--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/tools/test_mutants.sh.lua	Tue Oct 11 11:53:48 2022 +0100
@@ -0,0 +1,217 @@
+#!/bin/bash
+
+POLYGLOT=1--[===[
+
+set -o pipefail
+
+if [[ "$#" == "0" ]]; then
+	echo "Lua mutation testing tool"
+	echo
+	echo "Usage:"
+	echo "    $BASH_SOURCE MODULE_NAME SPEC_FILE"
+	echo
+	echo "Requires 'lua', 'ltokenp' and 'busted' in PATH"
+	exit 1;
+fi
+
+MOD_NAME="$1"
+MOD_FILE="$(lua "$BASH_SOURCE" resolve "$MOD_NAME")"
+
+if [[ "$MOD_FILE" == "" || ! -f "$MOD_FILE" ]]; then
+	echo "EE: Failed to locate module '$MOD_NAME' ($MOD_FILE)";
+	exit 1;
+fi
+
+SPEC_FILE="$2"
+
+if [[ "$SPEC_FILE" == "" ]]; then
+	SPEC_FILE="spec/${MOD_NAME/./_}_spec.lua"
+fi
+
+if [[ "$SPEC_FILE" == "" || ! -f "$SPEC_FILE" ]]; then
+	echo "EE: Failed to find test spec file ($SPEC_FILE)"
+	exit 1;
+fi
+
+if ! busted "$SPEC_FILE"; then
+	echo "EE: Tests fail on original source. Fix it"\!;
+	exit 1;
+fi
+
+export MUTANT_N=0
+LIVING_MUTANTS=0
+
+FILE_PREFIX="${MOD_FILE%.*}.mutant-"
+FILE_SUFFIX=".${MOD_FILE##*.}"
+
+gen_mutant () {
+	echo "Generating mutant $2 to $3..."
+	ltokenp -s "$BASH_SOURCE" "$1" > "$3"
+	return "$?"
+}
+
+# $1 = MOD_NAME, $2 = MUTANT_N, $3 = SPEC_FILE
+test_mutant () {
+	(
+		ulimit -m 131072 # 128MB
+		ulimit -t 16     # 16s
+		ulimit -f 32768  # 128MB (?)
+		exec busted --helper="$BASH_SOURCE" -Xhelper mutate="$1":"$2" "$3"
+	) >/dev/null
+	return "$?";
+}
+
+MUTANT_FILE="${FILE_PREFIX}${MUTANT_N}${FILE_SUFFIX}"
+
+gen_mutant "$MOD_FILE" "$MUTANT_N" "$MUTANT_FILE"
+while [[ "$?" == "0" ]]; do
+	if ! test_mutant "$MOD_NAME" "$MUTANT_N" "$SPEC_FILE"; then
+		echo "Tests successfully killed mutant $MUTANT_N";
+		rm "$MUTANT_FILE";
+	else
+		echo "Mutant $MUTANT_N lives on"\!
+		LIVING_MUTANTS=$((LIVING_MUTANTS+1))
+	fi
+	MUTANT_N=$((MUTANT_N+1))
+	MUTANT_FILE="${FILE_PREFIX}${MUTANT_N}${FILE_SUFFIX}"
+	gen_mutant "$MOD_FILE" "$MUTANT_N" "$MUTANT_FILE"
+done
+
+if [[ "$?" != "2" ]]; then
+	echo "Failed: $?"
