nu-path crate refactor (#3730)

* Resolve rebase artifacts

* Remove leftover dependencies on removed feature

* Remove unnecessary 'pub'

* Start taking notes and fooling around

* Split canonicalize to two versions; Add TODOs

One that takes `relative_to` and one that doesn't.
More TODO notes.

* Merge absolutize to and rename resolve_dots

* Add custom absolutize fn and use it in path expand

* Convert a couple of dunce::canonicalize to ours

* Update nu-path description

* Replace all canonicalize with nu-path version

* Remove leftover dunce dependencies

* Fix broken autocd with trailing slash

Trailing slash is preserved *only* in paths that do not contain "." or
"..". This should be fixed in the future to cover all paths but for now
it at least covers basic cases.

* Use dunce::canonicalize for canonicalizing

* Alow cd recovery from non-existent cwd

* Disable removed canonicalize functionality tests

Remove unused import

* Break down nu-path into separate modules

* Remove unused public imports

* Remove abundant cow mapping

* Fix clippy warning

* Reformulate old canonicalize tests to expand_path

They wouldn't work with the new canonicalize.

* Canonicalize also ~ and ndots; Unify path joining

Also, add doc comments in nu_path::expansions.

* Add comment

* Avoid expanding ndots if path is not valid UTF-8

With this change, no lossy path->string conversion should happen in the
nu-path crate.

