add missing test_repo package

Signed-off-by: Gregory Becker <becker33@llnl.gov>

lib/spack/spack/config.py

@@ -60,6 +60,7 @@
 import spack.schema.modules
 import spack.schema.packages
 import spack.schema.repos
+import spack.schema.toolchains
 import spack.schema.upstreams
 import spack.schema.view
 import spack.util.remote_file_cache as rfc_util
@@ -87,6 +88,7 @@
     "bootstrap": spack.schema.bootstrap.schema,
     "ci": spack.schema.ci.schema,
     "cdash": spack.schema.cdash.schema,
+    "toolchains": spack.schema.toolchains.schema,
 }
 
 # Same as above, but including keys for environments

lib/spack/spack/main.py

@@ -1090,12 +1090,13 @@ def _handle_solver_bug(
             stream=out,
         )
     if wrong_output:
-        msg = (
-            "internal solver error: the following specs were concretized, but do not satisfy the "
-            "input:\n    - "
-            + "\n    - ".join(str(s) for s, _ in wrong_output)
-            + "\n    Please report a bug at https://github.com/spack/spack/issues"
-        )
+        msg = "internal solver error: the following specs were concretized, but do not satisfy "
+        msg += "the input:\n"
+        for in_spec, out_spec in wrong_output:
+            msg += f"    - input: {in_spec}\n"
+            msg += f"      output: {out_spec.long_spec}\n"
+        msg += "\n    Please report a bug at https://github.com/spack/spack/issues"
+
         # try to write the input/output specs to a temporary directory for bug reports
         try:
             tmpdir = tempfile.mkdtemp(prefix="spack-asp-", dir=root)

lib/spack/spack/schema/toolchains.py

@@ -0,0 +1,23 @@
+# Copyright Spack Project Developers. See COPYRIGHT file for details.
+#
+# SPDX-License-Identifier: (Apache-2.0 OR MIT)
+
+"""Schema for repos.yaml configuration file.
+
+.. literalinclude:: _spack_root/lib/spack/spack/schema/toolchains.py
+   :lines: 14-
+"""
+from typing import Any, Dict
+
+#: Properties for inclusion in other schemas
+properties: Dict[str, Any] = {"toolchains": {"type": "object", "default": {}}}
+
+
+#: Full schema with metadata
+schema = {
+    "$schema": "http://json-schema.org/draft-07/schema#",
+    "title": "Spack toolchain configuration file schema",
+    "type": "object",
+    "additionalProperties": False,
+    "properties": properties,
+}

lib/spack/spack/solver/asp.py

@@ -572,7 +572,7 @@ def format_unsolved(unsolved_specs):
         for input_spec, candidate in unsolved_specs:
             msg += f"\n\tInput spec: {str(input_spec)}"
             if candidate:
-                msg += f"\n\tCandidate spec: {str(candidate)}"
+                msg += f"\n\tCandidate spec: {candidate.long_spec}"
             else:
                 msg += "\n\t(No candidate specs from solver)"
         return msg
@@ -1416,12 +1416,17 @@ class ConstraintOrigin(enum.Enum):
     result.
     """
 
+    CONDITIONAL_SPEC = 0
     DEPENDS_ON = 1
     REQUIRE = 2
 
     @staticmethod
     def _SUFFIXES() -> Dict["ConstraintOrigin", str]:
-        return {ConstraintOrigin.DEPENDS_ON: "_dep", ConstraintOrigin.REQUIRE: "_req"}
+        return {
+            ConstraintOrigin.CONDITIONAL_SPEC: "_cond",
+            ConstraintOrigin.DEPENDS_ON: "_dep",
+            ConstraintOrigin.REQUIRE: "_req",
+        }
 
     @staticmethod
     def append_type_suffix(pkg_id: str, kind: "ConstraintOrigin") -> str:
@@ -1877,6 +1882,73 @@ def _get_condition_id(
 
         return cond_id
 
+    def condition_clauses(
+        self,
+        required_spec: spack.spec.Spec,
+        imposed_spec: Optional[spack.spec.Spec] = None,
+        *,
+        required_name: Optional[str] = None,
+        imposed_name: Optional[str] = None,
+        msg: Optional[str] = None,
+        context: Optional[ConditionContext] = None,
+    ):
+        """Generate facts for a dependency or virtual provider condition.
+
+        Arguments:
+            required_spec: the constraints that triggers this condition
+            imposed_spec: the constraints that are imposed when this condition is triggered
+            required_name: name for ``required_spec``
+                (required if required_spec is anonymous, ignored if not)
+            imposed_name: name for ``imposed_spec``
+                (required if imposed_spec is anonymous, ignored if not)
+            msg: description of the condition
+            context: if provided, indicates how to modify the clause-sets for the required/imposed
+                specs based on the type of constraint they are generated for (e.g. `depends_on`)
+        Returns:
+            int: id of the condition created by this function
+        """
+        clauses = []
+        required_name = required_spec.name or required_name
+        if not required_name:
+            raise ValueError(f"Must provide a name for anonymous condition: '{required_spec}'")
+
+        if not context:
+            context = ConditionContext()
+            context.transform_imposed = remove_facts("node", "virtual_node")
+
+        if imposed_spec:
+            imposed_name = imposed_spec.name or imposed_name
+            if not imposed_name:
+                raise ValueError(f"Must provide a name for imposed constraint: '{imposed_spec}'")
+
+        with named_spec(required_spec, required_name), named_spec(imposed_spec, imposed_name):
+            # Check if we can emit the requirements before updating the condition ID counter.
+            # In this way, if a condition can't be emitted but the exception is handled in the
+            # caller, we won't emit partial facts.
+
+            condition_id = next(self._id_counter)
+            requirement_context = context.requirement_context()
+            trigger_id = self._get_condition_id(
+                required_spec, cache=self._trigger_cache, body=True, context=requirement_context
+            )
+            clauses.append(fn.pkg_fact(required_spec.name, fn.condition(condition_id)))
+            clauses.append(fn.condition_reason(condition_id, msg))
+            clauses.append(
+                fn.pkg_fact(required_spec.name, fn.condition_trigger(condition_id, trigger_id))
+            )
+            if not imposed_spec:
+                return clauses, condition_id
+
+            impose_context = context.impose_context()
+            effect_id = self._get_condition_id(
+                imposed_spec, cache=self._effect_cache, body=False, context=impose_context
+            )
+            clauses.append(
+                fn.pkg_fact(required_spec.name, fn.condition_effect(condition_id, effect_id))
+            )
+
+            return clauses, condition_id
+
     def condition(
         self,
         required_spec: spack.spec.Spec,
@@ -1902,46 +1974,18 @@ def condition(
         Returns:
             int: id of the condition created by this function
         """
-        required_name = required_spec.name or required_name
-        if not required_name:
-            raise ValueError(f"Must provide a name for anonymous condition: '{required_spec}'")
+        clauses, condition_id = self.condition_clauses(
+            required_spec=required_spec,
+            imposed_spec=imposed_spec,
+            required_name=required_name,
+            imposed_name=imposed_name,
+            msg=msg,
+            context=context,
+        )
+        for clause in clauses:
+            self.gen.fact(clause)
 
