environment.py: only install root specs explicitly (#31645)

2 files changed, 6 insertions, 3 deletions

diff --git a/lib/spack/spack/cmd/install.py b/lib/spack/spack/cmd/install.py
index fe41316330..bda6850db0 100644
--- a/lib/spack/spack/cmd/install.py
+++ b/lib/spack/spack/cmd/install.py
@@ -131,8 +131,9 @@ which is useful for CI pipeline troubleshooting""")
         help='(with environment) only install already concretized specs')
     subparser.add_argument(
         '--no-add', action='store_true', default=False,
-        help="""(with environment) only install specs provided as argument
-if they are already in the concretized environment""")
+        help="""(with environment) partially install an environment, limiting
+to concrete specs in the environment matching the arguments.
+Non-roots remain installed implicitly.""")
     subparser.add_argument(
         '-f', '--file', action='append', default=[],
         dest='specfiles', metavar='SPEC_YAML_FILE',
diff --git a/lib/spack/spack/environment/environment.py b/lib/spack/spack/environment/environment.py
index ddfae0c783..83c33905aa 100644
--- a/lib/spack/spack/environment/environment.py
+++ b/lib/spack/spack/environment/environment.py
@@ -1643,7 +1643,9 @@ class Environment(object):
 
         installs = []
         for spec in specs_to_install:
-            installs.append((spec.package, install_args))
+            pkg_install_args = install_args.copy()
+            pkg_install_args['explicit'] = spec in self.roots()
+            installs.append((spec.package, pkg_install_args))
 
         try:
             builder = PackageInstaller(installs)