rust-index: implementation of __getitem__

Although the removed panic tends to prove if the full test suite
did pass that the case when the input is a node id does not happen,
it is best not to remove it right now.

Raising IndexError is crucial for iteration on the index to stop,
given the default CPython sequence iterator, see for instance
https://github.com/zpoint/CPython-Internals/blobs/master/BasicObject/iter/iter.md
This was spotted by `test-rust-ancestors.py`, which does simple interations on
indexes (as preflight checks).

In `revlog.c`, `index_getitem` defaults to `index_get` when called
on revision numbers, which does raise `IndexError` with the same message as
the one we are introducing here.

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

@@ -123,6 +123,10 b' impl IndexData {'
         }
         Ok(())
     }
+
+    fn is_new(&self) -> bool {
+        self.bytes.is_empty()
+    }
 }
 
 impl std::ops::Index<std::ops::Range<usize>> for IndexData {
@@ -146,6 +150,7 b' impl std::ops::Index<std::ops::Range<usi'
     }
 }
 
+#[derive(Debug, PartialEq, Eq)]
 pub struct RevisionDataParams {
     pub flags: u16,
     pub data_offset: u64,
@@ -163,6 +168,27 b' pub struct RevisionDataParams {'
     pub _rank: i32,
 }
 
+impl Default for RevisionDataParams {
+    fn default() -> Self {
+        Self {
+            flags: 0,
+            data_offset: 0,
+            data_compressed_length: 0,
+            data_uncompressed_length: 0,
+            data_delta_base: -1,
+            link_rev: -1,
+            parent_rev_1: -1,
+            parent_rev_2: -1,
+            node_id: [0; NODE_BYTES_LENGTH],
+            _sidedata_offset: 0,
+            _sidedata_compressed_length: 0,
+            data_compression_mode: COMPRESSION_MODE_INLINE,
+            _sidedata_compression_mode: COMPRESSION_MODE_INLINE,
+            _rank: -1,
+        }
+    }
+}
+
 #[derive(BytesCast)]
 #[repr(C)]
 pub struct RevisionDataV1 {
@@ -397,6 +423,29 b' impl Index {'
         })
     }
 
+    pub fn entry_as_params(
+        &self,
+        rev: UncheckedRevision,
+    ) -> Option<RevisionDataParams> {
+        let rev = self.check_revision(rev)?;
+        self.get_entry(rev).map(|e| RevisionDataParams {
+            flags: e.flags(),
+            data_offset: if rev.0 == 0 && !self.bytes.is_new() {
+                e.flags() as u64
+            } else {
+                e.raw_offset()
+            },
+            data_compressed_length: e.compressed_len().try_into().unwrap(),
+            data_uncompressed_length: e.uncompressed_len(),
+            data_delta_base: e.base_revision_or_base_of_delta_chain().0,
+            link_rev: e.link_revision().0,
+            parent_rev_1: e.p1().0,
+            parent_rev_2: e.p2().0,
+            node_id: e.hash().as_bytes().try_into().unwrap(),
+            ..Default::default()
+        })
+    }
+
     fn get_entry_inline(
         &self,
         rev: Revision,
@@ -519,6 +568,9 b" impl<'a> IndexEntry<'a> {"
             BigEndian::read_u64(&bytes[..]) as usize
         }
     }
+    pub fn raw_offset(&self) -> u64 {
+        BigEndian::read_u64(&self.bytes[0..8])
+    }
 
     pub fn flags(&self) -> u16 {
         BigEndian::read_u16(&self.bytes[6..=7])

rust/hg-cpython/src/revlog.rs

@@ -17,11 +17,10 b' use cpython::{'
     PyObject, PyResult, PyString, PyTuple, Python, PythonObject, ToPyObject,
 };
 use hg::{
-    index::IndexHeader,
-    index::{RevisionDataParams, COMPRESSION_MODE_INLINE},
+    index::{IndexHeader, RevisionDataParams},
     nodemap::{Block, NodeMapError, NodeTree},
     revlog::{nodemap::NodeMap, NodePrefix, RevlogIndex},
-    BaseRevision, Revision, UncheckedRevision,
+    BaseRevision, Revision, UncheckedRevision, NULL_REVISION,
 };
 use std::cell::RefCell;
 
@@ -237,11 +236,6 b' py_class!(pub class MixedIndex |py| {'
         Ok(rust_res)
     }
 
