gccrs: make distinction between error and empty for substution args

When handling generics of only lifetimes we have an empty
SubstitutionArgumentMappings which was being detected as an error but this
is not the case as we don't currently handle const generics or generic
lifetimes so this makes the distinction between an error occurred or its
simply empty because it was all only lifetime arguments and we don't care
about it.

Addresses #2043 #2039

gcc/rust/ChangeLog:

	* typecheck/rust-tyty-bounds.cc (TypeBoundPredicate::TypeBoundPredicate): this is an empty
	(TypeBoundPredicate::operator=): likewise
	* typecheck/rust-tyty-subst.cc (SubstitutionArgumentMappings::empty): new interface
	(SubstitutionArgumentMappings::is_error): this marks it as an error
	* typecheck/rust-tyty-subst.h: update prototypes

Signed-off-by: Philip Herron <herron.philip@googlemail.com>

3 files changed, 23 insertions, 10 deletions

diff --git a/gcc/rust/typecheck/rust-tyty-bounds.cc b/gcc/rust/typecheck/rust-tyty-bounds.cc
index af9c5e2..0fb6e7d 100644
--- a/gcc/rust/typecheck/rust-tyty-bounds.cc
+++ b/gcc/rust/typecheck/rust-tyty-bounds.cc
@@ -271,7 +271,7 @@ namespace TyTy {
 
 TypeBoundPredicate::TypeBoundPredicate (
   const Resolver::TraitReference &trait_reference, Location locus)
-  : SubstitutionRef ({}, SubstitutionArgumentMappings::error ()),
+  : SubstitutionRef ({}, SubstitutionArgumentMappings::empty ()),
     reference (trait_reference.get_mappings ().get_defid ()), locus (locus),
     error_flag (false)
 {
@@ -286,7 +286,7 @@ TypeBoundPredicate::TypeBoundPredicate (
 
 TypeBoundPredicate::TypeBoundPredicate (
   DefId reference, std::vector<SubstitutionParamMapping> subst, Location locus)
-  : SubstitutionRef ({}, SubstitutionArgumentMappings::error ()),
+  : SubstitutionRef ({}, SubstitutionArgumentMappings::empty ()),
     reference (reference), locus (locus), error_flag (false)
 {
   substitutions.clear ();
@@ -299,7 +299,7 @@ TypeBoundPredicate::TypeBoundPredicate (
 }
 
 TypeBoundPredicate::TypeBoundPredicate (const TypeBoundPredicate &other)
-  : SubstitutionRef ({}, SubstitutionArgumentMappings::error ()),
+  : SubstitutionRef ({}, SubstitutionArgumentMappings::empty ()),
     reference (other.reference), locus (other.locus),
     error_flag (other.error_flag)
 {
@@ -337,7 +337,7 @@ TypeBoundPredicate::operator= (const TypeBoundPredicate &other)
   reference = other.reference;
   locus = other.locus;
   error_flag = other.error_flag;
-  used_arguments = SubstitutionArgumentMappings::error ();
+  used_arguments = SubstitutionArgumentMappings::empty ();
 
   substitutions.clear ();
   for (const auto &p : other.get_substs ())
diff --git a/gcc/rust/typecheck/rust-tyty-subst.cc b/gcc/rust/typecheck/rust-tyty-subst.cc
index db31ff9..60bf219 100644
--- a/gcc/rust/typecheck/rust-tyty-subst.cc
+++ b/gcc/rust/typecheck/rust-tyty-subst.cc
@@ -236,16 +236,17 @@ SubstitutionArg::as_string () const
 SubstitutionArgumentMappings::SubstitutionArgumentMappings (
   std::vector<SubstitutionArg> mappings,
   std::map<std::string, BaseType *> binding_args, Location locus,
-  ParamSubstCb param_subst_cb, bool trait_item_flag)
+  ParamSubstCb param_subst_cb, bool trait_item_flag, bool error_flag)
   : mappings (mappings), binding_args (binding_args), locus (locus),
-    param_subst_cb (param_subst_cb), trait_item_flag (trait_item_flag)
+    param_subst_cb (param_subst_cb), trait_item_flag (trait_item_flag),
+    error_flag (error_flag)
 {}
 
 SubstitutionArgumentMappings::SubstitutionArgumentMappings (
   const SubstitutionArgumentMappings &other)
   : mappings (other.mappings), binding_args (other.binding_args),
     locus (other.locus), param_subst_cb (nullptr),
-    trait_item_flag (other.trait_item_flag)
+    trait_item_flag (other.trait_item_flag), error_flag (other.error_flag)
 {}
 
 SubstitutionArgumentMappings &
@@ -257,6 +258,7 @@ SubstitutionArgumentMappings::operator= (
   locus = other.locus;
   param_subst_cb = nullptr;
   trait_item_flag = other.trait_item_flag;
+  error_flag = other.error_flag;
 
   return *this;
 }
@@ -264,13 +266,21 @@ SubstitutionArgumentMappings::operator= (
 SubstitutionArgumentMappings
 SubstitutionArgumentMappings::error ()
 {
-  return SubstitutionArgumentMappings ({}, {}, Location (), nullptr, false);
+  return SubstitutionArgumentMappings ({}, {}, Location (), nullptr, false,
+				       true);
+}
+
+SubstitutionArgumentMappings
+SubstitutionArgumentMappings::empty ()
+{
+  return SubstitutionArgumentMappings ({}, {}, Location (), nullptr, false,
+				       false);
 }
 
 bool
 SubstitutionArgumentMappings::is_error () const
 {
-  return mappings.size () == 0;
+  return error_flag;
 }
 
 bool
diff --git a/gcc/rust/typecheck/rust-tyty-subst.h b/gcc/rust/typecheck/rust-tyty-subst.h
index b5a4181..639a275 100644
--- a/gcc/rust/typecheck/rust-tyty-subst.h
+++ b/gcc/rust/typecheck/rust-tyty-subst.h
@@ -109,7 +109,8 @@ public:
 				std::map<std::string, BaseType *> binding_args,
 				Location locus,
 				ParamSubstCb param_subst_cb = nullptr,
-				bool trait_item_flag = false);
+				bool trait_item_flag = false,
+				bool error_flag = false);
 
   SubstitutionArgumentMappings (const SubstitutionArgumentMappings &other);
   SubstitutionArgumentMappings &
@@ -120,6 +121,7 @@ public:
     = default;
 
   static SubstitutionArgumentMappings error ();
+  static SubstitutionArgumentMappings empty ();
 
   bool is_error () const;
 
@@ -161,6 +163,7 @@ private:
   Location locus;
   ParamSubstCb param_subst_cb;
   bool trait_item_flag;
+  bool error_flag;
 };
 
 class SubstitutionRef