Merge pull request #7485 from xmake-io/pairs

improve pairs for lua5.5

5 files changed, 117 insertions, 52 deletions

diff --git a/xmake/core/base/hashset.lua b/xmake/core/base/hashset.lua
index c052d36ee..405a23474 100644
--- a/xmake/core/base/hashset.lua
+++ b/xmake/core/base/hashset.lua
@@ -119,15 +119,27 @@ end
 -- end
 -- @endcode
 --
+-- Stateful closure so the loop body can safely reassign the first loop
+-- variable under lua 5.4+ (paired with the RDKCONST->VDKREG compile-time
+-- patch in core/src/lua/xmake.lua).
 function hashset:items()
-    return function (t, item)
-        local k, _ = next(t._DATA, item)
-        if k == hashset._NIL then
-            return nil
-        else
-            return k
-        end
-    end, self, nil
+    -- keep `next`'s key in an upvalue so the loop body can safely reassign
+    -- the first loop variable. In lua 5.4+ the for-in control slot is
+    -- merged with the first user variable; threading the key through the
+    -- loop would otherwise corrupt `next` on the following iteration.
+    --
+    -- nil-as-a-member is stored under the `_NIL` sentinel. For-loop
+    -- semantics don't let us yield nil (it would end the loop), so we
+    -- skip the sentinel and continue to the next real key; the nil
+    -- member is omitted but entries after it are still visited.
+    local data = self._DATA
+    local k = nil
+    return function ()
+        repeat
+            k = next(data, k)
+        until k ~= hashset._NIL
+        return k
+    end
 end
 
 -- iterate order items
@@ -154,16 +166,18 @@ function hashset:orderitems()
         end
         return a < b
     end)
-    local i = 1
-    return function (t, k)
-        k = orderkeys[i]
-        i = i + 1
-        if k == hashset._NIL then
-            return nil
-        else
-            return k
-        end
-    end, self, nil
+    -- see hashset:items() for the `_NIL` handling rationale
+    local n = #orderkeys
+    local i = 0
+    return function ()
+        local k
+        repeat
+            i = i + 1
+            if i > n then return nil end
+            k = orderkeys[i]
+        until k ~= hashset._NIL
+        return k
+    end
 end
 
 -- iterate keys (deprecated, please use items())
@@ -175,14 +189,19 @@ end
 -- @endcode
 --
 function hashset:keys()
-    return function (t, key)
-        local k, _ = next(t._DATA, key)
-        if k == hashset._NIL then
-            return k, nil
-        else
-            return k, k
+    -- see hashset:items() for the stateful-closure rationale and the
+    -- `_NIL` skipping behavior.
+    local data = self._DATA
+    local k = nil
+    return function ()
+        repeat
+            k = next(data, k)
+        until k ~= hashset._NIL
+        if k == nil then
+            return nil
         end
-    end, self, nil
+        return k, k
+    end
 end
 
 -- iterate order keys (deprecated, please use orderitems())
@@ -194,6 +213,8 @@ end
 -- @endcode
 --
 function hashset:orderkeys()
+    -- see hashset:items() for the stateful-closure rationale and the
+    -- `_NIL` skipping behavior.
     local orderkeys = table.keys(self._DATA)
     table.sort(orderkeys, function (a, b)
         if a == hashset._NIL then
@@ -210,16 +231,17 @@ function hashset:orderkeys()
         end
         return a < b
     end)
-    local i = 1
-    return function (t, k)
-        k = orderkeys[i]
-        i = i + 1
-        if k == hashset._NIL then
-            return k, nil
-        else
-            return k, k
-        end
-    end, self, nil
+    local n = #orderkeys
+    local i = 0
+    return function ()
+        local k
+        repeat
+            i = i + 1
+            if i > n then return nil end
+            k = orderkeys[i]
+        until k ~= hashset._NIL
+        return k, k
+    end
 end
 
 -- get size of hashset
diff --git a/xmake/core/base/list.lua b/xmake/core/base/list.lua
index 4caed81bc..222a6e85d 100644
--- a/xmake/core/base/list.lua
+++ b/xmake/core/base/list.lua
@@ -238,22 +238,31 @@ end
 --
 -- @return      the iterator function
 --
+-- Stateful closure so the loop body can safely reassign the first loop
+-- variable under lua 5.4+ (paired with the RDKCONST->VDKREG compile-time
+-- patch in core/src/lua/xmake.lua).
 function list:items()
-    local iter = function (list, item)
-        return list:next(item)
+    -- stateful closure: keep the cursor in an upvalue so the loop body
+    -- can safely reassign the first loop variable (lua 5.4+ merges the
+    -- for-in control slot with the first user variable).
+    local item = nil
+    return function ()
+        item = self:next(item)
+        return item
     end
-    return iter, self, nil
 end
 
