lint: Fix shadow issues

Fix shadowing by using variables with a different name or _.

I don't think any of these warnings were actual bugs and fixed them to
maintain the same behaviour.

.luacheckrc

@@ -8,13 +8,6 @@ return {
         "213", -- Unused loop variable.
         "231", -- Local variable is set but never accessed.
         "311", -- Value assigned to a local variable is unused.
-        "412", -- Redefining an argument.
-        "413", -- Redefining a loop variable.
-        "421", -- Shadowing a local variable.
-        "422", -- Shadowing an argument.
-        "423", -- Shadowing a loop variable.
-        "423", -- Shadowing a loop variable.
-        "432", -- Shadowing an upvalue argument.
         "631", -- Line is too long.
     },
     files = {

assert.lua

@@ -75,7 +75,7 @@ end
 
 --replace everything in assert with nop functions that just return their second argument, for near-zero overhead on release
 function assert:nop()
-	local nop = function(self, a)
+	local nop = function(_, a)
 		return a
 	end
 	setmetatable(self, {

functional.lua

@@ -209,7 +209,7 @@ end
 function functional.stitch(t, f)
 	local result = {}
 	for i, v in ipairs(t) do
-		local v = f(v, i)
+		v = f(v, i)
 		if v ~= nil then
 			if type(v) == "table" then
 				for _, e in ipairs(v) do

sort.lua

@@ -56,8 +56,8 @@ function sort._merge(array, workspace, low, middle, high, less)
 	local i, j, k
 	i = 1
 	-- copy first half of array to auxiliary array
-	for j = low, middle do
-		workspace[i] = array[j]
+	for w = low, middle do
+		workspace[i] = array[w]
 		i = i + 1
 	end
 	-- sieve through
@@ -78,8 +78,8 @@ function sort._merge(array, workspace, low, middle, high, less)
 		k = k + 1
 	end
 	-- copy back any remaining elements of first half
-	for k = k, j - 1 do
-		array[k] = workspace[i]
+	for w = k, j - 1 do
+		array[w] = workspace[i]
 		i = i + 1
 	end
 end
@@ -121,7 +121,8 @@ end
 
 function sort.stable_sort(array, less)
 	--setup
-	local trivial, n, less = sort._sort_setup(array, less)
+	local trivial, n
+	trivial, n, less = sort._sort_setup(array, less)
 	if not trivial then
 		--temp storage; allocate ahead of time
 		local workspace = {}
@@ -135,7 +136,8 @@ end
 
 function sort.insertion_sort(array, less)
 	--setup
-	local trivial, n, less = sort._sort_setup(array, less)
+	local trivial, n
+	trivial, n, less = sort._sort_setup(array, less)
 	if not trivial then
 		sort._insertion_sort_impl(array, 1, n, less)
 	end

tablex.lua

@@ -398,8 +398,8 @@ function tablex.collapse(t)
 	local r = {}
 	for _, v in ipairs(t) do
 		if type(v) == "table" then
-			for _, v in ipairs(v) do
-				table.insert(r, v)
+			for _, w in ipairs(v) do
+				table.insert(r, w)
 			end
 		else
 			table.insert(r, v)