[clang] [APINotes] Upstream Sema logic to apply API Notes to decls (PR #78445)

[Saleem Abdulrasool via cfe-commits]

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@@ -0,0 +1,989 @@
+//===--- SemaAPINotes.cpp - API Notes Handling ----------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+//  This file implements the mapping from API notes to declaration attributes.
+//
+//===----------------------------------------------------------------------===//
+
+#include "clang/APINotes/APINotesReader.h"
+#include "clang/AST/Decl.h"
+#include "clang/AST/DeclObjC.h"
+#include "clang/Basic/SourceLocation.h"
+#include "clang/Lex/Lexer.h"
+#include "clang/Sema/SemaInternal.h"
+
+using namespace clang;
+
+namespace {
+enum class IsActive_t : bool { Inactive, Active };
+enum class IsReplacement_t : bool { Original, Replacement };
+
+struct VersionedInfoMetadata {
+  /// An empty version refers to unversioned metadata.
+  VersionTuple Version;
+  unsigned IsActive : 1;
+  unsigned IsReplacement : 1;
+
+  VersionedInfoMetadata(VersionTuple Version, IsActive_t Active,
+                        IsReplacement_t Replacement)
+      : Version(Version), IsActive(Active == IsActive_t::Active),
+        IsReplacement(Replacement == IsReplacement_t::Replacement) {}
+};
+} // end anonymous namespace
+
+/// Determine whether this is a multi-level pointer type.
+static bool isIndirectPointerType(QualType Type) {
+  QualType Pointee = Type->getPointeeType();
+  if (Pointee.isNull())
+    return false;
+
+  return Pointee->isAnyPointerType() || Pointee->isObjCObjectPointerType() ||
+         Pointee->isMemberPointerType();
+}
+
+/// Apply nullability to the given declaration.
+static void applyNullability(Sema &S, Decl *D, NullabilityKind Nullability,
+                             VersionedInfoMetadata Metadata) {
+  if (!Metadata.IsActive)
+    return;
+
+  auto IsUnmodified = [&](Decl *D, QualType QT,
+                          NullabilityKind Nullability) -> bool {
+    QualType Original = QT;
+    S.CheckImplicitNullabilityTypeSpecifier(QT, Nullability, D->getLocation(),
+                                            isa<ParmVarDecl>(D),
+                                            /*OverrideExisting=*/true);
+    return QT.getTypePtr() == Original.getTypePtr();
+  };
+
+  if (auto Function = dyn_cast<FunctionDecl>(D)) {
+    if (!IsUnmodified(D, Function->getReturnType(), Nullability)) {
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compnerd wrote:

An alternative to consider: rename the function to `IsModified` and return the negated value so simplify the callees.

https://github.com/llvm/llvm-project/pull/78445