ROOT does not work when launched from non-accessible folder

[ktf]

• [x ] Checked for duplicates

Describe the bug

ROOT 6.28.00 does not work correctly when $PWD is not accessible by the user.

If I do:

mkdir -p foo
cd foo
chmod 000 .
root

it fails with:

input_line_2:1:10: fatal error: cannot open file './cling/Interpreter/RuntimeUniverse.h': Permission denied
#include "cling/Interpreter/RuntimeUniverse.h"
         ^
Replaced symbol atexit cannot be found in JIT!
Replaced symbol at_quick_exit cannot be found in JIT!
input_line_4:2:10: fatal error: cannot open file './TError.h': Permission denied
#include "TError.h"
         ^
input_line_5:1:10: fatal error: cannot open file './cling/Interpreter/DynamicLookupRuntimeUniverse.h': Permission denied
#include "cling/Interpreter/DynamicLookupRuntimeUniverse.h"

the same snippet works fine with 6.26.10.

Notice things work fine with just the x bit set (i.e. chmod 100 . still works).

Expected behavior

The standard root prompt without any error.

To Reproduce

See above.

mkdir -p foo
cd foo
chmod 000 .
root

Setup

ROOT 6.28.00, both el7 and ubuntu.

Additional context

While this can look like a corner case, it reflects the way ALICE runs its online reconstruction jobs, so it's rather critical for us. I am in parallel trying to understand if the unaccessible cwd can be avoided, but this might have non trivial implications (and its for sure beyond my responsibilities).

[ktf]

@knopers @vascobarroso FYI

[ktf]

@Barthelemy

[ktf]

I had a typo in the reproducer, now corrected.

[ktf]

For ALICE people see also https://alice.its.cern.ch/jira/browse/O2-3591.

[ktf]

FYI @pzhristov

[Axel-Naumann]

Update: I can reproduce this with the (for our tests nicer) case

mkdir cling
chmod a-xr cling
root

which gives the same diagnostics as above.

[Axel-Naumann]

clang does not work when launched from non-accessible folder, either:

$ mkdir noread
$ cd noread/
$ chmod a-rwx .
$ echo '#include "ROOT/config/RVersion.hxx"' | clang++ -I. -I$ROOTSYS/include/  -fsyntax-only -x c++ -
<stdin>:1:10: fatal error: cannot open file './ROOT/config/RVersion.hxx': Permission denied
#include "ROOT/config/RVersion.hxx"
         ^
1 error generated.

I.e. clang tries to argue "don't do that". But I would argue "clang, please." because it even just goes on and finds the header!

This was introduced here, with subsequent refinements to not have so many irrelevant errors. #12418 now adds another case.

[Axel-Naumann]

Fixed in master and 6.28/02, thanks for reporting!

[Axel-Naumann]

Follow-up to potentially upstream this: https://discourse.llvm.org/t/evil-elements-in-header-search-path-cause-havoc/70705