Merge branch 'jennis/introduce_artifact_delete' into 'master'

31 files changed, 275 insertions, 31 deletions

diff --git a/NEWS b/NEWS
index 0ff7702aa..85bf27c2c 100644
--- a/NEWS
+++ b/NEWS
@@ -2,6 +2,10 @@
 buildstream 1.3.1
 =================
 
+  o Added `bst artifact delete` subcommand. This command removes artifacts from
+    the local cache. Mulitple element names and artifact refs can be specified
+    as arguments.
+
   o BREAKING CHANGE: The top level commands `checkout`, `push` and `pull` have
     been moved to the `bst artifact` subcommand group and are now obsolete.
     For example, you must now use `bst artifact pull hello.bst`.
diff --git a/buildstream/_artifactcache.py b/buildstream/_artifactcache.py
index 330365025..7da2d959c 100644
--- a/buildstream/_artifactcache.py
+++ b/buildstream/_artifactcache.py
@@ -415,12 +415,21 @@ class ArtifactCache():
     # Args:
     #     ref (artifact_name): The name of the artifact to remove (as
     #                          generated by `Element.get_artifact_name`)
+    #     defer_prune (bool): Optionally declare whether pruning should
+    #                         occur immediately after the ref is removed.
     #
     # Returns:
     #    (int): The amount of space recovered in the cache, in bytes
     #
-    def remove(self, ref):
-        return self.cas.remove(ref)
+    def remove(self, ref, *, defer_prune=False):
+        return self.cas.remove(ref, defer_prune=defer_prune)
+
+    # prune():
+    #
+    # Prune the artifact cache of unreachable refs
+    #
+    def prune(self):
+        return self.cas.prune()
 
     # get_artifact_directory():
     #
diff --git a/buildstream/_artifactelement.py b/buildstream/_artifactelement.py
index a88e83aab..a7915eb28 100644
--- a/buildstream/_artifactelement.py
+++ b/buildstream/_artifactelement.py
@@ -59,6 +59,10 @@ class ArtifactElement(Element):
     def _calculate_cache_key(self, dependencies=None):
         return self._key
 
+    # Override Element._get_cache_key()
+    def _get_cache_key(self, strength=None):
+        return self._key
+
 
 # verify_artifact_ref()
 #
diff --git a/buildstream/_cas/cascache.py b/buildstream/_cas/cascache.py
index 802fc13fd..02030bb68 100644
--- a/buildstream/_cas/cascache.py
+++ b/buildstream/_cas/cascache.py
@@ -791,16 +791,20 @@ class CASCache():
     def _reachable_refs_dir(self, reachable, tree, update_mtime=False):
         if tree.hash in reachable:
             return
+        try:
+            if update_mtime:
+                os.utime(self.objpath(tree))
 
-        if update_mtime:
-            os.utime(self.objpath(tree))
+            reachable.add(tree.hash)
 
-        reachable.add(tree.hash)
+            directory = remote_execution_pb2.Directory()
 
-        directory = remote_execution_pb2.Directory()
+            with open(self.objpath(tree), 'rb') as f:
+                directory.ParseFromString(f.read())
 
-        with open(self.objpath(tree), 'rb') as f:
-            directory.ParseFromString(f.read())
+        except FileNotFoundError:
+            # Just exit early if the file doesn't exist
+            return
 
         for filenode in directory.files:
             if update_mtime:
diff --git a/buildstream/_frontend/cli.py b/buildstream/_frontend/cli.py
index 02ca52e85..d8c46ce0c 100644
--- a/buildstream/_frontend/cli.py
+++ b/buildstream/_frontend/cli.py
@@ -1106,6 +1106,20 @@ def artifact_log(app, artifacts):
                         click.echo_via_pager(data)
 
