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README: fix direnv_layout_dir setup

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The static setup of `direnv_layout_dir` in `direnvrc` leads to the
creation of separate layout dirs and nix shell caches for each
subdirectory of a project.
Reason: When `direnvrc` is evaluated, `PWD` has the value of the calling
user's shell, instead of pointing to the project directory (the dir containing `.envrc`).

Fix this by dynamically evaluating `$PWD` in a function.
Dynamic evaluation is also required when `.envrc` includes (via `source_*`) `.envrc`
files from other projects because `$PWD` changes in this case.

Cache the computed layout paths because `shasum` is
fairly expensive (13 ms on my desktop system).
This commit is contained in:
Erik Arvstedt 2020-10-23 15:15:35 +02:00
parent a751ddd538
commit 2aa433e90e
1 changed files with 10 additions and 3 deletions
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13
README.md
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@ -170,7 +170,7 @@ $ direnv allow
A `.direnv` directory will be created in each `use_nix` project, which might
interact badly with backups (e.g. Dropbox) or IDEs.
Therefore it's possible to override a variable called `$direnv_layout_dir` in
Therefore it's possible to override a function called `direnv_layout_dir` in
`$HOME/.config/direnv/direnvrc` or in each project's `.envrc`.
The following example will create a unique directory name per project
@ -179,9 +179,16 @@ in `$HOME/.cache/direnv/layouts/`:
```bash
# $HOME/.config/direnv/direnvrc
: ${XDG_CACHE_HOME:=$HOME/.cache}
pwd_hash=$(echo -n $PWD | shasum | cut -d ' ' -f 1)
direnv_layout_dir=$XDG_CACHE_HOME/direnv/layouts/$pwd_hash
declare -A direnv_layout_dirs
direnv_layout_dir() {
echo "${direnv_layout_dirs[$PWD]:=$(
echo -n "$XDG_CACHE_HOME"/direnv/layouts/;
echo -n "$PWD" | shasum | cut -d ' ' -f 1
)}"
}
```
During direnv setup `direnv_layout_dir` can be called multiple times and with different values of `$PWD`
(when including other `.envrc` files). Therefore cache its results in dictionary `direnv_layout_dirs`.
## Manually re-triggering evaluation