docs(c++): std::filesystem is generally supported (#5003) (IDFGH-12755)

[nebkat]

Have been using most std::filesystem features successfully since IDF v5.1, and now std::filesystem::directory_iterator is also fixed since 994b4ed459269be1f6548137eac84ec3f9a8e37f.

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[igrr]

sha=cae6a35ac71eb827024c6e46c7ad4512567b1658

[igrr]

@nebkat Thanks for the PR!

In #5003 you wrote,

I have found most std::filesystem functions actually work quite well, except for some unusual cases in path concatenation, and std::filesystem::directory_iterator does not work at all.

Do you recall what were the "some unusual cases in path concatenation"? We probably need to add some tests if we want to claim that std::filesystem is supported, so I'm wondering if we should check something specific.

[igrr]

Actually we found that some functions used by std::filesystem aren't implemented in IDF, resulting in linker errors. For example, fpathconf, dirfd and others. We'll probably need to implement these first, before merging this PR.

[nebkat]

I believe the issue I encountered was with copying std::filesystem::paths - I had to do std::filesystem::path copy { other.c_str() } as other directly resulted in an empty string. This was however over a year ago, I will test again later this week.

For dirfd at least there is _GLIBCXX_HAVE_DIRFD, not sure about others. If you can share the functions that are causing linker errors I can do some further investigating if that would be of assistance!

[igrr]

@nebkat Here is my current changeset on top of your commit. You can see the few added stub functions there.

esp-idf-13cf3f6-333f1db.patch.txt

We will take a look at _GLIBCXX_HAVE_DIRFD and other config options. Not all of the current settings seem to make sense to me.

[nebkat]

Actually we found that some functions used by std::filesystem aren't implemented in IDF, resulting in linker errors. For example, fpathconf, dirfd and others. We'll probably need to implement these first, before merging this PR.

Ironically v5.3-beta1 has seemingly completely broken <filesystem> for me, not sure if related to your linker errors?

