refactor: Index provided virtuals by `when` spec

Part 4 of reworking all package metadata to key by `when` conditions.

Changes conflict dictionary structure from this:

    { provided_spec: {when_spec, ...} }

to this:

    { when_spec: {provided_spec, ...} }

7 files changed, 64 insertions, 51 deletions

diff --git a/lib/spack/spack/audit.py b/lib/spack/spack/audit.py
index fedb6c1138..a3591346be 100644
--- a/lib/spack/spack/audit.py
+++ b/lib/spack/spack/audit.py
@@ -702,15 +702,13 @@ def _unknown_variants_in_directives(pkgs, error_cls):
                 )
             )
 
-        # Check "patch" directive
-        for _, triggers in pkg_cls.provided.items():
-            triggers = [spack.spec.Spec(x) for x in triggers]
-            for vrn in triggers:
-                errors.extend(
-                    _analyze_variants_in_directive(
-                        pkg_cls, vrn, directive="patch", error_cls=error_cls
-                    )
+        # Check "provides" directive
+        for when_spec in pkg_cls.provided:
+            errors.extend(
+                _analyze_variants_in_directive(
+                    pkg_cls, when_spec, directive="provides", error_cls=error_cls
                 )
+            )
 
         # Check "resource" directive
         for vrn in pkg_cls.resources:
@@ -752,6 +750,18 @@ def _issues_in_depends_on_directive(pkgs, error_cls):
                     ]
                     errors.append(error_cls(summary=summary, details=details))
 
+                def check_virtual_with_variants(spec, msg):
+                    if not spec.virtual or not spec.variants:
+                        return
+                    error = error_cls(
+                        f"{pkg_name}: {msg}",
+                        f"remove variants from '{spec}' in depends_on directive in {filename}",
+                    )
+                    errors.append(error)
+
+                check_virtual_with_variants(dep.spec, "virtual dependency cannot have variants")
+                check_virtual_with_variants(dep.spec, "virtual when= spec cannot have variants")
+
                 # No need to analyze virtual packages
                 if spack.repo.PATH.is_virtual(dep_name):
                     continue
@@ -963,9 +973,11 @@ def _named_specs_in_when_arguments(pkgs, error_cls):
             summary = f"{pkg_name}: wrong 'when=' condition for the '{vname}' variant"
             errors.extend(_extracts_errors(triggers, summary))
 
-        for provided, triggers in pkg_cls.provided.items():
-            summary = f"{pkg_name}: wrong 'when=' condition for the '{provided}' virtual"
-            errors.extend(_extracts_errors(triggers, summary))
+        for when, providers, details in _error_items(pkg_cls.provided):
+            errors.extend(
+                error_cls(f"{pkg_name}: wrong 'when=' condition for '{provided}' virtual", details)
+                for provided in providers
+            )
 
         for when, requirements, details in _error_items(pkg_cls.requirements):
             errors.append(
diff --git a/lib/spack/spack/cmd/info.py b/lib/spack/spack/cmd/info.py
index fd5ccc5087..b007c60516 100644
--- a/lib/spack/spack/cmd/info.py
+++ b/lib/spack/spack/cmd/info.py
@@ -474,13 +474,7 @@ def print_virtuals(pkg, args):
     color.cprint("")
     color.cprint(section_title("Virtual Packages: "))
     if pkg.provided:
-        inverse_map = {}
-        for spec, whens in pkg.provided.items():
-            for when in whens:
-                if when not in inverse_map:
-                    inverse_map[when] = set()
-                inverse_map[when].add(spec)
-        for when, specs in reversed(sorted(inverse_map.items())):
+        for when, specs in reversed(sorted(pkg.provided.items())):
             line = "    %s provides %s" % (
                 when.colorized(),
                 ", ".join(s.colorized() for s in specs),
diff --git a/lib/spack/spack/directives.py b/lib/spack/spack/directives.py
index 80aee968c8..2524562428 100644
--- a/lib/spack/spack/directives.py
+++ b/lib/spack/spack/directives.py
@@ -613,7 +613,7 @@ def extends(spec, when=None, type=("build", "run"), patches=None):
 
 
 @directive(dicts=("provided", "provided_together"))
-def provides(*specs, when: Optional[str] = None):
+def provides(*specs: SpecType, when: WhenType = None):
     """Allows packages to provide a virtual dependency.
 
