Cache directory resolving to root folder if HOME environment is not present

[freef4ll]

Expected behavior

The environmental variable $HOME not to be dependent on the cache directory location resolving, since non-cache settings are being resolved correctly.

Actual behavior

Package manager is not able to determine the cache directory to use and reverts to try to use /.cache, for which it it won't be able to have permissions to do so. For example strace shows the following system calls where the configuration directory is being resolved correctly:

1683338 13:06:58 openat(AT_FDCWD, "/tmp/_home_actions_.swiftpm.lock", O_WRONLY|O_CREAT|O_CLOEXEC, 0666) = 6
1683338 13:06:58 flock(6, LOCK_EX)      = 0
1683338 13:06:58 geteuid()              = 1000
1683338 13:06:58 getegid()              = 1000
1683338 13:06:58 openat(AT_FDCWD, "/etc/passwd", O_RDONLY|O_CLOEXEC) = 7
1683338 13:06:58 lseek(7, 0, SEEK_CUR)  = 0
1683338 13:06:58 fstat(7, {st_mode=S_IFREG|0644, st_size=969, ...}) = 0
1683338 13:06:58 read(7, "root:x:0:0:root:/root:/bin/bash\n"..., 4096) = 969
1683338 13:06:58 close(7)               = 0
1683338 13:06:58 lstat("/home/actions/.swiftpm/configuration", {st_mode=S_IFDIR|0755, st_size=6, ...}) = 0 <-- home directory being resolved correctly
1683338 13:06:58 openat(AT_FDCWD, "/etc/passwd", O_RDONLY|O_CLOEXEC) = 7
1683338 13:06:58 lseek(7, 0, SEEK_CUR)  = 0
1683338 13:06:58 fstat(7, {st_mode=S_IFREG|0644, st_size=969, ...}) = 0
1683338 13:06:58 read(7, "root:x:0:0:root:/root:/bin/bash\n"..., 4096) = 969
1683338 13:06:58 close(7)               = 0
1683338 13:06:58 openat(AT_FDCWD, "/etc/group", O_RDONLY|O_CLOEXEC) = 7
1683338 13:06:58 lseek(7, 0, SEEK_CUR)  = 0
1683338 13:06:58 fstat(7, {st_mode=S_IFREG|0644, st_size=473, ...}) = 0
1683338 13:06:58 read(7, "root:x:0:\ndaemon:x:1:\nbin:x:2:\ns"..., 4096) = 473
1683338 13:06:58 close(7)               = 0
1683338 13:06:58 flock(6, LOCK_UN)      = 0
1683338 13:06:58 close(6)               = 0
1683338 13:06:58 lstat("/home/actions/.swiftpm/configuration", {st_mode=S_IFDIR|0755, st_size=6, ...}) = 0
1683338 13:06:58 getpid()               = 339974
1683338 13:06:58 openat(AT_FDCWD, "/home/actions/.swiftpm/configuration/TemporaryFile.cyQtsq", O_RDWR|O_CREAT|O_EXCL, 0600) = 6
1683338 13:06:58 unlink("/home/actions/.swiftpm/configuration/TemporaryFile.cyQtsq") = 0
1683338 13:06:58 close(6)               = 0
1683338 13:06:58 lstat("/.cache/org.swift.swiftpm", 0x7ffe6f4be480) = -1 ENOENT (No such file or directory)
1683338 13:06:58 lstat("/.cache/org.swift.swiftpm", 0x7ffe6f4be460) = -1 ENOENT (No such file or directory)
1683338 13:06:58 lstat("/.cache/org.swift.swiftpm", 0x7ffe6f4be360) = -1 ENOENT (No such file or directory)
1683338 13:06:58 lstat("/.cache", 0x7ffe6f4be360) = -1 ENOENT (No such file or directory)
1683338 13:06:58 lstat("/.cache", 0x7ffe6f4be260) = -1 ENOENT (No such file or directory)
1683338 13:06:58 lstat("/", {st_mode=S_IFDIR|0755, st_size=29, ...}) = 0
1683338 13:06:58 mkdir("/.cache", 0777) = -1 EACCES (Permission denied) <--- no permission to write to root 
1683338 13:06:58 futex(0x7f74a2bc89b0, FUTEX_WAKE_PRIVATE, 2147483647) = 0
1683338 13:06:58 futex(0x7f74a24163b0, FUTEX_WAKE_PRIVATE, 2147483647) = 0
1683338 13:06:58 futex(0x7f74a2311a84, FUTEX_WAKE_PRIVATE, 2147483647) = 0
1683338 13:06:58 futex(0x7f74a242d420, FUTEX_WAKE_PRIVATE, 2147483647) = 0
1683338 13:06:58 futex(0x555bde4b5be0, FUTEX_WAKE_PRIVATE, 2147483647) = 0
1683338 13:06:58 ioctl(2, TCGETS, 0x7ffe6f4be3b0) = -1 ENOTTY (Inappropriate ioctl for device)
1683338 13:06:58 futex(0x555bde438680, FUTEX_WAKE_PRIVATE, 2147483647) = 0
1683338 13:06:58 futex(0x7f74a2bc8fb8, FUTEX_WAKE_PRIVATE, 2147483647) = 0
1683338 13:06:58 write(2, "warning: ", 9) = 9
1683338 13:06:58 write(2, "Failed creating default cache lo"..., 111) = 111

Steps to reproduce

Simplest way to reproduce would be to allow the /nonexistent home directory to be present and writable for user nobody via a docker container; (or in a working non-root user Linux environment just unset HOME) :

docker run -ti --user nobody -v /var/tmp:/nonexistent  swift:5.6-focal  /bin/bash

# In the container 
git -C /tmp  clone https://github.com/apple/swift-nio-examples.git
cd /tmp/swift-nio-examples/json-rpc/

unset HOME
swift package test
warning: Failed creating default cache location, Error Domain=NSCocoaErrorDomain Code=513 "You don’t have permission."
[...]

The same is happening in 5.7 nightly if executed under swiftlang/swift:nightly-focal instead of swift:5.6-focal, but here the warning is better:

warning: /.cache/org.swift.swiftpm is not accessible or not writable, disabling user-level cache features.

$ swift --version
Swift version 5.7-dev (LLVM cd62c186b914a47, Swift c58d4dba34ef37a)
Target: x86_64-unknown-linux-gnu

The background for this is that Github Runner setup scripts can unset all environment flags, and then the cache can run into this (actions/runner#1864)

Swift Package Manager version/commit hash

$ swift --version
Swift version 5.6.1 (swift-5.6.1-RELEASE)
Target: x86_64-unknown-linux-gnu

[the Swift Package Manager tag/commit hash]

Swift & OS version

$ swift --version && uname -a
Swift version 5.7-dev (LLVM cd62c186b914a47, Swift c58d4dba34ef37a)
Target: x86_64-unknown-linux-gnu
Linux 80f85cd927fb 5.4.0-109-generic #123-Ubuntu SMP Fri Apr 8 09:10:54 UTC 2022 x86_64 x86_64 x86_64 GNU/Linux

[tomerd]

thanks for reporting @freef4ll iiuc SwiftPM disables the shared cache in this case, but otherwise operational. Is that correct?