 
+###################################################################
+#                     Artifact Delete Command                     #
+###################################################################
+@artifact.command(name='delete', short_help="Remove artifacts from the local cache")
+@click.option('--no-prune', 'no_prune', default=False, is_flag=True,
+              help="Do not prune the local cache of unreachable refs")
+@click.argument('artifacts', type=click.Path(), nargs=-1)
+@click.pass_obj
+def artifact_delete(app, artifacts, no_prune):
+    """Remove artifacts from the local cache"""
+    with app.initialized():
+        app.stream.artifact_delete(artifacts, no_prune)
+
+
 ##################################################################
 #                      DEPRECATED Commands                       #
 ##################################################################
diff --git a/buildstream/_stream.py b/buildstream/_stream.py
index b0fce3817..5c880427c 100644
--- a/buildstream/_stream.py
+++ b/buildstream/_stream.py
@@ -30,11 +30,12 @@ from contextlib import contextmanager, suppress
 from fnmatch import fnmatch
 
 from ._artifactelement import verify_artifact_ref
-from ._exceptions import StreamError, ImplError, BstError, ArtifactElementError, set_last_task_error
+from ._exceptions import StreamError, ImplError, BstError, ArtifactElementError, CASCacheError, set_last_task_error
 from ._message import Message, MessageType
 from ._scheduler import Scheduler, SchedStatus, TrackQueue, FetchQueue, BuildQueue, PullQueue, PushQueue
 from ._pipeline import Pipeline, PipelineSelection
 from ._profile import Topics, profile_start, profile_end
+from .types import _KeyStrength
 from . import utils, _yaml, _site
 from . import Scope, Consistency
 
@@ -520,6 +521,45 @@ class Stream():
 
         return logsdirs
 
+    # artifact_delete()
+    #
+    # Remove artifacts from the local cache
+    #
+    # Args:
+    #    targets (str): Targets to remove
+    #    no_prune (bool): Whether to prune the unreachable refs, default False
+    #
+    def artifact_delete(self, targets, no_prune):
+        # Return list of Element and/or ArtifactElement objects
+        target_objects = self.load_selection(targets, selection=PipelineSelection.NONE, load_refs=True)
+
+        # Some of the targets may refer to the same key, so first obtain a
+        # set of the refs to be removed.
+        remove_refs = set()
+        for obj in target_objects:
+            for key_strength in [_KeyStrength.STRONG, _KeyStrength.WEAK]:
+                key = obj._get_cache_key(strength=key_strength)
+                remove_refs.add(obj.get_artifact_name(key=key))
+
+        ref_removed = False
+        for ref in remove_refs:
+            try:
+                self._artifacts.remove(ref, defer_prune=True)
+            except CASCacheError as e:
+                self._message(MessageType.WARN, "{}".format(e))
+                continue
+
+            self._message(MessageType.INFO, "Removed: {}".format(ref))
+            ref_removed = True
+
+        # Prune the artifact cache
+        if ref_removed and not no_prune:
+            with self._context.timed_activity("Pruning artifact cache"):
+                self._artifacts.prune()
+
+        if not ref_removed:
+            self._message(MessageType.INFO, "No artifacts were removed")
+
     # source_checkout()
     #
     # Checkout sources of the target element to the specified location
diff --git a/doc/source/using_commands.rst b/doc/source/using_commands.rst
index 312b907f8..53c36197e 100644
--- a/doc/source/using_commands.rst
+++ b/doc/source/using_commands.rst
@@ -101,6 +101,13 @@ Artifact subcommands
 .. click:: buildstream._frontend.cli:artifact_push
    :prog: bst artifact push
 
+----
+
+.. _invoking_artifact_delete:
+
+.. click:: buildstream._frontend.cli:artifact_delete
+   :prog: bst artifact delete
+
 