-        if not context:
-            context = ConditionContext()
-            context.transform_imposed = remove_facts("node", "virtual_node")
-
-        if imposed_spec:
-            imposed_name = imposed_spec.name or imposed_name
-            if not imposed_name:
-                raise ValueError(f"Must provide a name for imposed constraint: '{imposed_spec}'")
-
-        with named_spec(required_spec, required_name), named_spec(imposed_spec, imposed_name):
-            # Check if we can emit the requirements before updating the condition ID counter.
-            # In this way, if a condition can't be emitted but the exception is handled in the
-            # caller, we won't emit partial facts.
-
-            condition_id = next(self._id_counter)
-            requirement_context = context.requirement_context()
-            trigger_id = self._get_condition_id(
-                required_spec, cache=self._trigger_cache, body=True, context=requirement_context
-            )
-            self.gen.fact(fn.pkg_fact(required_spec.name, fn.condition(condition_id)))
-            self.gen.fact(fn.condition_reason(condition_id, msg))
-            self.gen.fact(
-                fn.pkg_fact(required_spec.name, fn.condition_trigger(condition_id, trigger_id))
-            )
-            if not imposed_spec:
-                return condition_id
-
-            impose_context = context.impose_context()
-            effect_id = self._get_condition_id(
-                imposed_spec, cache=self._effect_cache, body=False, context=impose_context
-            )
-            self.gen.fact(
-                fn.pkg_fact(required_spec.name, fn.condition_effect(condition_id, effect_id))
-            )
-
-            return condition_id
+        return condition_id
 
     def impose(self, condition_id, imposed_spec, node=True, body=False):
         imposed_constraints = self.spec_clauses(imposed_spec, body=body)
@@ -2212,6 +2256,10 @@ def emit_facts_from_requirement_rules(self, rules: List[RequirementRule]):
                         msg=f"{input_spec} is a requirement for package {pkg_name}",
                         context=context,
                     )
+
+                    # Conditions don't handle conditional dependencies directly
+                    # Those are handled separately here
+                    self.generate_conditional_dep_conditions(spec, member_id)
                 except Exception as e:
                     # Do not raise if the rule comes from the 'all' subsection, since usability
                     # would be impaired. If a rule does not apply for a specific package, just
@@ -2574,6 +2622,10 @@ def _spec_clauses(
         if transitive:
             # TODO: Eventually distinguish 2 deps on the same pkg (build and link)
             for dspec in spec.edges_to_dependencies():
+                # Ignore conditional dependencies, they are handled by caller
+                if dspec.when != spack.spec.Spec():
+                    continue
+
                 dep = dspec.spec
 
                 if spec.concrete:
@@ -3200,6 +3252,9 @@ def setup(
         self.gen.h1("Spec Constraints")
         self.literal_specs(specs)
 
+        self.trigger_rules()
+        self.effect_rules()
+
         self.gen.h1("Variant Values defined in specs")
         self.define_variant_values()
 
@@ -3333,11 +3388,49 @@ def literal_specs(self, specs):
             cache[imposed_spec_key] = (effect_id, requirements)
             self.gen.fact(fn.pkg_fact(spec.name, fn.condition_effect(condition_id, effect_id)))
 
+            # Create subcondition with any conditional dependencies
+            # self.spec_clauses does not do anything with conditional
+            # dependencies
+            self.generate_conditional_dep_conditions(spec, condition_id)
+
             if self.concretize_everything:
                 self.gen.fact(fn.solve_literal(trigger_id))
 
         self.effect_rules()
 
+    def generate_conditional_dep_conditions(self, spec, condition_id):
+        for dspec in spec.traverse_edges():
+            # Ignore unconditional deps
+            if dspec.when == spack.spec.Spec():
+                continue
+
+            # Cannot use "virtual_node" attr as key for condition
+            # because reused specs do not track virtual nodes.
+            # Instead, track whether the parent uses the virtual
+            def virtual_handler(input_spec, requirements):
+                ret = remove_facts("virtual_node")(input_spec, requirements)
+                for edge in input_spec.traverse_edges(root=False, cover="edges"):
+                    if spack.repo.PATH.is_virtual(edge.spec.name):
+                        ret.append(fn.attr("uses_virtual", edge.parent.name, edge.spec.name))
+                return ret
+
+            context = ConditionContext()
+            context.source = ConstraintOrigin.append_type_suffix(
+                dspec.parent.name, ConstraintOrigin.CONDITIONAL_SPEC
+            )
+            # Default is to remove node-like attrs, override here
+            context.transform_required = virtual_handler
+            context.transform_imposed = lambda x, y: y
+
+            subcondition_id = self.condition(
+                dspec.when,
+                dspec.spec,
+                required_name=dspec.parent.name,
+                context=context,
+                msg=f"Conditional dependency in literal ^[when={dspec.when}]{dspec.spec}",
+            )
+            self.gen.fact(fn.subcondition(subcondition_id, condition_id))
+
     def validate_and_define_versions_from_requirements(
         self, *, allow_deprecated: bool, require_checksum: bool
     ):
@@ -3785,6 +3878,7 @@ class SpecBuilder:
                 r"^package_hash$",
                 r"^root$",
                 r"^track_dependencies$",
+                r"^uses_virtual$",
                 r"^variant_default_value_from_cli$",
                 r"^virtual_node$",
                 r"^virtual_on_incoming_edges$",

lib/spack/spack/solver/concretize.lp

@@ -429,8 +429,23 @@ trigger_and_effect(Package, TriggerID, EffectID)
 
 % condition_holds(ID, node(ID, Package)) implies all imposed_constraints, unless do_not_impose(ID, node(ID, Package))
 % is derived. This allows imposed constraints to be canceled in special cases.
+
+% Effects of direct conditions hold if the trigger holds
 impose(EffectID, node(X, Package))
-  :- trigger_and_effect(Package, TriggerID, EffectID),
+  :- pkg_fact(Package, condition_effect(ConditionID, EffectID)),
+     not subcondition(ConditionID, _),
+     trigger_and_effect(Package, TriggerID, EffectID),
+     trigger_node(TriggerID, _, node(X, Package)),
+     trigger_condition_holds(TriggerID, node(X, Package)),
+     not do_not_impose(EffectID, node(X, Package)).
+
+% Effects of subconditions hold if the trigger holds and the
+% primary condition holds
+impose(EffectID, node(X, Package))
+  :- pkg_fact(Package, condition_effect(SubconditionId, EffectID)),
+     subcondition(SubconditionID, ConditionID),
+     condition_holds(ConditionID, node(X, Package)),
+     trigger_and_effect(Package, TriggerID, EffectID),
      trigger_node(TriggerID, _, node(X, Package)),
      trigger_condition_holds(TriggerID, node(X, Package)),
      not do_not_impose(EffectID, node(X, Package)).
@@ -645,6 +660,16 @@ virtual_condition_holds(node(Y, A2), Virtual)
      attr("virtual_on_edge", node(X, A1), node(Y, A2), Virtual),
      not build(node(X, A1)).
 
