feat: diff between worktree and index

Author: pascalkuthe

gix-worktree/src/diff.rs

@@ -0,0 +1,292 @@
+use std::io::{self, ErrorKind};
+use std::path::{Path, PathBuf};
+use std::time::{Duration, SystemTimeError};
+
+use bstr::BString;
+use gix_features::hash;
+use gix_hash::ObjectId;
+use gix_index as index;
+use gix_object::encode::loose_header;
+use gix_path as path;
+
+use crate::fs;
+use crate::read::{self, read_blob_to_buf_with_meta};
+
+/// How the mode of an index entry has changed
+#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Debug)]
+pub enum ModeChange {
+    /// Shown as `typechange` in git status
+    /// For example if a normal file was replaced with a symlink.
+    /// Note: Except for submodules only files/symlinks are present in the
+    /// the index so anything turning into a directory is counted as a removal
+    TypeChange,
+    /// The executable bit of a file changed
+    ExecutableChange,
+}
+
+/// How a worktree file changed compared to an index entry
+#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Debug)]
+pub struct FileModification {
+    /// How the mode has changed
+    pub mode_change: Option<ModeChange>,
+    /// mtime/ctime changed. If this is false then we can assume
+    /// that the file is uncahged (with the exception of racy timestamps).
+    /// If this is true however the file might still be unchaged. We need
+    /// to read the file from disk and compare it to the object in
+    /// index.
+    pub stat_changed: bool,
+    /// The data of this entry has changed. This can be quickly
+    /// determined if the size of the stat data is mismatched.
+    /// Otherwise a data change must be detected by reading the file
+    /// from disk and comparing it to the file stored in the index
+    /// (only needs to be done if `self.stat_changed` is true)
+    pub data_changed: bool,
+}
+
+impl FileModification {
+    /// Computes the status of an entry by comparing its stat to `symlink_metadata()`
+    pub fn from_stat(
+        entry: &index::Entry,
+        fs_stat: &std::fs::Metadata,
+        capabilites: &fs::Capabilities,
+    ) -> Result<FileModification, SystemTimeError> {
+        #[cfg(unix)]
+        use std::os::unix::fs::MetadataExt;
+
+        let mode_change = match entry.mode {
+            index::entry::Mode::FILE if !fs_stat.is_file() => Some(ModeChange::TypeChange),
+            #[cfg(unix)]
+            index::entry::Mode::FILE if capabilites.executable_bit && fs_stat.mode() & 0o111 != 0 => {
+                Some(ModeChange::ExecutableChange)
+            }
+            #[cfg(unix)]
+            index::entry::Mode::FILE_EXECUTABLE if capabilites.executable_bit && fs_stat.mode() & 0o111 == 0 => {
+                Some(ModeChange::ExecutableChange)
+            }
+            index::entry::Mode::SYMLINK if capabilites.symlink && !fs_stat.is_symlink() => Some(ModeChange::TypeChange),
+            index::entry::Mode::SYMLINK if !capabilites.symlink && !fs_stat.is_file() => Some(ModeChange::TypeChange),
+            index::entry::Mode::COMMIT if !fs_stat.is_dir() => Some(ModeChange::TypeChange),
+            _ => None, // TODO: log/errror invalid file type
+        };
+
+        let data_changed = entry.stat.size as u64 != fs_stat.len();
+
+        let ctime = fs_stat
+            .created()
+            .map_or(Ok(Duration::default()), |x| x.duration_since(std::time::UNIX_EPOCH))?;
+        let mtime = fs_stat
+            .modified()
+            .map_or(Ok(Duration::default()), |x| x.duration_since(std::time::UNIX_EPOCH))?;
+
+        let stat = &entry.stat;
+        let stat_changed = stat.mtime.secs
+            != mtime
+                .as_secs()
+                .try_into()
+                .expect("by 2038 we found a solution for this")
+            || stat.mtime.nsecs != mtime.subsec_nanos()
+            || stat.ctime.secs
+                != ctime
+                    .as_secs()
+                    .try_into()
+                    .expect("by 2038 we found a solution for this")
+            || stat.ctime.nsecs != ctime.subsec_nanos();
+
+        Ok(Self {
+            mode_change,
+            stat_changed,
+            data_changed,
+        })
+    }
+
+    /// Marks this entries stats as changed if there is a potential fs race condition
+    pub fn detect_racy_stat(&mut self, index: &index::State, index_entry: &index::Entry) {
+        self.stat_changed = self.stat_changed || index_entry.stat.mtime >= index.timestamp()
+    }
+
+    /// returns true if this entry has any changes
+    /// usually `detect_racy_stat` should be called first to avoid race condition
+    pub fn changed(&self) -> bool {
+        self.mode_change.is_some() || self.stat_changed || self.data_changed
+    }
+
+    /// Reads the worktree file from the disk and compares it to
+    /// the index entries oid to check if the actual data of the file is changed
+    /// and sets [`Entry::data_changed`] accordingly
+    pub fn compare_data(
+        &mut self,
+        worktree_path: &Path,
+        index_entry: &index::Entry,
+        buf: &mut Vec<u8>,
+        capabilities: &fs::Capabilities,
+    ) -> Result<(), read::Error> {
+        if self.mode_change.is_some() || !self.stat_changed || self.data_changed {
+            return Ok(());
+        }
+        let data = read_blob_to_buf_with_meta(
+            worktree_path,
+            index_entry.mode.contains(index::entry::Mode::SYMLINK),
+            buf,
+            capabilities,
+        )?;
+        let header = loose_header(gix_object::Kind::Blob, data.len());
+        let hash_changed = match index_entry.id {
+            ObjectId::Sha1(entry_hash) => {
+                let mut file_hash = hash::Sha1::default();
