fix: emit bxor, not bnot, for binary '~' at gen-target 5.1 (#1168)

The '~' token is both unary bitwise NOT and binary bitwise XOR, and the
5.1 compat pass matched on the operator token alone. Binary '~' was
rewritten to bit32.bnot(a), dropping the right operand and changing the
operation; a __bxor metamethod call was dispatched to __bnot. Check the
arity so binary '~' falls through to the existing bit_operators branch.

spec/util.lua built its line arrays with gmatch("([^\n]*)\n"), which
drops the final line, so a util.gen mismatch confined to the last line
of generated output was never reported. That hid the metamethod half of
this bug from the new test and from the existing __bnot metamethod test.

Co-authored-by: Dylan Pulver <dylanpulver@users.noreply.github.com>

Author: dylanpulver

spec/lang/compat/lua_versions_spec.lua

@@ -30,6 +30,20 @@ describe("Lua version compatibility", function()
       local x = bit32.band(2, (bit32.bor(bit32.rshift(c, bit32.bnot(4)), 0xff)))
    ]], "5.1"))
 
+   it("distinguishes unary and binary '~' operators", util.gen([[
+
+
+      local c = 0xcafebabe
+      local x = c ~ 0xff
+      local y = ~c ~ c
+   ]], [[
+      local bit32 = bit32; if not bit32 then local p, m = pcall(require, 'bit32'); if p then bit32 = m end end
+
+      local c = 0xcafebabe
+      local x = bit32.bxor(c, 0xff)
+      local y = bit32.bxor(bit32.bnot(c), c)
+   ]], "5.1"))
+
    it("generates compat code for bitwise unary operator metamethods", util.gen([[
 
       local type Rec = record
@@ -100,6 +114,42 @@ describe("Lua version compatibility", function()
       print(_tl_mt("__shl", 1, r, s))
    ]], "5.1"))
 
+   it("generates compat code for the binary '~' operator metamethod", util.gen([[
+
+      local type Rec = record
+         x: number
+         metamethod __bxor: function(Rec, Rec): number
+      end
+
+      local rec_mt: metatable<Rec> = {
+         __bxor = function(a: Rec, b: Rec): number
+            return a.x + b.x
+         end
+      }
+
+      local r = setmetatable({} as Rec, rec_mt)
+      local s = setmetatable({} as Rec, rec_mt)
+
+      print(r ~ s)
+   ]], [[
+      local _tl_mt = function(m, s, a, b) return (getmetatable(s == 1 and a or b)[m](a, b)) end
+
+
+
+
+
+      local rec_mt = {
+         __bxor = function(a, b)
+            return a.x + b.x
+         end,
+      }
+
+      local r = setmetatable({}, rec_mt)
+      local s = setmetatable({}, rec_mt)
+
+      print(_tl_mt("__bxor", 1, r, s))
+   ]], "5.1"))
+
    -- varargs
    it("generates compatibility code for named varargs with Lua 5.1", util.gen([[
 

spec/util.lua

@@ -743,12 +743,12 @@ local function gen(lax, code, expected, gen_target, type_errors)
          local expected_code = util.dedent(expected):match("^(.-)%s*$")
 
          local expected_lines = {}
-         for line in expected_code:gmatch("([^\n]*)\n") do
+         for line in expected_code:gmatch("([^\n]*)\n?") do
            table.insert(expected_lines, line)
          end
 
          local output_lines = {}
-         for line in output_code:gmatch("([^\n]*)\n") do
+         for line in output_code:gmatch("([^\n]*)\n?") do
            table.insert(output_lines, line)
          end
 

teal.lua

@@ -11277,7 +11277,8 @@ local function adjust_code(ast, needs_compat, gen_compat, gen_target)
                      needs_compat[key] = true
                   end
                end
-            elseif node.op.op == "~" and gen_target == "5.1" then
+
+            elseif node.op.op == "~" and node.op.arity == 1 and gen_target == "5.1" then
                if node.op.meta_on_operand then
                   needs_compat["mt"] = true
                   convert_node_to_compat_mt_call(node, unop_to_metamethod[node.op.op], 1, node.e1)

teal/gen/lua_compat.lua

@@ -231,7 +231,8 @@ local function adjust_code(ast, needs_compat, gen_compat, gen_target)
                      needs_compat[key] = true
                   end
                end
-            elseif node.op.op == "~" and gen_target == "5.1" then
+
+            elseif node.op.op == "~" and node.op.arity == 1 and gen_target == "5.1" then
                if node.op.meta_on_operand then
                   needs_compat["mt"] = true
                   convert_node_to_compat_mt_call(node, unop_to_metamethod[node.op.op], 1, node.e1)

teal/gen/lua_compat.tl

@@ -231,7 +231,8 @@ local function adjust_code(ast: Node, needs_compat: {string:boolean}, gen_compat
                      needs_compat[key] = true
                   end
                end
-            elseif node.op.op == "~" and gen_target == "5.1" then
+            -- unary '~' only; binary '~' is bxor, handled below
+            elseif node.op.op == "~" and node.op.arity == 1 and gen_target == "5.1" then
                if node.op.meta_on_operand then
                   needs_compat["mt"] = true
                   convert_node_to_compat_mt_call(node, unop_to_metamethod[node.op.op], 1, node.e1)

tl.lua

@@ -11531,7 +11531,8 @@ local function adjust_code(ast, needs_compat, gen_compat, gen_target)
                      needs_compat[key] = true
                   end
                end
-            elseif node.op.op == "~" and gen_target == "5.1" then
+
+            elseif node.op.op == "~" and node.op.arity == 1 and gen_target == "5.1" then
                if node.op.meta_on_operand then
                   needs_compat["mt"] = true
                   convert_node_to_compat_mt_call(node, unop_to_metamethod[node.op.op], 1, node.e1)