This patch fixes#16614 and #16741.
The first issue was caused by the fact that both `/share` and
`/share/fish/vendor_completions.d` end in the `pathsToLink`. The
`pkgs/build-support/buildenv/builder.pl` creates `/share`, then links
`/share/fish` under `/share` and then tries to create the directory
`/share/fish/vendor_completions.d` and fails because it already exists.
The simplest way to reproduce the issue is to build the next Nix
expression:
```nix
let pkgs = import <nixpkgs> { };
in pkgs.buildEnv {
name = "buildenv-issue";
paths = [
pkgs.fish
pkgs.vim
];
pathsToLink = [
"/share"
"/share/fish/vendor_completions.d"
];
}
```
The second issue is more critical and was caused by the fact findFiles
doesn't recurse deep enough. It stops at first unique directory for the
package (e.g., "/share" or even "/") and later the scripts decides it
shouldn't link it as it doesn't match pathsToLink (e.g., "/share/fish"),
so the result is empty.
The test:
```nix
let pkgs = import <nixpkgs> { };
in pkgs.buildEnv {
name = "buildenv-issue";
paths = [
pkgs.fish
pkgs.vim
];
pathsToLink = [
"/share/fish/functions"
];
}
```
or
```nix
let pkgs = import <nixpkgs> { };
in pkgs.buildEnv {
name = "buildenv-issue";
paths = [
pkgs.vim
];
pathsToLink = [
"/share"
];
}
```
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