+                file_hash.update(&header);
+                file_hash.update(&data);
+                let file_hash = file_hash.digest();
+                entry_hash != file_hash
+            }
+        };
+        self.data_changed = hash_changed;
+        Ok(())
+    }
+}
+
+#[allow(missing_docs)]
+#[derive(Debug, thiserror::Error)]
+pub enum Error {
+    #[error("Could not convert path to UTF8 {path}")]
+    IllformedUtf8 { path: BString },
+    #[error("The clock was off when reading file related metadata after updating a file on disk")]
+    Time(#[from] std::time::SystemTimeError),
+    #[error("IO error while writing blob or reading file metadata or changing filetype")]
+    Io(#[from] io::Error),
+}
+
+#[derive(Clone, Debug)]
+/// A change between the index and the worktree computed by [`compate_to_index`]
+pub struct Change<'a> {
+    /// The index entry that changed
+    pub index_entry: &'a index::Entry,
+    /// The on-disk worktree path corresponding to this entry
+    pub worktree_path: PathBuf,
+    /// How this index entry changed
+    pub kind: ChangeKind,
+    /// file metadata that can be reused (optimization)
+    pub fstat: Option<std::fs::Metadata>,
+}
+
+#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Debug)]
+///
+pub enum ChangeKind {
+    /// An index entry has no corresponding file in the worktree
+    Removed,
+    /// Ar new files that has been marked with git add but has not yet been
+    /// checked in yet. No diff is computed for these files because whatever is
+    /// on disk at commit time will be used
+    Added,
+    /// Called for files that may have changed in some form as indicated by `change`.
+    /// Note that this doesn't necessarily mean that the *content* of the file changed
+    /// see [`FileStatus`] for details
+    Modified {
+        /// How the file was modified exactly
+        modification: FileModification,
+        /// Whether this (changed) file also has an unresolved merge conflict
+        conflict: bool,
+    },
+    /// There are unresolved merge conflicts for this file
+    /// but it has not changed on disk
+    Conflict,
+}
+
+/// Computes the changes between the index and the worktree
+pub fn compare_to_index<'a: 'b, 'b>(
+    index: &'a index::State,
+    // TODO: use worktree cache instead
+    worktree: &'b Path,
+    capabilities: &'b fs::Capabilities,
+) -> impl Iterator<Item = Result<Change<'a>, Error>> + 'b {
+    // TODO: parallel with rayon
+    index.entries().iter().filter_map(|index_entry| {
+        let conflict = match index_entry.stage() {
+            0 => false,
+            1 => true,
+            _ => return None,
+        };
+        let git_path = index_entry.path(index);
+        if index_entry.flags.intersects(
+            index::entry::Flags::UPTODATE
+                | index::entry::Flags::SKIP_WORKTREE
+                | index::entry::Flags::ASSUME_VALID
+                | index::entry::Flags::FSMONITOR_VALID,
+        ) {
+            return None;
+        }
+
+        let path = if let Ok(path) = path::try_from_bstr(git_path) {
+            path
+        } else {
+            return Some(Err(Error::IllformedUtf8 {
+                path: git_path.to_owned(),
+            }));
+        };
+
+        let worktree_path = worktree.join(path);
+        let metadata = match worktree_path.symlink_metadata() {
+            // TODO: check if any parent directory is a symlink
+            // we need to use fs::Cache for that
+            Ok(metadata) if metadata.is_dir() => {
+                // index entries are normally only for files/symlinks
+                // if a file turned into a directory it was removed
+                // the only exception here are submodules which are
+                // part of the index despite being directories
+                //
+                // TODO: submodules:
+                //   if entry.mode.contains(Mode::COMMIT) &&
+                //     resolve_gitlink_ref(ce->name, "HEAD", &sub))
+                return Some(Ok(Change {
+                    kind: ChangeKind::Removed,
+                    index_entry,
+                    worktree_path,
+                    fstat: Some(metadata),
+                }));
+            }
+            Ok(metdata) => metdata,
+            Err(err) if err.kind() == ErrorKind::NotFound => {
+                return Some(Ok(Change {
+                    kind: ChangeKind::Removed,
+                    index_entry,
+                    worktree_path,
+                    fstat: None,
+                }))
+            }
+            Err(err) => {
+                // TODO: strict mode?
+                return Some(Err(err.into()));
+            }
+        };
+        if index_entry.flags.contains(index::entry::Flags::INTENT_TO_ADD) {
+            return Some(Ok(Change {
+                kind: ChangeKind::Added,
+                index_entry,
+                worktree_path,
+                fstat: None,
+            }));
+        }
+        let mut change = match FileModification::from_stat(index_entry, &metadata, capabilities) {
+            Ok(change) => change,
+            Err(err) => return Some(Err(err.into())),
+        };
+        change.detect_racy_stat(index, index_entry);
+
+        let kind = if change.changed() {
+            ChangeKind::Modified {
+                modification: change,
+                conflict,
+            }
+        } else if conflict {
+            ChangeKind::Conflict
+        } else {
+            return None;
+        };
+
+        Some(Ok(Change {
+            kind,
+            index_entry,
+            worktree_path,
+            fstat: Some(metadata),
+        }))
+    })
+}

