feat(parse): recognize template specialization

Author: JohelEGP

regression-tests/pure2-template-specialization.cpp2

@@ -0,0 +1,2 @@
+t: @struct <T: type> type < T> type = { }
+main: ()                            = { }

regression-tests/test-results/clang-18/pure2-template-specialization.cpp.execution

@@ -0,0 +1,25 @@
+
+#define CPP2_USE_MODULES         Yes
+
+//=== Cpp2 type declarations ====================================================
+
+
+#include "cpp2util.h"
+
+#line 1 "pure2-template-specialization.cpp2"
+template<typename T> class t;
+
+
+//=== Cpp2 type definitions and function declarations ===========================
+
+#line 1 "pure2-template-specialization.cpp2"
+template<typename T> class t {};
+auto main() -> int;
+
+
+//=== Cpp2 function definitions =================================================
+
+
+#line 2 "pure2-template-specialization.cpp2"
+auto main() -> int                  {}
+

regression-tests/test-results/clang-18/pure2-template-specialization.cpp.output

@@ -0,0 +1,2 @@
+pure2-template-specialization.cpp2... ok (all Cpp2, passes safety checks)
+

regression-tests/test-results/pure2-template-specialization.cpp

@@ -2362,6 +2362,7 @@ struct declaration_node
 
     std::vector<std::unique_ptr<id_expression_node>> meta_functions;
     std::unique_ptr<parameter_declaration_list_node> template_parameters;
+    std::unique_ptr<unqualified_id_node>             specialization_template_arguments;
     source_position                                  requires_pos = {};
     std::unique_ptr<logical_or_expression_node>      requires_clause_expression;
 
@@ -4982,6 +4983,7 @@ class parser
     //G
     //G template-argument-list:
     //G     template-argument-list ',' template-argument
+    //G     template-argument
     //G
     //G template-argument:
     //G     # note: < > << >> are not allowed in expressions until new ( is opened
@@ -5031,20 +5033,20 @@ class parser
                         }
                         return expression(false);   // false == disallow unparenthesized relational comparisons in template args
                     }()
-                ) 
+                )
                 {
                     term.arg = std::move(e);
                 }
-                    
+
                 //  Else try parsing it as a type id
                 else if (auto i = type_id()) {
                     term.arg = std::move(i);
                 }
-                    
+
                 else {
                     break;
                 }
-                
+
                 n->template_args.push_back( std::move(term) );
             }
             //  Use the lambda trick to jam in a "next" clause
@@ -6452,9 +6454,9 @@ class parser
 
     //G unnamed-declaration:
     //G     ':' meta-functions-list? template-parameter-declaration-list? function-type requires-clause? '=' statement
-    //G     ':' meta-functions-list? template-parameter-declaration-list? type-id? requires-clause? '=' statement
+    //G     ':' meta-functions-list? template-parameter-declaration-list? template-specialization-argument-list? type-id? requires-clause? '=' statement
     //G     ':' meta-functions-list? template-parameter-declaration-list? type-id
-    //G     ':' meta-functions-list? template-parameter-declaration-list? 'final'? 'type' requires-clause? '=' statement
+    //G     ':' meta-functions-list? template-parameter-declaration-list? template-specialization-argument-list? 'final'? 'type' requires-clause? '=' statement
     //G     ':' 'namespace' '=' statement
     //G
     //G meta-functions-list:
@@ -6465,7 +6467,10 @@ class parser
     //G     'requires' logical-or-expression
     //G
     //G template-parameter-declaration-list
-    //G     '<' parameter-declaration-seq '>'
+    //G     '<' parameter-declaration-seq? '>'
+    //G
+    //G template-specialization-argument-list:
+    //G     'type' '<' template-argument-list '>'
     //G
     auto unnamed_declaration(
         source_position                      start,
@@ -6602,6 +6607,21 @@ class parser
             n->template_parameters = std::move(template_parameters);
         }
 
+        //  Next is an optional template specialization argument list
+        if (
+            curr() == "type"
+            && peek(1)
+            && peek(1)->type() == lexeme::Less
+            )
+        {
+          auto specialization_template_arguments = unqualified_id();
+          if (!specialization_template_arguments) {
+            error("invalid template specialization argument list");
+            return {};
+          }
+          n->specialization_template_arguments = std::move(specialization_template_arguments);
+        }
+
         auto guard =
             captures_allowed
             ? std::make_unique<capture_groups_stack_guard>(this, &n->captures)