Isolate variables at compile time

Cargo.lock

@@ -145,6 +145,7 @@ dependencies = [
  "grep-cli",
  "home",
  "indexmap 2.1.0",
+ "itertools",
  "nix",
  "nu-ansi-term",
  "once_cell",

Cargo.toml

@@ -101,6 +101,7 @@ nix = { version = "0.26.4", default-features = false, features = ["term"] }
 [build-dependencies]
 anyhow = "1.0.75"
 indexmap = { version = "2.1.0", features = ["serde"] }
+itertools = "0.11.0"
 serde = { version = "1.0", features = ["derive"] }
 serde_with = "3.4.0"
 toml = { version = "0.8.6", features = ["preserve_order"] }

build/syntax_mapping.rs

@@ -1,7 +1,8 @@
 use std::{convert::Infallible, env, fs, path::Path, str::FromStr};
 
-use anyhow::anyhow;
+use anyhow::{anyhow, bail};
 use indexmap::IndexMap;
+use itertools::Itertools;
 use serde::Deserialize;
 use serde_with::DeserializeFromStr;
 use walkdir::WalkDir;
@@ -17,7 +18,6 @@ pub enum MappingTarget {
 }
 impl FromStr for MappingTarget {
     type Err = Infallible;
-
     fn from_str(s: &str) -> Result<Self, Self::Err> {
         match s {
             "MappingTarget::MapToUnknown" => Ok(Self::MapToUnknown),
@@ -36,10 +36,136 @@ impl MappingTarget {
     }
 }
 
+#[derive(Clone, Debug, DeserializeFromStr)]
+/// A single matcher.
+///
+/// Corresponds to `syntax_mapping::BuiltinMatcher`.
+struct Matcher(Vec<MatcherSegment>);
+/// Parse a matcher.
+///
+/// Note that this implementation is rather strict: when it sees a '$', '{', or
+/// '}' where it does not make sense, it will immediately hard-error.
+///
+/// The reason for this strictness is I currently cannot think of a valid reason
+/// why you would ever need '$', '{', or '}' as plaintext in a glob pattern.
+/// Therefore any such occurrences are likely human errors.
+///
+/// If we later discover some edge cases, it's okay to make it more permissive.
+impl FromStr for Matcher {
+    type Err = anyhow::Error;
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        use MatcherSegment as Seg;
+
+        if s.is_empty() {
+            bail!("Empty string is not a valid glob matcher");
+        }
+
+        let mut segments = Vec::new();
+        let mut buf = String::new();
+        let mut is_in_var = false;
+
+        let mut char_it = s.chars();
+        loop {
+            match char_it.next() {
+                Some('$') => {
+                    if is_in_var {
+                        bail!(r#"Saw a '$' when already in a variable: "{s}""#);
+                    }
+                    match char_it.next() {
+                        Some('{') => {
+                            // push text unless empty
+                            if !buf.is_empty() {
+                                segments.push(Seg::Text(buf.clone()));
+                                buf.clear();
+                            }
+                            // open var
+                            is_in_var = true;
+                        }
+                        Some(_) | None => {
+                            bail!(r#"Expected a '{{' after '$': "{s}""#);
+                        }
+                    }
+                }
+                Some('{') => {
+                    bail!(r#"Saw a hanging '{{': "{s}""#);
+                }
+                Some('}') => {
+                    if !is_in_var {
+                        bail!(r#"Saw a '}}' when not in a variable: "{s}""#);
+                    }
+                    if buf.is_empty() {
+                        // `${}`
+                        bail!(r#"Variable name cannot be empty: "{s}""#);
+                    }
+                    // push variable
+                    segments.push(Seg::Env(buf.clone()));
+                    buf.clear();
+                    // close var
+                    is_in_var = false;
+                }
+                Some(' ') if is_in_var => {
+                    bail!(r#"' ' Cannot be part of a variable's name: "{s}""#);
+                }
+                Some(c) => {
+                    // either plaintext or variable name
+                    buf.push(c);
+                }
+                None => {
+                    if is_in_var {
+                        bail!(r#"Variable unclosed: "{s}""#);
+                    }
+                    segments.push(Seg::Text(buf.clone()));
+                    break;
+                }
+            }
+        }
+
+        Ok(Self(segments))
+    }
+}
+impl Matcher {
+    fn codegen(&self) -> String {
+        match self.0.len() {
+            0 => unreachable!("0-length matcher should never be created"),
+            // if-let guard would be ideal here
+            // see: https://github.com/rust-lang/rust/issues/51114
+            1 if matches!(self.0[0], MatcherSegment::Text(_)) => {
+                let MatcherSegment::Text(ref s) = self.0[0] else {
+                    unreachable!()
+                };
+                format!(r###"BuiltinMatcher::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!("|| join_segments(&[{segments_codegen}])");
+                format!("BuiltinMatcher::Dynamic(Lazy::new({closure}))")
+            }
+        }
+    }
+}
+
+/// A segment in a matcher.
+///
+/// Corresponds to `syntax_mapping::MatcherSegment`.
+#[derive(Debug, Clone)]
+enum MatcherSegment {
+    Text(String),
+    Env(String),
+}
+impl MatcherSegment {
+    fn codegen(&self) -> String {
+        match self {
+            Self::Text(s) => format!(r###"MatcherSegment::Text(r#"{s}"#)"###),
+            Self::Env(s) => format!(r###"MatcherSegment::Env(r#"{s}"#)"###),
+        }
+    }
+}
+
 /// A struct that models a single .toml file in /src/syntax_mapping/builtins/.
 #[derive(Clone, Debug, Deserialize)]
 struct MappingDefModel {
-    mappings: IndexMap<MappingTarget, Vec<String>>,
+    mappings: IndexMap<MappingTarget, Vec<Matcher>>,
 }
 impl MappingDefModel {
     fn into_mapping_list(self) -> MappingList {
@@ -58,18 +184,20 @@ impl MappingDefModel {
 }
 
