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Load themes lazily for improved startup time
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This is for sharkdp#951. Syntax lazy-loading will come later and have a much bigger
impact, but lazy-loading of themes does not have negligible impact.
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Enselic committed Dec 1, 2021
1 parent 544ad4b commit 78c00dc
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Showing 4 changed files with 130 additions and 16 deletions.
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28 changes: 18 additions & 10 deletions src/assets.rs
Original file line number Diff line number Diff line change
Expand Up @@ -4,7 +4,7 @@ use std::path::Path;

use once_cell::unsync::OnceCell;

use syntect::highlighting::{Theme, ThemeSet};
use syntect::highlighting::Theme;
use syntect::parsing::{SyntaxReference, SyntaxSet};

use path_abs::PathAbs;
Expand All @@ -15,6 +15,8 @@ use crate::syntax_mapping::ignored_suffixes::IgnoredSuffixes;
use crate::syntax_mapping::MappingTarget;
use crate::{bat_warning, SyntaxMapping};

use lazy_theme_set::LazyThemeSet;

use serialized_syntax_set::*;

#[cfg(feature = "build-assets")]
Expand All @@ -23,14 +25,15 @@ pub use crate::assets::build_assets::*;
pub(crate) mod assets_metadata;
#[cfg(feature = "build-assets")]
mod build_assets;
mod lazy_theme_set;
mod serialized_syntax_set;

#[derive(Debug)]
pub struct HighlightingAssets {
syntax_set_cell: OnceCell<SyntaxSet>,
serialized_syntax_set: SerializedSyntaxSet,

theme_set: ThemeSet,
theme_set: LazyThemeSet,
fallback_theme: Option<&'static str>,
}

Expand All @@ -43,11 +46,17 @@ pub struct SyntaxReferenceInSet<'a> {
/// Compress for size of ~700 kB instead of ~4600 kB at the cost of ~30% longer deserialization time
pub(crate) const COMPRESS_SYNTAXES: bool = true;

/// Compress for size of ~20 kB instead of ~200 kB at the cost of ~30% longer deserialization time
pub(crate) const COMPRESS_THEMES: bool = true;
/// We don't want to compress our [LazyThemeSet] since the lazy-loaded themes
/// within it are already compressed, and compressing another time just makes
/// performance suffer
pub(crate) const COMPRESS_THEMES: bool = false;

/// Compress for size of ~40 kB instead of ~200 kB without much difference in
/// performance due to lazy-loading
pub(crate) const COMPRESS_LAZY_THEMES: bool = true;

impl HighlightingAssets {
fn new(serialized_syntax_set: SerializedSyntaxSet, theme_set: ThemeSet) -> Self {
fn new(serialized_syntax_set: SerializedSyntaxSet, theme_set: LazyThemeSet) -> Self {
HighlightingAssets {
syntax_set_cell: OnceCell::new(),
serialized_syntax_set,
Expand Down Expand Up @@ -95,12 +104,12 @@ impl HighlightingAssets {
Ok(self.get_syntax_set()?.syntaxes())
}

fn get_theme_set(&self) -> &ThemeSet {
fn get_theme_set(&self) -> &LazyThemeSet {
&self.theme_set
}

pub fn themes(&self) -> impl Iterator<Item = &str> {
self.get_theme_set().themes.keys().map(|s| s.as_ref())
self.get_theme_set().themes()
}

/// Use [Self::get_syntax_for_path] instead
Expand Down Expand Up @@ -175,7 +184,7 @@ impl HighlightingAssets {
}

pub(crate) fn get_theme(&self, theme: &str) -> &Theme {
match self.get_theme_set().themes.get(theme) {
match self.get_theme_set().get(theme) {
Some(theme) => theme,
None => {
if theme == "ansi-light" || theme == "ansi-dark" {
Expand All @@ -186,7 +195,6 @@ impl HighlightingAssets {
bat_warning!("Unknown theme '{}', using default.", theme)
}
self.get_theme_set()
.themes
.get(self.fallback_theme.unwrap_or_else(|| Self::default_theme()))
.expect("something is very wrong if the default theme is missing")
}
Expand Down Expand Up @@ -293,7 +301,7 @@ pub(crate) fn get_serialized_integrated_syntaxset() -> &'static [u8] {
include_bytes!("../assets/syntaxes.bin")
}

pub(crate) fn get_integrated_themeset() -> ThemeSet {
pub(crate) fn get_integrated_themeset() -> LazyThemeSet {
from_binary(include_bytes!("../assets/themes.bin"), COMPRESS_THEMES)
}

Expand Down
14 changes: 8 additions & 6 deletions src/assets/build_assets.rs
Original file line number Diff line number Diff line change
@@ -1,4 +1,6 @@
use std::convert::TryInto;
use std::path::Path;

use syntect::highlighting::ThemeSet;
use syntect::parsing::{SyntaxSet, SyntaxSetBuilder};

