From c0763eac05f6e8adf05a1d94fc80ded1a9e14f2c Mon Sep 17 00:00:00 2001
From: Pierre-Emmanuel Patry <pierre-emmanuel.patry@embecosm.com>
Date: Wed, 26 Jul 2023 16:48:37 +0200
Subject: [PATCH] gccrs: proc_macro: Add is_available callback

Add a callback from gcc to determine wether the bridge is available or
not.

gcc/rust/ChangeLog:

	* expand/rust-proc-macro.cc (available): Add symbol
	registration.
	(load_macros_array): Likewise.

libgrust/ChangeLog:

	* libproc_macro/proc_macro.cc (not_available): Add a
	function to express bridge unavailability.
	* libproc_macro/proc_macro.h (not_available): Likewise.
	* libproc_macro/registration.h: Add symbol type.

Signed-off-by: Pierre-Emmanuel Patry <pierre-emmanuel.patry@embecosm.com>
---
 gcc/rust/expand/rust-proc-macro.cc    | 9 +++++++++
 libgrust/libproc_macro/proc_macro.cc  | 8 ++++++++
 libgrust/libproc_macro/proc_macro.h   | 3 +++
 libgrust/libproc_macro/registration.h | 3 +++
 4 files changed, 23 insertions(+)

diff --git a/gcc/rust/expand/rust-proc-macro.cc b/gcc/rust/expand/rust-proc-macro.cc
index 7843ead4412..b6cfe254394 100644
--- a/gcc/rust/expand/rust-proc-macro.cc
+++ b/gcc/rust/expand/rust-proc-macro.cc
@@ -56,6 +56,12 @@ static_assert (
 	       ProcMacro::from_str_function_t>::value,
   "Registration callback signature not synced, check proc macro internals.");
 
+static bool
+available ()
+{
+  return true;
+}
+
 template <typename Symbol, typename Callback>
 bool
 register_callback (void *handle, Symbol, std::string symbol_name,
@@ -95,6 +101,9 @@ load_macros_array (std::string path)
   if (!REGISTER_CALLBACK (handle, __gccrs_proc_macro_from_str_fn,
 			  tokenstream_from_string))
     return nullptr;
+  if (!REGISTER_CALLBACK (handle, __gccrs_proc_macro_is_available_fn,
+			  available))
+    return nullptr;
 
   // FIXME: Add CrateStableId handling, right now all versions may be loaded,
   // even incompatible ones.
diff --git a/libgrust/libproc_macro/proc_macro.cc b/libgrust/libproc_macro/proc_macro.cc
index a4046919721..1e9e3fdfaed 100644
--- a/libgrust/libproc_macro/proc_macro.cc
+++ b/libgrust/libproc_macro/proc_macro.cc
@@ -49,6 +49,14 @@ Procmacro::make_bang (const char *name, BangMacro macro)
   return {BANG, payload};
 }
 
+bool
+not_available ()
+{
+  return false;
+}
+
 } // namespace ProcMacro
 
 ProcMacro::from_str_function_t __gccrs_proc_macro_from_str_fn = nullptr;
+ProcMacro::is_available_function_t __gccrs_proc_macro_is_available_fn
+  = ProcMacro::not_available;
diff --git a/libgrust/libproc_macro/proc_macro.h b/libgrust/libproc_macro/proc_macro.h
index 80dd28216af..0b3ec3c4d55 100644
--- a/libgrust/libproc_macro/proc_macro.h
+++ b/libgrust/libproc_macro/proc_macro.h
@@ -99,6 +99,9 @@ struct ProcmacroArray
   Procmacro *macros;
 };
 
+bool
+not_available ();
+
 } // namespace ProcMacro
 
 #endif /* ! PROC_MACRO_H */
diff --git a/libgrust/libproc_macro/registration.h b/libgrust/libproc_macro/registration.h
index 5cefc37de11..76688632ced 100644
--- a/libgrust/libproc_macro/registration.h
+++ b/libgrust/libproc_macro/registration.h
@@ -29,9 +29,12 @@
 namespace ProcMacro {
 
 using from_str_function_t = ProcMacro::TokenStream (*) (std::string &, bool &);
+using is_available_function_t = bool (*) ();
 
 } // namespace ProcMacro
 
 extern "C" ProcMacro::from_str_function_t __gccrs_proc_macro_from_str_fn;
+extern "C" ProcMacro::is_available_function_t
+  __gccrs_proc_macro_is_available_fn;
 
 #endif /* !REGISTRATION_H */