+% Simplified virtual information for conditionl requirements in
+% conditional dependencies
+% Most specs track virtuals on edges
+attr("uses_virtual", PackageNode, Virtual) :-
+  attr("virtual_on_edge", PackageNode, _, Virtual).
+
+% Reused specs don't track a real edge to build-only deps
+attr("uses_virtual", PackageNode, Virtual) :-
+  attr("virtual_on_build_edge", PackageNode, _, Virtual).
+
 % we cannot have additional variant values when we are working with concrete specs
 :- attr("node", node(ID, Package)),
    attr("hash", node(ID, Package), Hash),
@@ -660,6 +685,7 @@ virtual_condition_holds(node(Y, A2), Virtual)
    internal_error("imposed hash without imposing all flag values").
 
 #defined condition/2.
+#defined subcondition/2.
 #defined condition_requirement/3.
 #defined condition_requirement/4.
 #defined condition_requirement/5.

lib/spack/spack/spec.py

@@ -720,7 +720,7 @@ class DependencySpec:
         virtuals: virtual packages provided from child to parent node.
     """
 
-    __slots__ = "parent", "spec", "depflag", "virtuals", "direct"
+    __slots__ = "parent", "spec", "depflag", "virtuals", "direct", "when"
 
     def __init__(
         self,
@@ -730,12 +730,14 @@ def __init__(
         depflag: dt.DepFlag,
         virtuals: Tuple[str, ...],
         direct: bool = False,
+        when: Optional["Spec"] = None,
     ):
         self.parent = parent
         self.spec = spec
         self.depflag = depflag
         self.virtuals = tuple(sorted(set(virtuals)))
         self.direct = direct
+        self.when = when or Spec()
 
     def update_deptypes(self, depflag: dt.DepFlag) -> bool:
         """Update the current dependency types"""
@@ -766,6 +768,7 @@ def copy(self) -> "DependencySpec":
             depflag=self.depflag,
             virtuals=self.virtuals,
             direct=self.direct,
+            when=self.when,
         )
 
     def _cmp_iter(self):
@@ -777,10 +780,13 @@ def _cmp_iter(self):
     def __str__(self) -> str:
         parent = self.parent.name if self.parent else None
         child = self.spec.name if self.spec else None
-        return f"{parent} {self.depflag}[virtuals={','.join(self.virtuals)}] --> {child}"
+        virtuals_string = f"virtuals={','.join(self.virtuals)}" if self.virtuals else ""
+        when_string = f"when='{self.when}'" if self.when != Spec() else ""
+        edge_attrs = filter(lambda x: bool(x), (virtuals_string, when_string))
+        return f"{parent} {self.depflag}[{' '.join(edge_attrs)}] --> {child}"
 
     def flip(self) -> "DependencySpec":
-        """Flip the dependency, and drop virtual information"""
+        """Flip the dependency, and drop virtual and conditional information"""
         return DependencySpec(
             parent=self.spec, spec=self.parent, depflag=self.depflag, virtuals=()
         )
@@ -1021,6 +1027,7 @@ def select(
         child: Optional[str] = None,
         depflag: dt.DepFlag = dt.ALL,
         virtuals: Optional[Union[str, Sequence[str]]] = None,
+        when: Optional["Spec"] = None,
     ) -> List[DependencySpec]:
         """Selects a list of edges and returns them.
 
@@ -1040,6 +1047,7 @@ def select(
             child: name of the child package
             depflag: allowed dependency types in flag form
             virtuals: list of virtuals or specific virtual on the edge
+            when: condition on conditional dependency, or Spec() for unconditional dependency only
         """
         if not depflag:
             return []
@@ -1065,6 +1073,9 @@ def select(
             else:
                 selected = (dep for dep in selected if any(v in dep.virtuals for v in virtuals))
 
+        if when is not None:
+            selected = (dep for dep in selected if dep.when == when)
+
         return list(selected)
 
     def clear(self):
@@ -1612,6 +1623,7 @@ def edges_to_dependencies(
         depflag: dt.DepFlag = dt.ALL,
         *,
         virtuals: Optional[Union[str, Sequence[str]]] = None,
+        when: Optional["Spec"] = None,
     ) -> List[DependencySpec]:
         """Returns a list of edges connecting this node in the DAG to children.
 
@@ -1619,9 +1631,13 @@ def edges_to_dependencies(
             name: filter dependencies by package name
             depflag: allowed dependency types
             virtuals: allowed virtuals
+            when: condition on conditional dependencies (or Spec() for unconditional)
         """
         return [
-            d for d in self._dependencies.select(child=name, depflag=depflag, virtuals=virtuals)
+            d
+            for d in self._dependencies.select(
+                child=name, depflag=depflag, virtuals=virtuals, when=when
+            )
         ]
 
     @property
@@ -1633,20 +1649,26 @@ def edge_attributes(self) -> str:
 
         union = DependencySpec(parent=Spec(), spec=self, depflag=0, virtuals=())
         all_direct_edges = all(x.direct for x in edges)
+        dep_conditions = set()
 
         for edge in edges:
             union.update_deptypes(edge.depflag)
             union.update_virtuals(edge.virtuals)
+            dep_conditions.add(edge.when)
 
         deptypes_str = ""
         if not all_direct_edges and union.depflag:
             deptypes_str = f"deptypes={','.join(dt.flag_to_tuple(union.depflag))}"
 
         virtuals_str = f"virtuals={','.join(union.virtuals)}" if union.virtuals else ""
-        if not deptypes_str and not virtuals_str:
-            return ""
-        result = f"{deptypes_str} {virtuals_str}".strip()
-        return f"[{result}]"
+
+        conditions = [str(c) for c in dep_conditions if c != Spec()]
+        when_str = f"when='{','.join(conditions)}'" if conditions else ""
+
+        result = " ".join(filter(lambda x: bool(x), (when_str, deptypes_str, virtuals_str)))
+        if result:
+            result = f"[{result}]"
+        return result
 
     def dependencies(
         self,
@@ -1654,6 +1676,7 @@ def dependencies(
         deptype: Union[dt.DepTypes, dt.DepFlag] = dt.ALL,
         *,
         virtuals: Optional[Union[str, Sequence[str]]] = None,
+        when: Optional["Spec"] = None,
     ) -> List["Spec"]:
         """Returns a list of direct dependencies (nodes in the DAG)
 