Expand All @@ -10,7 +12,7 @@ pub fn build(
target_dir: &Path,
current_version: &str,
) -> Result<()> {
let theme_set = build_theme_set(source_dir, include_integrated_assets);
let theme_set = build_theme_set(source_dir, include_integrated_assets)?;

let syntax_set_builder = build_syntax_set_builder(source_dir, include_integrated_assets)?;

Expand All @@ -21,9 +23,9 @@ pub fn build(
write_assets(&theme_set, &syntax_set, target_dir, current_version)
}

fn build_theme_set(source_dir: &Path, include_integrated_assets: bool) -> ThemeSet {
fn build_theme_set(source_dir: &Path, include_integrated_assets: bool) -> Result<LazyThemeSet> {
let mut theme_set = if include_integrated_assets {
crate::assets::get_integrated_themeset()
crate::assets::get_integrated_themeset().try_into()?
} else {
ThemeSet::new()
};
Expand All @@ -45,7 +47,7 @@ fn build_theme_set(source_dir: &Path, include_integrated_assets: bool) -> ThemeS
);
}

theme_set
theme_set.try_into()
}

fn build_syntax_set_builder(
Expand Down Expand Up @@ -85,7 +87,7 @@ fn print_unlinked_contexts(syntax_set: &SyntaxSet) {
}

fn write_assets(
theme_set: &ThemeSet,
theme_set: &LazyThemeSet,
syntax_set: &SyntaxSet,
target_dir: &Path,
current_version: &str,
Expand Down Expand Up @@ -114,7 +116,7 @@ fn write_assets(
Ok(())
}

fn asset_to_contents<T: serde::Serialize>(
pub(crate) fn asset_to_contents<T: serde::Serialize>(
asset: &T,
description: &str,
compressed: bool,
Expand Down
104 changes: 104 additions & 0 deletions src/assets/lazy_theme_set.rs
Original file line number Diff line number Diff line change
@@ -0,0 +1,104 @@
use super::*;

use std::collections::BTreeMap;
use std::convert::TryFrom;

use serde::Deserialize;
use serde::Serialize;

use once_cell::unsync::OnceCell;

use syntect::highlighting::{Theme, ThemeSet};

/// Same structure as a [`syntect::highlighting::ThemeSet`] but with themes
/// stored in raw serialized form, and deserialized on demand.
#[derive(Debug, Default, Serialize, Deserialize)]
pub struct LazyThemeSet {
/// This is a [`BTreeMap`] because that's what [`syntect::highlighting::ThemeSet`] uses
themes: BTreeMap<String, LazyTheme>,
}

/// Stores raw serialized data for a theme with methods to lazily deserialize
/// (load) the theme.
#[derive(Debug, Serialize, Deserialize)]
struct LazyTheme {
serialized: Vec<u8>,

#[serde(skip, default = "OnceCell::new")]
deserialized: OnceCell<syntect::highlighting::Theme>,
}

impl LazyThemeSet {
/// Lazily load the given theme
pub fn get(&self, name: &str) -> Option<&Theme> {
self.themes.get(name).and_then(|lazy_theme| {
lazy_theme
.deserialized
.get_or_try_init(|| lazy_theme.deserialize())
.ok()
})
}

/// Returns the name of all themes.
pub fn themes(&self) -> impl Iterator<Item = &str> {
self.themes.keys().map(|name| name.as_ref())
}
}

impl LazyTheme {
fn deserialize(&self) -> Result<Theme> {
asset_from_contents(
&self.serialized[..],
"lazy-loaded theme",
COMPRESS_LAZY_THEMES,
)
}
}

impl TryFrom<LazyThemeSet> for ThemeSet {
type Error = Error;

/// Since the user might want to add custom themes to bat, we need a way to
/// convert from a `LazyThemeSet` to a regular [`ThemeSet`] so that more
/// themes can be added. This function does that pretty straight-forward
/// conversion.
fn try_from(lazy_theme_set: LazyThemeSet) -> Result<Self> {
let mut theme_set = ThemeSet::default();

for (name, lazy_theme) in lazy_theme_set.themes {
theme_set.themes.insert(name, lazy_theme.deserialize()?);
}

Ok(theme_set)
}
}

#[cfg(feature = "build-assets")]
impl TryFrom<ThemeSet> for LazyThemeSet {
type Error = Error;

/// To collect themes, a [`ThemeSet`] is needed. Once all desired themes
/// have been added, we need a way to convert that into [`LazyThemeSet`] so
/// that themes can be lazy-loaded later. This function does that
/// conversion.
fn try_from(theme_set: ThemeSet) -> Result<Self> {
let mut lazy_theme_set = LazyThemeSet::default();

for (name, theme) in theme_set.themes {
// All we have to do is to serialize the theme
let lazy_theme = LazyTheme {
serialized: crate::assets::build_assets::asset_to_contents(
&theme,
&format!("theme {}", name),
COMPRESS_LAZY_THEMES,
)?,
deserialized: OnceCell::new(),
};

// Ok done, now we can add it
lazy_theme_set.themes.insert(name, lazy_theme);
}

Ok(lazy_theme_set)
}
}

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