Merge branch 'tristan/link-element' into 'master'

Add new core `link` element kind

See merge request BuildStream/buildstream!1948

71 files changed, 630 insertions, 216 deletions

diff --git a/NEWS b/NEWS
index 2aa5e32f9..22ef7e670 100644
--- a/NEWS
+++ b/NEWS
@@ -18,18 +18,19 @@ Format
   o BREAKING CHANGE: Now deprecation warnings are suppressed using the `allow-deprecated`
     configuration with the plugin origins in project.conf, instead of on the
     source/element overrides section (See issue #1291)
+  o BREAKING CHANGE: The `target` option of junctions has been completely removed,
+    Use `link` elements instead.
   o Variables from an element can now be used in source configurations
 
-
 Plugins
 -------
 
   o Cache keys will change for all elements that have defined the
     `command-subdir` variable. This is the result of fixing a bug where this
     variable was not included in the cache key correctly.
-
   o The `pip` element has been removed. Please use the one from bst-plugins-experimental
-
+  o Introduced new `link` element which can be used as a symbolic link to other
+    elements or junctions, in the local project or in subprojects.
 
 API
 ---
diff --git a/doc/source/core_plugins.rst b/doc/source/core_plugins.rst
index b40728669..7b968b7b9 100644
--- a/doc/source/core_plugins.rst
+++ b/doc/source/core_plugins.rst
@@ -19,6 +19,7 @@ General elements
    elements/import
    elements/compose
    elements/script
+   elements/link
    elements/junction
    elements/filter
 
diff --git a/src/buildstream/_loader/loadelement.pyx b/src/buildstream/_loader/loadelement.pyx
index 31c3aef1a..2f4e7a0f9 100644
--- a/src/buildstream/_loader/loadelement.pyx
+++ b/src/buildstream/_loader/loadelement.pyx
@@ -21,8 +21,11 @@ from functools import cmp_to_key
 
 from pyroaring import BitMap, FrozenBitMap  # pylint: disable=no-name-in-module
 
-from ..node cimport MappingNode
-from .types import Symbol
+from .._exceptions import LoadError
+from ..exceptions import LoadErrorReason
+from ..element import Element
+from ..node cimport MappingNode, ProvenanceInformation
+from .types import Symbol, extract_depends_from_node
 
 
 # Counter to get ids to LoadElements
@@ -74,6 +77,8 @@ cdef class LoadElement:
     cdef public bint meta_done
     cdef int node_id
     cdef readonly object _loader
+    cdef readonly str link_target
+    cdef readonly ProvenanceInformation link_target_provenance
     # TODO: if/when pyroaring exports symbols, we could type this statically
     cdef object _dep_cache
     cdef readonly list dependencies
@@ -88,6 +93,8 @@ cdef class LoadElement:
         self.full_name = None   # The element full name (with associated junction)
         self.meta_done = False  # If the MetaElement for this LoadElement is done
         self.node_id = _next_synthetic_counter()
+        self.link_target = None  # The target of a link element
+        self.link_target_provenance = None  # The provenance of the link target
 
         #
         # Private members
@@ -105,6 +112,8 @@ cdef class LoadElement:
             # dependency is in top-level project
             self.full_name = self.name
 
+        self.dependencies = []
+
         # Ensure the root node is valid
         self.node.validate_keys([
             'kind', 'depends', 'sources', 'sandbox',
@@ -113,7 +122,27 @@ cdef class LoadElement:
             'build-depends', 'runtime-depends',
         ])
 
-        self.dependencies = []
+        #
+        # If this is a link, resolve it right away and just
+        # store the link target and provenance
+        #
+        if self.node.get_str(Symbol.KIND, default=None) == 'link':
+            meta_element = self._loader.collect_element_no_deps(self, None)
+            element = Element._new_from_meta(meta_element)
+            element._initialize_state()
+
+            # Custom error for link dependencies, since we don't completely
+            # parse their dependencies we cannot rely on the built-in ElementError.
+            deps = extract_depends_from_node(self.node)
+            if deps:
+                provenance = self.node
+                raise LoadError(
+                    "{}: Dependencies are forbidden for 'link' elements".format(element),
+                    LoadErrorReason.LINK_FORBIDDEN_DEPENDENCIES
+                )
+
+            self.link_target = element.target
+            self.link_target_provenance = element.target_provenance
 
     @property
     def junction(self):
diff --git a/src/buildstream/_loader/loader.py b/src/buildstream/_loader/loader.py
index 49018629e..b73f5b862 100644
--- a/src/buildstream/_loader/loader.py
+++ b/src/buildstream/_loader/loader.py
@@ -217,6 +217,27 @@ class Loader:
             self._loaders[filename] = None
             return None
 
+        # At this point we've loaded the LoadElement
+        load_element = self._elements[filename]
+
+        # If the loaded element is a link, then just follow it
+        # immediately and move on to the target.
+        #
+        if load_element.link_target:
+
+            _, filename, loader = self._parse_name(load_element.link_target, rewritable, ticker)
+
+            if loader != self:
+                level = level + 1
+
+            return loader.get_loader(
+                filename,
+                rewritable=rewritable,
+                ticker=ticker,
+                level=level,
+                provenance=load_element.link_target_provenance,
+            )
+
         # meta junction element
         #
         # Note that junction elements are not allowed to have
@@ -227,7 +248,7 @@ class Loader:
         #
         # Any task counting *inside* the junction will be handled by
         # its loader.
-        meta_element = self._collect_element_no_deps(self._elements[filename])
+        meta_element = self.collect_element_no_deps(self._elements[filename])
         if meta_element.kind != "junction":
             raise LoadError(
                 "{}{}: Expected junction but element kind is {}".format(provenance_str, filename, meta_element.kind),
@@ -247,24 +268,12 @@ class Loader:
         # through the entire loading process), which is nice UX. It
         # would be nice if this could be done for *all* element types,
         # but since we haven't loaded those yet that's impossible.
-        if self._elements[filename].dependencies:
+        if load_element.dependencies:
             raise LoadError("Dependencies are forbidden for 'junction' elements", LoadErrorReason.INVALID_JUNCTION)
 
         element = Element._new_from_meta(meta_element)
         element._initialize_state()
 
