--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/rust/hg-core/src/revlog/options.rs	Wed Sep 25 18:24:15 2024 +0200
@@ -0,0 +1,393 @@
+//! Helpers for the revlog config and opening options
+
+use std::collections::HashSet;
+
+use crate::{
+    config::{Config, ResourceProfileValue},
+    errors::HgError,
+    requirements::{
+        CHANGELOGV2_REQUIREMENT, GENERALDELTA_REQUIREMENT, NARROW_REQUIREMENT,
+        NODEMAP_REQUIREMENT, REVLOGV1_REQUIREMENT, REVLOGV2_REQUIREMENT,
+        SPARSEREVLOG_REQUIREMENT,
+    },
+};
+
+use super::{compression::CompressionConfig, RevlogType};
+
+const DEFAULT_CHUNK_CACHE_SIZE: u64 = 65536;
+const DEFAULT_SPARSE_READ_DENSITY_THRESHOLD: f64 = 0.50;
+const DEFAULT_SPARSE_READ_MIN_GAP_SIZE: u64 = 262144;
+
+/// The known revlog versions and their options
+#[derive(Debug, Copy, Clone, PartialEq)]
+pub enum RevlogVersionOptions {
+    V0,
+    V1 { general_delta: bool, inline: bool },
+    V2,
+    ChangelogV2 { compute_rank: bool },
+}
+
+/// Options to govern how a revlog should be opened, usually from the
+/// repository configuration or requirements.
+#[derive(Debug, Copy, Clone)]
+pub struct RevlogOpenOptions {
+    /// The revlog version, along with any option specific to this version
+    pub version: RevlogVersionOptions,
+    /// Whether the revlog uses a persistent nodemap.
+    pub use_nodemap: bool,
+    pub delta_config: RevlogDeltaConfig,
+    pub data_config: RevlogDataConfig,
+    pub feature_config: RevlogFeatureConfig,
+}
+
+#[cfg(test)]
+impl Default for RevlogOpenOptions {
+    fn default() -> Self {
+        Self {
+            version: RevlogVersionOptions::V1 {
+                general_delta: true,
+                inline: false,
+            },
+            use_nodemap: true,
+            data_config: Default::default(),
+            delta_config: Default::default(),
+            feature_config: Default::default(),
+        }
+    }
+}
+
+impl RevlogOpenOptions {
+    pub fn new(
+        inline: bool,
+        data_config: RevlogDataConfig,
+        delta_config: RevlogDeltaConfig,
+        feature_config: RevlogFeatureConfig,
+    ) -> Self {
+        Self {
+            version: RevlogVersionOptions::V1 {
+                general_delta: data_config.general_delta,
+                inline,
+            },
+            use_nodemap: false,
+            data_config,
+            delta_config,
+            feature_config,
+        }
+    }
+
+    pub fn index_header(&self) -> super::index::IndexHeader {
+        super::index::IndexHeader {
+            header_bytes: match self.version {
+                RevlogVersionOptions::V0 => [0, 0, 0, 0],
+                RevlogVersionOptions::V1 {
+                    general_delta,
+                    inline,
+                } => [
+                    0,
+                    if general_delta && inline {
+                        3
+                    } else if general_delta {
+                        2
+                    } else {
+                        u8::from(inline)
+                    },
+                    0,
+                    1,
+                ],
+                RevlogVersionOptions::V2 => 0xDEADu32.to_be_bytes(),
+                RevlogVersionOptions::ChangelogV2 { compute_rank: _ } => {
+                    0xD34Du32.to_be_bytes()
+                }
+            },
+        }
+    }
+}
+
+#[derive(Debug, Clone, Copy, PartialEq)]
+/// Holds configuration values about how the revlog data is read
+pub struct RevlogDataConfig {
+    /// Should we try to open the "pending" version of the revlog
+    pub try_pending: bool,
+    /// Should we try to open the "split" version of the revlog
+    pub try_split: bool,
+    /// When True, `indexfile` should be opened with `checkambig=True` at
+    /// writing time, to avoid file stat ambiguity
+    pub check_ambig: bool,
+    /// If true, use mmap instead of reading to deal with large indexes
+    pub mmap_large_index: bool,
+    /// How much data is considered large
+    pub mmap_index_threshold: Option<u64>,
+    /// How much data to read and cache into the raw revlog data cache
+    pub chunk_cache_size: u64,
+    /// The size of the uncompressed cache compared to the largest revision
+    /// seen
+    pub uncompressed_cache_factor: Option<f64>,
+    /// The number of chunks cached
+    pub uncompressed_cache_count: Option<u64>,
+    /// Allow sparse reading of the revlog data
+    pub with_sparse_read: bool,
+    /// Minimal density of a sparse read chunk
+    pub sr_density_threshold: f64,
+    /// Minimal size of the data we skip when performing sparse reads
+    pub sr_min_gap_size: u64,
+    /// Whether deltas are encoded against arbitrary bases
+    pub general_delta: bool,
+}
+
+impl RevlogDataConfig {
+    pub fn new(
+        config: &Config,
+        requirements: &HashSet<String>,
+    ) -> Result<Self, HgError> {
+        let mut data_config = Self::default();
+        if let Some(chunk_cache_size) =
+            config.get_byte_size(b"format", b"chunkcachesize")?
