Unscannable directory stopping the build

[FooB4r]

I encountered this when building using jbuilder and having some weird permissions on unrelated files/directories in the same directory as my sources.

$ jbuilder build test_server.exe
Error: exception Sys_error("output/queue: Permission denied")
Backtrace:
Raised by primitive operation at file "src/path.ml", line 431, characters 16-41
Called from file "src/file_tree.ml", line 51, characters 6-23
Called from file "src/file_tree.ml", line 89, characters 13-31
Called from file "list.ml", line 67, characters 20-23
Called from file "src/file_tree.ml", line 83, characters 6-232
Called from file "src/file_tree.ml", line 89, characters 13-31
Called from file "list.ml", line 67, characters 20-23
Called from file "list.ml", line 67, characters 32-39
Called from file "src/file_tree.ml", line 83, characters 6-232
Called from file "src/file_tree.ml", line 98, characters 13-37
Called from file "src/jbuild_load.ml", line 185, characters 14-62
Called from file "src/main.ml", line 42, characters 4-70
Called from file "bin/main.ml", line 674, characters 7-29
Called from file "vendor/cmdliner/src/cmdliner_term.ml", line 27, characters 19-24
Called from file "vendor/cmdliner/src/cmdliner.ml", line 106, characters 32-39
Called from file "vendor/cmdliner/src/cmdliner.ml", line 136, characters 18-36
Called from file "vendor/cmdliner/src/cmdliner.ml", line 251, characters 22-48
Called from file "bin/main.ml", line 1420, characters 10-51

Those files/directories were owned by root and jbuilder stopped scanning the files when encountering them.

$ ls -l output/
drwx------. 2 root root  4096 19 avril 13:04 crashes/
-rw-------. 1 root root 65536 19 avril 13:13 fuzz_bitmap
-rw-------. 1 root root   762 19 avril 13:13 fuzzer_stats
drwx------. 2 root root  4096 19 avril 13:12 hangs/
-rw-------. 1 root root  4062 19 avril 13:13 plot_data
drwx------. 3 root root  4096 19 avril 13:13 queue/

Even though those this problem has a good work-around with jbuild-ignore, it would probably be better to just issue a warning for unscannable directories and not completly crash the build.