-        # If this junction element points to a sub-sub-project, we need to
-        # find loader for that project.
-        if element.target:
-            subproject_loader = self.get_loader(
-                element.target_junction, rewritable=rewritable, ticker=ticker, level=level, provenance=provenance
-            )
-            loader = subproject_loader.get_loader(
-                element.target_element, rewritable=rewritable, ticker=ticker, level=level, provenance=provenance
-            )
-            self._loaders[filename] = loader
-            return loader
-
         # Handle the case where a subproject has no ref
         #
         if not element._has_all_sources_resolved():
@@ -368,6 +377,81 @@ class Loader:
 
         return state
 
+    # collect_element_no_deps()
+    #
+    # Collect a single element, without its dependencies, into a meta_element
+    #
+    # NOTE: This is declared public in order to share with the LoadElement
+    #       and should not be used outside of that `_loader` module.
+    #
+    # Args:
+    #    element (LoadElement): The element for which to load a MetaElement
+    #    task (Task): A task to write progress information to
+    #
+    # Returns:
+    #    (MetaElement): A partially loaded MetaElement
+    #
+    def collect_element_no_deps(self, element, task=None):
+        # Return the already built one, if we already built it
+        meta_element = self._meta_elements.get(element.name)
+        if meta_element:
+            return meta_element
+
+        node = element.node
+        elt_provenance = node.get_provenance()
+        meta_sources = []
+
+        element_kind = node.get_str(Symbol.KIND)
+
+        # if there's a workspace for this element then just append a dummy workspace
+        # metasource.
+        workspace = self._context.get_workspaces().get_workspace(element.name)
+        skip_workspace = True
+        if workspace:
+            workspace_node = {"kind": "workspace"}
+            workspace_node["path"] = workspace.get_absolute_path()
+            workspace_node["last_build"] = str(workspace.to_dict().get("last_build", ""))
+            node[Symbol.SOURCES] = [workspace_node]
+            skip_workspace = False
+
+        sources = node.get_sequence(Symbol.SOURCES, default=[])
+        for index, source in enumerate(sources):
+            kind = source.get_str(Symbol.KIND)
+            # the workspace source plugin cannot be used unless the element is workspaced
+            if kind == "workspace" and skip_workspace:
+                continue
+
+            del source[Symbol.KIND]
+
+            # Directory is optional
+            directory = source.get_str(Symbol.DIRECTORY, default=None)
+            if directory:
+                del source[Symbol.DIRECTORY]
+            meta_source = MetaSource(element.name, index, element_kind, kind, source, directory)
+            meta_sources.append(meta_source)
+
+        meta_element = MetaElement(
+            self.project,
+            element.name,
+            element_kind,
+            elt_provenance,
+            meta_sources,
+            node.get_mapping(Symbol.CONFIG, default={}),
+            node.get_mapping(Symbol.VARIABLES, default={}),
+            node.get_mapping(Symbol.ENVIRONMENT, default={}),
+            node.get_str_list(Symbol.ENV_NOCACHE, default=[]),
+            node.get_mapping(Symbol.PUBLIC, default={}),
+            node.get_mapping(Symbol.SANDBOX, default={}),
+            element_kind == "junction",
+        )
+
+        # Cache it now, make sure it's already there before recursing
+        self._meta_elements[element.name] = meta_element
+        if task:
+            task.add_current_progress()
+
+        return meta_element
+
     ###########################################
     #            Private Methods              #
     ###########################################
@@ -474,6 +558,13 @@ class Loader:
             ticker(filename)
 
         top_element = self._load_file_no_deps(filename, rewritable, provenance)
+
+        # If this element is a link then we need to resolve it
+        # and replace the dependency we've processed with this one
+        if top_element.link_target is not None:
+            _, filename, loader = self._parse_name(top_element.link_target, rewritable, ticker)
+            top_element = loader._load_file(filename, rewritable, ticker, top_element.link_target_provenance)
+
         dependencies = extract_depends_from_node(top_element.node)
         # The loader queue is a stack of tuples
         # [0] is the LoadElement instance
@@ -513,6 +604,12 @@ class Loader:
                                 "{}: Cannot depend on junction".format(dep.provenance), LoadErrorReason.INVALID_DATA
                             )
 
+                # If this dependency is a link then we need to resolve it
+                # and replace the dependency we've processed with this one
+                if dep_element.link_target:
+                    _, filename, loader = self._parse_name(dep_element.link_target, rewritable, ticker)
+                    dep_element = loader._load_file(filename, rewritable, ticker, dep_element.link_target_provenance)
+
                 # All is well, push the dependency onto the LoadElement
                 # Pylint is not very happy with Cython and can't understand 'dependencies' is a list
                 current_element[0].dependencies.append(  # pylint: disable=no-member
@@ -581,78 +678,6 @@ class Loader:
                 check_elements.remove(this_element)
                 validated.add(this_element)
 
-    # _collect_element_no_deps()
-    #
-    # Collect a single element, without its dependencies, into a meta_element
-    #
-    # Args:
-    #    element (LoadElement): The element for which to load a MetaElement
-    #    task (Task): A task to write progress information to
-    #
-    # Returns:
-    #    (MetaElement): A partially loaded MetaElement
-    #
-    def _collect_element_no_deps(self, element, task=None):
-        # Return the already built one, if we already built it
-        meta_element = self._meta_elements.get(element.name)
-        if meta_element:
-            return meta_element
-
-        node = element.node
-        elt_provenance = node.get_provenance()
-        meta_sources = []
-
-        element_kind = node.get_str(Symbol.KIND)
-
-        # if there's a workspace for this element then just append a dummy workspace
-        # metasource.
-        workspace = self._context.get_workspaces().get_workspace(element.name)
-        skip_workspace = True
-        if workspace:
-            workspace_node = {"kind": "workspace"}
-            workspace_node["path"] = workspace.get_absolute_path()
-            workspace_node["last_build"] = str(workspace.to_dict().get("last_build", ""))
-            node[Symbol.SOURCES] = [workspace_node]
-            skip_workspace = False
-
-        sources = node.get_sequence(Symbol.SOURCES, default=[])
-        for index, source in enumerate(sources):
-            kind = source.get_str(Symbol.KIND)
-            # the workspace source plugin cannot be used unless the element is workspaced
-            if kind == "workspace" and skip_workspace:
-                continue
-
-            del source[Symbol.KIND]
-
-            # Directory is optional
-            directory = source.get_str(Symbol.DIRECTORY, default=None)
-            if directory:
-                del source[Symbol.DIRECTORY]
-            meta_source = MetaSource(element.name, index, element_kind, kind, source, directory)
-            meta_sources.append(meta_source)
-
-        meta_element = MetaElement(
-            self.project,
-            element.name,
-            element_kind,
-            elt_provenance,
-            meta_sources,
-            node.get_mapping(Symbol.CONFIG, default={}),
-            node.get_mapping(Symbol.VARIABLES, default={}),
-            node.get_mapping(Symbol.ENVIRONMENT, default={}),
-            node.get_str_list(Symbol.ENV_NOCACHE, default=[]),
-            node.get_mapping(Symbol.PUBLIC, default={}),
-            node.get_mapping(Symbol.SANDBOX, default={}),
-            element_kind == "junction",
-        )
-
-        # Cache it now, make sure it's already there before recursing
-        self._meta_elements[element.name] = meta_element
-        if task:
-            task.add_current_progress()
-
-        return meta_element
-
     # _collect_element()
     #
     # Collect the toplevel elements we have
@@ -666,7 +691,7 @@ class Loader:
     #
     def _collect_element(self, top_element, task=None):
         element_queue = [top_element]
-        meta_element_queue = [self._collect_element_no_deps(top_element, task)]
+        meta_element_queue = [self.collect_element_no_deps(top_element, task)]
 
         while element_queue:
             element = element_queue.pop()
@@ -683,7 +708,7 @@ class Loader:
                 name = dep.element.name
 
                 if name not in loader._meta_elements:
-                    meta_dep = loader._collect_element_no_deps(dep.element, task)
+                    meta_dep = loader.collect_element_no_deps(dep.element, task)
                     element_queue.append(dep.element)
                     meta_element_queue.append(meta_dep)
                 else:
diff --git a/src/buildstream/exceptions.py b/src/buildstream/exceptions.py
index cc2bd6381..2c455be84 100644
--- a/src/buildstream/exceptions.py
+++ b/src/buildstream/exceptions.py
@@ -139,3 +139,6 @@ class LoadErrorReason(Enum):
 
