Only write scripts.c if modified by embed action

scripts/embed.lua

@@ -78,27 +78,54 @@
 
 
 	function doembed()
-		local srcdir = path.join(basedir, "src")
 
-		-- load the manifest of script files
-		scripts = dofile(path.join(srcdir, "_manifest.lua"))
+		-- Find and run the manifest file. Checks the normal search paths to
+		-- allow for manifest and _premake_main customizations, then falls
+		-- back to the canonical version at ../src if not found.
 
-		-- main script always goes first
+		local dir = os.pathsearch("_manifest.lua", _OPTIONS["scripts"], os.getenv("PREMAKE_PATH"))
+		if not dir then
+			dir = path.join(basedir, "src")
+		end
+
+		scripts = dofile(path.join(dir, "_manifest.lua"))
+
+		-- Main script always goes first
 		table.insert(scripts, 1, "_premake_main.lua")
 
-		-- open scripts.c and write the file header
-		local out = io.open(path.join(srcdir, "host/scripts.c"), "w+b")
+		-- Embed all the scripts to a temporary file first
+		local out = io.tmpfile()
 		out:write("/* Premake's Lua scripts, as static data buffers for release mode builds */\n")
 		out:write("/* DO NOT EDIT - this file is autogenerated - see BUILD.txt */\n")
 		out:write("/* To regenerate this file, run: premake5 embed */ \n\n")
 		out:write("const char* builtin_scripts[] = {\n")
 
 		for i,fn in ipairs(scripts) do
-			print(fn)
-			local s = stripfile(path.join(srcdir, fn))
+			local s = stripfile(path.join(dir, fn))
 			writefile(out, fn, s)
 		end
 
 		out:write("\t0\n};\n");
+
+		-- Now read it back in and compare it to the current scripts.c; only
+		-- write it out if changed.
+
+		out:seek("set", 0)
+		local newVersion = out:read("*a")
 		out:close()
+
+		local oldVersion
+		local scriptsFile = io.open(path.join(basedir, "src/host/scripts.c"), "r")
+		if scriptsFile then
+			oldVersion = scriptsFile:read("*a")
+			scriptsFile:close()
+		end
+
+		if newVersion ~= oldVersion then
+			print("Writing scripts.c")
+			scriptsFile = io.open("src/host/scripts.c", "w+b")
+			scriptsFile:write(newVersion)
+			scriptsFile:close()
+		end
+
 	end