junctions: Remove all traces of the `target` option

This removes:

  * The `target` feature from the junction plugin

  * Special case code in the loader for the `target` feature

  * The `target` related cases in tests/format/junctions.py

This also adjusts the `target` related documentation in
the `junction` element to suggest using a `link` element for
the purpose of using a subproject junction configuration to
access a common sub-subproject.

15 files changed, 13 insertions, 167 deletions

diff --git a/src/buildstream/_loader/loader.py b/src/buildstream/_loader/loader.py
index ed0d345a3..b73f5b862 100644
--- a/src/buildstream/_loader/loader.py
+++ b/src/buildstream/_loader/loader.py
@@ -274,18 +274,6 @@ class Loader:
         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():
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/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/no-junction.bst b/tests/format/junctions/config-target/elements/no-junction.bst
deleted file mode 100644
index 15d1842f6..000000000
--- a/tests/format/junctions/config-target/elements/no-junction.bst
+++ /dev/null
@@ -1,4 +0,0 @@
-kind: junction
-
-config:
-  target: subproject.bst
diff --git a/tests/format/junctions/config-target/elements/subproject.bst b/tests/format/junctions/config-target/elements/subproject.bst
deleted file mode 100644
index 6664eeec6..000000000
--- a/tests/format/junctions/config-target/elements/subproject.bst
+++ /dev/null
@@ -1,5 +0,0 @@
-kind: junction
-
-sources:
-- kind: local
-  path: subproject
diff --git a/tests/format/junctions/config-target/elements/subsubproject.bst b/tests/format/junctions/config-target/elements/subsubproject.bst
deleted file mode 100644
index 20dc4a0c4..000000000
--- a/tests/format/junctions/config-target/elements/subsubproject.bst
+++ /dev/null
@@ -1,4 +0,0 @@
-kind: junction
-
-config:
-  target: subproject.bst:subsubproject-junction.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/junctions/config-target/project.conf b/tests/format/junctions/config-target/project.conf
deleted file mode 100644
index d9e1d7a4f..000000000
--- a/tests/format/junctions/config-target/project.conf
+++ /dev/null
@@ -1,4 +0,0 @@
-name: config-target
-min-version: 2.0
-
-element-path: elements
diff --git a/tests/format/junctions/config-target/subproject/elements/subsubproject-junction.bst b/tests/format/junctions/config-target/subproject/elements/subsubproject-junction.bst
deleted file mode 100644
index 018fb8ec4..000000000
--- a/tests/format/junctions/config-target/subproject/elements/subsubproject-junction.bst
+++ /dev/null
@@ -1,5 +0,0 @@
-kind: junction
-
-sources:
-- kind: local
-  path: subsubproject
diff --git a/tests/format/junctions/config-target/subproject/project.conf b/tests/format/junctions/config-target/subproject/project.conf
deleted file mode 100644
index 1529ece04..000000000
--- a/tests/format/junctions/config-target/subproject/project.conf
+++ /dev/null
@@ -1,4 +0,0 @@
-name: subproject
-min-version: 2.0
-
-element-path: elements
diff --git a/tests/format/junctions/config-target/subproject/subsubproject/elements/hello.bst b/tests/format/junctions/config-target/subproject/subsubproject/elements/hello.bst
deleted file mode 100644
index a04a856cd..000000000
--- a/tests/format/junctions/config-target/subproject/subsubproject/elements/hello.bst
+++ /dev/null
@@ -1,5 +0,0 @@
-kind: import
-
-sources:
-- kind: local
-  path: files/hello.txt
diff --git a/tests/format/junctions/config-target/subproject/subsubproject/files/hello.txt b/tests/format/junctions/config-target/subproject/subsubproject/files/hello.txt
deleted file mode 100644
index ce0136250..000000000
--- a/tests/format/junctions/config-target/subproject/subsubproject/files/hello.txt
+++ /dev/null
@@ -1 +0,0 @@
-hello
diff --git a/tests/format/junctions/config-target/subproject/subsubproject/project.conf b/tests/format/junctions/config-target/subproject/subsubproject/project.conf
deleted file mode 100644
index 162143c80..000000000
--- a/tests/format/junctions/config-target/subproject/subsubproject/project.conf
+++ /dev/null
@@ -1,4 +0,0 @@
-name: subsubproject
-min-version: 2.0
-
-element-path: elements