 Source subcommands
 ------------------
diff --git a/man/bst-artifact-checkout.1 b/man/bst-artifact-checkout.1
index 2c11852c8..27b9954f4 100644
--- a/man/bst-artifact-checkout.1
+++ b/man/bst-artifact-checkout.1
@@ -1,4 +1,4 @@
-.TH "BST ARTIFACT CHECKOUT" "1" "12-Feb-2019" "" "bst artifact checkout Manual"
+.TH "BST ARTIFACT CHECKOUT" "1" "13-Mar-2019" "" "bst artifact checkout Manual"
 .SH NAME
 bst\-artifact\-checkout \- Checkout contents of an artifact
 .SH SYNOPSIS
diff --git a/man/bst-artifact-delete.1 b/man/bst-artifact-delete.1
new file mode 100644
index 000000000..43ef9bb47
--- /dev/null
+++ b/man/bst-artifact-delete.1
@@ -0,0 +1,12 @@
+.TH "BST ARTIFACT DELETE" "1" "13-Mar-2019" "" "bst artifact delete Manual"
+.SH NAME
+bst\-artifact\-delete \- Remove artifacts from the local cache
+.SH SYNOPSIS
+.B bst artifact delete
+[OPTIONS] [ARTIFACTS]...
+.SH DESCRIPTION
+Show logs of all artifacts
+.SH OPTIONS
+.TP
+\fB\-\-no\-prune\fP
+Do not prune the local cache of unreachable refs
diff --git a/man/bst-artifact-log.1 b/man/bst-artifact-log.1
index 6045e2587..2be77021f 100644
--- a/man/bst-artifact-log.1
+++ b/man/bst-artifact-log.1
@@ -1,4 +1,4 @@
-.TH "BST ARTIFACT LOG" "1" "12-Feb-2019" "" "bst artifact log Manual"
+.TH "BST ARTIFACT LOG" "1" "13-Mar-2019" "" "bst artifact log Manual"
 .SH NAME
 bst\-artifact\-log \- Show logs of an artifact
 .SH SYNOPSIS
diff --git a/man/bst-artifact-pull.1 b/man/bst-artifact-pull.1
index b01b2bb15..890090a44 100644
--- a/man/bst-artifact-pull.1
+++ b/man/bst-artifact-pull.1
@@ -1,4 +1,4 @@
-.TH "BST ARTIFACT PULL" "1" "12-Feb-2019" "" "bst artifact pull Manual"
+.TH "BST ARTIFACT PULL" "1" "13-Mar-2019" "" "bst artifact pull Manual"
 .SH NAME
 bst\-artifact\-pull \- Pull a built artifact
 .SH SYNOPSIS
diff --git a/man/bst-artifact-push.1 b/man/bst-artifact-push.1
index bc87c8287..09b068449 100644
--- a/man/bst-artifact-push.1
+++ b/man/bst-artifact-push.1
@@ -1,4 +1,4 @@
-.TH "BST ARTIFACT PUSH" "1" "12-Feb-2019" "" "bst artifact push Manual"
+.TH "BST ARTIFACT PUSH" "1" "13-Mar-2019" "" "bst artifact push Manual"
 .SH NAME
 bst\-artifact\-push \- Push a built artifact
 .SH SYNOPSIS
diff --git a/man/bst-artifact-server.1 b/man/bst-artifact-server.1
index f196b878d..d5d9b8cde 100644
--- a/man/bst-artifact-server.1
+++ b/man/bst-artifact-server.1
@@ -1,4 +1,4 @@
-.TH "BST-ARTIFACT-SERVER" "1" "12-Feb-2019" "" "bst-artifact-server Manual"
+.TH "BST-ARTIFACT-SERVER" "1" "13-Mar-2019" "" "bst-artifact-server Manual"
 .SH NAME
 bst-artifact-server \- CAS Artifact Server
 .SH SYNOPSIS
diff --git a/man/bst-artifact.1 b/man/bst-artifact.1
index a4bbeb7b2..aa46e2ef0 100644
--- a/man/bst-artifact.1
+++ b/man/bst-artifact.1
@@ -1,4 +1,4 @@
-.TH "BST ARTIFACT" "1" "12-Feb-2019" "" "bst artifact Manual"
+.TH "BST ARTIFACT" "1" "13-Mar-2019" "" "bst artifact Manual"
 .SH NAME
 bst\-artifact \- Manipulate cached artifacts
 .SH SYNOPSIS
@@ -23,3 +23,7 @@ Manipulate cached artifacts
 \fBlog\fP
   Show logs of an artifact
   See \fBbst artifact-log(1)\fP for full documentation on the \fBlog\fP command.
+.PP
+\fBdelete\fP
+  Remove artifacts from the local cache
