c++, contracts: Add support for a contract scope.

This allows us to associate a scope with contract checks which
is necessary to disambiguate cases where lambdas are permitted
to have captures.

Signed-off-by: Iain Sandoe <[email protected]>

Author: iains

gcc/cp/name-lookup.cc

@@ -4630,7 +4630,8 @@ cp_binding_level_descriptor (cp_binding_level *scope)
     "template-parameter-scope",
     "template-explicit-spec-scope",
     "transaction-scope",
-    "openmp-scope"
+    "openmp-scope",
+    "contract-check-scope"
   };
   static_assert (ARRAY_SIZE (scope_kind_names) == sk_count,
 		 "must keep names aligned with scope_kind enum");
@@ -4720,6 +4721,7 @@ begin_scope (scope_kind kind, tree entity)
     case sk_scoped_enum:
     case sk_transaction:
     case sk_omp:
+    case sk_contract:
     case sk_stmt_expr:
       scope->keep = keep_next_level_flag;
       break;

gcc/cp/name-lookup.h

@@ -214,6 +214,7 @@ enum scope_kind {
 			"template <>", this scope is always empty.  */
   sk_transaction,    /* A synchronized or atomic statement.  */
   sk_omp,	     /* An OpenMP structured block.  */
+  sk_contract,	     /* A P2900 contract.  */
   sk_count	     /* Number of scope_kind enumerations.  */
 };
 
@@ -287,7 +288,7 @@ struct GTY(()) cp_binding_level {
   /* The kind of scope that this object represents.  However, a
       SK_TEMPLATE_SPEC scope is represented with KIND set to
       SK_TEMPLATE_PARMS and EXPLICIT_SPEC_P set to true.  */
-  ENUM_BITFIELD (scope_kind) kind : 4;
+  ENUM_BITFIELD (scope_kind) kind : 5;
 
   /* True if this scope is an SK_TEMPLATE_SPEC scope.  This field is
       only valid if KIND == SK_TEMPLATE_PARMS.  */
@@ -315,7 +316,7 @@ struct GTY(()) cp_binding_level {
      parent scope.  */
   unsigned artificial : 1;
 
-  /* 21 bits left to fill a 32-bit word.  */
+  /* 20 bits left to fill a 32-bit word.  */
 };
 
 /* The binding level currently in effect.  */