refactor: Index conflicts by `when` spec

Part 2 of reworking all package metadata to key by `when` conditions.

Changes conflict dictionary structure from this:

    { conflict_spec: [(when_spec, msg), ...] }

to this:

    { when_spec: [(conflict_spec, msg), ...] }

Also attempts to consistently name the variables used to iterate over conflict
dictionaries.

7 files changed, 33 insertions, 34 deletions

diff --git a/lib/spack/spack/audit.py b/lib/spack/spack/audit.py
index d9b2610267..40bd04e9bc 100644
--- a/lib/spack/spack/audit.py
+++ b/lib/spack/spack/audit.py
@@ -667,8 +667,8 @@ def _unknown_variants_in_directives(pkgs, error_cls):
         pkg_cls = spack.repo.PATH.get_pkg_class(pkg_name)
 
         # Check "conflicts" directive
-        for conflict, triggers in pkg_cls.conflicts.items():
-            for trigger, _ in triggers:
+        for trigger, conflicts in pkg_cls.conflicts.items():
+            for conflict, _ in conflicts:
                 vrn = spack.spec.Spec(conflict)
                 try:
                     vrn.constrain(trigger)
diff --git a/lib/spack/spack/directives.py b/lib/spack/spack/directives.py
index e837f497af..75cda9f90b 100644
--- a/lib/spack/spack/directives.py
+++ b/lib/spack/spack/directives.py
@@ -525,7 +525,7 @@ def _depends_on(
 
 
 @directive("conflicts")
-def conflicts(conflict_spec, when=None, msg=None):
+def conflicts(conflict_spec: SpecType, when: WhenType = None, msg: Optional[str] = None):
     """Allows a package to define a conflict.
 
     Currently, a "conflict" is a concretized configuration that is known
@@ -545,16 +545,16 @@ def conflicts(conflict_spec, when=None, msg=None):
         msg (str): optional user defined message
     """
 
-    def _execute_conflicts(pkg):
+    def _execute_conflicts(pkg: "spack.package_base.PackageBase"):
         # If when is not specified the conflict always holds
         when_spec = make_when_spec(when)
         if not when_spec:
             return
 
         # Save in a list the conflicts and the associated custom messages
-        when_spec_list = pkg.conflicts.setdefault(conflict_spec, [])
+        conflict_spec_list = pkg.conflicts.setdefault(when_spec, [])
         msg_with_name = f"{pkg.name}: {msg}" if msg is not None else msg
-        when_spec_list.append((when_spec, msg_with_name))
+        conflict_spec_list.append((spack.spec.Spec(conflict_spec), msg_with_name))
 
     return _execute_conflicts
 
diff --git a/lib/spack/spack/package_base.py b/lib/spack/spack/package_base.py
index 926df89181..9b1b1c17c8 100644
--- a/lib/spack/spack/package_base.py
+++ b/lib/spack/spack/package_base.py
@@ -560,11 +560,8 @@ class PackageBase(WindowsRPath, PackageViewMixin, metaclass=PackageMeta):
     # Declare versions dictionary as placeholder for values.
     # This allows analysis tools to correctly interpret the class attributes.
     versions: dict
-
-    # Same for dependencies
     dependencies: Dict["spack.spec.Spec", Dict[str, "spack.dependency.Dependency"]]
-
-    # and patches
+    conflicts: Dict["spack.spec.Spec", List[Tuple["spack.spec.Spec", Optional[str]]]]
     patches: Dict["spack.spec.Spec", List["spack.patch.Patch"]]
 
     #: By default, packages are not virtual
diff --git a/lib/spack/spack/solver/asp.py b/lib/spack/spack/solver/asp.py
index aa00600d0b..3a0267a50c 100644
--- a/lib/spack/spack/solver/asp.py
+++ b/lib/spack/spack/solver/asp.py
@@ -1234,29 +1234,30 @@ class SpackSolverSetup:
         return [fn.attr("node_target_satisfies", spec.name, target)]
 
     def conflict_rules(self, pkg):
-        default_msg = "{0}: '{1}' conflicts with '{2}'"
-        no_constraint_msg = "{0}: conflicts with '{1}'"
-        for trigger, constraints in pkg.conflicts.items():
-            trigger_msg = f"conflict is triggered when {str(trigger)}"
-            trigger_spec = spack.spec.Spec(trigger)
-            trigger_id = self.condition(
-                trigger_spec, name=trigger_spec.name or pkg.name, msg=trigger_msg
-            )
+        for when_spec, conflict_specs in pkg.conflicts.items():
+            when_spec_msg = "conflict constraint %s" % str(when_spec)
+            when_spec_id = self.condition(when_spec, name=pkg.name, msg=when_spec_msg)
 