+  See \fBbst artifact-delete(1)\fP for full documentation on the \fBdelete\fP command.
diff --git a/man/bst-build.1 b/man/bst-build.1
index deee1301e..edb67a499 100644
--- a/man/bst-build.1
+++ b/man/bst-build.1
@@ -1,4 +1,4 @@
-.TH "BST BUILD" "1" "12-Feb-2019" "" "bst build Manual"
+.TH "BST BUILD" "1" "13-Mar-2019" "" "bst build Manual"
 .SH NAME
 bst\-build \- Build elements in a pipeline
 .SH SYNOPSIS
diff --git a/man/bst-help.1 b/man/bst-help.1
index 35675db1d..feebf2463 100644
--- a/man/bst-help.1
+++ b/man/bst-help.1
@@ -1,4 +1,4 @@
-.TH "BST HELP" "1" "12-Feb-2019" "" "bst help Manual"
+.TH "BST HELP" "1" "13-Mar-2019" "" "bst help Manual"
 .SH NAME
 bst\-help \- Print usage information
 .SH SYNOPSIS
diff --git a/man/bst-init.1 b/man/bst-init.1
index 9b7b119d9..6f41d97d9 100644
--- a/man/bst-init.1
+++ b/man/bst-init.1
@@ -1,4 +1,4 @@
-.TH "BST INIT" "1" "12-Feb-2019" "" "bst init Manual"
+.TH "BST INIT" "1" "13-Mar-2019" "" "bst init Manual"
 .SH NAME
 bst\-init \- Initialize a new BuildStream project
 .SH SYNOPSIS
@@ -18,7 +18,7 @@ interactive session.
 The project name to use
 .TP
 \fB\-\-format\-version\fP INTEGER
-The required format version (default: 21)
+The required format version (default: 23)
 .TP
 \fB\-\-element\-path\fP PATH
 The subdirectory to store elements in (default: elements)
diff --git a/man/bst-shell.1 b/man/bst-shell.1
index d223d0d20..376cddb4b 100644
--- a/man/bst-shell.1
+++ b/man/bst-shell.1
@@ -1,4 +1,4 @@
-.TH "BST SHELL" "1" "12-Feb-2019" "" "bst shell Manual"
+.TH "BST SHELL" "1" "13-Mar-2019" "" "bst shell Manual"
 .SH NAME
 bst\-shell \- Shell into an element's sandbox environment
 .SH SYNOPSIS
diff --git a/man/bst-show.1 b/man/bst-show.1
index 4fe0b71c2..54d02c3b6 100644
--- a/man/bst-show.1
+++ b/man/bst-show.1
@@ -1,4 +1,4 @@
-.TH "BST SHOW" "1" "12-Feb-2019" "" "bst show Manual"
+.TH "BST SHOW" "1" "13-Mar-2019" "" "bst show Manual"
 .SH NAME
 bst\-show \- Show elements in the pipeline
 .SH SYNOPSIS
diff --git a/man/bst-source-checkout.1 b/man/bst-source-checkout.1
index f3101b679..aed31db7a 100644
--- a/man/bst-source-checkout.1
+++ b/man/bst-source-checkout.1
@@ -1,4 +1,4 @@
-.TH "BST SOURCE CHECKOUT" "1" "12-Feb-2019" "" "bst source checkout Manual"
+.TH "BST SOURCE CHECKOUT" "1" "13-Mar-2019" "" "bst source checkout Manual"
 .SH NAME
 bst\-source\-checkout \- Checkout sources for an element
 .SH SYNOPSIS
diff --git a/man/bst-source-fetch.1 b/man/bst-source-fetch.1
index 0fb63a6d7..ddcd557e4 100644
--- a/man/bst-source-fetch.1
+++ b/man/bst-source-fetch.1
@@ -1,4 +1,4 @@
-.TH "BST SOURCE FETCH" "1" "12-Feb-2019" "" "bst source fetch Manual"
+.TH "BST SOURCE FETCH" "1" "13-Mar-2019" "" "bst source fetch Manual"
 .SH NAME
 bst\-source\-fetch \- Fetch sources in a pipeline
 .SH SYNOPSIS
diff --git a/man/bst-source-track.1 b/man/bst-source-track.1
index 92f8cd310..9a24619a1 100644
--- a/man/bst-source-track.1
+++ b/man/bst-source-track.1
@@ -1,4 +1,4 @@
-.TH "BST SOURCE TRACK" "1" "12-Feb-2019" "" "bst source track Manual"
+.TH "BST SOURCE TRACK" "1" "13-Mar-2019" "" "bst source track Manual"
 .SH NAME
 bst\-source\-track \- Track new source references
