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Remove BuiltinMatcher
enum
Explanation added as comments in code Using plain `Lazy<Option<GlobMatcher>>` is just better
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@ -41,7 +41,7 @@ impl MappingTarget {
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#[derive(Clone, Debug, DeserializeFromStr)]
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/// A single matcher.
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///
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/// Corresponds to `syntax_mapping::BuiltinMatcher`.
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/// Codegen converts this into a `Lazy<GlobMatcher>`.
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struct Matcher(Vec<MatcherSegment>);
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/// Parse a matcher.
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///
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@ -110,13 +110,12 @@ impl Matcher {
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let MatcherSegment::Text(ref s) = self.0[0] else {
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unreachable!()
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};
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format!(r###"BuiltinMatcher::Fixed(r#"{s}"#)"###)
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format!(r###"Lazy::new(|| Some(build_matcher_fixed(r#"{s}"#)))"###)
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}
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// parser logic ensures that this case can only happen when there are dynamic segments
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_ => {
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let segments_codegen = self.0.iter().map(MatcherSegment::codegen).join(", ");
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let closure = format!("|| build_glob_string(&[{segments_codegen}])");
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format!("BuiltinMatcher::Dynamic(Lazy::new({closure}))")
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let segs = self.0.iter().map(MatcherSegment::codegen).join(", ");
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format!(r###"Lazy::new(|| build_matcher_dynamic(&[{segs}]))"###)
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}
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}
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}
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@ -174,7 +173,7 @@ impl MappingList {
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let len = array_items.len();
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format!(
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"static BUILTIN_MAPPINGS: [(BuiltinMatcher, MappingTarget); {len}] = [\n{items}\n];",
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"static BUILTIN_MAPPINGS: [(Lazy<Option<GlobMatcher>>, MappingTarget); {len}] = [\n{items}\n];",
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items = array_items.join(",\n")
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)
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}
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@ -15,38 +15,60 @@ include!(concat!(
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"/codegen_static_syntax_mappings.rs"
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));
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/// A glob matcher generated from analysing the matcher string at compile time.
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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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/// This is so that the string searches are moved from run time to compile time,
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/// thus improving startup performance.
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#[derive(Debug)]
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enum BuiltinMatcher {
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/// A plaintext matcher.
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Fixed(&'static str),
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/// A matcher that needs dynamic environment variable replacement.
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/// A failure to compile is a fatal error.
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///
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/// Evaluates to `None` when any environment variable replacement fails.
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Dynamic(Lazy<Option<String>>),
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}
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impl BuiltinMatcher {
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/// Finalise into a glob matcher.
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///
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/// Returns `None` if any environment variable replacement fails (only
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/// possible for dynamic matchers).
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fn to_glob_matcher(&self) -> Option<GlobMatcher> {
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let glob_str = match self {
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Self::Fixed(s) => *s,
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Self::Dynamic(s) => s.as_ref()?.as_str(),
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};
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Some(make_glob_matcher(glob_str).expect("A builtin glob matcher failed to compile"))
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}
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/// Used internally by `Lazy<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. Returns `None` if any replacement fails.
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/// environment variables, then compile to a glob matcher.
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///
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/// Used internally by `BuiltinMatcher::Dynamic`'s lazy evaluation closure.
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fn build_glob_string(segs: &[MatcherSegment]) -> Option<String> {
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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<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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@ -57,12 +79,14 @@ fn build_glob_string(segs: &[MatcherSegment]) -> Option<String> {
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}
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}
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}
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Some(buf)
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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 `BuiltinMatcher::Dynamic`'s lazy evaluation closure.
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/// Used internally by `Lazy<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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