Description
I ran into this issue while attempting to build Chromium from source. I can confirm that this issue occurs on at least clang versions 7.0.1-8 (installed via apt) and 10.0.0 (from the Chromium build chain). It should be noted that I was doing this build under the Windows Subsystem for Linux running Ubuntu.
Here are some shell commands to create the file and directory structure needed to reproduce the issue:
mkdir -p "Common"
echo '#include "Thread.hpp"' > "Common/MutexLock.hpp"
echo '' > "Common/Thread.hpp"
mkdir -p "Package/common"
echo '#include "Common/MutexLock.hpp"' > "Package/common/Object.hpp"
# This file being in a subdirectory appears to be important.
# When placed elsewhere, the bug does not occur.
mkdir -p "Package/lib"
echo '
#include "common/Object.hpp"
#include "Common/Thread.hpp"
' > "Package/lib/bug.cpp"
# The order of the include directories is also important.
# When reversed (i.e. -I./Package -I.), the error does not occur.
clang++ -I. -I./Package -Werror -Wall ./Package/lib/bug.cpp
The result will be:
./Package/lib/bug.cpp:3:10: error: non-portable path to file '"common/Thread.hpp"'; specified path differs in case from file name on disk [-Werror,-Wnonportable-include-path]
#include "Common/Thread.hpp"
^~~~~~~~~~~~~~~~~~~
"common/Thread.hpp"
1 error generated.
This is absolutely incorrect. The file common/Thread.hpp doesn't even exist, nor was it ever referenced. It seems to be confusing the directory capitalization of ./Package/common and ./Common
It should be noted that the issue seems to have some rather specific criteria for being triggered. For example, the file being built must be at a different folder depth than the other files. Furthermore, the order of the -I flags matters. When reversed, the issue does not occur.
This seems possibly related to bug 32436, but that one appears to involve symlinks whereas this one only involves actual files.