Utility::FileWatcher watching wrong filepath when using with Utility::Tweakable on Linux

[Antoine-dh]

When trying to use CORRADE_TWEAKABLE() with Utility::Tweakable I get a runtime error message from Utility::FileWatcher on Linux

Utility::FileWatcher: can't stat home/ad/CLionProjects/MagnumProject/src/MyApplication.cpp: No such file or directory, aborting watch
Utility::Tweakable: watching for changes in home/ad/CLionProjects/MagnumProject/src/MyApplication.cpp

I believe the root / was not inserted at the begin of the filepath string causing the filepath to be relative instead of absolute and the file not to be found.

[mosra]

Hi! The path is gathered from the __FILE__ preprocessor macro, so if your buildsystem underneath does something like

cd /
g++ home/ad/CLionProjects/MagnumProject/src/MyApplication.cpp -o MyApplication

then you'll get the path without the initial slash in __FILE__. I suspect this is something CLion does. As another example, in my case, when using ninja, the paths are relative to the build directory, so instead I'd get ../src/MyApplication.cpp in __FILE__ (which is nice and short). OTOH with plain make, as far as I remember, the paths were always full and absolute.

There's the Tweakable::enable(const std::string&, const std::string&) overload that allows you to set the path prefix explicitly, it's there to cover exactly these cases. From the top of my head, I think calling

tweakable.enable("", "/");

could do the trick. Hope this helps! :)

[Antoine-dh]

Hello, thanks for your answer.
tweakable.enable("", "/"); actually did the trick
but I still think there is an issue on your side as printing __FILE__ using the same build system gives me the correct path with the root slash

[mosra]

Oh, okay, thanks for the heads-up! 👍 Looking at the code, I think I know where the problem is (and I'm sorry about the conspiration theories above). This is what I get for testing just with Ninja, which has always relative paths 😅

Is it possible for you to try the following patch (and running with just the argument-less enable()) and tell me if it works correctly in your case?

diff --git a/src/Corrade/Utility/Tweakable.cpp b/src/Corrade/Utility/Tweakable.cpp
index 8e0f8b7c..f51d847d 100644
--- a/src/Corrade/Utility/Tweakable.cpp
+++ b/src/Corrade/Utility/Tweakable.cpp
@@ -110,7 +110,7 @@ std::pair<bool, void*> Tweakable::registerVariable(const char* const file, const
            works correctly. */
         /** @todo maybe some Directory utility for this? */
         std::string stripped = String::stripPrefix(Directory::fromNativeSeparators(file), _data->prefix);
-        if(!stripped.empty() && stripped.front() == '/')
+        if(!_data->prefix.empty() && !stripped.empty() && stripped.front() == '/')
             stripped.erase(0, 1);
 
         const std::string watchPath = Directory::join(_data->replace, stripped);

Thanks a lot!

[Antoine-dh]

I applied your patch and it did fix the initial issue, thank you

[mosra]

Fixed on master: edeeedb. Thanks for the report and testing! 👍