[5/7] Linking CXX executable mdf-firmware.elf
FAILED: mdf-firmware.elf
cmd.exe /C "cd . && C:\Users\Nebojsa\.espressif\tools\xtensa-esp-elf\esp-13.2.0_20240305\xtensa-esp-elf\bin\xtensa-esp32s3-elf-g++.exe -mlongcalls  -fno-builtin-memcpy -fno-builtin-memset -fno-builtin-bzero -fno-builtin-stpcpy -fno-builtin-strncpy -Wl,--cref -Wl,--defsym=IDF_TARGET_ESP32S3=0 -Wl,--Map=C:/Users/Nebojsa/Work/Troo/mdf-firmware/build/rtk_v1_7_dbg/mdf-firmware.map -Wl,--no-warn-rwx-segments -fno-rtti -fno-lto -Wl,--gc-sections -Wl,--warn-common -T esp32s3.peripherals.ld -T esp32s3.rom.ld -T esp32s3.rom.api.ld -T esp32s3.rom.libgcc.ld -T esp32s3.rom.wdt.ld -T esp32s3.rom.version.ld -T esp32s3.rom.newlib.ld -T memory.ld -T sections.ld @CMakeFiles\mdf-firmware.elf.rsp -o mdf-firmware.elf  && cd ."
C:/Users/Nebojsa/.espressif/tools/xtensa-esp-elf/esp-13.2.0_20240305/xtensa-esp-elf/bin/../lib/gcc/xtensa-esp-elf/13.2.0/../../../../xtensa-esp-elf/bin/ld.exe: C:/Users/Nebojsa/.espressif/tools/xtensa-esp-elf/esp-13.2.0_20240305/xtensa-esp-elf/bin/../lib/gcc/xtensa-esp-elf/13.2.0/../../../../xtensa-esp-elf/lib/esp32s3/no-rtti\libstdc++.a(fs_ops.o):(.literal._ZNSt10filesystem12current_pathB5cxx11ERSt10error_code+0x8): warning: pathconf is not implemented and will always fail
C:/Users/Nebojsa/.espressif/tools/xtensa-esp-elf/esp-13.2.0_20240305/xtensa-esp-elf/bin/../lib/gcc/xtensa-esp-elf/13.2.0/../../../../xtensa-esp-elf/bin/ld.exe: C:/Users/Nebojsa/.espressif/tools/xtensa-esp-elf/esp-13.2.0_20240305/xtensa-esp-elf/bin/../lib/gcc/xtensa-esp-elf/13.2.0/../../../../xtensa-esp-elf/lib/esp32s3/no-rtti\libstdc++.a(fs_ops.o):(.literal._ZNSt10filesystem11permissionsERKNS_7__cxx114pathENS_5permsENS_12perm_optionsERSt10error_code+0xc): warning: chmod is not implemented and will always fail
C:/Users/Nebojsa/.espressif/tools/xtensa-esp-elf/esp-13.2.0_20240305/xtensa-esp-elf/bin/../lib/gcc/xtensa-esp-elf/13.2.0/../../../../xtensa-esp-elf/bin/ld.exe: C:/Users/Nebojsa/.espressif/tools/xtensa-esp-elf/esp-13.2.0_20240305/xtensa-esp-elf/bin/../lib/gcc/xtensa-esp-elf/13.2.0/../../../../xtensa-esp-elf/lib/esp32s3/no-rtti\libstdc++.a(fs_dir.o):(.literal._ZNKSt10filesystem7__cxx114_Dir7currentEv[_ZNKSt10filesystem7__cxx114_Dir7currentEv]+0x4): warning: dirfd is not implemented and will always fail
C:/Users/Nebojsa/.espressif/tools/xtensa-esp-elf/esp-13.2.0_20240305/xtensa-esp-elf/bin/../lib/gcc/xtensa-esp-elf/13.2.0/../../../../xtensa-esp-elf/bin/ld.exe: esp-idf/mbedtls/mbedtls/library/libmbedx509.a(x509_crt.c.obj):(.literal.mbedtls_x509_crt_parse_path+0x28): warning: readdir is not implemented and will always fail
C:/Users/Nebojsa/.espressif/tools/xtensa-esp-elf/esp-13.2.0_20240305/xtensa-esp-elf/bin/../lib/gcc/xtensa-esp-elf/13.2.0/../../../../xtensa-esp-elf/bin/ld.exe: C:/Users/Nebojsa/.espressif/tools/xtensa-esp-elf/esp-13.2.0_20240305/xtensa-esp-elf/bin/../lib/gcc/xtensa-esp-elf/13.2.0/../../../../xtensa-esp-elf/lib/esp32s3/no-rtti\libstdc++.a(fs_ops.o):(.literal._ZNSt10filesystem12current_pathERKNS_7__cxx114pathERSt10error_code+0x0): warning: chdir is not implemented and will always fail
C:/Users/Nebojsa/.espressif/tools/xtensa-esp-elf/esp-13.2.0_20240305/xtensa-esp-elf/bin/../lib/gcc/xtensa-esp-elf/13.2.0/../../../../xtensa-esp-elf/bin/ld.exe: C:/Users/Nebojsa/.espressif/tools/xtensa-esp-elf/esp-13.2.0_20240305/xtensa-esp-elf/bin/../lib/gcc/xtensa-esp-elf/13.2.0/../../../../xtensa-esp-elf/lib/esp32s3/no-rtti\libstdc++.a(fs_ops.o):(.literal._ZNSt10filesystem12current_pathB5cxx11ERSt10error_code+0x14): warning: getcwd is not implemented and will always fail
