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RequirementMachine: Teach generating conformances to understand protocol refinement

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For implementation reasons we want the requirement signature of a
protocol to directly include all protocol refinement relationships,
even if they can be derived via same-type requirements between Self
and some nested type.

Therefore, a protocol refinement rule [P].[Q] => [P] can only be
replaced with a generating conformance equation that consists
entirely of other conformance rules.

This exactly simulates the existing behavior of the GSB's redundant
requirements algorithm.
This commit is contained in:
Slava Pestov
2021-10-07 16:00:48 -04:00
parent 371366eb4b
commit 70233aceb7
3 changed files with 45 additions and 0 deletions
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29
lib/AST/RequirementMachine/GeneratingConformances.cpp
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@@ -369,6 +369,23 @@ bool RewriteSystem::isValidConformancePath(
return true;
}
/// Rules of the form [P].[Q] => [P] encode protocol refinement and can only
/// be redundant if they're equivalent to a sequence of other protocol
/// refinements.
///
/// This helps ensure that the inheritance clause of a protocol is complete
/// and correct, allowing name lookup to find associated types of inherited
/// protocols while building the protocol requirement signature.
bool RewriteSystem::isValidRefinementPath(
const llvm::SmallVectorImpl<unsigned> &path) const {
for (unsigned ruleID : path) {
if (!getRule(ruleID).isProtocolRefinementRule())
return false;
}
return true;
}
void RewriteSystem::dumpGeneratingConformanceEquation(
llvm::raw_ostream &out,
unsigned baseRuleID,
@@ -444,6 +461,8 @@ void RewriteSystem::computeGeneratingConformances(
llvm::DenseSet<unsigned> &redundantConformances) {
llvm::MapVector<unsigned, std::vector<SmallVector<unsigned, 2>>> conformancePaths;
llvm::DenseSet<unsigned> protocolRefinements;
// Prepare the initial set of equations: every non-redundant conformance rule
// can be expressed as itself.
for (unsigned ruleID : indices(Rules)) {
@@ -457,6 +476,9 @@ void RewriteSystem::computeGeneratingConformances(
SmallVector<unsigned, 2> path;
path.push_back(ruleID);
conformancePaths[ruleID].push_back(path);
if (rule.isProtocolRefinementRule())
protocolRefinements.insert(ruleID);
}
computeCandidateConformancePaths(conformancePaths);
@@ -475,7 +497,14 @@ void RewriteSystem::computeGeneratingConformances(
// Find a minimal set of generating conformances.
for (const auto &pair : conformancePaths) {
bool isProtocolRefinement = protocolRefinements.count(pair.first) > 0;
for (const auto &path : pair.second) {
// Only consider a protocol refinement rule to be redundant if it is
// witnessed by a composition of other protocol refinement rules.
if (isProtocolRefinement && !isValidRefinementPath(path))
continue;
llvm::SmallDenseSet<unsigned, 4> visited;
visited.insert(pair.first);