Add table.foreachi(), phase out ipairs() in API so nil values can be included in lists

src/base/api.lua

@@ -140,9 +140,9 @@
 
 		function recurse(value)
 			if type(value) == "table" then
-				for _, v in ipairs(value) do
+				table.foreachi(value, function(v)
 					recurse(v)
-				end
+				end)
 			else
 				remover(removes, value)
 			end
@@ -182,7 +182,9 @@
 			if type(field.allowed) == "function" then
 				return field.allowed(value)
 			else
-				for _,v in ipairs(field.allowed) do
+				local n = #field.allowed
+				for i = 1, n do
+					local v = field.allowed[i]
 					if value:lower() == v:lower() then
 						return v
 					end
@@ -341,10 +343,10 @@
 	function api.setfile(target, name, field, value)
 		if value:find("*") then
 			local values = os.matchfiles(value)
-			for _, value in ipairs(values) do
-				api.setfile(target, name, field, value)
+			table.foreachi(values, function(v)
+				api.setfile(target, name, field, v)
 				name = name + 1
-			end
+			end)
 		else
 			target[name] = path.getabsolute(value)
 		end
@@ -353,10 +355,10 @@
 	function api.setdirectory(target, name, field, value)
 		if value:find("*") then
 			local values = os.matchdirs(value)
-			for _, value in ipairs(values) do
-				api.setdirectory(target, name, field, value)
+			table.foreachi(values, function(v)
+				api.setdirectory(target, name, field, values[i])
 				name = name + 1
-			end
+			end)
 		else
 			target[name] = path.getabsolute(value)
 		end
@@ -411,9 +413,9 @@
 		local result = {}
 		function recurse(value)
 			if type(value) == "table" then
-				for _, v in ipairs(value) do
-					recurse(v)
-				end
+				table.foreachi(value, function (value)
+					recurse(value)
+				end)
 			else
 				setter(result, #result + 1, field, value)
 			end

src/base/table.lua

@@ -81,13 +81,15 @@
 --
 
 	function table.flatten(arr)
-		local result = { }
+		local result = {}
 
 		local function flatten(arr)
-			for _, v in ipairs(arr) do
+			local n = #arr
+			for i = 1, n do
+				local v = arr[i]
 				if type(v) == "table" then
 					flatten(v)
-				else
+				elseif v then
 					table.insert(result, v)
 				end
 			end
@@ -98,6 +100,29 @@
 	end
 
 
+--
+-- Walk the elements of an array and call the specified function
+-- for each non-nil element. This works around a "feature" of the
+-- ipairs() function that stops iteration at the first nil.
+--
+-- @param arr
+--    The array to iterate.
+-- @param func
+--    The function to call. The value (not the index) will be passed
+--    as the only argument.
+--
+
+	function table.foreachi(arr, func)
+		local n = #arr
+		for i = 1, n do
+			local v = arr[i]
+			if v then
+				func(v)
+			end
+		end
+	end
+
+
 --
 -- Merge two lists into an array of objects, containing pairs
 -- of values, one from each list.