Guard against overwiting function table for #1100 (#1104)

* Guard against overwiting function table for #1100

* set new slot to false as suggested by @zauguin

* change log for #1100

base/changes.txt

@@ -29,6 +29,12 @@ are not part of the distribution.
     * ltfilehook.dtx (subsection{Declaring a file substitution}):
     Drop a redundant \ExplSyntaxOff
 
+2023-07-02  David Carlisle  <David.Carlisle@latex-project.org>
+
+	* ltluatex.dtx modify new_luafunction to ensure
+	\e@alloc@luafunction@count always matches the size of the Lua
+	table of function allocations (gh100)
+
 2023-06-12  Joseph Wright  <Joseph.Wright@latex-project.org>
 
 	* usrguide.tex

base/ltluatex.dtx

@@ -1284,14 +1284,19 @@ luatexbase.new_chunkname = new_chunkname
 %
 % \begin{macro}{new_luafunction}
 % \changes{v1.1i}{2018/10/21}{Function added}
+% \changes{v1.2c}{2023/07/02}{Ensure existing table entries not overwritten gh/1100}
 % Much the same as for attribute allocation in Lua.
 % The optional \meta{name} argument is used in the log if given.
 %    \begin{macrocode}
 local luafunction_count_name =
                          luafunction_count_name or "e@alloc@luafunction@count"
 local function new_luafunction(name)
   tex_setcount("global", luafunction_count_name,
-                         tex_count[luafunction_count_name] + 1)
+                         math.max(
+                           #(lua.get_functions_table()),
+                           tex_count[luafunction_count_name])
+                          + 1)
+  lua.get_functions_table()[tex_count[luafunction_count_name]] = false
   if tex_count[luafunction_count_name] > 65534 then
     luatexbase_error("No room for a new luafunction register")
   end

base/testfiles-TU/github-1100.luatex.tlg

@@ -0,0 +1,9 @@
+This is a generated file for the LaTeX2e validation system.
+Don't change this file in any respect.
+> \fone=expandable luacall 25.
+l. ...\show\fone
+Lua function ftwo = ...
+> \ftwo=expandable luacall 26.
+l. ...\show\ftwo
+f1: FUNCTION 1
+f2: FUNCTION 2

base/testfiles-TU/github-1100.lvt

@@ -0,0 +1,32 @@
+\input test2e
+% github issue 1100
+\START
+\ifx\directlua\undefined
+  \expandafter\END
+\fi
+
+\directlua{
+  local lft = lua.get_functions_table()
+  lft[\string#lft+1] = function()
+  tex.sprint(-2, "FUNCTION 1")
+  end
+  token.set_lua("fone", \string#lft, "global")
+  }
+
+\show\fone
+
+\directlua{
+local func = luatexbase.new_luafunction('ftwo')
+token.set_lua('ftwo', func)
+lua.get_functions_table()[func] = function()
+ tex.sprint(-2, "FUNCTION 2")
+end
+}
+
+% should not be same as fone
+\show\ftwo
+
+\typeout{f1: \fone}
+\typeout{f2: \ftwo}
+
+\END

base/testfiles-TU/github-1100.tlg

@@ -0,0 +1,2 @@
+This is a generated file for the LaTeX2e validation system.
+Don't change this file in any respect.