Follow links when cache-key is a glob (#13438)
## Summary
There's some inconsistent behaviour in handling symlinks when
`cache-key` is a glob or a file path. This PR attempts to address that.
- When cache-key is a path,
[`Path::metadata()`](https://doc.rust-lang.org/std/path/struct.Path.html#method.metadata)
is used to check if it's a file or not. According to the docs:
> This function will traverse symbolic links to query information about
the destination file.
So, if the target file is a symlink, it will be resolved and the
metadata will be queried for the underlying file.
- When cache-key is a glob, `globwalk` is used, specifically allowing
for symlinks:
```rust
.file_type(globwalk::FileType::FILE | globwalk::FileType::SYMLINK)
```
- However, without enabling link following, `DirEntry::metadata()` will
return an equivalent of `Path::symlink_metadata()` (and not
`Path::metadata()`), which will have a file type that looks like
```rust
FileType {
is_file: false,
is_dir: false,
is_symlink: true,
..
}
```
- Then, there's a check for `metadata.is_file()` which fails and
complains that the target entry "is a directory when file was expected".
- TLDR: glob cache-keys don't work with symlinks.
## Solutions
Option 1 (current PR): follow symlinks.
Option 2 (also doable): don't follow symlinks, but resolve the resulting
target entry manually in case its file type is a symlink. However, this
would be a little weird and unobvious in that we resolve files but not
directories for some reason. Also, symlinking directories is pretty
useful if you want to symlink directories of local dependencies that are
not under the project's path.
## Test Plan
This has been tested manually:
```rust
fn main() {
for follow_links in [false, true] {
let walker = globwalk::GlobWalkerBuilder::from_patterns(".", &["a/*"])
.file_type(globwalk::FileType::FILE | globwalk::FileType::SYMLINK)
.follow_links(follow_links)
.build()
.unwrap();
let entry = walker.into_iter().next().unwrap().unwrap();
dbg!(&entry);
dbg!(entry.file_type());
dbg!(entry.path_is_symlink());
dbg!(entry.path());
let meta = entry.metadata().unwrap();
dbg!(meta.is_file());
}
let path = std::path::PathBuf::from("./a/b");
dbg!(path.metadata().unwrap().file_type());
dbg!(path.symlink_metadata().unwrap().file_type());
}
```
Current behaviour (glob cache-key, don't follow links):
```
[src/main.rs:9:9] &entry = DirEntry("./a/b")
[src/main.rs:10:9] entry.file_type() = FileType {
is_file: false,
is_dir: false,
is_symlink: true,
..
}
[src/main.rs:11:9] entry.path_is_symlink() = true
[src/main.rs:12:9] entry.path() = "./a/b"
[src/main.rs:14:9] meta.is_file() = false
```
Glob cache-key, follow links:
```
[src/main.rs:9:9] &entry = DirEntry("./a/b")
[src/main.rs:10:9] entry.file_type() = FileType {
is_file: true,
is_dir: false,
is_symlink: false,
..
}
[src/main.rs:11:9] entry.path_is_symlink() = true
[src/main.rs:12:9] entry.path() = "./a/b"
[src/main.rs:14:9] meta.is_file() = true
```
Using `path.metadata()` for a non-glob cache key:
```
[src/main.rs:18:5] path.metadata().unwrap().file_type() = FileType {
is_file: true,
is_dir: false,
is_symlink: false,
..
}
[src/main.rs:19:5] path.symlink_metadata().unwrap().file_type() = FileType {
is_file: false,
is_dir: false,
is_symlink: true,
..
}
```
