Return early in do_fetch when there is no code or a package is external (#26926)

Co-authored-by: Ryan Krattiger <ryan.krattiger@kitware.com>

lib/spack/spack/cmd/fetch.py

@@ -76,10 +76,6 @@ def fetch(parser, args):
                 if args.missing and package.installed:
                     continue
 
-                # Do not attempt to fetch externals (they're local)
-                if package.spec.external:
-                    continue
-
                 package.do_fetch()
 
         package = spack.repo.get(spec)

lib/spack/spack/package.py

@@ -1333,9 +1333,9 @@ def do_fetch(self, mirror_only=False):
         Creates a stage directory and downloads the tarball for this package.
         Working directory will be set to the stage directory.
         """
-        if not self.has_code:
-            tty.debug('No fetch required for {0}: package has no code.'
-                      .format(self.name))
+        if not self.has_code or self.spec.external:
+            tty.debug('No fetch required for {0}'.format(self.name))
+            return
 
         checksum = spack.config.get('config:checksum')
         fetch = self.stage.managed_by_spack

lib/spack/spack/test/packaging.py

@@ -19,6 +19,7 @@
 
 import spack.binary_distribution as bindist
 import spack.cmd.buildcache as buildcache
+import spack.package
 import spack.repo
 import spack.store
 import spack.util.gpg
@@ -598,3 +599,31 @@ def _instr(pkg):
     expected = pkg.download_instr if manual else 'All fetchers failed'
     with pytest.raises(spack.fetch_strategy.FetchError, match=expected):
         pkg.do_fetch()
+
+
+@pytest.fixture()
+def fetching_not_allowed(monkeypatch):
+    class FetchingNotAllowed(spack.fetch_strategy.FetchStrategy):
+        def mirror_id(self):
+            return None
+
+        def fetch(self):
+            raise Exception("Sources are fetched but shouldn't have been")
+    fetcher = FetchStrategyComposite()
+    fetcher.append(FetchingNotAllowed())
+    monkeypatch.setattr(spack.package.PackageBase, 'fetcher', fetcher)
+
+
+def test_fetch_without_code_is_noop(install_mockery, fetching_not_allowed):
+    """do_fetch for packages without code should be a no-op"""
+    pkg = Spec('a').concretized().package
+    pkg.has_code = False
+    pkg.do_fetch()
+
+
+def test_fetch_external_package_is_noop(install_mockery, fetching_not_allowed):
+    """do_fetch for packages without code should be a no-op"""
+    spec = Spec('a').concretized()
+    spec.external_path = "/some/where"
+    assert spec.external
+    spec.package.do_fetch()