From 33addfbf9cc21cd69b3d6476eb0c062bb2c6fcfb Mon Sep 17 00:00:00 2001
From: Bent Bisballe Nyeng <deva@aasimon.org>
Date: Tue, 15 Jun 2021 19:14:45 +0200
Subject: Re-link if link flags change.

---
 task_ld.cc | 66 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++--
 task_ld.h  |  3 +++
 2 files changed, 67 insertions(+), 2 deletions(-)

diff --git a/task_ld.cc b/task_ld.cc
index 0cd4c95..de74af2 100644
--- a/task_ld.cc
+++ b/task_ld.cc
@@ -7,6 +7,22 @@
 #include "settings.h"
 #include "execute.h"
 
+namespace
+{
+std::string readFile(const std::string &fileName)
+{
+	std::ifstream ifs(fileName.c_str(), std::ios::in | std::ios::binary | std::ios::ate);
+
+	std::ifstream::pos_type fileSize = ifs.tellg();
+	ifs.seekg(0, std::ios::beg);
+
+	std::vector<char> bytes(fileSize);
+	ifs.read(bytes.data(), fileSize);
+
+	return std::string(bytes.data(), fileSize);
+}
+} // namespace ::
+
 TaskLD::TaskLD(const BuildConfiguration& config,
                const Settings& settings,
                const std::string& target,
@@ -21,6 +37,9 @@ TaskLD::TaskLD(const BuildConfiguration& config,
 		std::filesystem::path objectFile = object;
 		objectFiles.push_back(objectFile);
 	}
+
+	flagsFile = settings.builddir / targetFile.stem();
+	flagsFile += ".flags";
 }
 
 bool TaskLD::dirty()
@@ -30,6 +49,11 @@ bool TaskLD::dirty()
 		return true;
 	}
 
+	if(!std::filesystem::exists(flagsFile))
+	{
+		return true;
+	}
+
 	for(const auto& objectFile : objectFiles)
 	{
 		if(std::filesystem::last_write_time(targetFile) <=
@@ -39,6 +63,15 @@ bool TaskLD::dirty()
 		}
 	}
 
+	{
+		auto lastFlags = readFile(flagsFile);
+		if(flagsString() != lastFlags)
+		{
+			//std::cout << "The compiler flags changed\n";
+			return true;
+		}
+	}
+
 	return false;
 }
 
@@ -66,12 +99,28 @@ int TaskLD::run()
 	args.push_back("-o");
 	args.push_back(std::string(targetFile));
 
+	{ // Write flags to file.
+		std::ofstream flagsStream(flagsFile);
+		flagsStream << flagsString();
+	}
+
 	return execute("/usr/bin/g++", args);
 }
 
 int TaskLD::clean()
 {
-	std::filesystem::remove(targetFile);
+	if(std::filesystem::exists(targetFile))
+	{
+		std::cout << "Removing " << std::string(targetFile) << "\n";
+		std::filesystem::remove(targetFile);
+	}
+
+	if(std::filesystem::exists(flagsFile))
+	{
+		std::cout << "Removing " << std::string(flagsFile) << "\n";
+		std::filesystem::remove(flagsFile);
+	}
+
 	return 0;
 }
 
@@ -82,6 +131,19 @@ std::vector<std::string> TaskLD::depends() const
 
 std::string TaskLD::target() const
 {
-	std::cout << "Removing " << std::string(targetFile) << "\n";
 	return std::string(targetFile);
 }
+
+std::string TaskLD::flagsString() const
+{
+	std::string flagsStr;
+	for(const auto& flag : config.ldflags)
+	{
+		if(!flagsStr.empty())
+		{
+			flagsStr += " ";
+		}
+		flagsStr += flag;
+	}
+	return flagsStr;
+}
diff --git a/task_ld.h b/task_ld.h
index 709f238..286fe39 100644
--- a/task_ld.h
+++ b/task_ld.h
@@ -30,8 +30,11 @@ public:
 	std::string target() const override;
 
 private:
+	std::string flagsString() const;
+
 	std::vector<std::filesystem::path> objectFiles;
 	std::filesystem::path targetFile;
+	std::filesystem::path flagsFile;
 
 	const BuildConfiguration& config;
 	const Settings& settings;
-- 
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