 -- iterate elements from back to front
 --
 -- @return      the reverse iterator function
 --
+-- Stateful closure; see `list:items()` for the rationale.
 function list:ritems()
-    local iter = function (list, item)
-        return list:prev(item)
+    local item = nil
+    return function ()
+        item = self:prev(item)
+        return item
     end
-    return iter, self, nil
 end
 
 -- create a new doubly-linked list
diff --git a/xmake/core/sandbox/modules/ipairs.lua b/xmake/core/sandbox/modules/ipairs.lua
index 19591fce5..d910eb2b7 100644
--- a/xmake/core/sandbox/modules/ipairs.lua
+++ b/xmake/core/sandbox/modules/ipairs.lua
@@ -22,6 +22,10 @@
 local table = require("base/table")
 
 -- improve ipairs, wrap nil and single value
+--
+-- Like sandbox `pairs`, this is a stateful closure so the loop body can
+-- safely reassign the first loop variable under lua 5.4+ (paired with
+-- the RDKCONST->VDKREG compile-time patch in core/src/lua/xmake.lua).
 function sandbox_ipairs(t)
 
     -- exists the custom ipairs?
@@ -34,15 +38,21 @@ function sandbox_ipairs(t)
     if not is_table then
         t = t ~= nil and {t} or {}
     end
-    return function (t, i)
+    -- keep the index in an upvalue so the loop body can safely reassign
+    -- the first loop variable. In lua 5.4+ the for-in control slot is
+    -- merged with the first user variable; writes to it would otherwise
+    -- silently skip or repeat entries on the next iteration.
+    local i = 0
+    return function ()
         i = i + 1
         local v = t[i]
         if v ~= nil then
             return i, v
         end
-    end, t, 0
+    end
 end
 
+
 -- load module
 return sandbox_ipairs
 
diff --git a/xmake/core/sandbox/modules/irpairs.lua b/xmake/core/sandbox/modules/irpairs.lua
index 486f89506..c2224b2e1 100644
--- a/xmake/core/sandbox/modules/irpairs.lua
+++ b/xmake/core/sandbox/modules/irpairs.lua
@@ -40,14 +40,22 @@ local table = require("base/table")
 -- end
 --
 -- @endcode
+--
+-- Implemented as a stateful closure so the loop body can safely
+-- reassign the first loop variable under lua 5.4+ (paired with the
+-- RDKCONST->VDKREG compile-time patch in core/src/lua/xmake.lua).
 function sandbox_irpairs(t, filter, ...)
 
     -- has filter?
     local has_filter = type(filter) == "function"
 
-    -- init iterator
+    -- stateful closure: keep the index in an upvalue so the loop body
+    -- can safely reassign the first loop variable (lua 5.4+ merges the
+    -- for-in control slot with the first user variable).
     local args = table.pack(...)
-    local iter = function (t, i)
+    t = table.wrap(t)
+    local i = table.getn(t) + 1
+    return function ()
         i = i - 1
         local v = t[i]
         if v ~= nil then
@@ -57,10 +65,6 @@ function sandbox_irpairs(t, filter, ...)
             return i, v
         end
     end
-
-    -- return iterator and initialized state
-    t = table.wrap(t)
-    return iter, t, table.getn(t) + 1
 end
 
 -- load module
diff --git a/xmake/core/sandbox/modules/pairs.lua b/xmake/core/sandbox/modules/pairs.lua
index 50fa4d10e..dc162bc47 100644
--- a/xmake/core/sandbox/modules/pairs.lua
+++ b/xmake/core/sandbox/modules/pairs.lua
@@ -22,6 +22,19 @@
 local table = require("base/table")
 
 -- improve pairs, wrap nil/single value
+--
+-- Unlike the stock lua `pairs`, this sandbox version tolerates the loop
+-- body reassigning the first loop variable, e.g.:
+--
+--   for k, v in pairs(t) do
+--       k = k:gsub("_", "-")   -- safe here
+--       ...
+--   end
+--
+-- This works together with the `RDKCONST -> VDKREG` compile-time patch
+-- applied to lparser.c in core/src/lua/xmake.lua (and xmake.sh): that
+-- patch lifts lua 5.4+'s ban on writing to the for-in control variable,
+-- and this stateful closure makes such writes harmless at runtime.
 function sandbox_pairs(t)
 
     -- exists the custom ipairs?
@@ -34,9 +47,16 @@ function sandbox_pairs(t)
     if not is_table then
         t = t ~= nil and {t} or {}
     end
-    return function (t, i)
-        return next(t, i)
-    end, t, nil
+    -- keep `next`'s key in an upvalue so the loop body can safely reassign
+    -- the first loop variable. In lua 5.4+ the for-in control slot is
+    -- merged with the first user variable; if we threaded the key through
+    -- the loop it would corrupt `next` on the following iteration.
+    local k = nil
+    return function ()
+        local nk, nv = next(t, k)
+        k = nk
+        return nk, nv
+    end
 end
 
 -- load module