PALNoAlloc should delegate more to underlying PAL

src/pal/pal_concept.h

@@ -8,17 +8,29 @@
 
 namespace snmalloc
 {
+
+  /*
+   * These concepts enforce that these are indeed constants that fit in the
+   * desired types.  (This is subtly different from saying that they are the
+   * required types; C++ may handle constants without much regard for their
+   * claimed type.)
+   */
+
   /**
-   * PALs must advertize the bit vector of their supported features and the
-   * platform's page size.  This concept enforces that these are indeed
-   * constants that fit in the desired types.  (This is subtly different from
-   * saying that they are the required types; C++ may handle constants without
-   * much regard for their claimed type.)
+   * PALs must advertize the bit vector of their supported features.
    */
   template<typename PAL>
-  concept ConceptPAL_static_members = requires()
+  concept ConceptPAL_static_features = requires()
   {
     typename std::integral_constant<uint64_t, PAL::pal_features>;
+  };
+
+  /**
+   * PALs must advertise their page size
+   */
+  template<typename PAL>
+  concept ConceptPAL_static_sizes = requires()
+  {
     typename std::integral_constant<std::size_t, PAL::page_size>;
   };
 
@@ -93,7 +105,8 @@ namespace snmalloc
    */
   template<typename PAL>
   concept ConceptPAL =
-    ConceptPAL_static_members<PAL> &&
+    ConceptPAL_static_features<PAL> &&
+    ConceptPAL_static_sizes<PAL> &&
     ConceptPAL_error<PAL> &&
     ConceptPAL_memops<PAL> &&
     (!pal_supports<Entropy, PAL> ||

src/pal/pal_noalloc.h

@@ -4,23 +4,29 @@
 #pragma once
 
 #include "../aal/aal.h"
+#include "pal_concept.h"
 #include "pal_consts.h"
 
 #include <cstring>
 
 namespace snmalloc
 {
+#ifdef __cpp_concepts
+  /**
+   * The minimal subset of a PAL that we need for delegation
+   */
+  template<typename PAL>
+  concept PALNoAllocBase = ConceptPAL_static_sizes<PAL>&& ConceptPAL_error<PAL>;
+#endif
+
   /**
    * Platform abstraction layer that does not allow allocation.
    *
    * This is a minimal PAL for pre-reserved memory regions, where the
    * address-space manager is initialised with all of the memory that it will
    * ever use.
-   *
-   * It takes an error handler delegate as a template argument. This is
-   * expected to forward to the default PAL in most cases.
    */
-  template<typename ErrorHandler>
+  template<SNMALLOC_CONCEPT(PALNoAllocBase) BasePAL>
   struct PALNoAlloc
   {
     /**
@@ -29,14 +35,14 @@ namespace snmalloc
      */
     static constexpr uint64_t pal_features = NoAllocation;
 
-    static constexpr size_t page_size = Aal::smallest_page_size;
+    static constexpr size_t page_size = BasePAL::page_size;
 
     /**
      * Print a stack trace.
      */
     static void print_stack_trace()
     {
-      ErrorHandler::print_stack_trace();
+      BasePAL::print_stack_trace();
     }
 
     /**
@@ -44,7 +50,7 @@ namespace snmalloc
      */
     [[noreturn]] static void error(const char* const str) noexcept
     {
-      ErrorHandler::error(str);
+      BasePAL::error(str);
     }
 
     /**