 .SH SYNOPSIS
diff --git a/man/bst-source.1 b/man/bst-source.1
index 897642541..4d396b3d0 100644
--- a/man/bst-source.1
+++ b/man/bst-source.1
@@ -1,4 +1,4 @@
-.TH "BST SOURCE" "1" "12-Feb-2019" "" "bst source Manual"
+.TH "BST SOURCE" "1" "13-Mar-2019" "" "bst source Manual"
 .SH NAME
 bst\-source \- Manipulate sources for an element
 .SH SYNOPSIS
diff --git a/man/bst-workspace-close.1 b/man/bst-workspace-close.1
index 5c2659f63..0b43cdf22 100644
--- a/man/bst-workspace-close.1
+++ b/man/bst-workspace-close.1
@@ -1,4 +1,4 @@
-.TH "BST WORKSPACE CLOSE" "1" "12-Feb-2019" "" "bst workspace close Manual"
+.TH "BST WORKSPACE CLOSE" "1" "13-Mar-2019" "" "bst workspace close Manual"
 .SH NAME
 bst\-workspace\-close \- Close workspaces
 .SH SYNOPSIS
diff --git a/man/bst-workspace-list.1 b/man/bst-workspace-list.1
index 6be37d631..f5252670d 100644
--- a/man/bst-workspace-list.1
+++ b/man/bst-workspace-list.1
@@ -1,4 +1,4 @@
-.TH "BST WORKSPACE LIST" "1" "12-Feb-2019" "" "bst workspace list Manual"
+.TH "BST WORKSPACE LIST" "1" "13-Mar-2019" "" "bst workspace list Manual"
 .SH NAME
 bst\-workspace\-list \- List open workspaces
 .SH SYNOPSIS
diff --git a/man/bst-workspace-open.1 b/man/bst-workspace-open.1
index 4fd70fc15..4a1065d69 100644
--- a/man/bst-workspace-open.1
+++ b/man/bst-workspace-open.1
@@ -1,4 +1,4 @@
-.TH "BST WORKSPACE OPEN" "1" "12-Feb-2019" "" "bst workspace open Manual"
+.TH "BST WORKSPACE OPEN" "1" "13-Mar-2019" "" "bst workspace open Manual"
 .SH NAME
 bst\-workspace\-open \- Open a new workspace
 .SH SYNOPSIS
diff --git a/man/bst-workspace-reset.1 b/man/bst-workspace-reset.1
index ad2fc707a..d37a7f1c2 100644
--- a/man/bst-workspace-reset.1
+++ b/man/bst-workspace-reset.1
@@ -1,4 +1,4 @@
-.TH "BST WORKSPACE RESET" "1" "12-Feb-2019" "" "bst workspace reset Manual"
+.TH "BST WORKSPACE RESET" "1" "13-Mar-2019" "" "bst workspace reset Manual"
 .SH NAME
 bst\-workspace\-reset \- Reset a workspace to its original state
 .SH SYNOPSIS
diff --git a/man/bst-workspace.1 b/man/bst-workspace.1
index b90505e1a..337620584 100644
--- a/man/bst-workspace.1
+++ b/man/bst-workspace.1
@@ -1,4 +1,4 @@
-.TH "BST WORKSPACE" "1" "12-Feb-2019" "" "bst workspace Manual"
+.TH "BST WORKSPACE" "1" "13-Mar-2019" "" "bst workspace Manual"
 .SH NAME
 bst\-workspace \- Manipulate developer workspaces
 .SH SYNOPSIS
diff --git a/man/bst.1 b/man/bst.1
index b1f6e9f93..ff5e79b6f 100644
--- a/man/bst.1
+++ b/man/bst.1
@@ -1,4 +1,4 @@
-.TH "BST" "1" "12-Feb-2019" "" "bst Manual"
+.TH "BST" "1" "13-Mar-2019" "" "bst Manual"
 .SH NAME
 bst \- Build and manipulate BuildStream projects...
 .SH SYNOPSIS
@@ -67,6 +67,9 @@ The mirror to fetch from first, before attempting other mirrors
 .TP
 \fB\-\-pull\-buildtrees\fP
 Include an element's build tree when pulling remote element artifacts
+.TP
+\fB\-\-cache\-buildtrees\fP [always|failure|never]
+Cache artifact build tree content on creation
 .SH COMMANDS
 .PP
 \fBhelp\fP
diff --git a/tests/frontend/artifact.py b/tests/frontend/artifact.py
index c8301c529..b6f8fb91d 100644
--- a/tests/frontend/artifact.py
+++ b/tests/frontend/artifact.py
@@ -22,6 +22,7 @@ import os
 import pytest
 