     DUPLICATE_DEPENDENCY = 24
     """A duplicate dependency was detected"""
+
+    LINK_FORBIDDEN_DEPENDENCIES = 25
+    """A link element declared dependencies"""
diff --git a/src/buildstream/plugins/elements/junction.py b/src/buildstream/plugins/elements/junction.py
index 86d1de8f8..c9e78632f 100644
--- a/src/buildstream/plugins/elements/junction.py
+++ b/src/buildstream/plugins/elements/junction.py
@@ -48,13 +48,6 @@ Overview
      # Optionally look in a subpath of the source repository for the project
      path: projects/hello
 
-     # Optionally specify another junction element to serve as a target for
-     # this element. Target should be defined using the syntax
-     # ``{junction-name}:{element-name}``.
-     #
-     # Note that this option cannot be used in conjunction with sources.
-     target: sub-project.bst:sub-sub-project.bst
-
      # Optionally declare whether elements within the junction project
      # should interact with project remotes (default: False).
      cache-junction-elements: False
@@ -132,29 +125,24 @@ simply use one junction and ignore the others. Due to this, BuildStream requires
 the user to resolve possibly conflicting nested junctions by creating a junction
 with the same name in the top-level project, which then takes precedence.
 
-Targeting other junctions
-~~~~~~~~~~~~~~~~~~~~~~~~~
-When working with nested junctions, you can also create a junction element that
-targets another junction element in the sub-project. This can be useful if you
-need to ensure that both the top-level project and the sub-project are using
-the same version of the sub-sub-project.
+Linking to other junctions
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+When working with nested junctions, you often need to ensure that multiple
+projects are using the same version of a given subproject.
+
+In order to ensure that your project is using a junction to a sub-subproject
+declared by a direct subproject, then you can use a :mod:`link <elements.link>`
+element in place of declaring a junction.
 
-This can be done using the ``target`` configuration option. See below for an
-example:
+This lets you create a link to a junction in the subproject, which you
+can then treat as a regular junction in your toplevel project.
 
 .. code:: yaml
 
-   kind: junction
+   kind: link
 
    config:
      target: subproject.bst:subsubproject.bst
-
-In the above example, this junction element would be targeting the junction
-element named ``subsubproject.bst`` in the subproject referred to by
-``subproject.bst``.
-
-Note that when targeting another junction, the names of the junction element
-must not be the same as the name of the target.
 """
 
 from buildstream import Element, ElementError
@@ -173,39 +161,15 @@ class JunctionElement(Element):
 
     def configure(self, node):
 
-        node.validate_keys(["path", "options", "target", "cache-junction-elements", "ignore-junction-remotes"])
+        node.validate_keys(["path", "options", "cache-junction-elements", "ignore-junction-remotes"])
 
         self.path = node.get_str("path", default="")
         self.options = node.get_mapping("options", default={})
-        self.target = node.get_str("target", default=None)
-        self.target_element = None
-        self.target_junction = None
         self.cache_junction_elements = node.get_bool("cache-junction-elements", default=False)
         self.ignore_junction_remotes = node.get_bool("ignore-junction-remotes", default=False)
 
     def preflight(self):
-        # "target" cannot be used in conjunction with:
-        # 1. sources
-        # 2. config['options']
-        # 3. config['path']
-        if self.target and any(self.sources()):
-            raise ElementError("junction elements cannot define both 'sources' and 'target' config option")
-        if self.target and any(self.options.items()):
-            raise ElementError("junction elements cannot define both 'options' and 'target'")
-        if self.target and self.path:
-            raise ElementError("junction elements cannot define both 'path' and 'target'")
-
-        # Validate format of target, if defined
-        if self.target:
-            try:
-                self.target_junction, self.target_element = self.target.split(":")
-            except ValueError:
-                raise ElementError("'target' option must be in format '{junction-name}:{element-name}'")
-
-        # We cannot target a junction that has the same name as us, since that
-        # will cause an infinite recursion while trying to load it.
-        if self.name == self.target_element:
-            raise ElementError("junction elements cannot target an element with the same name")
+        pass
 
     def get_unique_key(self):
         # Junctions do not produce artifacts. get_unique_key() implementation
diff --git a/src/buildstream/plugins/elements/link.py b/src/buildstream/plugins/elements/link.py
new file mode 100644
index 000000000..611108241
--- /dev/null
+++ b/src/buildstream/plugins/elements/link.py
@@ -0,0 +1,90 @@
+#
+#  Copyright (C) 2020 Codethink Limited
+#
+#  This program is free software; you can redistribute it and/or
+#  modify it under the terms of the GNU Lesser General Public
+#  License as published by the Free Software Foundation; either
+#  version 2 of the License, or (at your option) any later version.
+#
+#  This library is distributed in the hope that it will be useful,
+#  but WITHOUT ANY WARRANTY; without even the implied warranty of
+#  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.	 See the GNU
+#  Lesser General Public License for more details.
+#
+#  You should have received a copy of the GNU Lesser General Public
+#  License along with this library. If not, see <http://www.gnu.org/licenses/>.
+#
+#  Authors:
+#        Tristan van Berkom <tristan.vanberkom@codethink.co.uk>
+
+"""
+link - Link elements
+================================
+This element is a link to another element, allowing one to create
+a symbolic element which will be resolved to another element.
+
+
+Overview
+--------
+The only configuration allowed in a ``link`` element is the specified
+target of the link.
+
+.. code:: yaml
+
+   kind: link
+
+   config:
+     target: element.bst
+
+The ``link`` element can be used to refer to elements in subprojects, and
+can be used to symbolically link junctions as well as other elements.
+"""
+
+from buildstream import Element
+
+
+# Element implementation for the 'link' kind.
+class LinkElement(Element):
+    # pylint: disable=attribute-defined-outside-init
+
+    BST_MIN_VERSION = "2.0"
+
+    # Links are not allowed any dependencies or sources
+    BST_FORBID_BDEPENDS = True
+    BST_FORBID_RDEPENDS = True
+    BST_FORBID_SOURCES = True
+
+    def configure(self, node):
+
+        node.validate_keys(["target"])
+
+        # Hold onto the provenance of the specified target,
+        # allowing the loader to raise errors with better context.
+        #
+        target_node = node.get_scalar("target")
+        self.target = target_node.as_str()
+        self.target_provenance = target_node.get_provenance()
+
+    def preflight(self):
+        pass
+
+    def get_unique_key(self):
+        # This is only used early on but later discarded
+        return 1
+
+    def configure_sandbox(self, sandbox):
+        assert False, "link elements should be discarded at load time"
+
+    def stage(self, sandbox):
+        assert False, "link elements should be discarded at load time"
+
+    def generate_script(self):
+        assert False, "link elements should be discarded at load time"
+
+    def assemble(self, sandbox):
+        assert False, "link elements should be discarded at load time"
+
+
+# Plugin entry point
+def setup():
+    return LinkElement
diff --git a/tests/format/junctions.py b/tests/format/junctions.py
index 70572ee3e..f097e0b8b 100644
--- a/tests/format/junctions.py
+++ b/tests/format/junctions.py
@@ -411,60 +411,6 @@ def test_build_git_cross_junction_names(cli, tmpdir, datafiles):
 
