apt: fix build-dep idempotency (#38999)

lib/ansible/modules/packaging/os/apt.py

@@ -578,7 +578,12 @@ def install(m, pkgspec, cache, upgrade=False, default_release=None,
         else:
             diff = {}
         status = True
-        data = dict(changed=True, stdout=out, stderr=err, diff=diff)
+
+        changed = True
+        if build_dep:
+            changed = APT_GET_ZERO not in out
+
+        data = dict(changed=changed, stdout=out, stderr=err, diff=diff)
         if rc:
             status = False
             data = dict(msg="'%s' failed: %s" % (cmd, err), stdout=out, stderr=err, rc=rc)

test/integration/targets/apt/tasks/apt.yml

@@ -213,3 +213,26 @@
   with_items:
     - libcaca-dev
     - libslang2-dev
+
+# https://github.com/ansible/ansible/issues/38995
+- name: build-dep for a package
+  apt:
+    name: tree
+    state: build-dep
+  register: apt_result
+
+- name: Check the result
+  assert:
+    that:
+      - apt_result is changed
+
+- name: build-dep for a package (idempotency)
+  apt:
+    name: tree
+    state: build-dep
+  register: apt_result
+
+- name: Check the result
+  assert:
+    that:
+      - apt_result is not changed