[ConstraintSystem] Requestify isDeclSubstitutable from CSStep.cpp

Author: hborla

include/swift/AST/TypeCheckRequests.h

@@ -1883,6 +1883,27 @@ class CompareDeclSpecializationRequest
   bool isCached() const { return true; }
 };
 
+/// Checks whether substituting the first generic function decl with the
+/// second generic function decl will satisfy all requirements and produce
+/// the same function type.
+class IsDeclSubstitutableRequest
+    : public SimpleRequest<IsDeclSubstitutableRequest,
+                           bool(ValueDecl *, ValueDecl *),
+                           RequestFlags::Cached> {
+public:
+  using SimpleRequest::SimpleRequest;
+
+private:
+  friend SimpleRequest;
+
+  // Evaluation.
+  bool evaluate(Evaluator &evaluator, ValueDecl *declA, ValueDecl *declB) const;
+
+public:
+  // Caching.
+  bool isCached() const { return true; }
+};
+
 /// Checks whether this declaration inherits its superclass' designated and
 /// convenience initializers.
 class InheritsSuperclassInitializersRequest

include/swift/AST/TypeCheckerTypeIDZone.def

@@ -41,6 +41,9 @@ SWIFT_REQUEST(TypeChecker, CodeCompletionFileRequest,
 SWIFT_REQUEST(TypeChecker, CompareDeclSpecializationRequest,
               bool (DeclContext *, ValueDecl *, ValueDecl *, bool), Cached,
               NoLocationInfo)
+SWIFT_REQUEST(TypeChecker, IsDeclSubstitutableRequest,
+              bool (ValueDecl *, ValueDecl *),
+              Cached, NoLocationInfo)
 SWIFT_REQUEST(TypeChecker, CustomAttrTypeRequest,
               Type(CustomAttr *, DeclContext *, CustomAttrTypeKind),
               SeparatelyCached, NoLocationInfo)

lib/Sema/CSStep.cpp

@@ -18,6 +18,7 @@
 #include "CSStep.h"
 #include "TypeChecker.h"
 #include "swift/AST/Types.h"
+#include "swift/AST/TypeCheckRequests.h"
 #include "swift/AST/GenericEnvironment.h"
 #include "swift/Sema/ConstraintSystem.h"
 #include "llvm/ADT/ArrayRef.h"
@@ -529,7 +530,9 @@ StepResult DisjunctionStep::resume(bool prevFailed) {
   return take(prevFailed);
 }
 
-static bool isDeclSubstitutable(ValueDecl *declA, ValueDecl *declB) {
+bool IsDeclSubstitutableRequest::evaluate(Evaluator &evaluator,
+                                          ValueDecl *declA,
+                                          ValueDecl *declB) const {
   auto *typeA = declA->getInterfaceType()->getAs<GenericFunctionType>();
   auto *typeB = declB->getInterfaceType()->getAs<GenericFunctionType>();
 
@@ -571,6 +574,12 @@ static bool isDeclSubstitutable(ValueDecl *declA, ValueDecl *declB) {
   return substTypeA->isEqual(substTypeB);
 }
 
+static bool isDeclSubstitutable(ValueDecl *declA, ValueDecl *declB) {
+  return evaluateOrDefault(declA->getASTContext().evaluator,
+                           IsDeclSubstitutableRequest{ declA, declB },
+                           false);
+}
+
 static bool isGenericDisjunctionChoice(Constraint *constraint) {
   if (constraint->getKind() != ConstraintKind::BindOverload)
     return false;