+	exit "$?";
+fi
+
+MUTANT_SCORE="$(lua -e "print(('%0.2f'):format((1-($LIVING_MUTANTS/$MUTANT_N))*100))")"
+if test -f mutant-scores.txt; then
+	echo "$MOD_NAME $MUTANT_SCORE" >> mutant-scores.txt
+fi
+echo "$MOD_NAME: All $MUTANT_N mutants generated, $LIVING_MUTANTS survived (score: $MUTANT_SCORE%)"
+rm "$MUTANT_FILE"; # Last file is always unmodified
+exit 0;
+]===]
+
+-- busted helper that runs mutations
+if arg then
+	if arg[1] == "resolve" then
+		local filename = package.searchpath(assert(arg[2], "no module name given"), package.path);
+		if filename then
+			print(filename);
+		end
+		os.exit(filename and 0 or 1);
+	end
+	local mutants = {};
+
+	for i = 1, #arg do
+		local opt = arg[i];
+		print("LOAD", i, opt)
+		local module_name, mutant_n = opt:match("^mutate=([^:]+):(%d+)");
+		if module_name then
+			mutants[module_name] = tonumber(mutant_n);
+		end
+	end
+
+	local orig_lua_searcher = package.searchers[2];
+
+	local function mutant_searcher(module_name)
+		local mutant_n = mutants[module_name];
+		if not mutant_n then
+			return orig_lua_searcher(module_name);
+		end
+		local base_file, err = package.searchpath(module_name, package.path);
+		if not base_file then
+			return base_file, err;
+		end
+		local mutant_file = base_file:gsub("%.lua$", (".mutant-%d.lua"):format(mutant_n));
+		return loadfile(mutant_file), mutant_file;
+	end
+
+	if next(mutants) then
+		table.insert(package.searchers, 1, mutant_searcher);
+	end
+end
+
+-- filter for ltokenp to mutate scripts
+do
+	local last_output = {};
+	local function emit(...)
+		last_output = {...};
+		io.write(...)
+		io.write(" ")
+		return true;
+	end
+
+	local did_mutate = false;
+	local count = -1;
+	local threshold = tonumber(os.getenv("MUTANT_N")) or 0;
+	local function should_mutate()
+		count = count + 1;
+		return count == threshold;
+	end
+
+	local function mutate(name, value)
+		if name == "if" then
+			-- Bypass conditionals
+			if should_mutate() then
+				return emit("if true or");
+			elseif should_mutate() then
+				return emit("if false and");
+			end
+		elseif name == "<integer>" then
+			-- Introduce off-by-one errors
+			if should_mutate() then
+				return emit(("%d"):format(tonumber(value)+1));
+			elseif should_mutate() then
+				return emit(("%d"):format(tonumber(value)-1));
+			end
+		elseif name == "and" then
+			if should_mutate() then
+				return emit("or");
+			end
+		elseif name == "or" then
+			if should_mutate() then
+				return emit("and");
+			end
+		end
+	end
+
+	local current_line_n, current_line_input, current_line_output = 0, {}, {};
+	function FILTER(line_n,token,name,value)
+		if current_line_n ~= line_n then -- Finished a line, moving to the next?
+			if did_mutate and did_mutate.line == current_line_n then
+				-- The line we finished was mutated. Store the original and modified outputs.
+				did_mutate.line_original_src = table.concat(current_line_input, " ");
+				did_mutate.line_modified_src = table.concat(current_line_output, " ");
+			end
+			current_line_input = {};
+			current_line_output = {};
+		end
+		current_line_n = line_n;
+		if name == "<file>" then return; end
+		if name == "<eof>" then
+			if not did_mutate then
+				return os.exit(2);
+			else
+				emit(("\n-- Mutated line %d (changed '%s' to '%s'):\n"):format(did_mutate.line, did_mutate.original, did_mutate.modified))
+				emit(  ("--   Original: %s\n"):format(did_mutate.line_original_src))
+				emit(  ("--   Modified: %s\n"):format(did_mutate.line_modified_src));
+				return;
+			end
+		end
+		if name == "<string>" then
+			value = string.format("%q",value);
+		end
+		if mutate(name, value) then
+			did_mutate = {
+				original = value;
+				modified = table.concat(last_output);
+				line = line_n;
+			};
+		else
+			emit(value);
+		end
+		table.insert(current_line_input, value);
+		table.insert(current_line_output, table.concat(last_output));
+	end
+end
+