D154328: [AST] Add API to iterate already loaded specializations

These new functions allow to look at specializations without triggering
deserialization, which might be problematic in some contexts.

Author: hahnjo

clang/include/clang/AST/DeclTemplate.h

@@ -1084,6 +1084,20 @@ class FunctionTemplateDecl : public RedeclarableTemplateDecl {
     return makeSpecIterator(getSpecializations(), true);
   }
 
+  /// All specializations that that have already been loaded, ie avoiding
+  /// deserialization of lazily registered specializations.
+  spec_range loaded_specializations() const {
+    return spec_range(loaded_spec_begin(), loaded_spec_end());
+  }
+
+  spec_iterator loaded_spec_begin() const {
+    return makeSpecIterator(getCommonPtr()->Specializations, false);
+  }
+
+  spec_iterator loaded_spec_end() const {
+    return makeSpecIterator(getCommonPtr()->Specializations, true);
+  }
+
   /// Return whether this function template is an abbreviated function template,
   /// e.g. `void foo(auto x)` or `template<typename T> void foo(auto x)`
   bool isAbbreviated() const {
@@ -2421,6 +2435,20 @@ class ClassTemplateDecl : public RedeclarableTemplateDecl {
     return makeSpecIterator(getSpecializations(), true);
   }
 
+  /// All specializations that that have already been loaded, ie avoiding
+  /// deserialization of lazily registered specializations.
+  spec_range loaded_specializations() const {
+    return spec_range(loaded_spec_begin(), loaded_spec_end());
+  }
+
+  spec_iterator loaded_spec_begin() const {
+    return makeSpecIterator(getCommonPtr()->Specializations, false);
+  }
+
+  spec_iterator loaded_spec_end() const {
+    return makeSpecIterator(getCommonPtr()->Specializations, true);
+  }
+
   // Implement isa/cast/dyncast support
   static bool classof(const Decl *D) { return classofKind(D->getKind()); }
   static bool classofKind(Kind K) { return K == ClassTemplate; }
@@ -3166,6 +3194,20 @@ class VarTemplateDecl : public RedeclarableTemplateDecl {
     return makeSpecIterator(getSpecializations(), true);
   }
 
+  /// All specializations that that have already been loaded, ie avoiding
+  /// deserialization of lazily registered specializations.
+  spec_range loaded_specializations() const {
+    return spec_range(loaded_spec_begin(), loaded_spec_end());
+  }
+
+  spec_iterator loaded_spec_begin() const {
+    return makeSpecIterator(getCommonPtr()->Specializations, false);
+  }
+
+  spec_iterator loaded_spec_end() const {
+    return makeSpecIterator(getCommonPtr()->Specializations, true);
+  }
+
   // Implement isa/cast/dyncast support
   static bool classof(const Decl *D) { return classofKind(D->getKind()); }
   static bool classofKind(Kind K) { return K == VarTemplate; }