@@ -1661,11 +1684,15 @@ def dependencies(
             name: filter dependencies by package name
             deptype: allowed dependency types
             virtuals: allowed virtuals
+            when: condition on conditional dependency or Spec() for unconditional
         """
         if not isinstance(deptype, dt.DepFlag):
             deptype = dt.canonicalize(deptype)
         return [
-            d.spec for d in self.edges_to_dependencies(name, depflag=deptype, virtuals=virtuals)
+            d.spec
+            for d in self.edges_to_dependencies(
+                name, depflag=deptype, virtuals=virtuals, when=when
+            )
         ]
 
     def dependents(
@@ -1752,7 +1779,13 @@ def _set_architecture(self, **kwargs):
                     setattr(self.architecture, new_attr, new_value)
 
     def _add_dependency(
-        self, spec: "Spec", *, depflag: dt.DepFlag, virtuals: Tuple[str, ...], direct: bool = False
+        self,
+        spec: "Spec",
+        *,
+        depflag: dt.DepFlag,
+        virtuals: Tuple[str, ...],
+        direct: bool = False,
+        when: Optional["Spec"] = None,
     ):
         """Called by the parser to add another spec as a dependency.
 
@@ -1760,23 +1793,33 @@ def _add_dependency(
             depflag: dependency type for this edge
             virtuals: virtuals on this edge
             direct: if True denotes a direct dependency (associated with the % sigil)
+            when: if non-None, condition under which dependency holds
         """
+        if when is None:
+            when = Spec()
+
         if spec.name not in self._dependencies or not spec.name:
-            self.add_dependency_edge(spec, depflag=depflag, virtuals=virtuals, direct=direct)
+            self.add_dependency_edge(
+                spec, depflag=depflag, virtuals=virtuals, direct=direct, when=when
+            )
             return
 
         # Keep the intersection of constraints when a dependency is added multiple times with
         # the same deptype. Add a new dependency if it is added with a compatible deptype
-        # (for example, a build-only dependency is compatible with a link-only dependenyc).
+        # (for example, a build-only dependency is compatible with a link-only dependency).
         # The only restrictions, currently, are that we cannot add edges with overlapping
         # dependency types and we cannot add multiple edges that have link/run dependency types.
         # See ``spack.deptypes.compatible``.
         orig = self._dependencies[spec.name]
         try:
-            dspec = next(dspec for dspec in orig if depflag == dspec.depflag)
+            dspec = next(
+                dspec for dspec in orig if depflag == dspec.depflag and when == dspec.when
+            )
         except StopIteration:
             # Error if we have overlapping or incompatible deptypes
-            if any(not dt.compatible(dspec.depflag, depflag) for dspec in orig):
+            if any(not dt.compatible(dspec.depflag, depflag) for dspec in orig) and all(
+                dspec.when == when for dspec in orig
+            ):
                 edge_attrs = f"deptypes={dt.flag_to_chars(depflag).strip()}"
                 required_dep_str = f"^[{edge_attrs}] {str(spec)}"
 
@@ -1785,7 +1828,9 @@ def _add_dependency(
                     f"\t'{str(self)}' cannot depend on '{required_dep_str}'"
                 )
 
-            self.add_dependency_edge(spec, depflag=depflag, virtuals=virtuals, direct=direct)
+            self.add_dependency_edge(
+                spec, depflag=depflag, virtuals=virtuals, direct=direct, when=when
+            )
             return
 
         try:
@@ -1803,6 +1848,7 @@ def add_dependency_edge(
         depflag: dt.DepFlag,
         virtuals: Tuple[str, ...],
         direct: bool = False,
+        when: Optional["Spec"] = None,
     ):
         """Add a dependency edge to this spec.
 
@@ -1811,13 +1857,20 @@ def add_dependency_edge(
             deptypes: dependency types for this edge
             virtuals: virtuals provided by this edge
             direct: if True denotes a direct dependency
+            when: if non-None, condition under which dependency holds
         """
+        if when is None:
+            when = Spec()
+
         # Check if we need to update edges that are already present
         selected = self._dependencies.select(child=dependency_spec.name)
         for edge in selected:
             has_errors, details = False, []
             msg = f"cannot update the edge from {edge.parent.name} to {edge.spec.name}"
 
+            if edge.when != when:
+                continue
+
             # If the dependency is to an existing spec, we can update dependency
             # types. If it is to a new object, check deptype compatibility.
             if id(edge.spec) != id(dependency_spec) and not dt.compatible(edge.depflag, depflag):
@@ -1841,7 +1894,7 @@ def add_dependency_edge(
                 raise spack.error.SpecError(msg, "\n".join(details))
 
         for edge in selected:
-            if id(dependency_spec) == id(edge.spec):
+            if id(dependency_spec) == id(edge.spec) and edge.when == when:
                 # If we are here, it means the edge object was previously added to
                 # both the parent and the child. When we update this object they'll
                 # both see the deptype modification.
@@ -1850,7 +1903,7 @@ def add_dependency_edge(
                 return
 
         edge = DependencySpec(
-            self, dependency_spec, depflag=depflag, virtuals=virtuals, direct=direct
+            self, dependency_spec, depflag=depflag, virtuals=virtuals, direct=direct, when=when
         )
         self._dependencies.add(edge)
         dependency_spec._dependents.add(edge)
@@ -2085,14 +2138,14 @@ def long_spec(self):
             new_name = spack.aliases.BUILTIN_TO_LEGACY_COMPILER.get(current_name, current_name)
             # note: depflag not allowed, currently, on "direct" edges
             edge_attributes = ""
-            if item.virtuals:
+            if item.virtuals or item.when != Spec():
                 edge_attributes = item.spec.format("{edge_attributes}") + " "
 
             parts.append(f"%{edge_attributes}{item.spec.format()}".replace(current_name, new_name))
         for item in sorted(transitive, key=lambda x: x.spec.name):
             # Recurse to attach build deps in order
             edge_attributes = ""
-            if item.virtuals or item.depflag:
+            if item.virtuals or item.depflag or item.when != Spec():
                 edge_attributes = item.spec.format("{edge_attributes}") + " "
             parts.append(f"^{edge_attributes}{str(item.spec)}")
         return " ".join(parts).strip()
@@ -3126,41 +3179,22 @@ def _constrain_dependencies(self, other: "Spec") -> bool:
         if any(not d.name for d in other.traverse(root=False)):
             raise UnconstrainableDependencySpecError(other)
 
