
 let rec add_path bv ?(p = []) = function
   | Lident s ->
     let free =
-      try lookup_free (s :: p) bv with Not_found -> String_set.singleton s
+      try lookup_free (s :: p) bv
+      with Not_found -> (
+        (* Also record [S.M] for a qualified free path: when [S] is the
+           namespace of the module's own package, the build system resolves
+           [M] in that namespace, which [S] alone cannot tell it. *)
+        match p with
+        | [] -> String_set.singleton s
+        | m :: _ -> String_set.of_list [s; s ^ "." ^ m])
     in
     add_names free
   | Ldot (l, s) -> add_path bv ~p:(s :: p) l

rewatch/tests/compile/22-qualified-own-namespace-dependency.sh

@@ -0,0 +1,57 @@
+#!/bin/bash
+
+cd $(dirname $0)
+source "../utils.sh"
+
+bold "Test: A module reached only through its own namespace is a dependency"
+
+fixture=$(mktemp -d 2>/dev/null || mktemp -d -t rewatch-qualified-own-namespace)
+trap "rm -rf '$fixture'" EXIT
+
+mkdir -p "$fixture/src"
+
+cat > "$fixture/rescript.json" <<'JSON'
+{
+  "name": "rewatch-qualified-own-namespace",
+  "namespace": "Ns",
+  "sources": { "dir": "src" },
+  "package-specs": { "module": "esmodule", "in-source": true },
+  "suffix": ".mjs"
+}
+JSON
+
+# User names Target only as Ns.Target, so its AST header must say so: the
+# bare namespace does not tell the build system which module to wait for.
+cat > "$fixture/src/Target.res" <<'RES'
+let value = 1
+RES
+
+cat > "$fixture/src/User.res" <<'RES'
+let value = Ns.Target.value + 1
+RES
+
+cd "$fixture"
+if ! compiler_output=$("$REWATCH_EXECUTABLE" build 2>&1); then
+  error "Clean build compiled User before Target"
+  printf "%s\n" "$compiler_output" >&2
+  exit 1
+fi
+
+# Changing Target must recompile User and report its new type error.
+cat > src/Target.res <<'RES'
+let value = "not an int"
+RES
+
+if compiler_output=$("$REWATCH_EXECUTABLE" build 2>&1); then
+  error "Incremental build did not recompile User after Target changed"
+  printf "%s\n" "$compiler_output" >&2
+  exit 1
+fi
+
+if ! printf '%s\n' "$compiler_output" | grep -q "User.res"; then
+  error "Incremental build did not report the error in User"
+  printf "%s\n" "$compiler_output" >&2
+  exit 1
+fi
+
+success "Modules reached through their own namespace are dependencies"

rewatch/tests/suite.sh

@@ -87,6 +87,7 @@ fi
 ./compile/19-utf8-warning.sh &&
 ./compile/20-schedule-independent-modules-after-error.sh &&
 ./compile/21-rebuild-dependency-for-package-specs.sh &&
+./compile/22-qualified-own-namespace-dependency.sh &&
 ./compile/14-no-testrepo-changes.sh &&
 ./compile/15-no-new-files.sh &&
 ./compile/16-snapshots-unchanged.sh &&