AST: Simplify SubstitutionMap::get()

Author: slavapestov

include/swift/AST/SubstitutionMap.h

@@ -104,6 +104,15 @@ class SubstitutionMap {
                              ArrayRef<Type> replacementTypes,
                              LookupConformanceFn lookupConformance);
 
+  /// Build a substitution map from the substitutions represented by
+  /// the given in-flight substitution.
+  ///
+  /// This function should generally only be used by the substitution
+  /// subsystem.
+  static SubstitutionMap get(GenericSignature genericSig,
+                             ArrayRef<Type> replacementTypes,
+                             InFlightSubstitution &IFS);
+
   /// Build a substitution map from the substitutions represented by
   /// the given in-flight substitution.
   ///

include/swift/AST/TypeTransform.h

@@ -998,9 +998,7 @@ case TypeKind::Id:
       return subs;
 
     auto sig = subs.getGenericSignature();
-    return SubstitutionMap::get(sig,
-        QueryReplacementTypeArray{sig, newSubs},
-        LookUpConformanceInModule());
+    return SubstitutionMap::get(sig, newSubs, LookUpConformanceInModule());
   }
 
   CanType transformSILField(CanType fieldTy, TypePosition pos) {

lib/AST/SubstitutionMap.cpp

@@ -168,9 +168,28 @@ SubstitutionMap SubstitutionMap::get(GenericSignature genericSig,
 SubstitutionMap SubstitutionMap::get(GenericSignature genericSig,
                                      ArrayRef<Type> types,
                                      LookupConformanceFn lookupConformance) {
-  return get(genericSig,
-             QueryReplacementTypeArray{genericSig, types},
-             lookupConformance);
+  QueryReplacementTypeArray subs{genericSig, types};
+  InFlightSubstitution IFS(subs, lookupConformance, std::nullopt);
+  return get(genericSig, types, IFS);
+}
+
+SubstitutionMap SubstitutionMap::get(GenericSignature genericSig,
+                                     ArrayRef<Type> types,
+                                     InFlightSubstitution &IFS) {
+  // Form the stored conformances.
+  SmallVector<ProtocolConformanceRef, 4> conformances;
+  for (const auto &req : genericSig.getRequirements()) {
+    if (req.getKind() != RequirementKind::Conformance) continue;
+
+    CanType depTy = req.getFirstType()->getCanonicalType();
+    auto replacement = depTy.subst(IFS);
+    auto *proto = req.getProtocolDecl();
+    auto conformance = IFS.lookupConformance(depTy, replacement, proto,
+                                             /*level=*/0);
+    conformances.push_back(conformance);
+  }
+
+  return SubstitutionMap(genericSig, types, conformances);
 }
 
 SubstitutionMap SubstitutionMap::get(GenericSignature genericSig,
@@ -185,29 +204,17 @@ SubstitutionMap SubstitutionMap::get(GenericSignature genericSig,
 
   for (auto *gp : genericSig.getGenericParams()) {
     // Record the replacement.
-    Type replacement = Type(gp).subst(IFS);
-
-    assert((!replacement || replacement->hasError() ||
+    Type replacement = IFS.substType(gp, /*level=*/0);
+    if (!replacement)
+      replacement = ErrorType::get(gp->getASTContext());
+    assert((replacement->hasError() ||
             gp->isParameterPack() == replacement->is<PackType>()) &&
            "replacement for pack parameter must be a pack type");
 
     replacementTypes.push_back(replacement);
   }
 
-  // Form the stored conformances.
-  SmallVector<ProtocolConformanceRef, 4> conformances;
-  for (const auto &req : genericSig.getRequirements()) {
-    if (req.getKind() != RequirementKind::Conformance) continue;
-
-    CanType depTy = req.getFirstType()->getCanonicalType();
-    auto replacement = depTy.subst(IFS);
-    auto *proto = req.getProtocolDecl();
-    auto conformance = IFS.lookupConformance(depTy, replacement, proto,
-                                             /*level=*/0);
-    conformances.push_back(conformance);
-  }
-
-  return SubstitutionMap(genericSig, replacementTypes, conformances);
+  return SubstitutionMap::get(genericSig, replacementTypes, IFS);
 }
 
 Type SubstitutionMap::lookupSubstitution(GenericTypeParamType *genericParam) const {

lib/AST/TypeSubstitution.cpp

@@ -808,8 +808,7 @@ SubstitutionMap TypeBase::getContextSubstitutionMap() {
   std::reverse(replacementTypes.begin(), replacementTypes.end());
 
   auto subMap = SubstitutionMap::get(
-    genericSig,
-    QueryReplacementTypeArray{genericSig, replacementTypes},
+    genericSig, replacementTypes,
     LookUpConformanceInModule());
 
   nominalTy->ContextSubMap = subMap;