 
 @pytest.mark.datafiles(DATA_DIR)
-def test_config_target(cli, tmpdir, datafiles):
-    project = os.path.join(str(datafiles), "config-target")
-    checkoutdir = os.path.join(str(tmpdir), "checkout")
-
-    # Build, checkout
-    result = cli.run(project=project, args=["build", "target.bst"])
-    result.assert_success()
-    result = cli.run(project=project, args=["artifact", "checkout", "target.bst", "--directory", checkoutdir])
-    result.assert_success()
-
-    # Check that the checkout contains the expected files from sub-sub-project
-    assert os.path.exists(os.path.join(checkoutdir, "hello.txt"))
-
-
-@pytest.mark.datafiles(DATA_DIR)
-def test_invalid_sources_and_target(cli, tmpdir, datafiles):
-    project = os.path.join(str(datafiles), "config-target")
-
-    result = cli.run(project=project, args=["show", "invalid-source-target.bst"])
-    result.assert_main_error(ErrorDomain.ELEMENT, None)
-
-    assert "junction elements cannot define both 'sources' and 'target' config option" in result.stderr
-
-
-@pytest.mark.datafiles(DATA_DIR)
-def test_invalid_target_name(cli, tmpdir, datafiles):
-    project = os.path.join(str(datafiles), "config-target")
-
-    # Rename our junction element to the same name as its target
-    old_path = os.path.join(project, "elements/subsubproject.bst")
-    new_path = os.path.join(project, "elements/subsubproject-junction.bst")
-    os.rename(old_path, new_path)
-
-    # This should fail now
-    result = cli.run(project=project, args=["show", "subsubproject-junction.bst"])
-    result.assert_main_error(ErrorDomain.ELEMENT, None)
-
-    assert "junction elements cannot target an element with the same name" in result.stderr
-
-
-# We cannot exhaustively test all possible ways in which this can go wrong, so
-# test a couple of common ways in which we expect this to go wrong.
-@pytest.mark.parametrize("target", ["no-junction.bst", "nested-junction-target.bst"])
-@pytest.mark.datafiles(DATA_DIR)
-def test_invalid_target_format(cli, tmpdir, datafiles, target):
-    project = os.path.join(str(datafiles), "config-target")
-
-    result = cli.run(project=project, args=["show", target])
-    result.assert_main_error(ErrorDomain.ELEMENT, None)
-
-    assert "'target' option must be in format '{junction-name}:{element-name}'" in result.stderr
-
-
-@pytest.mark.datafiles(DATA_DIR)
 def test_junction_show(cli, tmpdir, datafiles):
     project = os.path.join(str(datafiles), "foo")
     copy_subprojects(project, datafiles, ["base"])
diff --git a/tests/format/junctions/config-target/elements/invalid-source-target.bst b/tests/format/junctions/config-target/elements/invalid-source-target.bst
deleted file mode 100644
index b97d09034..000000000
--- a/tests/format/junctions/config-target/elements/invalid-source-target.bst
+++ /dev/null
@@ -1,8 +0,0 @@
-kind: junction
-
-sources:
-- kind: local
-  path: subproject/subsubproject
-
-config:
-  target: subproject.bst:subsubproject-junction.bst
diff --git a/tests/format/junctions/config-target/elements/nested-junction-target.bst b/tests/format/junctions/config-target/elements/nested-junction-target.bst
deleted file mode 100644
index f76a264e5..000000000
--- a/tests/format/junctions/config-target/elements/nested-junction-target.bst
+++ /dev/null
@@ -1,4 +0,0 @@
-kind: junction
-
-config:
-  target: subproject.bst:subsubproject.bst:hello.bst
diff --git a/tests/format/junctions/config-target/elements/target.bst b/tests/format/junctions/config-target/elements/target.bst
deleted file mode 100644
index 50d74489a..000000000
--- a/tests/format/junctions/config-target/elements/target.bst
+++ /dev/null
@@ -1,4 +0,0 @@
-kind: stack
-
-depends:
-- subsubproject.bst:hello.bst
diff --git a/tests/format/link.py b/tests/format/link.py
new file mode 100644
index 000000000..47e19b90c
--- /dev/null
+++ b/tests/format/link.py
@@ -0,0 +1,145 @@
+# Pylint doesn't play well with fixtures and dependency injection from pytest
+# pylint: disable=redefined-outer-name
+
+import os
+
+import pytest
+
+from buildstream.testing import cli  # pylint: disable=unused-import
+from buildstream.exceptions import ErrorDomain, LoadErrorReason
+
+
+DATA_DIR = os.path.join(os.path.dirname(os.path.realpath(__file__)), "link",)
+
+#
+# Test links to elements, this tests both specifying the link as
+# the main target, and also as a dependency of the main target.
+#
+@pytest.mark.datafiles(DATA_DIR)
+@pytest.mark.parametrize("target", ["target.bst", "hello-link.bst"])
+def test_simple_link(cli, tmpdir, datafiles, target):
+    project = os.path.join(str(datafiles), "simple")
+    checkoutdir = os.path.join(str(tmpdir), "checkout")
+
+    # Build, checkout
+    result = cli.run(project=project, args=["build", target])
+    result.assert_success()
+    result = cli.run(project=project, args=["artifact", "checkout", target, "--directory", checkoutdir])
+    result.assert_success()
+
+    # Check that the checkout contains the expected files from sub-sub-project
+    assert os.path.exists(os.path.join(checkoutdir, "hello.txt"))
+
+
+#
+# Test links to elements, this tests both specifying the link as
+# the main target, and also as a dependency of the main target, while
+# also using a conditional statement in the link
+#
+@pytest.mark.datafiles(DATA_DIR)
+@pytest.mark.parametrize("target", ["target.bst", "target-link.bst"])
+@pytest.mark.parametrize("greeting,expected_file", [("hello", "hello.txt"), ("goodbye", "goodbye.txt")])
+def test_conditional_link(cli, tmpdir, datafiles, target, greeting, expected_file):
+    project = os.path.join(str(datafiles), "conditional")
+    checkoutdir = os.path.join(str(tmpdir), "checkout")
+
+    # Build, checkout
+    result = cli.run(project=project, args=["-o", "greeting", greeting, "build", target])
+    result.assert_success()
+    result = cli.run(
+        project=project, args=["-o", "greeting", greeting, "artifact", "checkout", target, "--directory", checkoutdir]
+    )
+    result.assert_success()
+
+    # Check that the checkout contains the expected files from sub-sub-project
+    assert os.path.exists(os.path.join(checkoutdir, expected_file))
+
+
+#
+# Test links to junctions from local projects and subprojects
+#
+@pytest.mark.datafiles(DATA_DIR)
+@pytest.mark.parametrize("target", ["target-local.bst", "target-nested.bst"])
+def test_simple_junctions(cli, tmpdir, datafiles, target):
+    project = os.path.join(str(datafiles), "simple-junctions")
+    checkoutdir = os.path.join(str(tmpdir), "checkout")
+
+    # Build, checkout
+    result = cli.run(project=project, args=["build", target])
+    result.assert_success()
+    result = cli.run(project=project, args=["artifact", "checkout", target, "--directory", checkoutdir])
+    result.assert_success()
+
+    # Check that the checkout contains the expected files from sub-sub-project
+    assert os.path.exists(os.path.join(checkoutdir, "hello.txt"))
+
+
+#
+# Test links which resolve junction targets conditionally
+#
+@pytest.mark.datafiles(DATA_DIR)
+@pytest.mark.parametrize("greeting,expected_file", [("hello", "hello.txt"), ("goodbye", "goodbye.txt")])
+def test_conditional_junctions(cli, tmpdir, datafiles, greeting, expected_file):
+    project = os.path.join(str(datafiles), "conditional-junctions")
+    checkoutdir = os.path.join(str(tmpdir), "checkout")
+
+    # Build, checkout
+    result = cli.run(project=project, args=["-o", "greeting", greeting, "build", "target.bst"])
+    result.assert_success()
+    result = cli.run(
+        project=project,
+        args=["-o", "greeting", greeting, "artifact", "checkout", "target.bst", "--directory", checkoutdir],
+    )
+    result.assert_success()
+
+    # Check that the checkout contains the expected files from sub-sub-project
+    assert os.path.exists(os.path.join(checkoutdir, expected_file))
+
+
+#
+# Tests links which refer to non-existing elements or junctions
+#
+@pytest.mark.datafiles(DATA_DIR)