-            for constraint, conflict_msg in constraints:
+            for conflict_spec, conflict_msg in conflict_specs:
+                conflict_spec = spack.spec.Spec(conflict_spec)
                 if conflict_msg is None:
-                    if constraint == spack.spec.Spec():
-                        conflict_msg = no_constraint_msg.format(pkg.name, trigger)
+                    conflict_msg = f"{pkg.name}: "
+                    if when_spec == spack.spec.Spec():
+                        conflict_msg += f"conflicts with '{conflict_spec}'"
                     else:
-                        conflict_msg = default_msg.format(pkg.name, trigger, constraint)
-
-                spec_for_msg = (
-                    spack.spec.Spec(pkg.name) if constraint == spack.spec.Spec() else constraint
+                        conflict_msg += f"'{conflict_spec}' conflicts with '{when_spec}'"
+
+                spec_for_msg = conflict_spec
+                if conflict_spec == spack.spec.Spec():
+                    spec_for_msg = spack.spec.Spec(pkg.name)
+                conflict_spec_msg = f"conflict is triggered when {str(spec_for_msg)}"
+                conflict_spec_id = self.condition(
+                    conflict_spec, name=conflict_spec.name or pkg.name, msg=conflict_spec_msg
                 )
-                constraint_msg = f"conflict applies to spec {str(spec_for_msg)}"
-                constraint_id = self.condition(constraint, name=pkg.name, msg=constraint_msg)
                 self.gen.fact(
-                    fn.pkg_fact(pkg.name, fn.conflict(trigger_id, constraint_id, conflict_msg))
+                    fn.pkg_fact(
+                        pkg.name, fn.conflict(conflict_spec_id, when_spec_id, conflict_msg)
+                    )
                 )
                 self.gen.newline()
 
diff --git a/lib/spack/spack/spec.py b/lib/spack/spack/spec.py
index a11e8ab915..b27272e8e1 100644
--- a/lib/spack/spack/spec.py
+++ b/lib/spack/spack/spec.py
@@ -2823,10 +2823,11 @@ class Spec:
                 # external specs are already built, don't worry about whether
                 # it's possible to build that configuration with Spack
                 continue
-            for conflict_spec, when_list in x.package_class.conflicts.items():
-                if x.satisfies(conflict_spec):
-                    for when_spec, msg in when_list:
-                        if x.satisfies(when_spec):
+
+            for when_spec, conflict_list in x.package_class.conflicts.items():
+                if x.satisfies(when_spec):
+                    for conflict_spec, msg in conflict_list:
+                        if x.satisfies(conflict_spec):
                             when = when_spec.copy()
                             when.name = x.name
                             matches.append((x, conflict_spec, when, msg))
diff --git a/lib/spack/spack/test/concretize.py b/lib/spack/spack/test/concretize.py
index c53dc0dd36..b6ddf6c4dd 100644
--- a/lib/spack/spack/test/concretize.py
+++ b/lib/spack/spack/test/concretize.py
@@ -1905,7 +1905,7 @@ class TestConcretize:
         """
         # Add a conflict to "mpich" that match an already installed "mpich~debug"
         pkg_cls = spack.repo.PATH.get_pkg_class("mpich")
-        monkeypatch.setitem(pkg_cls.conflicts, "~debug", [(Spec(), None)])
+        monkeypatch.setitem(pkg_cls.conflicts, Spec(), [("~debug", None)])
 
         # If we concretize with --fresh the conflict is taken into account
         with spack.config.override("concretizer:reuse", False):
diff --git a/lib/spack/spack/test/directives.py b/lib/spack/spack/test/directives.py
index 73d40365b9..5b34e40793 100644
--- a/lib/spack/spack/test/directives.py
+++ b/lib/spack/spack/test/directives.py
@@ -46,7 +46,7 @@ def test_constraints_from_context(mock_packages):
     assert "b" in pkg_cls.dependencies[spack.spec.Spec("@1.0")]
 
     assert pkg_cls.conflicts
-    assert (spack.spec.Spec("+foo@1.0"), None) in pkg_cls.conflicts["%gcc"]
+    assert (spack.spec.Spec("%gcc"), None) in pkg_cls.conflicts[spack.spec.Spec("+foo@1.0")]
 
 
 @pytest.mark.regression("26656")