Mark external as explicit only when installing explicitly (#31665)

lib/spack/spack/installer.py

@@ -330,11 +330,10 @@ def _process_external_package(pkg, explicit):
 
     try:
         # Check if the package was already registered in the DB.
-        # If this is the case, then just exit.
+        # If this is the case, then only make explicit if required.
         tty.debug('{0} already registered in DB'.format(pre))
-
-        # Update the explicit state if it is necessary
-        if explicit:
+        record = spack.store.db.get_record(spec)
+        if explicit and not record.explicit:
             spack.store.db.update_explicit(spec, explicit)
 
     except KeyError:
@@ -1115,7 +1114,8 @@ def _add_tasks(self, request, all_deps):
         #
         # External and upstream packages need to get flagged as installed to
         # ensure proper status tracking for environment build.
-        not_local = _handle_external_and_upstream(request.pkg, True)
+        explicit = request.install_args.get('explicit', True)
+        not_local = _handle_external_and_upstream(request.pkg, explicit)
         if not_local:
             self._flag_installed(request.pkg)
             return

lib/spack/spack/test/installer.py

@@ -1289,3 +1289,16 @@ def test_term_status_line():
     x.add("a")
     x.add("b")
     x.clear()
+
+
+@pytest.mark.parametrize('explicit_args,is_explicit', [
+    ({'explicit': False}, False),
+    ({'explicit': True}, True),
+    ({}, True)
+])
+def test_single_external_implicit_install(install_mockery, explicit_args, is_explicit):
+    pkg = 'trivial-install-test-package'
+    s = spack.spec.Spec(pkg).concretized()
+    s.external_path = '/usr'
+    create_installer([(s, explicit_args)]).install()
+    assert spack.store.db.get_record(pkg).explicit == is_explicit