+@pytest.mark.parametrize(
+    "target,provenance",
+    [
+        # Target is a link to a non-existing local element
+        ("link-target.bst", "link-target.bst [line 4 column 10]"),
+        # Target is a stack depending on a link to a non-existing local element
+        ("depends-on-link-target.bst", "link-target.bst [line 4 column 10]",),
+        # Depends on non-existing subproject element, via a local link
+        ("linked-local-junction-target.bst", "linked-local-junction-target.bst [line 4 column 2]",),
+        # Depends on non-existing subsubproject element, via a local link
+        ("linked-nested-junction-target.bst", "linked-nested-junction-target.bst [line 4 column 2]",),
+        # Depends on an element via a link to a non-existing local junction
+        ("linked-local-junction.bst", "subproject-link-notfound.bst [line 4 column 10]",),
+        # Depends on an element via a link to a non-existing subproject junction
+        ("linked-nested-junction.bst", "subsubproject-link-notfound.bst [line 4 column 10]",),
+    ],
+)
+def test_link_not_found(cli, tmpdir, datafiles, target, provenance):
+    project = os.path.join(str(datafiles), "notfound")
+    result = cli.run(project=project, args=["build", target])
+
+    result.assert_main_error(ErrorDomain.LOAD, LoadErrorReason.MISSING_FILE)
+    assert provenance in result.stderr
+
+
+#
+# Tests links with invalid configurations
+#
+@pytest.mark.datafiles(DATA_DIR)
+@pytest.mark.parametrize(
+    "target,expected_error,expected_reason",
+    [
+        # Test link which declares sources, either directly of via a dependency
+        ("link-with-sources.bst", ErrorDomain.ELEMENT, "element-forbidden-sources"),
+        ("target-link-with-sources.bst", ErrorDomain.ELEMENT, "element-forbidden-sources"),
+        # Test link which declares dependencies, either directly of via a dependency
+        ("link-with-dependencies.bst", ErrorDomain.LOAD, LoadErrorReason.LINK_FORBIDDEN_DEPENDENCIES),
+    ],
+)
+def test_link_invalid_config(cli, tmpdir, datafiles, target, expected_error, expected_reason):
+    project = os.path.join(str(datafiles), "invalid")
+    result = cli.run(project=project, args=["show", target])
+    result.assert_main_error(expected_error, expected_reason)
diff --git a/tests/format/junctions/config-target/elements/subproject.bst b/tests/format/link/conditional-junctions/elements/subproject.bst
index 6664eeec6..6664eeec6 100644
--- a/tests/format/junctions/config-target/elements/subproject.bst
+++ b/tests/format/link/conditional-junctions/elements/subproject.bst
diff --git a/tests/format/link/conditional-junctions/elements/subsubproject-link.bst b/tests/format/link/conditional-junctions/elements/subsubproject-link.bst
new file mode 100644
index 000000000..97e54c0ad
--- /dev/null
+++ b/tests/format/link/conditional-junctions/elements/subsubproject-link.bst
@@ -0,0 +1,8 @@
+kind: link
+
+config:
+  (?):
+  - greeting == "hello":
+      target: subproject.bst:subsubproject-hello-junction.bst
+  - greeting == "goodbye":
+      target: subproject.bst:subsubproject-goodbye-junction.bst
diff --git a/tests/format/link/conditional-junctions/elements/target.bst b/tests/format/link/conditional-junctions/elements/target.bst
new file mode 100644
index 000000000..583061a29
--- /dev/null
+++ b/tests/format/link/conditional-junctions/elements/target.bst
@@ -0,0 +1,4 @@
+kind: stack
+
+depends:
+- subsubproject-link.bst:target.bst
diff --git a/tests/format/link/conditional-junctions/project.conf b/tests/format/link/conditional-junctions/project.conf
new file mode 100644
index 000000000..aae690c84
--- /dev/null
+++ b/tests/format/link/conditional-junctions/project.conf
@@ -0,0 +1,13 @@
+name: conditional
+min-version: 2.0
+
+element-path: elements
+
+options:
+  greeting:
+    type: enum
+    description: The greeting
+    values:
+    - hello
+    - goodbye
+    default: hello
diff --git a/tests/format/junctions/config-target/subproject/subsubproject/elements/hello.bst b/tests/format/link/conditional-junctions/subproject/elements/hello.bst
index a04a856cd..a04a856cd 100644
--- a/tests/format/junctions/config-target/subproject/subsubproject/elements/hello.bst
+++ b/tests/format/link/conditional-junctions/subproject/elements/hello.bst
diff --git a/tests/format/link/conditional-junctions/subproject/elements/subsubproject-goodbye-junction.bst b/tests/format/link/conditional-junctions/subproject/elements/subsubproject-goodbye-junction.bst
new file mode 100644
index 000000000..ab37f9a45
--- /dev/null
+++ b/tests/format/link/conditional-junctions/subproject/elements/subsubproject-goodbye-junction.bst
@@ -0,0 +1,5 @@
+kind: junction
+
+sources:
+- kind: local
+  path: subsubproject-goodbye
diff --git a/tests/format/link/conditional-junctions/subproject/elements/subsubproject-hello-junction.bst b/tests/format/link/conditional-junctions/subproject/elements/subsubproject-hello-junction.bst
new file mode 100644
index 000000000..99db3b997
--- /dev/null
+++ b/tests/format/link/conditional-junctions/subproject/elements/subsubproject-hello-junction.bst
@@ -0,0 +1,5 @@
+kind: junction
+
+sources:
+- kind: local
+  path: subsubproject-hello
diff --git a/tests/format/junctions/config-target/subproject/project.conf b/tests/format/link/conditional-junctions/subproject/project.conf
index 1529ece04..1529ece04 100644
--- a/tests/format/junctions/config-target/subproject/project.conf
+++ b/tests/format/link/conditional-junctions/subproject/project.conf
diff --git a/tests/format/link/conditional-junctions/subproject/subsubproject-goodbye/elements/target.bst b/tests/format/link/conditional-junctions/subproject/subsubproject-goodbye/elements/target.bst
new file mode 100644
index 000000000..f7217c514
--- /dev/null
+++ b/tests/format/link/conditional-junctions/subproject/subsubproject-goodbye/elements/target.bst
@@ -0,0 +1,5 @@
+kind: import
+
+sources:
+- kind: local
+  path: files/goodbye.txt
diff --git a/tests/format/junctions/config-target/subproject/subsubproject/files/hello.txt b/tests/format/link/conditional-junctions/subproject/subsubproject-goodbye/files/goodbye.txt
index ce0136250..ce0136250 100644
--- a/tests/format/junctions/config-target/subproject/subsubproject/files/hello.txt
+++ b/tests/format/link/conditional-junctions/subproject/subsubproject-goodbye/files/goodbye.txt
diff --git a/tests/format/junctions/config-target/subproject/subsubproject/project.conf b/tests/format/link/conditional-junctions/subproject/subsubproject-goodbye/project.conf
index 162143c80..162143c80 100644
--- a/tests/format/junctions/config-target/subproject/subsubproject/project.conf
+++ b/tests/format/link/conditional-junctions/subproject/subsubproject-goodbye/project.conf
diff --git a/tests/format/link/conditional-junctions/subproject/subsubproject-hello/elements/target.bst b/tests/format/link/conditional-junctions/subproject/subsubproject-hello/elements/target.bst
new file mode 100644
index 000000000..a04a856cd
--- /dev/null
+++ b/tests/format/link/conditional-junctions/subproject/subsubproject-hello/elements/target.bst
@@ -0,0 +1,5 @@
+kind: import
+
+sources:
+- kind: local
+  path: files/hello.txt
diff --git a/tests/format/link/conditional-junctions/subproject/subsubproject-hello/files/hello.txt b/tests/format/link/conditional-junctions/subproject/subsubproject-hello/files/hello.txt
new file mode 100644
index 000000000..ce0136250
--- /dev/null
+++ b/tests/format/link/conditional-junctions/subproject/subsubproject-hello/files/hello.txt
@@ -0,0 +1 @@
+hello
diff --git a/tests/format/junctions/config-target/project.conf b/tests/format/link/conditional-junctions/subproject/subsubproject-hello/project.conf
index d9e1d7a4f..162143c80 100644
--- a/tests/format/junctions/config-target/project.conf
+++ b/tests/format/link/conditional-junctions/subproject/subsubproject-hello/project.conf
@@ -1,4 +1,4 @@
-name: config-target
+name: subsubproject
 min-version: 2.0
 