     If a package provides "mpi", other packages can declare that they depend on "mpi",
@@ -624,7 +624,7 @@ def provides(*specs, when: Optional[str] = None):
         when: condition when this provides clause needs to be considered
     """
 
-    def _execute_provides(pkg):
+    def _execute_provides(pkg: "spack.package_base.PackageBase"):
         import spack.parser  # Avoid circular dependency
 
         when_spec = _make_when_spec(when)
@@ -634,6 +634,7 @@ def provides(*specs, when: Optional[str] = None):
         # ``when`` specs for ``provides()`` need a name, as they are used
         # to build the ProviderIndex.
         when_spec.name = pkg.name
+
         spec_objs = [spack.spec.Spec(x) for x in specs]
         spec_names = [x.name for x in spec_objs]
         if len(spec_names) > 1:
@@ -643,9 +644,8 @@ def provides(*specs, when: Optional[str] = None):
             if pkg.name == provided_spec.name:
                 raise CircularReferenceError("Package '%s' cannot provide itself." % pkg.name)
 
-            if provided_spec not in pkg.provided:
-                pkg.provided[provided_spec] = set()
-            pkg.provided[provided_spec].add(when_spec)
+            provided_set = pkg.provided.setdefault(when_spec, set())
+            provided_set.add(provided_spec)
 
     return _execute_provides
 
diff --git a/lib/spack/spack/package_base.py b/lib/spack/spack/package_base.py
index bb9fb6408c..92c456f7fe 100644
--- a/lib/spack/spack/package_base.py
+++ b/lib/spack/spack/package_base.py
@@ -25,7 +25,7 @@ import textwrap
 import time
 import traceback
 import warnings
-from typing import Any, Callable, Dict, Iterable, List, Optional, Tuple, Type, TypeVar, Union
+from typing import Any, Callable, Dict, Iterable, List, Optional, Set, Tuple, Type, TypeVar, Union
 
 import llnl.util.filesystem as fsys
 import llnl.util.tty as tty
@@ -565,6 +565,8 @@ class PackageBase(WindowsRPath, PackageViewMixin, metaclass=PackageMeta):
     requirements: Dict[
         "spack.spec.Spec", List[Tuple[Tuple["spack.spec.Spec", ...], str, Optional[str]]]
     ]
+    provided: Dict["spack.spec.Spec", Set["spack.spec.Spec"]]
+    provided_together: Dict["spack.spec.Spec", List[Set[str]]]
     patches: Dict["spack.spec.Spec", List["spack.patch.Patch"]]
 
     #: By default, packages are not virtual
@@ -1342,9 +1344,9 @@ class PackageBase(WindowsRPath, PackageViewMixin, metaclass=PackageMeta):
         True if this package provides a virtual package with the specified name
         """
         return any(
-            any(self.spec.intersects(c) for c in constraints)
-            for s, constraints in self.provided.items()
-            if s.name == vpkg_name
+            any(spec.name == vpkg_name for spec in provided)
+            for when_spec, provided in self.provided.items()
+            if self.spec.intersects(when_spec)
         )
 
     @property
@@ -1354,10 +1356,16 @@ class PackageBase(WindowsRPath, PackageViewMixin, metaclass=PackageMeta):
         """
         return [
             vspec
-            for vspec, constraints in self.provided.items()
-            if any(self.spec.satisfies(c) for c in constraints)
+            for when_spec, provided in self.provided.items()
+            for vspec in provided
+            if self.spec.satisfies(when_spec)
         ]
 
+    @classmethod
+    def provided_virtual_names(cls):
+        """Return sorted list of names of virtuals that can be provided by this package."""
+        return sorted(set(vpkg.name for virtuals in cls.provided.values() for vpkg in virtuals))
+
     @property
     def prefix(self):
         """Get the prefix into which this package should be installed."""
diff --git a/lib/spack/spack/provider_index.py b/lib/spack/spack/provider_index.py
index a59cb1be80..29c32ce1b5 100644
--- a/lib/spack/spack/provider_index.py
+++ b/lib/spack/spack/provider_index.py
@@ -128,8 +128,8 @@ class ProviderIndex(_IndexBase):
         assert not self.repository.is_virtual_safe(spec.name), msg
 
