Bug: `stack build` and `stack --stack-yaml=stack.yaml build` interpret paths in YAML differently

[ntc2]

General summary/comments (optional)

When, at the top level of my project, I symlink to a stack.yaml in a
subdir, the way stack interprets the paths in that stack.yaml
depends on whether I explicitly tell stack where to find the YAML
file. I.e., a plain stack build succeeds, interpreting the paths in
the YAML file relative to the location of the symlink, whereas
the explicit stack --stack-yaml=stack.yaml build and
STACK_YAML=stack.yaml stack build both fail, interpreting the paths
in the YAML file relative the location of the target of the
symlink.

I would prefer that all three invocations interpret the paths relative
the location of the symlink -- because that avoids having to add a
bunch of ../ prefixes, and makes the actual YAML file robust to
mvs as long as the symlink is updated accordingly -- but the bug is
that the three invocations don't all behave the same.

Steps to reproduce

$ stack --version
Version 1.7.1, Git revision 681c800873816c022739ca7ed14755e85a579565 (5807 commits) x86_64 hpack-0.28.2
# Create a dir to work in
$ mkdir -p /var/tmp/tmp/stack-symlink-path-bug
$ cd /var/tmp/tmp/stack-symlink-path-bug
# Download a package to refer to in the stack.yaml file
$ stack unpack microlens --to deps
# Create stack.yaml
$ stack init --resolver lts-11.9 
$ grep -v '^#' stack.yaml
resolver: lts-11.9
packages:
- deps/microlens-0.4.9.1
# Move stack.yaml into subdir and create a symlink to it at top level
$ mkdir stack-yamls
$ mv stack.yaml stack-yamls
$ ln -s stack-yamls/stack.yaml ./
# Build with implicit stack.yaml: success
$ stack build
[success]
# Build with explicit stack.yaml: failure
$ stack --stack-yaml=stack.yaml build
/var/tmp/tmp/stack-symlink-path-bug/stack-yamls/deps/microlens-0.4.9.1/: getDirectoryContents:openDirStream: does not exist (No such file or directory)
# Build with explicit stack.yaml: failure
$ STACK_YAML=stack.yaml stack build
Getting project config file from STACK_YAML environment
/var/tmp/tmp/stack-symlink-path-bug/stack-yamls/deps/microlens-0.4.9.1/: getDirectoryContents:openDirStream: does not exist (No such file or directory)

Expected

I expect that all three stack build invocations would behave the same.

Actual

The stack build using the implicit stack.yaml behaves differently
from the two stack build invocations with an explicit stack.yaml.

Method of installation

Via stack upgrade.

[mgsloan]

Good catch! This should definitely be fixed. I'm guessing it has to do with path canonicalization logic.

[kirelagin]

I came to the issue tracker to suggest to change the path resolution logic and found this, so, I guess, I won’t open a new one and just add my 2 cents here.

When I have stack.yaml stored in another directory and do stack --stack-yaml=... relative paths are interpreted relative to the location of stack.yaml, not CWD. Arguably, this behaviour is not very useful, as I could just cd to the directory of stack.yaml and run stack from there. OTOH resolving paths relative to CWD is useful for the case when stack.yaml is stored separately from the project.
Changing this behaviour will trivially fix this issue as well, as the behaviour will no longer depend on the location of stack.yaml in any way.