 element-path: elements
diff --git a/tests/format/link/conditional/elements/goodbye.bst b/tests/format/link/conditional/elements/goodbye.bst
new file mode 100644
index 000000000..f7217c514
--- /dev/null
+++ b/tests/format/link/conditional/elements/goodbye.bst
@@ -0,0 +1,5 @@
+kind: import
+
+sources:
+- kind: local
+  path: files/goodbye.txt
diff --git a/tests/format/link/conditional/elements/hello.bst b/tests/format/link/conditional/elements/hello.bst
new file mode 100644
index 000000000..a04a856cd
--- /dev/null
+++ b/tests/format/link/conditional/elements/hello.bst
@@ -0,0 +1,5 @@
+kind: import
+
+sources:
+- kind: local
+  path: files/hello.txt
diff --git a/tests/format/link/conditional/elements/target-link.bst b/tests/format/link/conditional/elements/target-link.bst
new file mode 100644
index 000000000..43bffebce
--- /dev/null
+++ b/tests/format/link/conditional/elements/target-link.bst
@@ -0,0 +1,8 @@
+kind: link
+
+config:
+  (?):
+  - greeting == "hello":
+      target: hello.bst
+  - greeting == "goodbye":
+      target: goodbye.bst
diff --git a/tests/format/link/conditional/elements/target.bst b/tests/format/link/conditional/elements/target.bst
new file mode 100644
index 000000000..92ccc16a7
--- /dev/null
+++ b/tests/format/link/conditional/elements/target.bst
@@ -0,0 +1,4 @@
+kind: stack
+
+depends:
+- target-link.bst
diff --git a/tests/format/link/conditional/files/goodbye.txt b/tests/format/link/conditional/files/goodbye.txt
new file mode 100644
index 000000000..ce0136250
--- /dev/null
+++ b/tests/format/link/conditional/files/goodbye.txt
@@ -0,0 +1 @@
+hello
diff --git a/tests/format/link/conditional/files/hello.txt b/tests/format/link/conditional/files/hello.txt
new file mode 100644
index 000000000..ce0136250
--- /dev/null
+++ b/tests/format/link/conditional/files/hello.txt
@@ -0,0 +1 @@
+hello
diff --git a/tests/format/link/conditional/project.conf b/tests/format/link/conditional/project.conf
new file mode 100644
index 000000000..aae690c84
--- /dev/null
+++ b/tests/format/link/conditional/project.conf
@@ -0,0 +1,13 @@
+name: conditional
+min-version: 2.0
+
+element-path: elements
+
+options:
+  greeting:
+    type: enum
+    description: The greeting
+    values:
+    - hello
+    - goodbye
+    default: hello
diff --git a/tests/format/link/invalid/elements/base-file.bst b/tests/format/link/invalid/elements/base-file.bst
new file mode 100644
index 000000000..92948a068
--- /dev/null
+++ b/tests/format/link/invalid/elements/base-file.bst
@@ -0,0 +1,5 @@
+kind: import
+
+sources:
+- kind: local
+  path: .
diff --git a/tests/format/link/invalid/elements/link-with-dependencies.bst b/tests/format/link/invalid/elements/link-with-dependencies.bst
new file mode 100644
index 000000000..f30a00560
--- /dev/null
+++ b/tests/format/link/invalid/elements/link-with-dependencies.bst
@@ -0,0 +1,7 @@
+kind: link
+
+depends:
+- base-file.bst
+
+config:
+  target: base-file.bst
diff --git a/tests/format/link/invalid/elements/link-with-sources.bst b/tests/format/link/invalid/elements/link-with-sources.bst
new file mode 100644
index 000000000..90ef16601
--- /dev/null
+++ b/tests/format/link/invalid/elements/link-with-sources.bst
@@ -0,0 +1,8 @@
+kind: link
+
+sources:
+- kind: local
+  path: .
+
+config:
+  target: base-file.bst
diff --git a/tests/format/link/invalid/elements/target-link-with-sources.bst b/tests/format/link/invalid/elements/target-link-with-sources.bst
new file mode 100644
index 000000000..8fd00433d
--- /dev/null
+++ b/tests/format/link/invalid/elements/target-link-with-sources.bst
@@ -0,0 +1,4 @@
+kind: stack
+
+depends:
+- link-with-sources.bst
diff --git a/tests/format/link/invalid/project.conf b/tests/format/link/invalid/project.conf
new file mode 100644
index 000000000..b4fb73ba9
--- /dev/null
+++ b/tests/format/link/invalid/project.conf
@@ -0,0 +1,4 @@
+name: invalid
+min-version: 2.0
+
+element-path: elements
diff --git a/tests/format/link/notfound/elements/depends-on-link-target.bst b/tests/format/link/notfound/elements/depends-on-link-target.bst
new file mode 100644
index 000000000..1f3c7a61e
--- /dev/null
+++ b/tests/format/link/notfound/elements/depends-on-link-target.bst
@@ -0,0 +1,4 @@
+kind: stack
+
+depends:
+- link-target.bst
diff --git a/tests/format/link/notfound/elements/link-target.bst b/tests/format/link/notfound/elements/link-target.bst
new file mode 100644
index 000000000..7ab8902b0
--- /dev/null
+++ b/tests/format/link/notfound/elements/link-target.bst
@@ -0,0 +1,4 @@
+kind: link
+
+config:
+  target: no-element-found.bst
diff --git a/tests/format/link/notfound/elements/linked-local-junction-target.bst b/tests/format/link/notfound/elements/linked-local-junction-target.bst
new file mode 100644
index 000000000..ac89cf604
--- /dev/null
+++ b/tests/format/link/notfound/elements/linked-local-junction-target.bst
@@ -0,0 +1,4 @@
+kind: stack
+
+depends:
+- subproject-link.bst:hello.bst
diff --git a/tests/format/link/notfound/elements/linked-local-junction.bst b/tests/format/link/notfound/elements/linked-local-junction.bst
new file mode 100644
index 000000000..6b0be9370
--- /dev/null
+++ b/tests/format/link/notfound/elements/linked-local-junction.bst
@@ -0,0 +1,4 @@
+kind: stack
+
+depends:
+- subproject-link-notfound.bst:element.bst
diff --git a/tests/format/link/notfound/elements/linked-nested-junction-target.bst b/tests/format/link/notfound/elements/linked-nested-junction-target.bst
new file mode 100644
index 000000000..b39a75f0a
--- /dev/null
+++ b/tests/format/link/notfound/elements/linked-nested-junction-target.bst
@@ -0,0 +1,4 @@
+kind: stack
+
+depends:
+- subsubproject-link.bst:hello.bst
diff --git a/tests/format/link/notfound/elements/linked-nested-junction.bst b/tests/format/link/notfound/elements/linked-nested-junction.bst
new file mode 100644
index 000000000..5edf294e0
--- /dev/null
+++ b/tests/format/link/notfound/elements/linked-nested-junction.bst
@@ -0,0 +1,4 @@
+kind: stack
+
+depends:
+- subsubproject-link-notfound.bst:element.bst
diff --git a/tests/format/link/notfound/elements/subproject-link-notfound.bst b/tests/format/link/notfound/elements/subproject-link-notfound.bst
new file mode 100644
index 000000000..ec00414db
--- /dev/null
+++ b/tests/format/link/notfound/elements/subproject-link-notfound.bst
@@ -0,0 +1,4 @@
+kind: link
+
+config:
+  target: subproject-notfound.bst
diff --git a/tests/format/junctions/config-target/elements/no-junction.bst b/tests/format/link/notfound/elements/subproject-link.bst
index 15d1842f6..5e72e81f1 100644
--- a/tests/format/junctions/config-target/elements/no-junction.bst
+++ b/tests/format/link/notfound/elements/subproject-link.bst
@@ -1,4 +1,4 @@
-kind: junction
+kind: link
 