+        {
+            data_config.chunk_cache_size = chunk_cache_size;
+        }
+
+        let memory_profile = config.get_resource_profile(Some("memory"));
+        if memory_profile.value >= ResourceProfileValue::Medium {
+            data_config.uncompressed_cache_count = Some(10_000);
+            data_config.uncompressed_cache_factor = Some(4.0);
+            if memory_profile.value >= ResourceProfileValue::High {
+                data_config.uncompressed_cache_factor = Some(10.0)
+            }
+        }
+
+        if let Some(mmap_index_threshold) = config
+            .get_byte_size(b"storage", b"revlog.mmap.index:size-threshold")?
+        {
+            data_config.mmap_index_threshold = Some(mmap_index_threshold);
+        }
+
+        let with_sparse_read =
+            config.get_bool(b"experimental", b"sparse-read")?;
+        if let Some(sr_density_threshold) = config
+            .get_f64(b"experimental", b"sparse-read.density-threshold")?
+        {
+            data_config.sr_density_threshold = sr_density_threshold;
+        }
+        data_config.with_sparse_read = with_sparse_read;
+        if let Some(sr_min_gap_size) = config
+            .get_byte_size(b"experimental", b"sparse-read.min-gap-size")?
+        {
+            data_config.sr_min_gap_size = sr_min_gap_size;
+        }
+
+        data_config.with_sparse_read =
+            requirements.contains(SPARSEREVLOG_REQUIREMENT);
+
+        Ok(data_config)
+    }
+}
+
+impl Default for RevlogDataConfig {
+    fn default() -> Self {
+        Self {
+            chunk_cache_size: DEFAULT_CHUNK_CACHE_SIZE,
+            sr_density_threshold: DEFAULT_SPARSE_READ_DENSITY_THRESHOLD,
+            sr_min_gap_size: DEFAULT_SPARSE_READ_MIN_GAP_SIZE,
+            try_pending: Default::default(),
+            try_split: Default::default(),
+            check_ambig: Default::default(),
+            mmap_large_index: Default::default(),
+            mmap_index_threshold: Default::default(),
+            uncompressed_cache_factor: Default::default(),
+            uncompressed_cache_count: Default::default(),
+            with_sparse_read: Default::default(),
+            general_delta: Default::default(),
+        }
+    }
+}
+
+#[derive(Debug, Clone, Copy, PartialEq)]
+/// Holds configuration values about how new deltas are computed.
+///
+/// Some attributes are duplicated from [`RevlogDataConfig`] to help having
+/// each object self contained.
+pub struct RevlogDeltaConfig {
+    /// Whether deltas can be encoded against arbitrary bases
+    pub general_delta: bool,
+    /// Allow sparse writing of the revlog data
+    pub sparse_revlog: bool,
+    /// Maximum length of a delta chain
+    pub max_chain_len: Option<u64>,
+    /// Maximum distance between a delta chain's start and end
+    pub max_deltachain_span: Option<u64>,
+    /// If `upper_bound_comp` is not None, this is the expected maximal
+    /// gain from compression for the data content
+    pub upper_bound_comp: Option<f64>,
+    /// Should we try a delta against both parents
+    pub delta_both_parents: bool,
+    /// Test delta base candidate groups by chunks of this maximal size
+    pub candidate_group_chunk_size: u64,
+    /// Should we display debug information about delta computation
+    pub debug_delta: bool,
+    /// Trust incoming deltas by default
+    pub lazy_delta: bool,
+    /// Trust the base of incoming deltas by default
+    pub lazy_delta_base: bool,
+}
+
+impl RevlogDeltaConfig {
+    pub fn new(
+        config: &Config,
+        requirements: &HashSet<String>,
+        revlog_type: RevlogType,
+    ) -> Result<Self, HgError> {
+        let mut delta_config = Self {
+            delta_both_parents: config
+                .get_option_no_default(
+                    b"storage",
+                    b"revlog.optimize-delta-parent-choice",
+                )?
+                .unwrap_or(true),
+            candidate_group_chunk_size: config
+                .get_u64(
+                    b"storage",
+                    b"revlog.delta-parent-search.candidate-group-chunk-size",
+                )?
