rhg: do not fail when the repo is empty

Differential Revision: https://phab.mercurial-scm.org/D11651

rust/hg-core/src/revlog/revlog.rs

@@ -1,423 +1,429 b''
 use std::borrow::Cow;
 use std::io::Read;
 use std::ops::Deref;
 use std::path::Path;
 
 use byteorder::{BigEndian, ByteOrder};
 use flate2::read::ZlibDecoder;
 use micro_timer::timed;
 use sha1::{Digest, Sha1};
 use zstd;
 
 use super::index::Index;
 use super::node::{NodePrefix, NODE_BYTES_LENGTH, NULL_NODE};
 use super::nodemap;
 use super::nodemap::{NodeMap, NodeMapError};
 use super::nodemap_docket::NodeMapDocket;
 use super::patch;
 use crate::errors::HgError;
 use crate::repo::Repo;
 use crate::revlog::Revision;
 use crate::{Node, NULL_REVISION};
 
 #[derive(derive_more::From)]
 pub enum RevlogError {
     InvalidRevision,
     /// Working directory is not supported
     WDirUnsupported,
     /// Found more than one entry whose ID match the requested prefix
     AmbiguousPrefix,
     #[from]
     Other(HgError),
 }
 
 impl From<NodeMapError> for RevlogError {
     fn from(error: NodeMapError) -> Self {
         match error {
             NodeMapError::MultipleResults => RevlogError::AmbiguousPrefix,
             NodeMapError::RevisionNotInIndex(_) => RevlogError::corrupted(),
         }
     }
 }
 
 impl RevlogError {
     fn corrupted() -> Self {
         RevlogError::Other(HgError::corrupted("corrupted revlog"))
     }
 }
 
 /// Read only implementation of revlog.
 pub struct Revlog {
     /// When index and data are not interleaved: bytes of the revlog index.
     /// When index and data are interleaved: bytes of the revlog index and
     /// data.
     index: Index,
     /// When index and data are not interleaved: bytes of the revlog data
     data_bytes: Option<Box<dyn Deref<Target = [u8]> + Send>>,
     /// When present on disk: the persistent nodemap for this revlog
     nodemap: Option<nodemap::NodeTree>,
 }
 
 impl Revlog {
     /// Open a revlog index file.
     ///
     /// It will also open the associated data file if index and data are not
     /// interleaved.
     #[timed]
     pub fn open(
         repo: &Repo,
         index_path: impl AsRef<Path>,
         data_path: Option<&Path>,
     ) -> Result<Self, HgError> {
         let index_path = index_path.as_ref();
-        let index_mmap = repo.store_vfs().mmap_open(&index_path)?;
+        let index = {
+            match repo.store_vfs().mmap_open_opt(&index_path)? {
+                None => Index::new(Box::new(vec![])),
+                Some(index_mmap) => {
+                    let version = get_version(&index_mmap)?;
+                    if version != 1 {
+                        // A proper new version should have had a repo/store requirement.
+                        return Err(HgError::corrupted("corrupted revlog"));
+                    }
 
-        let version = get_version(&index_mmap)?;
-        if version != 1 {
-            // A proper new version should have had a repo/store requirement.
-            return Err(HgError::corrupted("corrupted revlog"));
-        }
-
-        let index = Index::new(Box::new(index_mmap))?;
+                    let index = Index::new(Box::new(index_mmap))?;
+                    Ok(index)
+                }
+            }
+        }?;
 
         let default_data_path = index_path.with_extension("d");
 
         // type annotation required
         // won't recognize Mmap as Deref<Target = [u8]>
         let data_bytes: Option<Box<dyn Deref<Target = [u8]> + Send>> =
             if index.is_inline() {
                 None
             } else {
                 let data_path = data_path.unwrap_or(&default_data_path);
                 let data_mmap = repo.store_vfs().mmap_open(data_path)?;
                 Some(Box::new(data_mmap))
             };
 
         let nodemap = NodeMapDocket::read_from_file(repo, index_path)?.map(
             |(docket, data)| {
                 nodemap::NodeTree::load_bytes(
                     Box::new(data),
                     docket.data_length,
                 )
             },
         );
 
