FunctionDepsFinder: Factor out closure logic

Factor-out the first part of the Closure computation so we can use it
in other parts of clang-extract.

Signed-off-by: Giuliano Belinassi <[email protected]>

libcextract/Closure.cpp

@@ -0,0 +1,74 @@
+//===- Closure.hh - Compute dependencies of a given symbol *- C++ -*-===//
+//
+// This project is licensed 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
+//
+//===----------------------------------------------------------------------===//
+//
+/// \file
+/// Compute a set of Decls that is necessary to compile a given symbol.
+//
+//===----------------------------------------------------------------------===//
+
+/* Author: Giuliano Belinassi  */
+
+#include "Closure.hh"
+
+/** Add a decl to the Dependencies set and all its previous declarations in the
+    AST. A function can have multiple definitions but its body may only be
+    defined later.  */
+bool ClosureSet::Add_Decl_And_Prevs(Decl *decl)
+{
+  bool inserted = false;
+
+  /* Do not insert builtin decls.  */
+  if (Is_Builtin_Decl(decl)) {
+    return false;
+  }
+
+  while (decl) {
+    if (!Is_Decl_Marked(decl)) {
+      Dependencies.insert(decl);
+      inserted = true;
+    }
+
+    decl = decl->getPreviousDecl();
+  }
+  return inserted;
+}
+
+void DeclClosureVisitor::Compute_Closure_Of_Symbols(const std::vector<std::string> &names,
+                                          std::unordered_set<std::string> *matched_names)
+{
+  /* FIXME: clang has a mechanism (DeclContext::lookup) which is SUPPOSED TO
+     return the list of all Decls that matches the lookup name.  However, this
+     method doesn't work as intented.  In kernel (see github issue #20) it
+     results in the lookup_result set not having the Decl that has the body of
+     the function, which is the most important!
+
+     Hence, do our own thing here.  Create a set and sweep the top level decls,
+     analyzing the symbol that matches the name in the set.  */
+
+  std::unordered_set<std::string> setof_names(std::make_move_iterator(names.begin()),
+                                              std::make_move_iterator(names.end()));
+
+  for (auto it = AST->top_level_begin(); it != AST->top_level_end(); ++it) {
+    NamedDecl *decl = dyn_cast<NamedDecl>(*it);
+
+    if (!decl) {
+      /* Decl does not have a name, thus skip it.  */
+      continue;
+    }
+
+    const std::string &decl_name = decl->getName().str();
+    /* If the symbol name is in the set...   */
+    if (setof_names.find(decl_name) != setof_names.end()) {
+      /* Mark that name as matched.  */
+      if (matched_names)
+        matched_names->insert(decl_name);
+      /* Find its dependencies.  */
+      TraverseDecl(decl);
+    }
+  }
+}