+                .unwrap_or_default(),
+            ..Default::default()
+        };
+
+        delta_config.debug_delta =
+            config.get_bool(b"debug", b"revlog.debug-delta")?;
+
+        delta_config.general_delta =
+            requirements.contains(GENERALDELTA_REQUIREMENT);
+
+        let lazy_delta =
+            config.get_bool(b"storage", b"revlog.reuse-external-delta")?;
+
+        if revlog_type == RevlogType::Manifestlog {
+            // upper bound of what we expect from compression
+            // (real life value seems to be 3)
+            delta_config.upper_bound_comp = Some(3.0)
+        }
+
+        let mut lazy_delta_base = false;
+        if lazy_delta {
+            lazy_delta_base = match config.get_option_no_default(
+                b"storage",
+                b"revlog.reuse-external-delta-parent",
+            )? {
+                Some(base) => base,
+                None => config.get_bool(b"format", b"generaldelta")?,
+            };
+        }
+        delta_config.lazy_delta = lazy_delta;
+        delta_config.lazy_delta_base = lazy_delta_base;
+
+        delta_config.max_deltachain_span =
+            match config.get_i64(b"experimental", b"maxdeltachainspan")? {
+                Some(span) => {
+                    if span < 0 {
+                        None
+                    } else {
+                        Some(span as u64)
+                    }
+                }
+                None => None,
+            };
+
+        delta_config.sparse_revlog =
+            requirements.contains(SPARSEREVLOG_REQUIREMENT);
+
+        delta_config.max_chain_len =
+            config.get_byte_size_no_default(b"format", b"maxchainlen")?;
+
+        Ok(delta_config)
+    }
+}
+
+impl Default for RevlogDeltaConfig {
+    fn default() -> Self {
+        Self {
+            delta_both_parents: true,
+            lazy_delta: true,
+            general_delta: Default::default(),
+            sparse_revlog: Default::default(),
+            max_chain_len: Default::default(),
+            max_deltachain_span: Default::default(),
+            upper_bound_comp: Default::default(),
+            candidate_group_chunk_size: Default::default(),
+            debug_delta: Default::default(),
+            lazy_delta_base: Default::default(),
+        }
+    }
+}
+
+#[derive(Debug, Default, Clone, Copy, PartialEq)]
+/// Holds configuration values about the available revlog features
+pub struct RevlogFeatureConfig {
+    /// The compression engine and its options
+    pub compression_engine: CompressionConfig,
+    /// Can we use censor on this revlog
+    pub censorable: bool,
+    /// Does this revlog use the "side data" feature
+    pub has_side_data: bool,
+    /// Might remove this configuration once the rank computation has no
+    /// impact
+    pub compute_rank: bool,
+    /// Parent order is supposed to be semantically irrelevant, so we
+    /// normally re-sort parents to ensure that the first parent is non-null,
+    /// if there is a non-null parent at all.
+    /// filelog abuses the parent order as a flag to mark some instances of
+    /// meta-encoded files, so allow it to disable this behavior.
+    pub canonical_parent_order: bool,
+    /// Can ellipsis commit be used
+    pub enable_ellipsis: bool,
+}
+
+impl RevlogFeatureConfig {
+    pub fn new(
+        config: &Config,
+        requirements: &HashSet<String>,
+    ) -> Result<Self, HgError> {
+        Ok(Self {
+            compression_engine: CompressionConfig::new(config, requirements)?,
+            enable_ellipsis: requirements.contains(NARROW_REQUIREMENT),
+            ..Default::default()
+        })
+    }
+}
+
+/// Return the default options for a revlog of `revlog_type` according to the
+/// current config and requirements.
+pub fn default_revlog_options(
+    config: &Config,
+    requirements: &HashSet<String>,
+    revlog_type: RevlogType,
+) -> Result<RevlogOpenOptions, HgError> {
+    let is_changelog = revlog_type == RevlogType::Changelog;
+    let version =
+        if is_changelog && requirements.contains(CHANGELOGV2_REQUIREMENT) {
+            let compute_rank = config
+                .get_bool(b"experimental", b"changelog-v2.compute-rank")?;
+            RevlogVersionOptions::ChangelogV2 { compute_rank }
+        } else if requirements.contains(REVLOGV2_REQUIREMENT) {
+            RevlogVersionOptions::V2
+        } else if requirements.contains(REVLOGV1_REQUIREMENT) {
+            RevlogVersionOptions::V1 {
+                general_delta: requirements.contains(GENERALDELTA_REQUIREMENT),
+                inline: !is_changelog,
+            }
+        } else {
+            RevlogVersionOptions::V0
+        };
+    Ok(RevlogOpenOptions {
+        version,
+        // We don't need to dance around the slow path like in the Python
+        // implementation since we know we have access to the fast code.
+        use_nodemap: requirements.contains(NODEMAP_REQUIREMENT),
+        delta_config: RevlogDeltaConfig::new(
+            config,
+            requirements,
+            revlog_type,
+        )?,
+        data_config: RevlogDataConfig::new(config, requirements)?,
+        feature_config: RevlogFeatureConfig::new(config, requirements)?,
+    })
+}