specs: better lookup by hash; allow references to missing dependency hashes

- previously spec parsing didn't allow you to look up missing (but still
  known) specs by hash

- This allows you to reference and potentially reinstall
  force-uninstalled dependencies

- add testing for force uninstall and for reference by spec

- cmd/install tests now use mutable_database

3 files changed, 155 insertions, 16 deletions

diff --git a/lib/spack/spack/database.py b/lib/spack/spack/database.py
index ad6475b026..4d532d1f00 100644
--- a/lib/spack/spack/database.py
+++ b/lib/spack/spack/database.py
@@ -937,6 +937,73 @@ class Database(object):
                 continue
             # TODO: conditional way to do this instead of catching exceptions
 
+    def get_by_hash_local(self, dag_hash, default=None, installed=any):
+        """Look up a spec in *this DB* by DAG hash, or by a DAG hash prefix.
+
+        Arguments:
+            dag_hash (str): hash (or hash prefix) to look up
+            default (object, optional): default value to return if dag_hash is
+                not in the DB (default: None)
+            installed (bool or any, optional): if ``True``, includes only
+                installed specs in the search; if ``False`` only missing specs,
+                and if ``any``, either installed or missing (default: any)
+
+        ``installed`` defaults to ``any`` so that we can refer to any
+        known hash.  Note that ``query()`` and ``query_one()`` differ in
+        that they only return installed specs by default.
+
+        Returns:
+            (list): a list of specs matching the hash or hash prefix
+
+        """
+        with self.read_transaction():
+            # hash is a full hash and is in the data somewhere
+            if dag_hash in self._data:
+                rec = self._data[dag_hash]
+                if installed is any or rec.installed == installed:
+                    return [rec.spec]
+                else:
+                    return default
+
+            # check if hash is a prefix of some installed (or previously
+            # installed) spec.
+            matches = [record.spec for h, record in self._data.items()
+                       if h.startswith(dag_hash) and
+                       (installed is any or installed == record.installed)]
+            if matches:
+                return matches
+
+            # nothing found
+            return default
+
+    def get_by_hash(self, dag_hash, default=None, installed=any):
+        """Look up a spec by DAG hash, or by a DAG hash prefix.
+
+        Arguments:
+            dag_hash (str): hash (or hash prefix) to look up
+            default (object, optional): default value to return if dag_hash is
+                not in the DB (default: None)
+            installed (bool or any, optional): if ``True``, includes only
+                installed specs in the search; if ``False`` only missing specs,
+                and if ``any``, either installed or missing (default: any)
+
+        ``installed`` defaults to ``any`` so that we can refer to any
+        known hash.  Note that ``query()`` and ``query_one()`` differ in
+        that they only return installed specs by default.
+
+        Returns:
+            (list): a list of specs matching the hash or hash prefix
+
+        """
+        search_path = [self] + self.upstream_dbs
+        for db in search_path:
+            spec = db.get_by_hash_local(
+                dag_hash, default=default, installed=installed)
+            if spec is not None:
+                return spec
+
+        return default
+
     def _query(
             self,
             query_spec=any,
diff --git a/lib/spack/spack/spec.py b/lib/spack/spack/spec.py
index 3586cb2aae..c7926ad3a3 100644
--- a/lib/spack/spack/spec.py
+++ b/lib/spack/spack/spec.py
@@ -3951,17 +3951,15 @@ class SpecParser(spack.parse.Parser):
     def spec_by_hash(self):
         self.expect(ID)
 
-        specs = spack.store.db.query()
-        matches = [spec for spec in specs if
-                   spec.dag_hash()[:len(self.token.value)] == self.token.value]
-
+        dag_hash = self.token.value
+        matches = spack.store.db.get_by_hash(dag_hash)
         if not matches:
-            raise NoSuchHashError(self.token.value)
+            raise NoSuchHashError(dag_hash)
 
         if len(matches) != 1:
             raise AmbiguousHashError(
                 "Multiple packages specify hash beginning '%s'."
-                % self.token.value, *matches)
+                % dag_hash, *matches)
 
         return matches[0]
 
diff --git a/lib/spack/spack/test/cmd/uninstall.py b/lib/spack/spack/test/cmd/uninstall.py
index f331b1a548..c9a23c48cf 100644
--- a/lib/spack/spack/test/cmd/uninstall.py
+++ b/lib/spack/spack/test/cmd/uninstall.py
@@ -8,6 +8,7 @@ import spack.store
 from spack.main import SpackCommand, SpackCommandError
 
 uninstall = SpackCommand('uninstall')
+install = SpackCommand('install')
 
 
 class MockArgs(object):
@@ -21,24 +22,21 @@ class MockArgs(object):
 
 
 @pytest.mark.db
-@pytest.mark.usefixtures('database')
-def test_multiple_matches():
+def test_multiple_matches(mutable_database):
     """Test unable to uninstall when multiple matches."""
     with pytest.raises(SpackCommandError):
         uninstall('-y', 'mpileaks')
 