-        # Handle common first-order constraints directly
-        # Note: This doesn't handle constraining transitive dependencies with the same name
-        # as direct dependencies
-        changed = False
-        common_dependencies = {x.name for x in self.dependencies()}
-        common_dependencies &= {x.name for x in other.dependencies()}
-        for name in common_dependencies:
-            changed |= self[name].constrain(other[name], deps=True)
-            if name in self._dependencies:
-                # WARNING: This function is an implementation detail of the
-                # WARNING: original concretizer. Since with that greedy
-                # WARNING: algorithm we don't allow multiple nodes from
-                # WARNING: the same package in a DAG, here we hard-code
-                # WARNING: using index 0 i.e. we assume that we have only
-                # WARNING: one edge from package "name"
-                edges_from_name = self._dependencies[name]
-                changed |= edges_from_name[0].update_deptypes(other._dependencies[name][0].depflag)
-                changed |= edges_from_name[0].update_virtuals(
-                    other._dependencies[name][0].virtuals
+        reference_spec = self.copy(deps=True)
+        for edge in other.edges_to_dependencies():
+            existing = self.edges_to_dependencies(edge.spec.name, when=edge.when)
+            if existing:
+                existing[0].spec.constrain(edge.spec)
+                existing[0].update_deptypes(edge.depflag)
+                existing[0].update_virtuals(edge.virtuals)
+            else:
+                self.add_dependency_edge(
+                    edge.spec,
+                    depflag=edge.depflag,
+                    virtuals=edge.virtuals,
+                    direct=edge.direct,
+                    when=edge.when,
                 )
-
-        # Update with additional constraints from other spec
-        # operate on direct dependencies only, because a concrete dep
-        # represented by hash may have structure that needs to be preserved
-        for name in other.direct_dep_difference(self):
-            dep_spec_copy = other._get_dependency(name)
-            self._add_dependency(
-                dep_spec_copy.spec.copy(),
-                depflag=dep_spec_copy.depflag,
-                virtuals=dep_spec_copy.virtuals,
-                direct=dep_spec_copy.direct,
-            )
-            changed = True
-
-        return changed
+        return self != reference_spec
 
     def common_dependencies(self, other):
         """Return names of dependencies that self and other have in common."""
@@ -3397,10 +3431,6 @@ def satisfies(self, other: Union[str, "Spec"], deps: bool = True) -> bool:
         if not other._dependencies:
             return True
 
-        # If we have no dependencies, we can't satisfy any constraints.
-        if not self._dependencies and self.original_spec_format() >= 5 and not self.external:
-            return False
-
         # If we arrived here, the lhs root node satisfies the rhs root node. Now we need to check
         # all the edges that have an abstract parent, and verify that they match some edge in the
         # lhs.
@@ -3411,6 +3441,11 @@ def satisfies(self, other: Union[str, "Spec"], deps: bool = True) -> bool:
         lhs_edges: Dict[str, Set[DependencySpec]] = collections.defaultdict(set)
         mock_nodes_from_old_specfiles = set()
         for rhs_edge in other.traverse_edges(root=False, cover="edges"):
+            # Skip checking any conditional edge that is not satisfied
+            if rhs_edge.when != Spec() and not self.satisfies(rhs_edge.when):
+                # TODO: this misses the case that the rhs statically satisfies its own condition
+                continue
+
             # If we are checking for ^mpi we need to verify if there is any edge
             if spack.repo.PATH.is_virtual(rhs_edge.spec.name):
                 rhs_edge.update_virtuals(virtuals=(rhs_edge.spec.name,))
@@ -3468,6 +3503,7 @@ def satisfies(self, other: Union[str, "Spec"], deps: bool = True) -> bool:
                 for lhs_edge in self.traverse_edges(
                     root=False, cover="edges", deptype=("link", "run")
                 ):
+                    # TODO: do we need to avoid conditional edges here
                     lhs_edges[lhs_edge.spec.name].add(lhs_edge)
                     for virtual_name in lhs_edge.virtuals:
                         lhs_edges[virtual_name].add(lhs_edge)
@@ -3484,6 +3520,7 @@ def satisfies(self, other: Union[str, "Spec"], deps: bool = True) -> bool:
                 return False
 
             for virtual in rhs_edge.virtuals:
+                # TODO: consider how this could apply to conditional edges
                 has_virtual = any(
                     virtual in edge.virtuals for edge in lhs_edges[current_dependency_name]
                 )
@@ -3491,11 +3528,22 @@ def satisfies(self, other: Union[str, "Spec"], deps: bool = True) -> bool:
                     return False
 
         # Edges have been checked above already, hence deps=False
-        lhs_nodes = [x for x in self.traverse(root=False)] + sorted(mock_nodes_from_old_specfiles)
-        return all(
-            any(lhs.satisfies(rhs, deps=False) for lhs in lhs_nodes)
-            for rhs in other.traverse(root=False)
-        )
+        lhs_nodes = list(self.traverse(root=False)) + sorted(mock_nodes_from_old_specfiles)
+        for rhs in other.traverse(root=False):
+            # Possible lhs nodes to match this rhs node
+            lhss = [lhs for lhs in lhs_nodes if lhs.satisfies(rhs, deps=False)]
+
+            # Check whether the node needs matching (not a conditional that isn't satisfied)
+            if not any(self.satisfies(e.when) for e in rhs.edges_from_dependents()):
+                # TODO: This technically misses the case that the edge is analogous
+                # to an edge lower in the DAG, and could give a false negative in that case
+                continue
+
+            # If there is no matching lhs for this rhs node
+            if not lhss:
+                return False
+
+        return True
 
     @property  # type: ignore[misc] # decorated prop not supported in mypy
     def patches(self):
@@ -3629,6 +3677,7 @@ def spid(spec):
                 depflag=edge.depflag,
                 virtuals=edge.virtuals,
                 direct=edge.direct,
+                when=edge.when,
             )
 
     def copy(self, deps: Union[bool, dt.DepTypes, dt.DepFlag] = True, **kwargs):

lib/spack/spack/spec_parser.py

@@ -56,16 +56,18 @@
 specs to avoid ambiguity.  Both are provided because ~ can cause shell
 expansion when it is the first character in an id typed on the command line.
 """
+import itertools
 import json
 import pathlib
 import re
 import sys
 import traceback
 import warnings
-from typing import Iterator, List, Optional, Tuple, Union
+from typing import Iterable, Iterator, List, Optional, Tuple, Union
 
 from llnl.util.tty import color
 
+import spack.config
 import spack.deptypes
 import spack.error
 import spack.paths
@@ -162,6 +164,15 @@ def tokenize(text: str) -> Iterator[Token]:
         yield token
 
