[Tarantool-patches] [PATCH v2] luajit: adde flag of partial comp. with Lua 5.2

[Olga Arkhangelskaia]

Although we do not turn on full compatibility with Lua 5.2 we do need pairs/ipairs
metamethods. Patch introduces LUAJIT_ENABLE_PAIRSMM flag.
If the flag is set - metamethods are available.
---
Closes #4560
Branch https://github.com/tarantool/luajit/tree/OKriw/gh-4560-Enable-LUAJIT_ENABLE_LUA52COMPAT-when-bulding-luajit

Changes in v2:
- flag is renamed
- now flag is used only for pairsmm
- added test case


 src/Makefile          |  3 +++
 src/lib_base.c        |  4 ++--
 src/lj_arch.h         |  6 ++++++
 src/lj_obj.h          |  2 +-
 src/vm_x86.dasc       |  4 ++--
 test/mmpairs_test.lua | 48 +++++++++++++++++++++++++++++++++++++++++++
 6 files changed, 62 insertions(+), 5 deletions(-)
 create mode 100755 test/mmpairs_test.lua

diff --git a/src/Makefile b/src/Makefile
index 827d4a4..af84f0c 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -101,6 +101,9 @@ XCFLAGS=
 # Note: this does not provide full compatibility with Lua 5.2 at this time.
 #XCFLAGS+= -DLUAJIT_ENABLE_LUA52COMPAT
 #
+#Enable pairs/ipairs methametods from  Lua 5.2.
+XCFLAGS+= -DLUAJIT_ENABLE_PAIRSMM
+#
 # Disable the JIT compiler, i.e. turn LuaJIT into a pure interpreter.
 #XCFLAGS+= -DLUAJIT_DISABLE_JIT
 #
diff --git a/src/lib_base.c b/src/lib_base.c
index 3a75787..950a580 100644
--- a/src/lib_base.c
+++ b/src/lib_base.c
@@ -81,12 +81,12 @@ LJLIB_ASM(next)
   return FFH_UNREACHABLE;
 }
 
-#if LJ_52 || LJ_HASFFI
+#if LJ_PAIRSMM || LJ_HASFFI
 static int ffh_pairs(lua_State *L, MMS mm)
 {
   TValue *o = lj_lib_checkany(L, 1);
   cTValue *mo = lj_meta_lookup(L, o, mm);
-  if ((LJ_52 || tviscdata(o)) && !tvisnil(mo)) {
+  if ((LJ_PAIRSMM || tviscdata(o)) && !tvisnil(mo)) {
     L->top = o+1;  /* Only keep one argument. */
     copyTV(L, L->base-1-LJ_FR2, mo);  /* Replace callable. */
     return FFH_TAILCALL;
diff --git a/src/lj_arch.h b/src/lj_arch.h
index c8d7138..6dfb4fb 100644
--- a/src/lj_arch.h
+++ b/src/lj_arch.h
@@ -564,4 +564,10 @@
 #define LJ_52			0
 #endif
 
+/* Partial compatibility with Lua 5.2 */
+#if defined(LUAJIT_ENABLE_PAIRSMM) || defined (LUAJIT_ENABLE_LUA52COMPAT)
+#define LJ_PAIRSMM			1
+#else
+#define LJ_PAIRSMM			0
+#endif
 #endif
diff --git a/src/lj_obj.h b/src/lj_obj.h
index f368578..4d0693f 100644
--- a/src/lj_obj.h
+++ b/src/lj_obj.h
@@ -530,7 +530,7 @@ enum {
 #define MMDEF_FFI(_)
 #endif
 
-#if LJ_52 || LJ_HASFFI
+#if LJ_HASFFI || LJ_PAIRSMM
 #define MMDEF_PAIRS(_) _(pairs) _(ipairs)
 #else
 #define MMDEF_PAIRS(_)
diff --git a/src/vm_x86.dasc b/src/vm_x86.dasc
index 56bee14..eae07f7 100644
--- a/src/vm_x86.dasc
+++ b/src/vm_x86.dasc
@@ -1724,7 +1724,7 @@ static void build_subroutines(BuildCtx *ctx)
   |.ffunc_1 pairs
   |  mov TAB:RB, [BASE]
   |  cmp dword [BASE+4], LJ_TTAB;  jne ->fff_fallback
-#if LJ_52
+#if LJ_PAIRSMM
   |  cmp dword TAB:RB->metatable, 0; jne ->fff_fallback
 #endif
   |  mov CFUNC:RB, [BASE-8]
@@ -1791,7 +1791,7 @@ static void build_subroutines(BuildCtx *ctx)
   |.ffunc_1 ipairs
   |  mov TAB:RB, [BASE]
   |  cmp dword [BASE+4], LJ_TTAB;  jne ->fff_fallback
-#if LJ_52
+#if LJ_PAIRSMM
   |  cmp dword TAB:RB->metatable, 0; jne ->fff_fallback
 #endif
   |  mov CFUNC:RB, [BASE-8]
diff --git a/test/mmpairs_test.lua b/test/mmpairs_test.lua
new file mode 100755
index 0000000..3334c2d
--- /dev/null
+++ b/test/mmpairs_test.lua
@@ -0,0 +1,48 @@
+#!/usr/bin/env tarantool
+
+tap = require('tap')
+
+test = tap.test("PAIRSMM-is-set")
+test:plan(2)
+
+--- To make sure that we are using only pairs/ipairs mmethods within Lua5.1
+--- we use os.execute, because its interface has changed significantly in 5.2
+
+local mt = {
+	__pairs = function(self)
+            local function stateless_iter(tbl, k)
+                local v
+                k, v = next(tbl, k)
+                while k and v > 0 do k, v = next(tbl, k) end
+                if v then return k,v end
+            end
+        return stateless_iter, self, nil 
+        end,
+        __ipairs = function(self)
+            local function stateless_iter(tbl, k)
+                local v
+                k, v = next(tbl, k)
+                while k and v < 0 do k, v = next(tbl, k) end
+                if v then return k,v end
+            end
+        return stateless_iter, self, nil 
+        end
+}
+
+local t = setmetatable({ }, mt)
+t[1]  = 10
+t[2]  = 20
+t[3] = -10
+t[4] = -20
+
+local pairs_res = 0
+local ipairs_res = 0
+for k, v in pairs(t) do
+    pairs_res = v + pairs_res
+end
+for k, v in ipairs(t) do
+    ipairs_res = v + ipairs_res
+end
+test:is(pairs_res + ipairs_res, 0)
+os_exec_res = os.execute()
+test:is(os_exec_res, 1)
-- 
2.20.1 (Apple Git-117)