 
 @pytest.mark.db
-@pytest.mark.usefixtures('database')
-def test_installed_dependents():
+def test_installed_dependents(mutable_database):
     """Test can't uninstall when ther are installed dependents."""
     with pytest.raises(SpackCommandError):
         uninstall('-y', 'libelf')
 
 
 @pytest.mark.db
-@pytest.mark.usefixtures('mutable_database')
-def test_recursive_uninstall():
+def test_recursive_uninstall(mutable_database):
     """Test recursive uninstall."""
     uninstall('-y', '-a', '--dependents', 'callpath')
 
@@ -56,12 +54,11 @@ def test_recursive_uninstall():
 
 @pytest.mark.db
 @pytest.mark.regression('3690')
-@pytest.mark.usefixtures('mutable_database')
 @pytest.mark.parametrize('constraint,expected_number_of_specs', [
     ('dyninst', 7), ('libelf', 5)
 ])
 def test_uninstall_spec_with_multiple_roots(
-        constraint, expected_number_of_specs
+        constraint, expected_number_of_specs, mutable_database
 ):
     uninstall('-y', '-a', '--dependents', constraint)
 
@@ -70,14 +67,91 @@ def test_uninstall_spec_with_multiple_roots(
 
 
 @pytest.mark.db
-@pytest.mark.usefixtures('mutable_database')
 @pytest.mark.parametrize('constraint,expected_number_of_specs', [
     ('dyninst', 13), ('libelf', 13)
 ])
 def test_force_uninstall_spec_with_ref_count_not_zero(
-        constraint, expected_number_of_specs
+        constraint, expected_number_of_specs, mutable_database
 ):
     uninstall('-f', '-y', constraint)
 
     all_specs = spack.store.layout.all_specs()
     assert len(all_specs) == expected_number_of_specs
+
+
+@pytest.mark.db
+def test_force_uninstall_and_reinstall_by_hash(mutable_database):
+    """Test forced uninstall and reinstall of old specs."""
+    # this is the spec to be removed
+    callpath_spec = spack.store.db.query_one('callpath ^mpich')
+    dag_hash = callpath_spec.dag_hash()
+
+    # ensure can look up by hash and that it's a dependent of mpileaks
+    def validate_callpath_spec(installed):
+        assert installed is True or installed is False
+
+        specs = spack.store.db.get_by_hash(dag_hash, installed=installed)
+        assert len(specs) == 1 and specs[0] == callpath_spec
+
+        specs = spack.store.db.get_by_hash(dag_hash[:7], installed=installed)
+        assert len(specs) == 1 and specs[0] == callpath_spec
+
+        specs = spack.store.db.get_by_hash(dag_hash, installed=any)
+        assert len(specs) == 1 and specs[0] == callpath_spec
+
+        specs = spack.store.db.get_by_hash(dag_hash[:7], installed=any)
+        assert len(specs) == 1 and specs[0] == callpath_spec
+
+        specs = spack.store.db.get_by_hash(dag_hash, installed=not installed)
+        assert specs is None
+
+        specs = spack.store.db.get_by_hash(dag_hash[:7],
+                                           installed=not installed)
+        assert specs is None
+
+        mpileaks_spec = spack.store.db.query_one('mpileaks ^mpich')
+        assert callpath_spec in mpileaks_spec
+
+        spec = spack.store.db.query_one('callpath ^mpich', installed=installed)
+        assert spec == callpath_spec
+
+        spec = spack.store.db.query_one('callpath ^mpich', installed=any)
+        assert spec == callpath_spec
+
+        spec = spack.store.db.query_one('callpath ^mpich',
+                                        installed=not installed)
+        assert spec is None
+
+    validate_callpath_spec(True)
+
+    uninstall('-y', '-f', 'callpath ^mpich')
+
+    # ensure that you can still look up by hash and see deps, EVEN though
+    # the callpath spec is missing.
+    validate_callpath_spec(False)
+
+    # BUT, make sure that the removed callpath spec is not in queries
+    def db_specs():
+        all_specs = spack.store.layout.all_specs()
+        return (
+            all_specs,
+            [s for s in all_specs if s.satisfies('mpileaks')],
+            [s for s in all_specs if s.satisfies('callpath')],
+            [s for s in all_specs if s.satisfies('mpi')]
+        )
+    all_specs, mpileaks_specs, callpath_specs, mpi_specs = db_specs()
+    assert len(all_specs) == 13
+    assert len(mpileaks_specs) == 3
+    assert len(callpath_specs) == 2
+    assert len(mpi_specs) == 3
+
+    # Now, REINSTALL the spec and make sure everything still holds
+    install('--fake', '/%s' % dag_hash[:7])
+
+    validate_callpath_spec(True)
+
+    all_specs, mpileaks_specs, callpath_specs, mpi_specs = db_specs()
+    assert len(all_specs) == 14      # back to 14
+    assert len(mpileaks_specs) == 3
+    assert len(callpath_specs) == 3  # back to 3
+    assert len(mpi_specs) == 3