         Ok(Revlog {
             index,
             data_bytes,
             nodemap,
         })
     }
 
     /// Return number of entries of the `Revlog`.
     pub fn len(&self) -> usize {
         self.index.len()
     }
 
     /// Returns `true` if the `Revlog` has zero `entries`.
     pub fn is_empty(&self) -> bool {
         self.index.is_empty()
     }
 
     /// Returns the node ID for the given revision number, if it exists in this
     /// revlog
     pub fn node_from_rev(&self, rev: Revision) -> Option<&Node> {
         Some(self.index.get_entry(rev)?.hash())
     }
 
     /// Return the revision number for the given node ID, if it exists in this
     /// revlog
     #[timed]
     pub fn rev_from_node(
         &self,
         node: NodePrefix,
     ) -> Result<Revision, RevlogError> {
         if node.is_prefix_of(&NULL_NODE) {
             return Ok(NULL_REVISION);
         }
 
         if let Some(nodemap) = &self.nodemap {
             return nodemap
                 .find_bin(&self.index, node)?
                 .ok_or(RevlogError::InvalidRevision);
         }
 
         // Fallback to linear scan when a persistent nodemap is not present.
         // This happens when the persistent-nodemap experimental feature is not
         // enabled, or for small revlogs.
         //
         // TODO: consider building a non-persistent nodemap in memory to
         // optimize these cases.
         let mut found_by_prefix = None;
         for rev in (0..self.len() as Revision).rev() {
             let index_entry =
                 self.index.get_entry(rev).ok_or(HgError::corrupted(
                     "revlog references a revision not in the index",
                 ))?;
             if node == *index_entry.hash() {
                 return Ok(rev);
             }
             if node.is_prefix_of(index_entry.hash()) {
                 if found_by_prefix.is_some() {
                     return Err(RevlogError::AmbiguousPrefix);
                 }
                 found_by_prefix = Some(rev)
             }
         }
         found_by_prefix.ok_or(RevlogError::InvalidRevision)
     }
 
     /// Returns whether the given revision exists in this revlog.
     pub fn has_rev(&self, rev: Revision) -> bool {
         self.index.get_entry(rev).is_some()
     }
 
     /// Return the full data associated to a revision.
     ///
     /// All entries required to build the final data out of deltas will be
     /// retrieved as needed, and the deltas will be applied to the inital
     /// snapshot to rebuild the final data.
     #[timed]
     pub fn get_rev_data(&self, rev: Revision) -> Result<Vec<u8>, RevlogError> {
         if rev == NULL_REVISION {
             return Ok(vec![]);
         };
         // Todo return -> Cow
         let mut entry = self.get_entry(rev)?;
         let mut delta_chain = vec![];
         while let Some(base_rev) = entry.base_rev {
             delta_chain.push(entry);
             entry = self
                 .get_entry(base_rev)
                 .map_err(|_| RevlogError::corrupted())?;
         }
 
         // TODO do not look twice in the index
         let index_entry = self
             .index
             .get_entry(rev)
             .ok_or(RevlogError::InvalidRevision)?;
 
         let data: Vec<u8> = if delta_chain.is_empty() {
             entry.data()?.into()
         } else {
             Revlog::build_data_from_deltas(entry, &delta_chain)?
         };
 
         if self.check_hash(
             index_entry.p1(),
             index_entry.p2(),
             index_entry.hash().as_bytes(),
             &data,
         ) {
             Ok(data)
         } else {
             Err(RevlogError::corrupted())
         }
     }
 
