From 095583f1fbab20937720f9311ddb9945ff2b9224 Mon Sep 17 00:00:00 2001
From: Boris Kolpackov <boris@codesynthesis.com>
Date: Mon, 18 Apr 2022 10:03:13 +0200
Subject: Switch recipe from std::function to butl::move_only_function_ex

---
 libbuild2/adhoc-rule-buildscript.cxx | 34 ++++------------------------------
 libbuild2/install/rule.cxx           |  2 +-
 libbuild2/recipe.cxx                 |  8 ++++----
 libbuild2/recipe.hxx                 | 19 ++++++++++---------
 libbuild2/types.hxx                  |  6 +++++-
 5 files changed, 24 insertions(+), 45 deletions(-)

diff --git a/libbuild2/adhoc-rule-buildscript.cxx b/libbuild2/adhoc-rule-buildscript.cxx
index 78891b9..aa30552 100644
--- a/libbuild2/adhoc-rule-buildscript.cxx
+++ b/libbuild2/adhoc-rule-buildscript.cxx
@@ -770,23 +770,10 @@ namespace build2
       mdb->bs = &bs;
       mdb->mt = update ? timestamp_nonexistent : mt;
 
-      // @@ TMP: re-enable once recipe becomes move_only_function.
-      //
-#if 0
-      return [this, md = move (mdb)] (action a, const target& t) mutable
-      {
-        auto r (perform_update_file_dyndep_byproduct (a, t, *md));
-        md.reset (); // @@ TMP: is this really necessary (+mutable)?
-        return r;
-      };
-#else
-      t.data (move (mdb));
-      return recipe ([this] (action a, const target& t) mutable
+      return [this, md = move (mdb)] (action a, const target& t)
       {
-        auto md (move (t.data<unique_ptr<match_data_byproduct>> ()));
         return perform_update_file_dyndep_byproduct (a, t, *md);
-      });
-#endif
+      };
     }
     else
     {
@@ -819,23 +806,10 @@ namespace build2
       md->mt = update ? timestamp_nonexistent : mt;
       md->deferred_failure = deferred_failure;
 
-      // @@ TMP: re-enable once recipe becomes move_only_function.
-      //
-#if 0
-      return [this, md = move (md)] (action a, const target& t) mutable
-      {
-        auto r (perform_update_file_dyndep (a, t, *md));
-        md.reset (); // @@ TMP: is this really necessary (+mutable)?
-        return r;
-      };
-#else
-      t.data (move (md));
-      return recipe ([this] (action a, const target& t) mutable
+      return [this, md = move (md)] (action a, const target& t)
       {
-        auto md (move (t.data<unique_ptr<match_data>> ()));
         return perform_update_file_dyndep (a, t, *md);
-      });
-#endif
+      };
     }
   }
 
diff --git a/libbuild2/install/rule.cxx b/libbuild2/install/rule.cxx
index 30f1755..1411143 100644
--- a/libbuild2/install/rule.cxx
+++ b/libbuild2/install/rule.cxx
@@ -342,7 +342,7 @@ namespace build2
     apply (action a, target& t) const
     {
       recipe r (apply_impl (a, t));
-      return r != nullptr ? r : noop_recipe;
+      return r != nullptr ? move (r) : noop_recipe;
     }
 
     recipe file_rule::
diff --git a/libbuild2/recipe.cxx b/libbuild2/recipe.cxx
index 3720059..eeafe87 100644
--- a/libbuild2/recipe.cxx
+++ b/libbuild2/recipe.cxx
@@ -7,8 +7,8 @@
 
 namespace build2
 {
-  const recipe empty_recipe;
-  const recipe noop_recipe (&noop_action);
-  const recipe default_recipe (&default_action);
-  const recipe group_recipe (&group_action);
+  recipe_function* const empty_recipe   = nullptr;
+  recipe_function* const noop_recipe    = &noop_action;
+  recipe_function* const default_recipe = &default_action;
+  recipe_function* const group_recipe   = &group_action;
 }
diff --git a/libbuild2/recipe.hxx b/libbuild2/recipe.hxx
index 508c059..dfe36ec 100644
--- a/libbuild2/recipe.hxx
+++ b/libbuild2/recipe.hxx
@@ -27,13 +27,14 @@ namespace build2
   // and while the prerequisite will be re-examined via another dependency,
   // this target is done).
   //
-  // Note that max size for the "small capture optimization" in std::function
-  // ranges (in pointer sizes) from 0 (GCC prior to 5) to 2 (GCC 5) to 6 (VC
-  // 14.2). With the size ranging (in bytes for 64-bit target) from 32 (GCC)
-  // to 64 (VC).
+  // Note that max size for the "small size optimization" in std::function
+  // (which is what move_only_function_ex is based on) ranges (in pointer
+  // sizes) from 0 (GCC libstdc++ prior to 5) to 2 (GCC 5 and later) to 3
+  // (Clang libc++) to 6 (VC 14.2). With the size ranging (in bytes for 64-bit
+  // target) from 32 (GCC) to 64 (VC).
   //
   using recipe_function = target_state (action, const target&);
-  using recipe = function<recipe_function>;
+  using recipe = move_only_function_ex<recipe_function>;
 
   // Commonly-used recipes.
   //
@@ -44,10 +45,10 @@ namespace build2
   // <libbuild2/algorithm.hxx> for details). The group recipe calls the
   // group's recipe.
   //
-  LIBBUILD2_SYMEXPORT extern const recipe empty_recipe;
-  LIBBUILD2_SYMEXPORT extern const recipe noop_recipe;
-  LIBBUILD2_SYMEXPORT extern const recipe default_recipe;
-  LIBBUILD2_SYMEXPORT extern const recipe group_recipe;
+  LIBBUILD2_SYMEXPORT extern recipe_function* const empty_recipe;
+  LIBBUILD2_SYMEXPORT extern recipe_function* const noop_recipe;
+  LIBBUILD2_SYMEXPORT extern recipe_function* const default_recipe;
+  LIBBUILD2_SYMEXPORT extern recipe_function* const group_recipe;
 }
 
 #endif // LIBBUILD2_RECIPE_HXX
diff --git a/libbuild2/types.hxx b/libbuild2/types.hxx
index 7bc6b32..cd6fdd8 100644
--- a/libbuild2/types.hxx
+++ b/libbuild2/types.hxx
@@ -59,6 +59,7 @@
 #include <libbutl/target-triplet.hxx>
 #include <libbutl/semantic-version.hxx>
 #include <libbutl/standard-version.hxx>
+#include <libbutl/move-only-function.hxx>
 
 #include <libbuild2/export.hxx>
 
@@ -82,9 +83,12 @@ namespace build2
   using std::pair;
   using std::tuple;
   using std::string;
-  using std::function;
   using std::reference_wrapper;
 
+  using std::function;
+  using butl::move_only_function;
+  using butl::move_only_function_ex;
+
   using strings = std::vector<string>;
   using cstrings = std::vector<const char*>;
 
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