[gcc r14-7991] gccrs: Clarify package import procedure

[gcc r14-7991] gccrs: Clarify package import procedure

[Arthur Cohen]

https://gcc.gnu.org/g:3713338d986b750a56ca60c9683727d972c47f90

commit r14-7991-g3713338d986b750a56ca60c9683727d972c47f90
Author: Pierre-Emmanuel Patry <pierre-emmanuel.patry@embecosm.com>
Date:   Mon Sep 4 12:19:13 2023 +0200

    gccrs: Clarify package import procedure
    
    This part of the code is a bit tricky as it calls multiple functions
    with almost the same name and slightly different behaviors. It was even
    more with a meaningless variable name.
    
    gcc/rust/ChangeLog:
    
            * rust-session-manager.cc (Session::load_extern_crate): Change
            variable name, add temporaries and comments.
    
    Signed-off-by: Pierre-Emmanuel Patry <pierre-emmanuel.patry@embecosm.com>

Diff:
---
 gcc/rust/rust-session-manager.cc | 24 ++++++++++++++++--------
 1 file changed, 16 insertions(+), 8 deletions(-)

diff --git a/gcc/rust/rust-session-manager.cc b/gcc/rust/rust-session-manager.cc
index 2a8ef972131..63f839e7c9d 100644
--- a/gcc/rust/rust-session-manager.cc
+++ b/gcc/rust/rust-session-manager.cc
@@ -1008,27 +1008,35 @@ Session::load_extern_crate (const std::string &crate_name, location_t locus)
   auto cli_extern_crate = extern_crates.find (crate_name);
 
   std::pair<std::unique_ptr<Import::Stream>, std::vector<ProcMacro::Procmacro>>
-    s;
+    package_result;
   if (cli_extern_crate != extern_crates.end ())
     {
       auto path = cli_extern_crate->second;
-      s = Import::try_package_in_directory (path, locus);
+      package_result = Import::try_package_in_directory (path, locus);
     }
   else
     {
-      s = Import::open_package (import_name, locus, relative_import_path);
+      package_result
+	= Import::open_package (import_name, locus, relative_import_path);
     }
-  if (s.first == NULL && s.second.empty ())
+
+  auto stream = std::move (package_result.first);
+  auto proc_macros = std::move (package_result.second);
+
+  if (stream == NULL	       // No stream and
+      && proc_macros.empty ()) // no proc macros
     {
       rust_error_at (locus, "failed to locate crate %<%s%>",
 		     import_name.c_str ());
       return UNKNOWN_NODEID;
     }
 
-  auto extern_crate = s.first == nullptr
-			? Imports::ExternCrate (crate_name, s.second)
-			: Imports::ExternCrate (*s.first);
-  if (s.first != nullptr)
+  auto extern_crate
+    = stream == nullptr
+	? Imports::ExternCrate (crate_name,
+				proc_macros) // Import proc macros
+	: Imports::ExternCrate (*stream);    // Import from stream
+  if (stream != nullptr)
     {
       bool ok = extern_crate.load (locus);
       if (!ok)