mirror of https://github.com/sharkdp/bat.git
92 lines
3.2 KiB
Rust
92 lines
3.2 KiB
Rust
use std::env;
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use globset::GlobMatcher;
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use once_cell::sync::Lazy;
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use crate::syntax_mapping::{make_glob_matcher, MappingTarget};
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// Static syntax mappings generated from /src/syntax_mapping/builtins/ by the
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// build script (/build/syntax_mapping.rs).
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include!(concat!(
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env!("OUT_DIR"),
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"/codegen_static_syntax_mappings.rs"
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));
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// The defined matcher strings are analysed at compile time and converted into
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// lazily-compiled `GlobMatcher`s. This is so that the string searches are moved
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// from run time to compile time, thus improving startup performance.
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//
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// To any future maintainer (including possibly myself) wondering why there is
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// not a `BuiltinMatcher` enum that looks like this:
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//
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// ```
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// enum BuiltinMatcher {
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// Fixed(&'static str),
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// Dynamic(Lazy<Option<String>>),
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// }
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// ```
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//
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// Because there was. I tried it and threw it out.
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//
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// Naively looking at the problem from a distance, this may seem like a good
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// design (strongly typed etc. etc.). It would also save on compiled size by
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// extracting out common behaviour into functions. But while actually
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// implementing the lazy matcher compilation logic, I realised that it's most
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// convenient for `BUILTIN_MAPPINGS` to have the following type:
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//
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// `[(Lazy<Option<GlobMatcher>>, MappingTarget); N]`
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//
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// The benefit for this is that operations like listing all builtin mappings
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// would be effectively memoised. The caller would not have to compile another
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// `GlobMatcher` for rules that they have previously visited.
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//
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// Unfortunately, this means we are going to have to store a distinct closure
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// for each rule anyway, which makes a `BuiltinMatcher` enum a pointless layer
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// of indirection.
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//
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// In the current implementation, the closure within each generated rule simply
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// calls either `build_matcher_fixed` or `build_matcher_dynamic`, depending on
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// whether the defined matcher contains dynamic segments or not.
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/// Compile a fixed glob string into a glob matcher.
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///
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/// A failure to compile is a fatal error.
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///
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/// Used internally by `Lazy<Option<GlobMatcher>>`'s lazy evaluation closure.
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fn build_matcher_fixed(from: &str) -> GlobMatcher {
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make_glob_matcher(from).expect("A builtin fixed glob matcher failed to compile")
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}
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/// Join a list of matcher segments to create a glob string, replacing all
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/// environment variables, then compile to a glob matcher.
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///
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/// Returns `None` if any replacement fails, or if the joined glob string fails
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/// to compile.
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///
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/// Used internally by `Lazy<Option<GlobMatcher>>`'s lazy evaluation closure.
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fn build_matcher_dynamic(segs: &[MatcherSegment]) -> Option<GlobMatcher> {
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// join segments
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let mut buf = String::new();
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for seg in segs {
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match seg {
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MatcherSegment::Text(s) => buf.push_str(s),
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MatcherSegment::Env(var) => {
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let replaced = env::var(var).ok()?;
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buf.push_str(&replaced);
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}
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}
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}
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// compile glob matcher
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let matcher = make_glob_matcher(&buf).ok()?;
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Some(matcher)
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}
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/// A segment of a dynamic builtin matcher.
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///
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/// Used internally by `Lazy<Option<GlobMatcher>>`'s lazy evaluation closure.
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#[derive(Clone, Debug)]
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enum MatcherSegment {
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Text(&'static str),
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Env(&'static str),
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}
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