 
+def parseable_tokens(text: str) -> Iterator[Token]:
+    """Return non-whitespace tokens from the text passed as input
+
+    Raises:
+        SpecTokenizationError: when unexpected characters are found in the text
+    """
+    return filter(lambda x: x.kind != SpecTokens.WS, tokenize(text))
+
+
 class TokenContext:
     """Token context passed around by parsers"""
 
@@ -189,6 +200,16 @@ def accept(self, kind: SpecTokens):
     def expect(self, *kinds: SpecTokens):
         return self.next_token and self.next_token.kind in kinds
 
+    def push(self, token_stream: Iterator[Token]):
+        # New tokens need to go before next_token, which comes before the rest of the stream
+        next_token_iterator: Iterable[Token] = (
+            iter((self.next_token,)) if self.next_token else iter(())
+        )
+        self.token_stream = itertools.chain(token_stream, next_token_iterator, self.token_stream)
+        self.current_token = None
+        self.next_token = None
+        self.advance()
+
 
 class SpecTokenizationError(spack.error.SpecSyntaxError):
     """Syntax error in a spec string"""
@@ -238,11 +259,13 @@ class SpecParser:
 
     def __init__(self, literal_str: str):
         self.literal_str = literal_str
-        self.ctx = TokenContext(filter(lambda x: x.kind != SpecTokens.WS, tokenize(literal_str)))
+        self.ctx = TokenContext(parseable_tokens(literal_str))
 
     def tokens(self) -> List[Token]:
         """Return the entire list of token from the initial text. White spaces are
         filtered out.
+
+        Note: This list will not show tokens pushed when parsing an alias
         """
         return list(filter(lambda x: x.kind != SpecTokens.WS, tokenize(self.literal_str)))
 
@@ -268,6 +291,9 @@ def add_dependency(dep, **edge_properties):
             except spack.error.SpecError as e:
                 raise SpecParsingError(str(e), self.ctx.current_token, self.literal_str) from e
 
+        # Get toolchain information outside of loop
+        toolchains = spack.config.CONFIG.get("toolchains", {})
+
         initial_spec = initial_spec or spack.spec.Spec()
         root_spec, parser_warnings = SpecNodeParser(self.ctx, self.literal_str).parse(initial_spec)
         current_spec = root_spec
@@ -297,6 +323,15 @@ def add_dependency(dep, **edge_properties):
                 add_dependency(dependency, **edge_properties)
 
             elif self.ctx.accept(SpecTokens.DEPENDENCY):
+                # String replacement for toolchains
+                # Look ahead to match upcoming value to list of toolchains
+                if self.ctx.next_token.value in toolchains:
+                    assert self.ctx.accept(SpecTokens.UNQUALIFIED_PACKAGE_NAME)
+                    # accepting the token advances it to be the current token
+                    # Push associated tokens back to the TokenContext
+                    self.ctx.push(parseable_tokens(toolchains[self.ctx.current_token.value]))
+                    continue
+
                 is_direct = self.ctx.current_token.value[0] == "%"
                 dependency, warnings = self._parse_node(root_spec)
                 edge_properties = {}
@@ -511,10 +546,10 @@ def parse(self):
                     name = name[:-1]
                 value = value.strip("'\" ").split(",")
                 attributes[name] = value
-                if name not in ("deptypes", "virtuals"):
+                if name not in ("deptypes", "virtuals", "when"):
                     msg = (
                         "the only edge attributes that are currently accepted "
-                        'are "deptypes" and "virtuals"'
+                        'are "deptypes", "virtuals", and "when"'
                     )
                     raise SpecParsingError(msg, self.ctx.current_token, self.literal_str)
             # TODO: Add code to accept bool variants here as soon as use variants are implemented
@@ -528,6 +563,11 @@ def parse(self):
         if "deptypes" in attributes:
             deptype_string = attributes.pop("deptypes")
             attributes["depflag"] = spack.deptypes.canonicalize(deptype_string)
+
+        # Turn "when" into a spec
+        if "when" in attributes:
+            attributes["when"] = spack.spec.Spec(attributes["when"][0])
+
         return attributes
 
 
@@ -573,8 +613,9 @@ class SpecParsingError(spack.error.SpecSyntaxError):
 
     def __init__(self, message, token, text):
         message += f"\n{text}"
-        underline = f"\n{' '*token.start}{'^'*(token.end - token.start)}"
-        message += color.colorize(f"@*r{{{underline}}}")
+        if token:
+            underline = f"\n{' '*token.start}{'^'*(token.end - token.start)}"
+            message += color.colorize(f"@*r{{{underline}}}")
         super().__init__(message)
 
 

lib/spack/spack/test/concretization/conditional_dependencies.py

@@ -0,0 +1,67 @@
+# Copyright Spack Project Developers. See COPYRIGHT file for details.
+#
+# SPDX-License-Identifier: (Apache-2.0 OR MIT)
+import pytest
+
+import spack.concretize
+import spack.config
+import spack.spec
+
+
+@pytest.mark.parametrize("holds,mpi", [(True, "zmpi"), (True, "mpich"), (False, "mpich")])
+def test_conditional_deps(holds, mpi, config, mock_packages):
+    sigil = "+" if holds else "~"
+    request = f"hdf5{sigil}mpi ^[when='^mpi' virtuals=mpi]{mpi}"
+    concrete = spack.concretize.concretize_one(request)
+
+    assert (mpi in concrete) == holds
+    assert ("mpi" in concrete) == holds
+
+
+@pytest.mark.parametrize("c", [True, False])
+@pytest.mark.parametrize("cxx", [True, False])
+@pytest.mark.parametrize("fortran", [True, False])
+def test_conditional_compilers(c, cxx, fortran, mutable_config, mock_packages):
+    # Configure two gcc compilers that could be concretized to
+    # We will confirm concretization matches the less preferred one
+    extra_attributes_block = {
+        "compilers": {"c": "/path/to/gcc", "cxx": "/path/to/g++", "fortran": "/path/to/fortran"}
+    }
+    spack.config.CONFIG.set(
+        "packages:gcc:externals::",
+        [
+            {
+                "spec": "gcc@12.3.1 languages=c,c++,fortran",
+                "prefix": "/path",
+                "extra_attributes": extra_attributes_block,
+            },
+            {
+                "spec": "gcc@10.3.1 languages=c,c++,fortran",
+                "prefix": "/path",
+                "extra_attributes": extra_attributes_block,
+            },
+        ],
+    )
+
+    # Abstract spec parametrized to depend/not on c/cxx/fortran
+    # and with conditional dependencies for each on the less preferred gcc
+    abstract = spack.spec.Spec("conditional-languages")
+    abstract.constrain(f"c={c}")
+    abstract.constrain(f"cxx={cxx}")
+    abstract.constrain(f"fortran={fortran}")
+
+    preferred_gcc = spack.concretize.concretize_one(abstract)
+    abstract.constrain(
+        "^[when='%c' virtuals=c]gcc@10.3.1 "
+        "^[when='%cxx' virtuals=cxx]gcc@10.3.1 "
+        "^[when='%fortran' virtuals=fortran]gcc@10.3.1"
+    )
+    concrete = spack.concretize.concretize_one(abstract)
+
+    # We should get the dependency we specified for each language we enabled
+    assert concrete.satisfies("%[virtuals=c]gcc@10.3.1") == c
+    assert concrete.satisfies("%[virtuals=cxx]gcc@10.3.1") == cxx
+    assert concrete.satisfies("%[virtuals=fortran]gcc@10.3.1") == fortran
+
+    # The only time the two concrete specs are the same is if we don't use gcc at all
+    assert (concrete == preferred_gcc) == (not any((c, cxx, fortran)))

