Only overwrite config.h if the contents changed - avoiding unnecessary rebuilds of project sorces that includes config.h.lazy_config_generation

1 files changed, 22 insertions, 7 deletions

diff --git a/src/configure.cc b/src/configure.cc
index 910b878..0755d42 100644
--- a/src/configure.cc
+++ b/src/configure.cc
@@ -6,6 +6,7 @@
 #include <iostream>
 #include <filesystem>
 #include <fstream>
+#include <sstream>
 #include <optional>
 #include <span>
 #include <cstring>
@@ -746,9 +747,8 @@ int regenerateCache(ctor::settings& settings,
 	ctor::conf_values[ctor::cfg::host_cxx] = host_cxx;
 	ctor::conf_values[ctor::cfg::build_cxx] = build_cxx;
 
-	std::cout << "Writing results to: " << configurationFile.string() << "\n";
-	{
-		std::ofstream istr(configurationFile);
+	std::cout << "Generating configuration: " << configurationFile.string() << "\n"; {
+		std::stringstream istr;
 		istr << "#include <ctor.h>\n\n";
 		istr << "const ctor::configuration& ctor::get_configuration()\n";
 		istr << "{\n";
@@ -900,13 +900,28 @@ int regenerateCache(ctor::settings& settings,
 		istr << "	};\n";
 		istr << "	return cfg;\n";
 		istr << "}\n";
+
+		auto new_configuration = istr.str();
+		auto current_configuration = readFile(configurationFile);
+		if(current_configuration != new_configuration)
+		{
+			std::ofstream configuration_stream(configurationFile);
+			configuration_stream << new_configuration;
+		}
 	}
 
 	{
-		std::ofstream istr(configHeaderFile);
-		istr << "#pragma once\n\n";
-		istr << "#define HAS_FOO 1\n";
-		istr << "//#define HAS_BAR 1\n";
+		std::stringstream new_config_stream;
+		new_config_stream << "#pragma once\n\n";
+		new_config_stream << "#define HAS_FOO 1\n";
+		new_config_stream << "//#define HAS_BAR 1\n";
+		auto new_config = new_config_stream.str();
+		auto current_config_content = readFile(configHeaderFile);
+		if(current_config_content != new_config)
+		{
+			std::ofstream config_file_stream(configHeaderFile);
+			config_file_stream << new_config;
+		}
 	}
 
 	return 0;