Remove BuiltinMatcher enum

Explanation added as comments in code
Using plain `Lazy<Option<GlobMatcher>>` is just better
This commit is contained in:
cyqsimon 2023-11-05 00:08:05 +08:00
parent c016b462c0
commit de6d418d42
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GPG Key ID: 1D8CE2F297390D65
2 changed files with 58 additions and 35 deletions

View File

@ -41,7 +41,7 @@ impl MappingTarget {
#[derive(Clone, Debug, DeserializeFromStr)]
/// A single matcher.
///
/// Corresponds to `syntax_mapping::BuiltinMatcher`.
/// Codegen converts this into a `Lazy<GlobMatcher>`.
struct Matcher(Vec<MatcherSegment>);
/// Parse a matcher.
///
@ -110,13 +110,12 @@ impl Matcher {
let MatcherSegment::Text(ref s) = self.0[0] else {
unreachable!()
};
format!(r###"BuiltinMatcher::Fixed(r#"{s}"#)"###)
format!(r###"Lazy::new(|| Some(build_matcher_fixed(r#"{s}"#)))"###)
}
// parser logic ensures that this case can only happen when there are dynamic segments
_ => {
let segments_codegen = self.0.iter().map(MatcherSegment::codegen).join(", ");
let closure = format!("|| build_glob_string(&[{segments_codegen}])");
format!("BuiltinMatcher::Dynamic(Lazy::new({closure}))")
let segs = self.0.iter().map(MatcherSegment::codegen).join(", ");
format!(r###"Lazy::new(|| build_matcher_dynamic(&[{segs}]))"###)
}
}
}
@ -174,7 +173,7 @@ impl MappingList {
let len = array_items.len();
format!(
"static BUILTIN_MAPPINGS: [(BuiltinMatcher, MappingTarget); {len}] = [\n{items}\n];",
"static BUILTIN_MAPPINGS: [(Lazy<Option<GlobMatcher>>, MappingTarget); {len}] = [\n{items}\n];",
items = array_items.join(",\n")
)
}

View File

@ -15,38 +15,60 @@ include!(concat!(
"/codegen_static_syntax_mappings.rs"
));
/// A glob matcher generated from analysing the matcher string at compile time.
// The defined matcher strings are analysed at compile time and converted into
// lazily-compiled `GlobMatcher`s. This is so that the string searches are moved
// from run time to compile time, thus improving startup performance.
//
// To any future maintainer (including possibly myself) wondering why there is
// not a `BuiltinMatcher` enum that looks like this:
//
// ```
// enum BuiltinMatcher {
// Fixed(&'static str),
// Dynamic(Lazy<Option<String>>),
// }
// ```
//
// Because there was. I tried it and threw it out.
//
// Naively looking at the problem from a distance, this may seem like a good
// design (strongly typed etc. etc.). It would also save on compiled size by
// extracting out common behaviour into functions. But while actually
// implementing the lazy matcher compilation logic, I realised that it's most
// convenient for `BUILTIN_MAPPINGS` to have the following type:
//
// `[(Lazy<Option<GlobMatcher>>, MappingTarget); N]`
//
// The benefit for this is that operations like listing all builtin mappings
// would be effectively memoised. The caller would not have to compile another
// `GlobMatcher` for rules that they have previously visited.
//
// Unfortunately, this means we are going to have to store a distinct closure
// for each rule anyway, which makes a `BuiltinMatcher` enum a pointless layer
// of indirection.
//
// In the current implementation, the closure within each generated rule simply
// calls either `build_matcher_fixed` or `build_matcher_dynamic`, depending on
// whether the defined matcher contains dynamic segments or not.
/// Compile a fixed glob string into a glob matcher.
///
/// This is so that the string searches are moved from run time to compile time,
/// thus improving startup performance.
#[derive(Debug)]
enum BuiltinMatcher {
/// A plaintext matcher.
Fixed(&'static str),
/// A matcher that needs dynamic environment variable replacement.
/// A failure to compile is a fatal error.
///
/// Evaluates to `None` when any environment variable replacement fails.
Dynamic(Lazy<Option<String>>),
}
impl BuiltinMatcher {
/// Finalise into a glob matcher.
///
/// Returns `None` if any environment variable replacement fails (only
/// possible for dynamic matchers).
fn to_glob_matcher(&self) -> Option<GlobMatcher> {
let glob_str = match self {
Self::Fixed(s) => *s,
Self::Dynamic(s) => s.as_ref()?.as_str(),
};
Some(make_glob_matcher(glob_str).expect("A builtin glob matcher failed to compile"))
}
/// Used internally by `Lazy<GlobMatcher>`'s lazy evaluation closure.
fn build_matcher_fixed(from: &str) -> GlobMatcher {
make_glob_matcher(from).expect("A builtin fixed glob matcher failed to compile")
}
/// Join a list of matcher segments to create a glob string, replacing all
/// environment variables. Returns `None` if any replacement fails.
/// environment variables, then compile to a glob matcher.
///
/// Used internally by `BuiltinMatcher::Dynamic`'s lazy evaluation closure.
fn build_glob_string(segs: &[MatcherSegment]) -> Option<String> {
/// Returns `None` if any replacement fails, or if the joined glob string fails
/// to compile.
///
/// Used internally by `Lazy<GlobMatcher>`'s lazy evaluation closure.
fn build_matcher_dynamic(segs: &[MatcherSegment]) -> Option<GlobMatcher> {
// join segments
let mut buf = String::new();
for seg in segs {
match seg {
@ -57,12 +79,14 @@ fn build_glob_string(segs: &[MatcherSegment]) -> Option<String> {
}
}
}
Some(buf)
// compile glob matcher
let matcher = make_glob_matcher(&buf).ok()?;
Some(matcher)
}
/// A segment of a dynamic builtin matcher.
///
/// Used internally by `BuiltinMatcher::Dynamic`'s lazy evaluation closure.
/// Used internally by `Lazy<GlobMatcher>`'s lazy evaluation closure.
#[derive(Clone, Debug)]
enum MatcherSegment {
Text(&'static str),