APIDigester: Break cycle between Frontend and APIDigester targets.

Also push a utility that was previously on `SILDeclRef` down to AST so that the SIL dependency can be removed entirely from APIDigester.

include/swift/AST/Decl.h

@@ -6908,6 +6908,11 @@ public:
   /// vtable.
   bool needsNewVTableEntry() const;
 
+  /// True if the decl is a method which introduces a new witness table entry.
+  bool requiresNewWitnessTableEntry() const {
+    return getOverriddenDecls().empty();
+  }
+
 public:
   /// Retrieve the source range of the function body.
   SourceRange getBodySourceRange() const;

include/swift/SIL/SILDeclRef.h

@@ -510,9 +510,6 @@ struct SILDeclRef {
   /// table entry.
   bool requiresNewWitnessTableEntry() const;
 
-  /// True if the decl is a method which introduces a new witness table entry.
-  static bool requiresNewWitnessTableEntry(AbstractFunctionDecl *func);
-
   /// Return a SILDeclRef to the declaration overridden by this one, or
   /// a null SILDeclRef if there is no override.
   SILDeclRef getOverridden() const;

include/swift/SIL/SILWitnessVisitor.h

@@ -125,7 +125,7 @@ public:
 
   void visitAbstractStorageDecl(AbstractStorageDecl *sd) {
     sd->visitOpaqueAccessors([&](AccessorDecl *accessor) {
-      if (SILDeclRef::requiresNewWitnessTableEntry(accessor)) {
+      if (accessor->requiresNewWitnessTableEntry()) {
         asDerived().addMethod(SILDeclRef(accessor, SILDeclRef::Kind::Func));
         addAutoDiffDerivativeMethodsIfRequired(accessor,
                                                SILDeclRef::Kind::Func);
@@ -134,7 +134,7 @@ public:
   }
 
   void visitConstructorDecl(ConstructorDecl *cd) {
-    if (SILDeclRef::requiresNewWitnessTableEntry(cd)) {
+    if (cd->requiresNewWitnessTableEntry()) {
       asDerived().addMethod(SILDeclRef(cd, SILDeclRef::Kind::Allocator));
       addAutoDiffDerivativeMethodsIfRequired(cd, SILDeclRef::Kind::Allocator);
     }
@@ -146,7 +146,7 @@ public:
 
   void visitFuncDecl(FuncDecl *func) {
     assert(!isa<AccessorDecl>(func));
-    if (SILDeclRef::requiresNewWitnessTableEntry(func)) {
+    if (func->requiresNewWitnessTableEntry()) {
       asDerived().addMethod(SILDeclRef(func, SILDeclRef::Kind::Func));
       addAutoDiffDerivativeMethodsIfRequired(func, SILDeclRef::Kind::Func);
       addDistributedWitnessMethodsIfRequired(func, SILDeclRef::Kind::Func);

lib/APIDigester/CMakeLists.txt

@@ -5,8 +5,6 @@ add_swift_host_library(swiftAPIDigester STATIC
   ModuleDiagsConsumer.cpp)
 
 target_link_libraries(swiftAPIDigester PRIVATE
-  swiftFrontend
-  swiftSIL
   swiftIDE)
 
 set_swift_llvm_is_available(swiftAPIDigester)

lib/APIDigester/ModuleAnalyzerNodes.cpp

@@ -2,7 +2,6 @@
 #include "swift/AST/ASTMangler.h"
 #include "swift/Basic/Defer.h"
 #include "swift/Sema/IDETypeChecking.h"
-#include "swift/SIL/SILDeclRef.h"
 #include <swift/APIDigester/ModuleAnalyzerNodes.h>
 #include <algorithm>
 
@@ -1491,7 +1490,7 @@ static bool isProtocolRequirement(ValueDecl *VD) {
 
 static bool requireWitnessTableEntry(ValueDecl *VD) {
   if (auto *FD = dyn_cast<AbstractFunctionDecl>(VD)) {
-    return SILDeclRef::requiresNewWitnessTableEntry(FD);
+    return FD->requiresNewWitnessTableEntry();
   }
   return false;
 }

lib/SIL/IR/SILDeclRef.cpp

@@ -1233,11 +1233,7 @@ bool SILDeclRef::requiresNewVTableEntry() const {
 }
 
 bool SILDeclRef::requiresNewWitnessTableEntry() const {
-  return requiresNewWitnessTableEntry(cast<AbstractFunctionDecl>(getDecl()));
-}
-
-bool SILDeclRef::requiresNewWitnessTableEntry(AbstractFunctionDecl *func) {
-  return func->getOverriddenDecls().empty();
+  return cast<AbstractFunctionDecl>(getDecl())->requiresNewWitnessTableEntry();
 }
 
 SILDeclRef SILDeclRef::getOverridden() const {

lib/SILGen/SILGenExpr.cpp

@@ -2864,7 +2864,7 @@ static SILFunction *getOrCreateKeyPathGetter(SILGenModule &SGM,
   // entry.
   if (isa<ProtocolDecl>(property->getDeclContext())) {
     auto accessor = getRepresentativeAccessorForKeyPath(property);
-    if (!SILDeclRef::requiresNewWitnessTableEntry(accessor)) {
+    if (!accessor->requiresNewWitnessTableEntry()) {
       // Find the getter that does have a witness table entry.
       auto wtableAccessor =
         cast<AccessorDecl>(SILDeclRef::getOverriddenWitnessTableEntry(accessor));
@@ -3027,7 +3027,7 @@ static SILFunction *getOrCreateKeyPathSetter(SILGenModule &SGM,
   // entry.
   if (isa<ProtocolDecl>(property->getDeclContext())) {
     auto setter = property->getOpaqueAccessor(AccessorKind::Set);
-    if (!SILDeclRef::requiresNewWitnessTableEntry(setter)) {
+    if (!setter->requiresNewWitnessTableEntry()) {
       // Find the setter that does have a witness table entry.
       auto wtableSetter =
         cast<AccessorDecl>(SILDeclRef::getOverriddenWitnessTableEntry(setter));