     /// Check the hash of some given data against the recorded hash.
     pub fn check_hash(
         &self,
         p1: Revision,
         p2: Revision,
         expected: &[u8],
         data: &[u8],
     ) -> bool {
         let e1 = self.index.get_entry(p1);
         let h1 = match e1 {
             Some(ref entry) => entry.hash(),
             None => &NULL_NODE,
         };
         let e2 = self.index.get_entry(p2);
         let h2 = match e2 {
             Some(ref entry) => entry.hash(),
             None => &NULL_NODE,
         };
 
         &hash(data, h1.as_bytes(), h2.as_bytes()) == expected
     }
 
     /// Build the full data of a revision out its snapshot
     /// and its deltas.
     #[timed]
     fn build_data_from_deltas(
         snapshot: RevlogEntry,
         deltas: &[RevlogEntry],
     ) -> Result<Vec<u8>, RevlogError> {
         let snapshot = snapshot.data()?;
         let deltas = deltas
             .iter()
             .rev()
             .map(RevlogEntry::data)
             .collect::<Result<Vec<Cow<'_, [u8]>>, RevlogError>>()?;
         let patches: Vec<_> =
             deltas.iter().map(|d| patch::PatchList::new(d)).collect();
         let patch = patch::fold_patch_lists(&patches);
         Ok(patch.apply(&snapshot))
     }
 
     /// Return the revlog data.
     fn data(&self) -> &[u8] {
         match self.data_bytes {
             Some(ref data_bytes) => &data_bytes,
             None => panic!(
                 "forgot to load the data or trying to access inline data"
             ),
         }
     }
 
     /// Get an entry of the revlog.
     fn get_entry(&self, rev: Revision) -> Result<RevlogEntry, RevlogError> {
         let index_entry = self
             .index
             .get_entry(rev)
             .ok_or(RevlogError::InvalidRevision)?;
         let start = index_entry.offset();
         let end = start + index_entry.compressed_len();
         let data = if self.index.is_inline() {
             self.index.data(start, end)
         } else {
             &self.data()[start..end]
         };
         let entry = RevlogEntry {
             rev,
             bytes: data,
             compressed_len: index_entry.compressed_len(),
             uncompressed_len: index_entry.uncompressed_len(),
             base_rev: if index_entry.base_revision() == rev {
                 None
             } else {
                 Some(index_entry.base_revision())
             },
         };
         Ok(entry)
     }
 }
 
 /// The revlog entry's bytes and the necessary informations to extract
 /// the entry's data.
 #[derive(Debug)]
 pub struct RevlogEntry<'a> {
     rev: Revision,
     bytes: &'a [u8],
     compressed_len: usize,
     uncompressed_len: usize,
     base_rev: Option<Revision>,
 }
 
 impl<'a> RevlogEntry<'a> {
     pub fn revision(&self) -> Revision {
         self.rev
     }
 
     /// Extract the data contained in the entry.
     pub fn data(&self) -> Result<Cow<'_, [u8]>, RevlogError> {
         if self.bytes.is_empty() {
             return Ok(Cow::Borrowed(&[]));
         }
         match self.bytes[0] {
             // Revision data is the entirety of the entry, including this
             // header.
             b'\0' => Ok(Cow::Borrowed(self.bytes)),
             // Raw revision data follows.
             b'u' => Ok(Cow::Borrowed(&self.bytes[1..])),
             // zlib (RFC 1950) data.
             b'x' => Ok(Cow::Owned(self.uncompressed_zlib_data()?)),
             // zstd data.
             b'\x28' => Ok(Cow::Owned(self.uncompressed_zstd_data()?)),
             // A proper new format should have had a repo/store requirement.
             _format_type => Err(RevlogError::corrupted()),
         }
     }
 
     fn uncompressed_zlib_data(&self) -> Result<Vec<u8>, RevlogError> {
         let mut decoder = ZlibDecoder::new(self.bytes);
         if self.is_delta() {
             let mut buf = Vec::with_capacity(self.compressed_len);
             decoder
                 .read_to_end(&mut buf)
                 .map_err(|_| RevlogError::corrupted())?;
             Ok(buf)
         } else {
             let mut buf = vec![0; self.uncompressed_len];
             decoder
                 .read_exact(&mut buf)
                 .map_err(|_| RevlogError::corrupted())?;
             Ok(buf)
         }
     }
 