C:/Users/Nebojsa/.espressif/tools/xtensa-esp-elf/esp-13.2.0_20240305/xtensa-esp-elf/bin/../lib/gcc/xtensa-esp-elf/13.2.0/../../../../xtensa-esp-elf/bin/ld.exe: C:/Users/Nebojsa/.espressif/tools/xtensa-esp-elf/esp-13.2.0_20240305/xtensa-esp-elf/bin/../lib/gcc/xtensa-esp-elf/13.2.0/../../../../xtensa-esp-elf/lib/esp32s3/no-rtti\libstdc++.a(fs_ops.o):(.literal._ZN12_GLOBAL__N_110create_dirERKNSt10filesystem7__cxx114pathENS0_5permsERSt10error_code+0x0): warning: mkdir is not implemented and will always fail
C:/Users/Nebojsa/.espressif/tools/xtensa-esp-elf/esp-13.2.0_20240305/xtensa-esp-elf/bin/../lib/gcc/xtensa-esp-elf/13.2.0/../../../../xtensa-esp-elf/bin/ld.exe: esp-idf/mbedtls/mbedtls/library/libmbedx509.a(x509_crt.c.obj):(.literal.mbedtls_x509_crt_parse_path+0x2c): warning: closedir is not implemented and will always fail
C:/Users/Nebojsa/.espressif/tools/xtensa-esp-elf/esp-13.2.0_20240305/xtensa-esp-elf/bin/../lib/gcc/xtensa-esp-elf/13.2.0/../../../../xtensa-esp-elf/bin/ld.exe: esp-idf/mbedtls/mbedtls/library/libmbedx509.a(x509_crt.c.obj):(.literal.mbedtls_x509_crt_parse_path+0x10): warning: opendir is not implemented and will always fail
C:/Users/Nebojsa/.espressif/tools/xtensa-esp-elf/esp-13.2.0_20240305/xtensa-esp-elf/bin/../lib/gcc/xtensa-esp-elf/13.2.0/../../../../xtensa-esp-elf/bin/ld.exe: C:/Users/Nebojsa/.espressif/tools/xtensa-esp-elf/esp-13.2.0_20240305/xtensa-esp-elf/bin/../lib/gcc/xtensa-esp-elf/13.2.0/../../../../xtensa-esp-elf/lib/esp32s3/no-rtti\libnosys.a(dir.o): in function `opendir':
/builds/idf/crosstool-NG/.build/HOST-x86_64-w64-mingw32/xtensa-esp-elf/src/newlib/libgloss/libnosys/dir.c:16: multiple definition of `opendir'; esp-idf/vfs/libvfs.a(vfs.c.obj):/IDF/components/vfs/vfs.c:733: first defined here
C:/Users/Nebojsa/.espressif/tools/xtensa-esp-elf/esp-13.2.0_20240305/xtensa-esp-elf/bin/../lib/gcc/xtensa-esp-elf/13.2.0/../../../../xtensa-esp-elf/bin/ld.exe: C:/Users/Nebojsa/.espressif/tools/xtensa-esp-elf/esp-13.2.0_20240305/xtensa-esp-elf/bin/../lib/gcc/xtensa-esp-elf/13.2.0/../../../../xtensa-esp-elf/lib/esp32s3/no-rtti\libnosys.a(dir.o): in function `closedir':
/builds/idf/crosstool-NG/.build/src/newlib-git-070bbf2f/newlib/libc/include/dirent.h:76: multiple definition of `closedir'; esp-idf/vfs/libvfs.a(vfs.c.obj):/IDF/components/vfs/vfs.c:805: first defined here
C:/Users/Nebojsa/.espressif/tools/xtensa-esp-elf/esp-13.2.0_20240305/xtensa-esp-elf/bin/../lib/gcc/xtensa-esp-elf/13.2.0/../../../../xtensa-esp-elf/bin/ld.exe: C:/Users/Nebojsa/.espressif/tools/xtensa-esp-elf/esp-13.2.0_20240305/xtensa-esp-elf/bin/../lib/gcc/xtensa-esp-elf/13.2.0/../../../../xtensa-esp-elf/lib/esp32s3/no-rtti\libnosys.a(dir.o): in function `mkdir':
/builds/idf/crosstool-NG/.build/HOST-x86_64-w64-mingw32/xtensa-esp-elf/src/newlib/libgloss/libnosys/dir.c:30: multiple definition of `mkdir'; esp-idf/vfs/libvfs.a(vfs.c.obj):/IDF/components/vfs/vfs.c:818: first defined here
C:/Users/Nebojsa/.espressif/tools/xtensa-esp-elf/esp-13.2.0_20240305/xtensa-esp-elf/bin/../lib/gcc/xtensa-esp-elf/13.2.0/../../../../xtensa-esp-elf/bin/ld.exe: C:/Users/Nebojsa/.espressif/tools/xtensa-esp-elf/esp-13.2.0_20240305/xtensa-esp-elf/bin/../lib/gcc/xtensa-esp-elf/13.2.0/../../../../xtensa-esp-elf/lib/esp32s3/no-rtti\libnosys.a(dir.o): in function `getcwd':
