[clang] [clang][ssaf] Add EntityLinkage data structure (PR #181718)

[Balázs Benics via cfe-commits]

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@@ -0,0 +1,50 @@
+//===- EntityLinkage.h ------------------------------------------*- C++ -*-===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_ANALYSIS_SCALABLE_MODEL_ENTITYLINKAGE_H
+#define LLVM_CLANG_ANALYSIS_SCALABLE_MODEL_ENTITYLINKAGE_H
+
+namespace clang::ssaf {
+
+/// Represents the linkage properties of an entity in the program model.
+///
+/// EntityLinkage captures whether an entity has no linkage, internal linkage,
+/// or external linkage, which determines its visibility and accessibility
+/// across translation units.
+class EntityLinkage {
+  friend class SerializationFormat;
+
+public:
+  /// Specifies the type of linkage an entity has.
+  enum class LinkageType {
+    None,     ///< No linkage (e.g., local variables, function parameters)
+    Internal, ///< Internal linkage (static functions/variables, anonymous
+              ///< namespace)
+    External  ///< External linkage (globally visible across translation units)
+  };
+
+  /// Constructs an EntityLinkage with no linkage (default).
+  EntityLinkage() : Linkage(LinkageType::None) {}
+
+  /// Constructs an EntityLinkage with the specified linkage type.
+  ///
+  /// \param L The linkage type to assign to this entity.
+  explicit EntityLinkage(LinkageType L) : Linkage(L) {}
+
+  /// Returns the linkage type of this entity.
+  ///
+  /// \return The LinkageType indicating the entity's linkage.
+  LinkageType getLinkage() const { return Linkage; }
+
+private:
+  LinkageType Linkage;
----------------
steakhal wrote:

How about we drop the default ctor and initialise this here.
```suggestion
  LinkageType Linkage = LinkageType::None;
```

https://github.com/llvm/llvm-project/pull/181718