     fn uncompressed_zstd_data(&self) -> Result<Vec<u8>, RevlogError> {
         if self.is_delta() {
             let mut buf = Vec::with_capacity(self.compressed_len);
             zstd::stream::copy_decode(self.bytes, &mut buf)
                 .map_err(|_| RevlogError::corrupted())?;
             Ok(buf)
         } else {
             let mut buf = vec![0; self.uncompressed_len];
             let len = zstd::block::decompress_to_buffer(self.bytes, &mut buf)
                 .map_err(|_| RevlogError::corrupted())?;
             if len != self.uncompressed_len {
                 Err(RevlogError::corrupted())
             } else {
                 Ok(buf)
             }
         }
     }
 
     /// Tell if the entry is a snapshot or a delta
     /// (influences on decompression).
     fn is_delta(&self) -> bool {
         self.base_rev.is_some()
     }
 }
 
 /// Format version of the revlog.
 pub fn get_version(index_bytes: &[u8]) -> Result<u16, HgError> {
     if index_bytes.len() == 0 {
         return Ok(1);
     };
     if index_bytes.len() < 4 {
         return Err(HgError::corrupted(
             "corrupted revlog: can't read the index format header",
         ));
     };
     Ok(BigEndian::read_u16(&index_bytes[2..=3]))
 }
 
 /// Calculate the hash of a revision given its data and its parents.
 fn hash(
     data: &[u8],
     p1_hash: &[u8],
     p2_hash: &[u8],
 ) -> [u8; NODE_BYTES_LENGTH] {
     let mut hasher = Sha1::new();
     let (a, b) = (p1_hash, p2_hash);
     if a > b {
         hasher.update(b);
         hasher.update(a);
     } else {
         hasher.update(a);
         hasher.update(b);
     }
     hasher.update(data);
     *hasher.finalize().as_ref()
 }
 
 #[cfg(test)]
 mod tests {
     use super::*;
 
     use super::super::index::IndexEntryBuilder;
 
     #[test]
     fn version_test() {
         let bytes = IndexEntryBuilder::new()
             .is_first(true)
             .with_version(1)
             .build();
 
-        assert_eq!(get_version(&bytes), 1)
+        assert_eq!(get_version(&bytes).map_err(|_err|()), Ok(1))
     }
 }

rust/hg-core/src/vfs.rs

@@ -1,73 +1,100 b''
 use crate::errors::{HgError, IoErrorContext, IoResultExt};
 use memmap2::{Mmap, MmapOptions};
 use std::io::ErrorKind;
 use std::path::{Path, PathBuf};
 
 /// Filesystem access abstraction for the contents of a given "base" diretory
 #[derive(Clone, Copy)]
 pub struct Vfs<'a> {
     pub(crate) base: &'a Path,
 }
 
+struct FileNotFound(std::io::Error, PathBuf);
+
 impl Vfs<'_> {
     pub fn join(&self, relative_path: impl AsRef<Path>) -> PathBuf {
         self.base.join(relative_path)
     }
 
     pub fn read(
         &self,
         relative_path: impl AsRef<Path>,
     ) -> Result<Vec<u8>, HgError> {
         let path = self.join(relative_path);
         std::fs::read(&path).when_reading_file(&path)
     }
 