 from buildstream.plugintestutils import cli
+from tests.testutils import create_artifact_share
 
 
 # Project directory
@@ -62,3 +63,144 @@ def test_artifact_log(cli, datafiles):
     assert result.exit_code == 0
     # The artifact is cached under both a strong key and a weak key
     assert (log + log) == result.output
+
+
+# Test that we can delete the artifact of the element which corresponds
+# to the current project state
+@pytest.mark.datafiles(DATA_DIR)
+def test_artifact_delete_element(cli, tmpdir, datafiles):
+    project = os.path.join(datafiles.dirname, datafiles.basename)
+    element = 'target.bst'
+
+    # Build the element and ensure it's cached
+    result = cli.run(project=project, args=['build', element])
+    result.assert_success()
+    assert cli.get_element_state(project, element) == 'cached'
+
+    result = cli.run(project=project, args=['artifact', 'delete', element])
+    result.assert_success()
+    assert cli.get_element_state(project, element) != 'cached'
+
+
+# Test that we can delete an artifact by specifying its ref.
+@pytest.mark.datafiles(DATA_DIR)
+def test_artifact_delete_artifact(cli, tmpdir, datafiles):
+    project = os.path.join(datafiles.dirname, datafiles.basename)
+    element = 'target.bst'
+
+    # Configure a local cache
+    local_cache = os.path.join(str(tmpdir), 'artifacts')
+    cli.configure({'cachedir': local_cache})
+
+    # First build an element so that we can find its artifact
+    result = cli.run(project=project, args=['build', element])
+    result.assert_success()
+
+    # Obtain the artifact ref
+    cache_key = cli.get_element_key(project, element)
+    artifact = os.path.join('test', os.path.splitext(element)[0], cache_key)
+
+    # Explicitly check that the ARTIFACT exists in the cache
+    assert os.path.exists(os.path.join(local_cache, 'cas', 'refs', 'heads', artifact))
+
+    # Delete the artifact
+    result = cli.run(project=project, args=['artifact', 'delete', artifact])
+    result.assert_success()
+
+    # Check that the ARTIFACT is no longer in the cache
+    assert not os.path.exists(os.path.join(local_cache, 'cas', 'refs', 'heads', artifact))
+
+
+# Test the `bst artifact delete` command with multiple, different arguments.
+@pytest.mark.datafiles(DATA_DIR)
+def test_artifact_delete_element_and_artifact(cli, tmpdir, datafiles):
+    project = os.path.join(datafiles.dirname, datafiles.basename)
+    element = 'target.bst'
+    dep = 'compose-all.bst'
+
+    # Configure a local cache
+    local_cache = os.path.join(str(tmpdir), 'artifacts')
+    cli.configure({'cachedir': local_cache})
+
+    # First build an element so that we can find its artifact
+    result = cli.run(project=project, args=['build', element])
+    result.assert_success()
+    assert cli.get_element_state(project, element) == 'cached'
+    assert cli.get_element_state(project, dep) == 'cached'
+
+    # Obtain the artifact ref
+    cache_key = cli.get_element_key(project, element)
+    artifact = os.path.join('test', os.path.splitext(element)[0], cache_key)
+
+    # Explicitly check that the ARTIFACT exists in the cache
+    assert os.path.exists(os.path.join(local_cache, 'cas', 'refs', 'heads', artifact))
+
+    # Delete the artifact
+    result = cli.run(project=project, args=['artifact', 'delete', artifact, dep])