* Fmt

* Slight expand_tilde refactor; Add doc comments

* Start nu-path integration tests

* Add tests TODO

* Fix docstring typo

* Fix some doc strings

* Add README for nu-path crate

* Add a couple of canonicalize tests

* Add nu-path integration tests

* Add trim trailing slashes tests

* Update nu-path dependency

* Remove unused import

* Regenerate lockfile

crates/nu-path/src/dots.rs

@@ -0,0 +1,259 @@
+use std::path::{is_separator, Component, Path, PathBuf};
+
+const EXPAND_STR: &str = if cfg!(windows) { r"..\" } else { "../" };
+
+fn handle_dots_push(string: &mut String, count: u8) {
+    if count < 1 {
+        return;
+    }
+
+    if count == 1 {
+        string.push('.');
+        return;
+    }
+
+    for _ in 0..(count - 1) {
+        string.push_str(EXPAND_STR);
+    }
+
+    string.pop(); // remove last '/'
+}
+
+/// Expands any occurence of more than two dots into a sequence of ../ (or ..\ on windows), e.g.,
+/// "..." into "../..", "...." into "../../../", etc.
+pub fn expand_ndots(path: impl AsRef<Path>) -> PathBuf {
+    // Check if path is valid UTF-8 and if not, return it as it is to avoid breaking it via string
+    // conversion.
+    let path_str = match path.as_ref().to_str() {
+        Some(s) => s,
+        None => return path.as_ref().into(),
+    };
+
+    // find if we need to expand any >2 dot paths and early exit if not
+    let mut dots_count = 0u8;
+    let ndots_present = {
+        for chr in path_str.chars() {
+            if chr == '.' {
+                dots_count += 1;
+            } else {
+                if is_separator(chr) && (dots_count > 2) {
+                    // this path component had >2 dots
+                    break;
+                }
+
+                dots_count = 0;
+            }
+        }
+
+        dots_count > 2
+    };
+
+    if !ndots_present {
+        return path.as_ref().into();
+    }
+
+    let mut dots_count = 0u8;
+    let mut expanded = String::new();
+    for chr in path_str.chars() {
+        if chr == '.' {
+            dots_count += 1;
+        } else {
+            if is_separator(chr) {
+                // check for dots expansion only at path component boundaries
+                handle_dots_push(&mut expanded, dots_count);
+                dots_count = 0;
+            } else {
+                // got non-dot within path component => do not expand any dots
+                while dots_count > 0 {
+                    expanded.push('.');
+                    dots_count -= 1;
+                }
+            }
+            expanded.push(chr);
+        }
+    }
+
+    handle_dots_push(&mut expanded, dots_count);
+
+    expanded.into()
+}
+
+/// Expand "." and ".." into nothing and parent directory, respectively.
+pub fn expand_dots(path: impl AsRef<Path>) -> PathBuf {
+    let path = path.as_ref();
+
+    // Early-exit if path does not contain '.' or '..'
+    if !path
+        .components()
+        .any(|c| std::matches!(c, Component::CurDir | Component::ParentDir))
+    {
+        return path.into();
+    }
+
+    let mut result = PathBuf::with_capacity(path.as_os_str().len());
+
+    // Only pop/skip path elements if the previous one was an actual path element
+    let prev_is_normal = |p: &Path| -> bool {
+        p.components()
+            .next_back()
+            .map(|c| std::matches!(c, Component::Normal(_)))
+            .unwrap_or(false)
+    };
+
+    path.components().for_each(|component| match component {
+        Component::ParentDir if prev_is_normal(&result) => {
+            result.pop();
+        }
+        Component::CurDir if prev_is_normal(&result) => {}
+        _ => result.push(component),
+    });
+
+    dunce::simplified(&result).to_path_buf()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn expand_two_dots() {
+        let path = Path::new("/foo/bar/..");
+
+        assert_eq!(
+            PathBuf::from("/foo"), // missing path
+            expand_dots(path)
+        );
+    }
+
+    #[test]
+    fn expand_dots_with_curdir() {
+        let path = Path::new("/foo/./bar/./baz");
+
+        assert_eq!(PathBuf::from("/foo/bar/baz"), expand_dots(path));
+    }
+
+    fn check_ndots_expansion(expected: &str, s: &str) {
+        let expanded = expand_ndots(Path::new(s));
+        assert_eq!(Path::new(expected), &expanded);
+    }
+
+    // common tests
+    #[test]
+    fn string_without_ndots() {
+        check_ndots_expansion("../hola", "../hola");
+    }
+
+    #[test]
+    fn string_with_three_ndots_and_chars() {
+        check_ndots_expansion("a...b", "a...b");
+    }
+
+    #[test]
+    fn string_with_two_ndots_and_chars() {
+        check_ndots_expansion("a..b", "a..b");
+    }
+
+    #[test]
+    fn string_with_one_dot_and_chars() {
+        check_ndots_expansion("a.b", "a.b");
+    }
+
+    #[test]
+    fn expand_dots_double_dots_no_change() {
+        // Can't resolve this as we don't know our parent dir
+        assert_eq!(Path::new(".."), expand_dots(Path::new("..")));
+    }
+
+    #[test]
+    fn expand_dots_single_dot_no_change() {
+        // Can't resolve this as we don't know our current dir
+        assert_eq!(Path::new("."), expand_dots(Path::new(".")));
+    }
+
+    #[test]
+    fn expand_dots_multi_single_dots_no_change() {
+        assert_eq!(Path::new("././."), expand_dots(Path::new("././.")));
+    }
+
+    #[test]
+    fn expand_multi_double_dots_no_change() {
+        assert_eq!(Path::new("../../../"), expand_dots(Path::new("../../../")));
+    }
+
+    #[test]
+    fn expand_dots_no_change_with_dirs() {
+        // Can't resolve this as we don't know our parent dir
+        assert_eq!(
+            Path::new("../../../dir1/dir2/"),
+            expand_dots(Path::new("../../../dir1/dir2"))
+        );
+    }
+
+    #[test]
+    fn expand_dots_simple() {
+        assert_eq!(Path::new("/foo"), expand_dots(Path::new("/foo/bar/..")));
+    }
+
+    #[test]
+    fn expand_dots_complex() {
+        assert_eq!(
+            Path::new("/test"),
+            expand_dots(Path::new("/foo/./bar/../../test/././test2/../"))
+        );
+    }
+
+    #[cfg(windows)]
+    mod windows {
+        use super::*;
+
+        #[test]
+        fn string_with_three_ndots() {
+            check_ndots_expansion(r"..\..", "...");
+        }
+
+        #[test]
+        fn string_with_mixed_ndots_and_chars() {
+            check_ndots_expansion(
+                r"a...b/./c..d/../e.f/..\..\..//.",
+                "a...b/./c..d/../e.f/....//.",
+            );
+        }
+
+        #[test]
+        fn string_with_three_ndots_and_final_slash() {
+            check_ndots_expansion(r"..\../", ".../");
+        }
+
+        #[test]
+        fn string_with_three_ndots_and_garbage() {
+            check_ndots_expansion(r"ls ..\../ garbage.*[", "ls .../ garbage.*[");
+        }
+    }
+
+    #[cfg(not(windows))]
+    mod non_windows {
+        use super::*;
+        #[test]
+        fn string_with_three_ndots() {
+            check_ndots_expansion(r"../..", "...");
+        }
+
+        #[test]
+        fn string_with_mixed_ndots_and_chars() {
+            check_ndots_expansion(
+                "a...b/./c..d/../e.f/../../..//.",
+                "a...b/./c..d/../e.f/....//.",
+            );
+        }
+
+        #[test]
+        fn string_with_three_ndots_and_final_slash() {
+            check_ndots_expansion("../../", ".../");
+        }
+
+        #[test]
+        fn string_with_three_ndots_and_garbage() {
+            check_ndots_expansion("ls ../../ garbage.*[", "ls .../ garbage.*[");
+        }
+    }
+}