[core] Centralize using decls injected into cling, add more.

core/clingutils/res/TClingUtils.h

@@ -740,6 +740,9 @@ void SetPathsForRelocatability(std::vector<std::string>& clingArgs);
 //______________________________________________________________________________
 void ReplaceAll(std::string& str, const std::string& from, const std::string& to, bool recurse=false);
 
+//______________________________________________________________________________
+std::string GetInjectedUsingDecls();
+
 // Functions for the printouts -------------------------------------------------
 
 //______________________________________________________________________________

core/clingutils/src/TClingUtils.cxx

@@ -5098,6 +5098,49 @@ bool ROOT::TMetaUtils::IsHeaderName(const std::string &filename)
           llvm::sys::path::extension(filename) == "HXX";
 }
 
+////////////////////////////////////////////////////////////////////////////////
+/// Get the using decls (and corresponding `#includes`) injected into cling for
+/// backward compatibility with the earlier `using namespace std`.
+std::string ROOT::TMetaUtils::GetInjectedUsingDecls() {
+   return R"CODE(#include <array>
+#include <bitset>
+#include <cmath>
+#include <iostream>
+#include <list>
+#include <map>
+#include <memory>
+#include <set>
+#include <string>
+#include <unordered_map>
+#include <unordered_set>
+#include <utility>
+#include <vector>
+using std::abs;
+using std::fabs;
+using std::array;
+using std::bitset;
+using std::cerr;
+using std::cos;
+using std::cout;
+using std::endl;
+using std::list;
+using std::map;
+using std::multimap;
+using std::multiset;
+using std::pair;
+using std::round;
+using std::set;
+using std::sin;
+using std::shared_ptr;
+using std::string;
+using std::tan;
+using std::unique_ptr;
+using std::unordered_map;
+using std::unordered_set;
+using std::vector;
+)CODE";
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 
 const std::string ROOT::TMetaUtils::AST2SourceTools::Decls2FwdDecls(const std::vector<const clang::Decl *> &decls,

core/dictgen/src/rootcling_impl.cxx

@@ -2841,27 +2841,12 @@ void CreateDictHeader(std::ostream &dictStream, const std::string &main_dictname
                << "#include \"TDataMember.h\"\n\n"; // To set their transiency
 
    if (main_dictname.length() > 11 && main_dictname.substr(main_dictname.length() - 11) == "_ACLiC_dict")
-      dictStream << "#include <bitset>\n"
-                    "#include <forward_list>\n"
-                    "#include <list>\n"
-                    "#include <map>\n"
-                    "#include <memory>\n"
-                    "#include <set>\n"
-                    "#include <string>\n"
-                    "#include <unordered_map>\n"
-                    "#include <unordered_set>\n"
-                    "#include <utility>\n"
-                    "#include <vector>\n"
-                    "using std::allocator; using std::bitset; using std::default_delete; using "
-                    "std::forward_list; using std::list; using std::map; using std::multimap; using "
-                    "std::multiset; using std::pair; using std::set; using std::shared_ptr; using std::string; "
-                    "using std::unique_ptr; using std::unordered_multimap; using std::unordered_map; using "
-                    "std::unordered_multiset; using std::unordered_set; using std::vector;\n";
+      dictStream << ROOT::TMetaUtils::GetInjectedUsingDecls();
 }
 
 ////////////////////////////////////////////////////////////////////////////////
 
-void AddNamespaceSTDdeclaration(std::ostream &dictStream)
+void AddNamespaceSTDdeclaration(std::ostream & dictStream)
 {
 }
 

core/metacling/src/TCling.cxx

@@ -1330,9 +1330,8 @@ static void RegisterPreIncludedHeaders(cling::Interpreter &clingInterp)
 #ifndef R__WIN32
    PreIncludes += "#include <cassert>\n";
 #endif
-   PreIncludes += "#include <string>\n"
-      "#include <vector>\n"
-      "using std::string; using std::vector;\n";
+   PreIncludes += ROOT::TMetaUtils::GetInjectedUsingDecls();
+
    clingInterp.declare(PreIncludes);
 }