-    /// get an index entry
-    def get(&self, *args, **kw) -> PyResult<PyObject> {
-        self.call_cindex(py, "get", args, kw)
-    }
-
     /// compute phases
     def computephasesmapsets(&self, *args, **kw) -> PyResult<PyObject> {
         self.call_cindex(py, "computephasesmapsets", args, kw)
@@ -292,23 +286,32 b' py_class!(pub class MixedIndex |py| {'
     // Since we call back through the high level Python API,
     // there's no point making a distinction between index_get
     // and index_getitem.
+    // gracinet 2023: this above is no longer true for the pure Rust impl
 
     def __len__(&self) -> PyResult<usize> {
         self.len(py)
     }
 
     def __getitem__(&self, key: PyObject) -> PyResult<PyObject> {
+        let rust_res = self.inner_getitem(py, key.clone_ref(py))?;
+
         // this conversion seems needless, but that's actually because
         // `index_getitem` does not handle conversion from PyLong,
         // which expressions such as [e for e in index] internally use.
         // Note that we don't seem to have a direct way to call
         // PySequence_GetItem (does the job), which would possibly be better
         // for performance
-        let key = match key.extract::<i32>(py) {
+        // gracinet 2023: the above comment can be removed when we use
+        // the pure Rust impl only. Note also that `key` can be a binary
+        // node id.
+        let c_key = match key.extract::<BaseRevision>(py) {
             Ok(rev) => rev.to_py_object(py).into_object(),
             Err(_) => key,
         };
-        self.cindex(py).borrow().inner().get_item(py, key)
+        let c_res = self.cindex(py).borrow().inner().get_item(py, c_key)?;
+
+        assert_py_eq(py, "__getitem__", &rust_res, &c_res)?;
+        Ok(rust_res)
     }
 
     def __contains__(&self, item: PyObject) -> PyResult<bool> {
@@ -426,13 +429,49 b' fn py_tuple_to_revision_data_params('
         parent_rev_1: tuple.get_item(py, 5).extract(py)?,
         parent_rev_2: tuple.get_item(py, 6).extract(py)?,
         node_id,
-        _sidedata_offset: 0,
-        _sidedata_compressed_length: 0,
-        data_compression_mode: COMPRESSION_MODE_INLINE,
-        _sidedata_compression_mode: COMPRESSION_MODE_INLINE,
-        _rank: -1,
+        ..Default::default()
     })
 }
+fn revision_data_params_to_py_tuple(
+    py: Python,
+    params: RevisionDataParams,
+) -> PyTuple {
+    PyTuple::new(
+        py,
+        &[
+            params.data_offset.into_py_object(py).into_object(),
+            params
+                .data_compressed_length
+                .into_py_object(py)
+                .into_object(),
+            params
+                .data_uncompressed_length
+                .into_py_object(py)
+                .into_object(),
+            params.data_delta_base.into_py_object(py).into_object(),
+            params.link_rev.into_py_object(py).into_object(),
+            params.parent_rev_1.into_py_object(py).into_object(),
+            params.parent_rev_2.into_py_object(py).into_object(),
+            PyBytes::new(py, &params.node_id)
+                .into_py_object(py)
+                .into_object(),
+            params._sidedata_offset.into_py_object(py).into_object(),
+            params
+                ._sidedata_compressed_length
+                .into_py_object(py)
+                .into_object(),
+            params
+                .data_compression_mode
+                .into_py_object(py)
+                .into_object(),
+            params
+                ._sidedata_compression_mode
+                .into_py_object(py)
+                .into_object(),
+            params._rank.into_py_object(py).into_object(),
+        ],
+    )
+}
 
 impl MixedIndex {
     fn new(
@@ -601,6 +640,34 b' impl MixedIndex {'
 
         Ok(py.None())
     }
+
+    fn inner_getitem(&self, py: Python, key: PyObject) -> PyResult<PyObject> {
+        let idx = self.index(py).borrow();
+        Ok(match key.extract::<BaseRevision>(py) {
+            Ok(key_as_int) => {
+                let entry_params = if key_as_int == NULL_REVISION.0 {
+                    RevisionDataParams::default()
+                } else {
+                    let rev = UncheckedRevision(key_as_int);
+                    match idx.entry_as_params(rev) {
+                        Some(e) => e,
+                        None => {
+                            return Err(PyErr::new::<IndexError, _>(
+                                py,
+                                "revlog index out of range",
+                            ));
+                        }
+                    }
+                };
+                revision_data_params_to_py_tuple(py, entry_params)
+                    .into_object()
+            }
+            _ => self.get_rev(py, key.extract::<PyBytes>(py)?)?.map_or_else(
+                || py.None(),
+                |py_rev| py_rev.into_py_object(py).into_object(),
+            ),
+        })
+    }
 }
 
 fn revlog_error(py: Python) -> PyErr {