 config:
   target: subproject.bst
diff --git a/tests/format/link/notfound/elements/subproject.bst b/tests/format/link/notfound/elements/subproject.bst
new file mode 100644
index 000000000..6664eeec6
--- /dev/null
+++ b/tests/format/link/notfound/elements/subproject.bst
@@ -0,0 +1,5 @@
+kind: junction
+
+sources:
+- kind: local
+  path: subproject
diff --git a/tests/format/link/notfound/elements/subsubproject-link-notfound.bst b/tests/format/link/notfound/elements/subsubproject-link-notfound.bst
new file mode 100644
index 000000000..1277713e7
--- /dev/null
+++ b/tests/format/link/notfound/elements/subsubproject-link-notfound.bst
@@ -0,0 +1,4 @@
+kind: link
+
+config:
+  target: subproject.bst:subsubproject-junction-notfound.bst
diff --git a/tests/format/junctions/config-target/elements/subsubproject.bst b/tests/format/link/notfound/elements/subsubproject-link.bst
index 20dc4a0c4..be08bb5fe 100644
--- a/tests/format/junctions/config-target/elements/subsubproject.bst
+++ b/tests/format/link/notfound/elements/subsubproject-link.bst
@@ -1,4 +1,4 @@
-kind: junction
+kind: link
 