         pkg_provided = self.repository.get_pkg_class(spec.name).provided
-        for provided_spec, provider_specs in pkg_provided.items():
-            for provider_spec_readonly in provider_specs:
+        for provider_spec_readonly, provided_specs in pkg_provided.items():
+            for provided_spec in provided_specs:
                 # TODO: fix this comment.
                 # We want satisfaction other than flags
                 provider_spec = provider_spec_readonly.copy()
diff --git a/lib/spack/spack/solver/asp.py b/lib/spack/spack/solver/asp.py
index 82eff23119..0f38331412 100644
--- a/lib/spack/spack/solver/asp.py
+++ b/lib/spack/spack/solver/asp.py
@@ -1628,19 +1628,20 @@ class SpackSolverSetup:
             self.gen.fact(fn.imposed_constraint(condition_id, *pred.args))
 
     def package_provider_rules(self, pkg):
-        for provider_name in sorted(set(s.name for s in pkg.provided.keys())):
-            if provider_name not in self.possible_virtuals:
+        for vpkg_name in pkg.provided_virtual_names():
+            if vpkg_name not in self.possible_virtuals:
                 continue
-            self.gen.fact(fn.pkg_fact(pkg.name, fn.possible_provider(provider_name)))
+            self.gen.fact(fn.pkg_fact(pkg.name, fn.possible_provider(vpkg_name)))
 
-        for provided, whens in pkg.provided.items():
-            if provided.name not in self.possible_virtuals:
-                continue
-            for when in whens:
-                msg = "%s provides %s when %s" % (pkg.name, provided, when)
-                condition_id = self.condition(when, provided, pkg.name, msg)
+        for when, provided in pkg.provided.items():
+            for vpkg in provided:
+                if vpkg.name not in self.possible_virtuals:
+                    continue
+
+                msg = f"{pkg.name} provides {vpkg} when {when}"
+                condition_id = self.condition(when, vpkg, pkg.name, msg)
                 self.gen.fact(
-                    fn.pkg_fact(when.name, fn.provider_condition(condition_id, provided.name))
+                    fn.pkg_fact(when.name, fn.provider_condition(condition_id, vpkg.name))
                 )
             self.gen.newline()
 
@@ -3383,7 +3384,7 @@ def _is_reusable(spec: spack.spec.Spec, packages, local: bool) -> bool:
             return True
 
     try:
-        provided = [p.name for p in spec.package.provided]
+        provided = spack.repo.PATH.get(spec).provided_virtual_names()
     except spack.repo.RepoError:
         provided = []
 
diff --git a/lib/spack/spack/spec.py b/lib/spack/spack/spec.py
index b27272e8e1..767a69ee67 100644
--- a/lib/spack/spack/spec.py
+++ b/lib/spack/spack/spec.py
@@ -2788,7 +2788,7 @@ class Spec:
         for dep in self.traverse():
             visited_user_specs.add(dep.name)
             pkg_cls = spack.repo.PATH.get_pkg_class(dep.name)
-            visited_user_specs.update(x.name for x in pkg_cls(dep).provided)
+            visited_user_specs.update(pkg_cls(dep).provided_virtual_names())
 
         extra = set(user_spec_deps.keys()).difference(visited_user_specs)
         if extra:
@@ -3774,11 +3774,9 @@ class Spec:
                     return False
 
                 if pkg.provides(virtual_spec.name):
-                    for provided, when_specs in pkg.provided.items():
-                        if any(
-                            non_virtual_spec.intersects(when, deps=False) for when in when_specs
-                        ):
-                            if provided.intersects(virtual_spec):
+                    for when_spec, provided in pkg.provided.items():
+                        if non_virtual_spec.intersects(when_spec, deps=False):
+                            if any(vpkg.intersects(virtual_spec) for vpkg in provided):
                                 return True
             return False
 
@@ -3881,9 +3879,9 @@ class Spec:
                     return False
 
                 if pkg.provides(other.name):
-                    for provided, when_specs in pkg.provided.items():
-                        if any(self.satisfies(when, deps=False) for when in when_specs):
-                            if provided.intersects(other):
+                    for when_spec, provided in pkg.provided.items():
+                        if self.satisfies(when_spec, deps=False):
+                            if any(vpkg.intersects(other) for vpkg in provided):
                                 return True
             return False