+    result.assert_success()
+
+    # Check that the ARTIFACT is no longer in the cache
+    assert not os.path.exists(os.path.join(local_cache, 'cas', 'refs', 'heads', artifact))
+
+    # Check that the dependency ELEMENT is no longer cached
+    assert cli.get_element_state(project, dep) != 'cached'
+
+
+# Test that we receive the appropriate stderr when we try to delete an artifact
+# that is not present in the cache.
+@pytest.mark.datafiles(DATA_DIR)
+def test_artifact_delete_unbuilt_artifact(cli, tmpdir, datafiles):
+    project = os.path.join(datafiles.dirname, datafiles.basename)
+    element = 'target.bst'
+
+    # delete it, just in case it's there
+    _ = cli.run(project=project, args=['artifact', 'delete', element])
+
+    # Ensure the element is not cached
+    assert cli.get_element_state(project, element) != 'cached'
+
+    # Now try and remove it again (now we know its not there)
+    result = cli.run(project=project, args=['artifact', 'delete', element])
+
+    cache_key = cli.get_element_key(project, element)
+    artifact = os.path.join('test', os.path.splitext(element)[0], cache_key)
+    expected_err = "WARNING Could not find ref '{}'".format(artifact)
+    assert expected_err in result.stderr
+
+
+# Test that an artifact pulled from it's remote cache (without it's buildtree) will not
+# throw an Exception when trying to prune the cache.
+@pytest.mark.datafiles(DATA_DIR)
+def test_artifact_delete_pulled_artifact_without_buildtree(cli, tmpdir, datafiles):
+    project = os.path.join(datafiles.dirname, datafiles.basename)
+    element = 'target.bst'
+
+    # Set up remote and local shares
+    local_cache = os.path.join(str(tmpdir), 'artifacts')
+    with create_artifact_share(os.path.join(str(tmpdir), 'remote')) as remote:
+        cli.configure({
+            'artifacts': {'url': remote.repo, 'push': True},
+            'cachedir': local_cache,
+        })
+
+        # Build the element
+        result = cli.run(project=project, args=['build', element])
+        result.assert_success()
+
+        # Make sure it's in the share
+        cache_key = cli.get_element_key(project, element)
+        assert remote.has_artifact('test', element, cache_key)
+
+        # Delete and then pull the artifact (without its buildtree)
+        result = cli.run(project=project, args=['artifact', 'delete', element])
+        result.assert_success()
+        assert cli.get_element_state(project, element) != 'cached'
+        result = cli.run(project=project, args=['artifact', 'pull', element])
+        result.assert_success()
+        assert cli.get_element_state(project, element) == 'cached'
+
+        # Now delete it again (it should have been pulled without the buildtree, but
+        # a digest of the buildtree is pointed to in the artifact's metadata
+        result = cli.run(project=project, args=['artifact', 'delete', element])
+        result.assert_success()
+        assert cli.get_element_state(project, element) != 'cached'
diff --git a/tests/frontend/completions.py b/tests/frontend/completions.py
index 1f29fdae6..7810a06d5 100644
--- a/tests/frontend/completions.py
+++ b/tests/frontend/completions.py
@@ -57,6 +57,7 @@ SOURCE_COMMANDS = [
 
 ARTIFACT_COMMANDS = [
     'checkout ',
+    'delete ',
     'push ',
     'pull ',
     'log ',