lib/spack/spack/test/concretization/errors.py

@@ -81,8 +81,10 @@ def test_internal_error_handling_formatting(tmp_path):
     assert "the following specs were not solved:\n    - baz+z\n" in output
     assert (
         "the following specs were concretized, but do not satisfy the input:\n"
-        "    - foo+x\n"
-        "    - bar+y\n"
+        "    - input: foo+x\n"
+        "      output: foo@=1.0~x\n"
+        "    - input: bar+y\n"
+        "      output: x@=1.0~y"
     ) in output
 
     files = {f.name: str(f) for f in tmp_path.glob("spack-asp-*/*.json")}

lib/spack/spack/test/concretization/requirements.py

@@ -12,6 +12,7 @@
 import spack.paths
 import spack.repo
 import spack.solver.asp
+import spack.spec
 import spack.store
 import spack.util.spack_yaml as syaml
 import spack.version
@@ -1301,3 +1302,52 @@ def test_requirements_on_compilers_and_reuse(
     assert is_pkgb_reused == expected_reuse
     for c in expected_contraints:
         assert pkga.satisfies(c)
+
+
+@pytest.mark.parametrize(
+    "abstract,req_is_noop",
+    [
+        ("hdf5+mpi", False),
+        ("hdf5~mpi", True),
+        ("conditional-languages+c", False),
+        ("conditional-languages+cxx", False),
+        ("conditional-languages+fortran", False),
+        ("conditional-languages~c~cxx~fortran", True),
+    ],
+)
+def test_requirements_conditional_deps(abstract, req_is_noop, mutable_config, mock_packages):
+    required_spec = (
+        "%[when='^c' virtuals=c]gcc@10.3.1 "
+        "%[when='^cxx' virtuals=cxx]gcc@10.3.1 "
+        "%[when='^fortran' virtuals=fortran]gcc@10.3.1 "
+        "^[when='^mpi' virtuals=mpi]zmpi"
+    )
+    abstract = spack.spec.Spec(abstract)
+
+    # Configure two gcc compilers that could be concretized to
+    # We will confirm concretization matches the less preferred one
+    extra_attributes_block = {
+        "compilers": {"c": "/path/to/gcc", "cxx": "/path/to/g++", "fortran": "/path/to/fortran"}
+    }
+    spack.config.CONFIG.set(
+        "packages:gcc:externals::",
+        [
+            {
+                "spec": "gcc@12.3.1 languages=c,c++,fortran",
+                "prefix": "/path",
+                "extra_attributes": extra_attributes_block,
+            },
+            {
+                "spec": "gcc@10.3.1 languages=c,c++,fortran",
+                "prefix": "/path",
+                "extra_attributes": extra_attributes_block,
+            },
+        ],
+    )
+
+    no_requirements = spack.concretize.concretize_one(abstract)
+    spack.config.CONFIG.set(f"packages:{abstract.name}", {"require": required_spec})
+    requirements = spack.concretize.concretize_one(abstract)
+
+    assert requirements.satisfies(required_spec)
+    assert (requirements == no_requirements) == req_is_noop  # show the reqs change concretization

lib/spack/spack/test/conftest.py

@@ -2054,7 +2054,7 @@ def shell_as(shell):
 @pytest.fixture()
 def nullify_globals(request, monkeypatch):
     ensure_configuration_fixture_run_before(request)
-    monkeypatch.setattr(spack.config, "CONFIG", None)
+    monkeypatch.setattr(spack.config, "CONFIG", {})  # So basic get operations do not throw
     monkeypatch.setattr(spack.caches, "MISC_CACHE", None)
     monkeypatch.setattr(spack.caches, "FETCH_CACHE", None)
     monkeypatch.setattr(spack.repo, "PATH", None)

lib/spack/spack/test/spec_semantics.py

@@ -327,6 +327,26 @@ class TestSpecSemantics:
                     "ba5e334fe247335f3a116decfb5284100791dc302b5571ff5e664d8f9a6806c2"
                 ),
             ),
+            (
+                "libelf",
+                "%[when='^c' virtuals=c]gcc ^[when='+mpi' virtuals=mpi]mpich",
+                "libelf %[when='^c' virtuals=c]gcc ^[when='+mpi' virtuals=mpi]mpich",
+            ),
+            (
+                "libelf %[when='^c' virtuals=c]gcc",
+                "%[when='^c' virtuals=c]gcc@10.3.1",
+                "libelf%[when='^c' virtuals=c]gcc@10.3.1",
+            ),
+            (
+                "libelf %[when='^c' virtuals=c]gcc",
+                "%[when='^c' virtuals=c]gcc@10.3.1 ^[when='+mpi'] mpich",
+                "libelf%[when='^c' virtuals=c]gcc@10.3.1 ^[when='+mpi']mpich",
+            ),
+            (
+                "libelf %[when='^c' virtuals=c]gcc",
+                "%[when='^cxx' virtuals=cxx]gcc@10.3.1",
+                "libelf%[when='^c' virtuals=c]gcc %[when='^cxx' virtuals=cxx]gcc@10.3.1",
+            ),
         ],
     )
     def test_abstract_specs_can_constrain_each_other(self, lhs, rhs, expected):
@@ -573,6 +593,14 @@ def test_abstract_specs_with_propagation(self, lhs, rhs, expected, constrained):
         c.constrain(lhs)
         assert c == constrained
 