/builds/idf/crosstool-NG/.build/HOST-x86_64-w64-mingw32/xtensa-esp-elf/src/newlib/libgloss/libnosys/dir.c:37: multiple definition of `getcwd'; esp-idf/newlib/libnewlib.a(realpath.c.obj):/IDF/components/newlib/realpath.c:111: first defined here
C:/Users/Nebojsa/.espressif/tools/xtensa-esp-elf/esp-13.2.0_20240305/xtensa-esp-elf/bin/../lib/gcc/xtensa-esp-elf/13.2.0/../../../../xtensa-esp-elf/bin/ld.exe: C:/Users/Nebojsa/.espressif/tools/xtensa-esp-elf/esp-13.2.0_20240305/xtensa-esp-elf/bin/../lib/gcc/xtensa-esp-elf/13.2.0/../../../../xtensa-esp-elf/lib/esp32s3/no-rtti\libnosys.a(dir.o): in function `chdir':
/builds/idf/crosstool-NG/.build/HOST-x86_64-w64-mingw32/xtensa-esp-elf/src/newlib/libgloss/libnosys/dir.c:42: multiple definition of `chdir'; esp-idf/newlib/libnewlib.a(realpath.c.obj):/IDF/components/newlib/realpath.c:120: first defined here
C:/Users/Nebojsa/.espressif/tools/xtensa-esp-elf/esp-13.2.0_20240305/xtensa-esp-elf/bin/../lib/gcc/xtensa-esp-elf/13.2.0/../../../../xtensa-esp-elf/bin/ld.exe: C:/Users/Nebojsa/.espressif/tools/xtensa-esp-elf/esp-13.2.0_20240305/xtensa-esp-elf/bin/../lib/gcc/xtensa-esp-elf/13.2.0/../../../../xtensa-esp-elf/lib/esp32s3/no-rtti\libnosys.a(dir.o): in function `readdir':
/builds/idf/crosstool-NG/.build/src/newlib-git-070bbf2f/newlib/libc/include/dirent.h:56: multiple definition of `readdir'; esp-idf/vfs/libvfs.a(vfs.c.obj):/IDF/components/vfs/vfs.c:750: first defined here
C:/Users/Nebojsa/.espressif/tools/xtensa-esp-elf/esp-13.2.0_20240305/xtensa-esp-elf/bin/../lib/gcc/xtensa-esp-elf/13.2.0/../../../../xtensa-esp-elf/bin/ld.exe: C:/Users/Nebojsa/.espressif/tools/xtensa-esp-elf/esp-13.2.0_20240305/xtensa-esp-elf/bin/../lib/gcc/xtensa-esp-elf/13.2.0/../../../../xtensa-esp-elf/lib/esp32s3/no-rtti\libnosys.a(dir.o): in function `telldir':
/builds/idf/crosstool-NG/.build/src/newlib-git-070bbf2f/newlib/libc/include/dirent.h:73: multiple definition of `telldir'; esp-idf/vfs/libvfs.a(vfs.c.obj):/IDF/components/vfs/vfs.c:776: first defined here
C:/Users/Nebojsa/.espressif/tools/xtensa-esp-elf/esp-13.2.0_20240305/xtensa-esp-elf/bin/../lib/gcc/xtensa-esp-elf/13.2.0/../../../../xtensa-esp-elf/bin/ld.exe: C:/Users/Nebojsa/.espressif/tools/xtensa-esp-elf/esp-13.2.0_20240305/xtensa-esp-elf/bin/../lib/gcc/xtensa-esp-elf/13.2.0/../../../../xtensa-esp-elf/lib/esp32s3/no-rtti\libnosys.a(dir.o): in function `seekdir':
/builds/idf/crosstool-NG/.build/HOST-x86_64-w64-mingw32/xtensa-esp-elf/src/newlib/libgloss/libnosys/dir.c:73: multiple definition of `seekdir'; esp-idf/vfs/libvfs.a(vfs.c.obj):/IDF/components/vfs/vfs.c:789: first defined here
C:/Users/Nebojsa/.espressif/tools/xtensa-esp-elf/esp-13.2.0_20240305/xtensa-esp-elf/bin/../lib/gcc/xtensa-esp-elf/13.2.0/../../../../xtensa-esp-elf/bin/ld.exe: C:/Users/Nebojsa/.espressif/tools/xtensa-esp-elf/esp-13.2.0_20240305/xtensa-esp-elf/bin/../lib/gcc/xtensa-esp-elf/13.2.0/../../../../xtensa-esp-elf/lib/esp32s3/no-rtti\libnosys.a(dir.o): in function `rewinddir':
/builds/idf/crosstool-NG/.build/HOST-x86_64-w64-mingw32/xtensa-esp-elf/src/newlib/libgloss/libnosys/dir.c:101: multiple definition of `rewinddir'; esp-idf/vfs/libvfs.a(vfs.c.obj):/IDF/components/vfs/vfs.c:800: first defined here
C:/Users/Nebojsa/.espressif/tools/xtensa-esp-elf/esp-13.2.0_20240305/xtensa-esp-elf/bin/../lib/gcc/xtensa-esp

[igrr]

@nebkat Yep, my patch above should fix these linking issues.