Inconsistent symlink following behavior in checkpoint/restart

[dschwen]

Reason

MOOSE's "paths relative to the input file" logic, follows symlinks. I.e. if I have two directories a and b and

a/input.i
b/input.i -> ../a/input.i

the file in b is a symlink back to a. And I want to run two different simulation in those dirs (let's say with CLI args to modify parameters)...
If I'm using restart, MOOSE looks for a/input_out_cp/* in both cases. Even though the b simulation CheckpointIO writes to b/input_out_cp/*...

Design

One part of the code seems to apply realPath to follow symlinks, while the other does not. Symlinking inputs to different directories to make it easy to keep multiple outputs seems like a very reasonable thing to do. And at the very least the behavior should be consistent.

I propose not following the symlinks.

Impact

Consistent restart behavior w.r.t. symlinks.

[dschwen]

Ok, I think it is time to push for std::filesystem, @permcody .

This issue can be solved easily by replacing MooseUtils::realPath(path) with std::filesystem::absolute(path). That's the right behavior IMO. It produces a full path that keeps symlinks intact. The current behavior is that of std::filesystem::canonical(path), which follows symlinks.

I'll go ahead and put up a PR to make this small change and see if/where our minimal compiler targets fail...

[dschwen]

Using this library may require additional compiler/linker options. GNU implementation prior to 9.1 requires linking with -lstdc++fs and LLVM implementation prior to LLVM 9.0 requires linking with -lc++fs.

Ugh

[dschwen]

We're at gcc7 and clang5, right?

[dschwen]

Ok, in the framework tests I only get two failing tests, and both cases are non matching expected errors, where the error message actually improved.

Failed to get real path for
->
Unable to open file "/home/schwd/Programs/moose-std-filesytsem/test/tests/misc/realpath_exception/not_exist.i". Check to make sure that it exists and that you have read permission.

and

Failed to get real path for missing_input_file.i
->
Unable to open file "/home/schwd/Programs/moose-std-filesytsem/test/tests/misc/check_error/missing_input_file.i". Check to make sure that it exists and that you have read permission.

[loganharbour]

Ah yeah.... I see you're talking to yourself here about the problem I discussed in #21137