+    fn mmap_open_gen(
+        &self,
+        relative_path: impl AsRef<Path>,
+    ) -> Result<Result<Mmap, FileNotFound>, HgError> {
+        let path = self.join(relative_path);
+        let file = match std::fs::File::open(&path) {
+            Err(err) => {
+                if let ErrorKind::NotFound = err.kind() {
+                    return Ok(Err(FileNotFound(err, path)));
+                };
+                return (Err(err)).when_reading_file(&path);
+            }
+            Ok(file) => file,
+        };
+        // TODO: what are the safety requirements here?
+        let mmap = unsafe { MmapOptions::new().map(&file) }
+            .when_reading_file(&path)?;
+        Ok(Ok(mmap))
+    }
+
+    pub fn mmap_open_opt(
+        &self,
+        relative_path: impl AsRef<Path>,
+    ) -> Result<Option<Mmap>, HgError> {
+        self.mmap_open_gen(relative_path).map(|res| res.ok())
+    }
+
     pub fn mmap_open(
         &self,
         relative_path: impl AsRef<Path>,
     ) -> Result<Mmap, HgError> {
-        let path = self.base.join(relative_path);
-        let file = std::fs::File::open(&path).when_reading_file(&path)?;
-        // TODO: what are the safety requirements here?
-        let mmap = unsafe { MmapOptions::new().map(&file) }
-            .when_reading_file(&path)?;
-        Ok(mmap)
+        match self.mmap_open_gen(relative_path)? {
+            Err(FileNotFound(err, path)) => Err(err).when_reading_file(&path),
+            Ok(res) => Ok(res),
+        }
     }
 
     pub fn rename(
         &self,
         relative_from: impl AsRef<Path>,
         relative_to: impl AsRef<Path>,
     ) -> Result<(), HgError> {
         let from = self.join(relative_from);
         let to = self.join(relative_to);
         std::fs::rename(&from, &to)
             .with_context(|| IoErrorContext::RenamingFile { from, to })
     }
 }
 
 fn fs_metadata(
     path: impl AsRef<Path>,
 ) -> Result<Option<std::fs::Metadata>, HgError> {
     let path = path.as_ref();
     match std::fs::metadata(path) {
         Ok(meta) => Ok(Some(meta)),
         Err(error) => match error.kind() {
             // TODO: when we require a Rust version where `NotADirectory` is
             // stable, invert this logic and return None for it and `NotFound`
             // and propagate any other error.
             ErrorKind::PermissionDenied => Err(error).with_context(|| {
                 IoErrorContext::ReadingMetadata(path.to_owned())
             }),
             _ => Ok(None),
         },
     }
 }
 
 pub(crate) fn is_dir(path: impl AsRef<Path>) -> Result<bool, HgError> {
     Ok(fs_metadata(path)?.map_or(false, |meta| meta.is_dir()))
 }
 
 pub(crate) fn is_file(path: impl AsRef<Path>) -> Result<bool, HgError> {
     Ok(fs_metadata(path)?.map_or(false, |meta| meta.is_file()))
 }

tests/test-empty-manifest-index.t

@@ -1,23 +1,27 b''
-Create a repo such that the changelog entry refers to a null manifest node:
+Test null revisions (node 0000000000000000000000000000000000000000, aka rev -1)
+in various circumstances.
+
+Make an empty repo:
 
   $ hg init a
   $ cd a
-  $ hg log
-  $ touch x
-  $ hg add x
-  $ hg commit -m "init"
-  $ hg rm x
-  $ hg commit -q --amend
 
-  $ wc -c < .hg/store/00manifest.i
-  0
-
-Make sure that the manifest can be read (and is empty):
-
-  $ hg --config rhg.on-unsupported=abort files -r .
+  $ hg files -r 0000000000000000000000000000000000000000
+  [1]
+  $ hg files -r .
   [1]
 
-Test a null changelog rev, too:
+Add an empty commit (this makes the changelog refer to a null manifest node):
+
+
+  $ hg commit -m "init" --config ui.allowemptycommit=true
 
-  $ hg --config rhg.on-unsupported=abort files -r 0000000000000000000000000000000000000000
+  $ hg files -r .
   [1]
+
+Strip that empty commit (this makes the changelog file empty, as opposed to missing):
+
+  $ hg --config 'extensions.strip=' strip . > /dev/null
+
+  $ hg files -r .
+  [1]