+    def test_satisfies_conditional_dep(self):
+        concrete = spack.concretize.concretize_one("mpileaks^mpich")
+        assert concrete.satisfies("^[when='^mpi' virtuals=mpi]mpich")
+        assert concrete.satisfies("^[when='^notapackage']zmpi")
+        assert not concrete.satisfies("^[virtuals=blas]mpich")
+        assert not concrete.satisfies("^[when='^mpi' virtuals=blas]mpich")
+        assert not concrete.satisfies("^[when='^mpi']zmpi")
+
     def test_satisfies_single_valued_variant(self):
         """Tests that the case reported in
         https://github.com/spack/spack/pull/2386#issuecomment-282147639

lib/spack/spack/test/spec_syntax.py

@@ -11,6 +11,7 @@
 import spack.binary_distribution
 import spack.cmd
 import spack.concretize
+import spack.config
 import spack.platforms.test
 import spack.repo
 import spack.solver.asp
@@ -737,6 +738,19 @@ def _specfile_for(spec_str, filename):
             ],
             "mvapich %gcc languages:='c,c++' arch=None-None-x86_64",
         ),
+        # Test conditional dependencies
+        (
+            "foo ^[when='%c' virtuals=c]gcc",
+            [
+                Token(SpecTokens.UNQUALIFIED_PACKAGE_NAME, "foo"),
+                Token(SpecTokens.START_EDGE_PROPERTIES, "^["),
+                Token(SpecTokens.KEY_VALUE_PAIR, "when='%c'"),
+                Token(SpecTokens.KEY_VALUE_PAIR, "virtuals=c"),
+                Token(SpecTokens.END_EDGE_PROPERTIES, "]"),
+                Token(SpecTokens.UNQUALIFIED_PACKAGE_NAME, "gcc"),
+            ],
+            "foo ^[when='%c' virtuals=c] gcc",
+        ),
     ],
 )
 def test_parse_single_spec(spec_str, tokens, expected_roundtrip, mock_git_test_package):
@@ -882,6 +896,39 @@ def test_cli_spec_roundtrip(args, expected):
     assert expected == output_string
 
 
+@pytest.mark.parametrize(
+    "spec_str,toolchain,expected_roundtrip",
+    [
+        (
+            "foo%my_toolchain",
+            {"my_toolchain": "%[when='%c' virtuals=c]gcc"},
+            ["foo %[when='%c' virtuals=c] gcc"],
+        ),
+        (
+            "foo%my_toolchain2",
+            {"my_toolchain2": "%[when='%c' virtuals=c]gcc ^[when='+mpi' virtuals=mpi]mpich"},
+            ["foo %[when='%c' virtuals=c] gcc ^[when='+mpi' virtuals=mpi] mpich"],
+        ),
+        (
+            "foo%my_toolchain bar%my_toolchain2",
+            {
+                "my_toolchain": "%[when='%c' virtuals=c]gcc",
+                "my_toolchain2": "%[when='%c' virtuals=c]gcc ^[when='+mpi' virtuals=mpi]mpich",
+            },
+            [
+                "foo %[when='%c' virtuals=c] gcc",
+                "bar %[when='%c' virtuals=c] gcc ^[when='+mpi' virtuals=mpi] mpich",
+            ],
+        ),
+    ],
+)
+def test_parse_toolchain(spec_str, toolchain, expected_roundtrip, mutable_config):
+    spack.config.CONFIG.set("toolchains", toolchain)
+    parser = SpecParser(spec_str)
+    for expected in expected_roundtrip:
+        assert expected == str(parser.next_spec())
+
+
 @pytest.mark.parametrize(
     "text,expected_in_error",
     [

share/spack/spack-completion.fish

@@ -1211,19 +1211,19 @@ complete -c spack -n '__fish_spack_using_command config' -l scope -r -d 'configu
 
 # spack config get
 set -g __fish_spack_optspecs_spack_config_get h/help
-complete -c spack -n '__fish_spack_using_command_pos 0 config get' -f -a 'bootstrap cdash ci compilers concretizer config definitions develop env_vars include mirrors modules packages repos upstreams view'
+complete -c spack -n '__fish_spack_using_command_pos 0 config get' -f -a 'bootstrap cdash ci compilers concretizer config definitions develop env_vars include mirrors modules packages repos toolchains upstreams view'
 complete -c spack -n '__fish_spack_using_command config get' -s h -l help -f -a help
 complete -c spack -n '__fish_spack_using_command config get' -s h -l help -d 'show this help message and exit'
 
 # spack config blame
 set -g __fish_spack_optspecs_spack_config_blame h/help
-complete -c spack -n '__fish_spack_using_command_pos 0 config blame' -f -a 'bootstrap cdash ci compilers concretizer config definitions develop env_vars include mirrors modules packages repos upstreams view'
+complete -c spack -n '__fish_spack_using_command_pos 0 config blame' -f -a 'bootstrap cdash ci compilers concretizer config definitions develop env_vars include mirrors modules packages repos toolchains upstreams view'
 complete -c spack -n '__fish_spack_using_command config blame' -s h -l help -f -a help
 complete -c spack -n '__fish_spack_using_command config blame' -s h -l help -d 'show this help message and exit'
 
 # spack config edit
 set -g __fish_spack_optspecs_spack_config_edit h/help print-file
-complete -c spack -n '__fish_spack_using_command_pos 0 config edit' -f -a 'bootstrap cdash ci compilers concretizer config definitions develop env_vars include mirrors modules packages repos upstreams view'
+complete -c spack -n '__fish_spack_using_command_pos 0 config edit' -f -a 'bootstrap cdash ci compilers concretizer config definitions develop env_vars include mirrors modules packages repos toolchains upstreams view'
 complete -c spack -n '__fish_spack_using_command config edit' -s h -l help -f -a help
 complete -c spack -n '__fish_spack_using_command config edit' -s h -l help -d 'show this help message and exit'
 complete -c spack -n '__fish_spack_using_command config edit' -l print-file -f -a print_file

var/spack/test_repos/builtin.mock/packages/conditional-languages/package.py

@@ -0,0 +1,20 @@
+# Copyright Spack Project Developers. See COPYRIGHT file for details.
+#
+# SPDX-License-Identifier: (Apache-2.0 OR MIT)
+from spack.package import *
+
+
+class ConditionalLanguages(Package):
+    """Conditional depends on c/cxx/fortran with a variant for each"""
+
+    homepage = "https://dev.null"
+
+    version("1.0")
+
+    variant("c", default=False, description="depend on c")
+    variant("cxx", default=False, description="depend on cxx")
+    variant("fortran", default=False, description="depend on fortran")
+
+    depends_on("c", type="build", when="+c")
+    depends_on("cxx", type="build", when="+cxx")
+    depends_on("fortran", type="build", when="+fortran")