gix-worktree/src/lib.rs

@@ -13,5 +13,12 @@ pub mod fs;
 pub mod index;
 
 pub(crate) mod os;
+
+///
+pub mod diff;
+
+///
+pub mod untracked;
+
 ///
 pub mod read;

gix-worktree/src/untracked.rs

@@ -0,0 +1 @@
+// TODO: untracked file detection, needs fs::Cache

gix-worktree/tests/worktree/index/diff.rs

@@ -0,0 +1,75 @@
+use std::fs::{self};
+use std::path::Path;
+
+use bstr::BString;
+use gix_worktree as worktree;
+use worktree::diff::{ChangeKind, FileModification};
+
+fn compute_diff(name: &str, make_worktree_dirty: impl FnOnce(&Path)) -> Vec<(ChangeKind, BString)> {
+    let work_tree =
+        gix_testtools::scripted_fixture_writable(Path::new(name).with_extension("sh")).expect("script works");
+    let git_dir = work_tree.path().join(".git");
+    make_worktree_dirty(work_tree.path());
+    let index = gix_index::File::at(git_dir.join("index"), gix_hash::Kind::Sha1, Default::default()).unwrap();
+    let capapilites = worktree::fs::Capabilities::probe(git_dir);
+    let mut buf = Vec::with_capacity(8 * 1024);
+    worktree::diff::compare_to_index(&index, work_tree.path(), &capapilites)
+        .filter_map(|change| {
+            let mut change = change.unwrap();
+            if let ChangeKind::Modified {
+                ref mut modification, ..
+            } = &mut change.kind
+            {
+                modification
+                    .compare_data(&change.worktree_path, change.index_entry, &mut buf, &capapilites)
+                    .unwrap();
+                if modification.mode_change.is_none() && !modification.data_changed {
+                    return None;
+                }
+            }
+            Some((change.kind, change.index_entry.path(&index).to_owned()))
+        })
+        .collect()
+}
+
+#[test]
+fn removed() {
+    let diff = compute_diff("make_mixed_without_submodules", |path| {
+        fs::remove_file(path.join("executable")).unwrap();
+        fs::remove_file(path.join("dir/content")).unwrap();
+        fs::remove_file(path.join("dir/sub-dir/symlink")).unwrap();
+    });
+
+    assert_eq!(
+        diff,
+        vec![
+            (ChangeKind::Removed, BString::new(b"dir/content".to_vec())),
+            (ChangeKind::Removed, BString::new(b"dir/sub-dir/symlink".to_vec())),
+            (ChangeKind::Removed, BString::new(b"executable".to_vec())),
+        ]
+    )
+}
+
+#[test]
+fn changed() {
+    let diff = compute_diff("make_mixed_without_submodules", |path| {
+        fs::write(path.join("dir/content"), "hello_world").unwrap();
+        // write same content to this file to simulate a touch command
+        fs::write(path.join("executable"), "content").unwrap();
+    });
+
+    assert_eq!(
+        diff,
+        vec![(
+            ChangeKind::Modified {
+                modification: FileModification {
+                    mode_change: None,
+                    stat_changed: true,
+                    data_changed: true
+                },
+                conflict: false
+            },
+            BString::new(b"dir/content".to_vec())
+        ),]
+    )
+}

gix-worktree/tests/worktree/index/mod.rs

@@ -1 +1,2 @@
 mod checkout;
+mod diff;