 config:
   target: subproject.bst:subsubproject-junction.bst
diff --git a/tests/format/link/notfound/project.conf b/tests/format/link/notfound/project.conf
new file mode 100644
index 000000000..b792ee157
--- /dev/null
+++ b/tests/format/link/notfound/project.conf
@@ -0,0 +1,4 @@
+name: notfound
+min-version: 2.0
+
+element-path: elements
diff --git a/tests/format/junctions/config-target/subproject/elements/subsubproject-junction.bst b/tests/format/link/notfound/subproject/elements/subsubproject-junction.bst
index 018fb8ec4..018fb8ec4 100644
--- a/tests/format/junctions/config-target/subproject/elements/subsubproject-junction.bst
+++ b/tests/format/link/notfound/subproject/elements/subsubproject-junction.bst
diff --git a/tests/format/link/notfound/subproject/project.conf b/tests/format/link/notfound/subproject/project.conf
new file mode 100644
index 000000000..1529ece04
--- /dev/null
+++ b/tests/format/link/notfound/subproject/project.conf
@@ -0,0 +1,4 @@
+name: subproject
+min-version: 2.0
+
+element-path: elements
diff --git a/tests/format/link/notfound/subproject/subsubproject/project.conf b/tests/format/link/notfound/subproject/subsubproject/project.conf
new file mode 100644
index 000000000..3b470ccf2
--- /dev/null
+++ b/tests/format/link/notfound/subproject/subsubproject/project.conf
@@ -0,0 +1,2 @@
+name: subsubproject
+min-version: 2.0
diff --git a/tests/format/link/simple-junctions/elements/subproject-link.bst b/tests/format/link/simple-junctions/elements/subproject-link.bst
new file mode 100644
index 000000000..5e72e81f1
--- /dev/null
+++ b/tests/format/link/simple-junctions/elements/subproject-link.bst
@@ -0,0 +1,4 @@
+kind: link
+
+config:
+  target: subproject.bst
diff --git a/tests/format/link/simple-junctions/elements/subproject.bst b/tests/format/link/simple-junctions/elements/subproject.bst
new file mode 100644
index 000000000..6664eeec6
--- /dev/null
+++ b/tests/format/link/simple-junctions/elements/subproject.bst
@@ -0,0 +1,5 @@
+kind: junction
+
+sources:
+- kind: local
+  path: subproject
diff --git a/tests/format/link/simple-junctions/elements/subsubproject-link.bst b/tests/format/link/simple-junctions/elements/subsubproject-link.bst
new file mode 100644
index 000000000..be08bb5fe
--- /dev/null
+++ b/tests/format/link/simple-junctions/elements/subsubproject-link.bst
@@ -0,0 +1,4 @@
+kind: link
+
+config:
+  target: subproject.bst:subsubproject-junction.bst
diff --git a/tests/format/link/simple-junctions/elements/target-local.bst b/tests/format/link/simple-junctions/elements/target-local.bst
new file mode 100644
index 000000000..ac89cf604
--- /dev/null
+++ b/tests/format/link/simple-junctions/elements/target-local.bst
@@ -0,0 +1,4 @@
+kind: stack
+
+depends:
+- subproject-link.bst:hello.bst
diff --git a/tests/format/link/simple-junctions/elements/target-nested.bst b/tests/format/link/simple-junctions/elements/target-nested.bst
new file mode 100644
index 000000000..b39a75f0a
--- /dev/null
+++ b/tests/format/link/simple-junctions/elements/target-nested.bst
@@ -0,0 +1,4 @@
+kind: stack
+
+depends:
+- subsubproject-link.bst:hello.bst
diff --git a/tests/format/link/simple-junctions/project.conf b/tests/format/link/simple-junctions/project.conf
new file mode 100644
index 000000000..4e2fb0063
--- /dev/null
+++ b/tests/format/link/simple-junctions/project.conf
@@ -0,0 +1,4 @@
+name: simple
+min-version: 2.0
+
+element-path: elements
diff --git a/tests/format/link/simple-junctions/subproject/elements/hello.bst b/tests/format/link/simple-junctions/subproject/elements/hello.bst
new file mode 100644
index 000000000..a04a856cd
--- /dev/null
+++ b/tests/format/link/simple-junctions/subproject/elements/hello.bst
@@ -0,0 +1,5 @@
+kind: import
+
+sources:
+- kind: local
+  path: files/hello.txt
diff --git a/tests/format/link/simple-junctions/subproject/elements/subsubproject-junction.bst b/tests/format/link/simple-junctions/subproject/elements/subsubproject-junction.bst
new file mode 100644
index 000000000..018fb8ec4
--- /dev/null
+++ b/tests/format/link/simple-junctions/subproject/elements/subsubproject-junction.bst
@@ -0,0 +1,5 @@
+kind: junction
+
+sources:
+- kind: local
+  path: subsubproject
diff --git a/tests/format/link/simple-junctions/subproject/files/hello.txt b/tests/format/link/simple-junctions/subproject/files/hello.txt
new file mode 100644
index 000000000..ce0136250
--- /dev/null
+++ b/tests/format/link/simple-junctions/subproject/files/hello.txt
@@ -0,0 +1 @@
+hello
diff --git a/tests/format/link/simple-junctions/subproject/project.conf b/tests/format/link/simple-junctions/subproject/project.conf
new file mode 100644
index 000000000..1529ece04
--- /dev/null
+++ b/tests/format/link/simple-junctions/subproject/project.conf
@@ -0,0 +1,4 @@
+name: subproject
+min-version: 2.0
+
+element-path: elements
diff --git a/tests/format/link/simple-junctions/subproject/subsubproject/elements/hello.bst b/tests/format/link/simple-junctions/subproject/subsubproject/elements/hello.bst
new file mode 100644
index 000000000..a04a856cd
--- /dev/null
+++ b/tests/format/link/simple-junctions/subproject/subsubproject/elements/hello.bst
@@ -0,0 +1,5 @@
+kind: import
+
+sources:
+- kind: local
+  path: files/hello.txt
diff --git a/tests/format/link/simple-junctions/subproject/subsubproject/files/hello.txt b/tests/format/link/simple-junctions/subproject/subsubproject/files/hello.txt
new file mode 100644
index 000000000..ce0136250
--- /dev/null
+++ b/tests/format/link/simple-junctions/subproject/subsubproject/files/hello.txt
@@ -0,0 +1 @@
+hello
diff --git a/tests/format/link/simple-junctions/subproject/subsubproject/project.conf b/tests/format/link/simple-junctions/subproject/subsubproject/project.conf
new file mode 100644
index 000000000..162143c80
--- /dev/null
+++ b/tests/format/link/simple-junctions/subproject/subsubproject/project.conf
@@ -0,0 +1,4 @@
+name: subsubproject
+min-version: 2.0
+
+element-path: elements
diff --git a/tests/format/link/simple/elements/hello-link.bst b/tests/format/link/simple/elements/hello-link.bst
new file mode 100644
index 000000000..83b0fbe46
--- /dev/null
+++ b/tests/format/link/simple/elements/hello-link.bst
@@ -0,0 +1,4 @@
+kind: link
+
+config:
+  target: hello.bst
diff --git a/tests/format/link/simple/elements/hello.bst b/tests/format/link/simple/elements/hello.bst
new file mode 100644
index 000000000..a04a856cd
--- /dev/null
+++ b/tests/format/link/simple/elements/hello.bst
@@ -0,0 +1,5 @@
+kind: import
+
+sources:
+- kind: local
+  path: files/hello.txt
diff --git a/tests/format/link/simple/elements/target.bst b/tests/format/link/simple/elements/target.bst
new file mode 100644
index 000000000..7c1be3a42
--- /dev/null
+++ b/tests/format/link/simple/elements/target.bst
@@ -0,0 +1,4 @@
+kind: stack
+
+depends:
+- hello-link.bst
diff --git a/tests/format/link/simple/files/hello.txt b/tests/format/link/simple/files/hello.txt
new file mode 100644
index 000000000..ce0136250
--- /dev/null
+++ b/tests/format/link/simple/files/hello.txt
@@ -0,0 +1 @@
+hello
diff --git a/tests/format/link/simple/project.conf b/tests/format/link/simple/project.conf
new file mode 100644
index 000000000..4e2fb0063
--- /dev/null
+++ b/tests/format/link/simple/project.conf
@@ -0,0 +1,4 @@
+name: simple
+min-version: 2.0
+
+element-path: elements