Partial implementation of better formatting machinery

plugin/fmt/init.lua

@@ -1,18 +1,85 @@
+local function writeFmt(buffer, template, ...)
+	local currentArg = 0
+	local i = 1
+	local len = #template
+
+	while i < len do
+		local openBrace = template:find("{", i)
+
+		if openBrace == nil then
+			buffer:writeRaw(template:sub(i))
+			break
+		else
+			if openBrace - i > 0 then
+				buffer:writeRaw(template:sub(i, openBrace - 1))
+			end
+
+			local charAfterBrace = template:sub(openBrace + 1, openBrace + 1)
+			if charAfterBrace == "{" then
+				buffer:writeRaw(template:sub(i, openBrace))
+				i = openBrace + 2
+			else
+				local closeBrace = template:find("}", openBrace + 1)
+				assert(closeBrace ~= nil, "Unclosed formatting specifier. Use '{{' to write an open brace.")
+
+				local formatSpecifier = template:sub(openBrace + 1, closeBrace - 1)
+
+				currentArg = currentArg + 1
+
+				if formatSpecifier == "" then
+					local arg = select(currentArg, ...)
+					buffer:writeRaw(tostring(arg))
+				else
+					error("unsupported format specifier " .. formatSpecifier, 2)
+				end
+
+				i = closeBrace + 1
+			end
+		end
+	end
+end
+
+local function writeLineFmt(buffer, template, ...)
+	writeFmt(buffer, template, ...)
+	table.insert(buffer, "\n")
+end
+
 local function debugOutputBuffer()
 	local buffer = {}
 	local indentLevel = 0
 	local indentation = ""
 
-	function buffer:push(template, ...)
+	function buffer:writeLine(template, ...)
-		local value = string.format(template, ...)
+		return writeLineFmt(self, template, ...)
+	end
 
+	function buffer:write(template, ...)
+		return writeFmt(self, template, ...)
+	end
+
+	function buffer:writeRaw(value)
 		if #indentation > 0 then
-			value = indentation .. value:gsub("\n", "\n" .. indentation)
+			value = value:gsub("\n", "\n" .. indentation)
 		end
 
 		table.insert(self, value)
 	end
 
+	function buffer:writeLineRaw(piece)
+		if #indentation > 0 then
+			self:writeRaw(indentation)
+		end
+
+		self:writeRaw(piece)
+		table.insert(self, "\n")
+	end
+
+	function buffer:push(template, ...)
+		local value = string.format(template, ...)
+
+		self:writeLineRaw(value)
+	end
+
 	function buffer:indent()
 		indentLevel = indentLevel + 1
 		indentation = string.rep("    ", indentLevel)
@@ -24,7 +91,7 @@ local function debugOutputBuffer()
 	end
 
 	function buffer:finish()
-		return table.concat(self, "\n")
+		return table.concat(self, "")
 	end
 
 	return buffer
@@ -51,4 +118,6 @@ end
 
 return {
 	debugOutputBuffer = debugOutputBuffer,
+	writeFmt = writeFmt,
+	writeLineFmt = writeLineFmt,
 }

plugin/src/ServeSession.lua

@@ -20,7 +20,7 @@ local function DEBUG_showPatch(patch)
 	output:indent()
 
 	for removed in ipairs(patch.removed) do
-		output:push("Remove ID %s", removed)
+		output:writeLine("Remove ID {}", removed)
 	end
 
 	for id, added in pairs(patch.added) do