 #[derive(Clone, Debug)]
-struct MappingList(Vec<(String, MappingTarget)>);
+struct MappingList(Vec<(Matcher, MappingTarget)>);
 impl MappingList {
     fn codegen(&self) -> String {
         let array_items: Vec<_> = self
             .0
             .iter()
-            .map(|(matcher, target)| format!(r###"(r#"{matcher}"#, {t})"###, t = target.codegen()))
+            .map(|(matcher, target)| {
+                format!("({m}, {t})", m = matcher.codegen(), t = target.codegen())
+            })
             .collect();
         let len = array_items.len();
 
         format!(
-            "static STATIC_RULES: [(&str, MappingTarget); {len}] = [\n{items}\n];",
+            "static STATIC_RULES: [(BuiltinMatcher, MappingTarget); {len}] = [\n{items}\n];",
             items = array_items.join(",\n")
         )
     }

src/syntax_mapping.rs

@@ -1,9 +1,10 @@
-use std::path::Path;
+use std::{env, path::Path};
 
 use crate::error::Result;
 use ignored_suffixes::IgnoredSuffixes;
 
 use globset::{Candidate, GlobBuilder, GlobMatcher};
+use once_cell::sync::Lazy;
 
 pub mod ignored_suffixes;
 
@@ -14,6 +15,60 @@ include!(concat!(
     "/codegen_static_syntax_mappings.rs"
 ));
 
+/// A glob matcher generated from analysing the matcher string at compile time.
+///
+/// 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.
+    ///
+    /// 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"))
+    }
+}
+
+/// Join a list of matcher segments, replacing all environment variables.
+/// Returns `None` if any replacement fails.
+///
+/// Used internally by `BuiltinMatcher::Dynamic`'s lazy evaluation closure.
+fn join_segments(segs: &[MatcherSegment]) -> Option<String> {
+    let mut buf = String::new();
+    for seg in segs {
+        match seg {
+            MatcherSegment::Text(s) => buf.push_str(s),
+            MatcherSegment::Env(var) => {
+                let replaced = env::var(var).ok()?;
+                buf.push_str(&replaced);
+            }
+        }
+    }
+    Some(buf)
+}
+
+/// A segment of a dynamic builtin matcher.
+///
+/// Used internally by `BuiltinMatcher::Dynamic`'s lazy evaluation closure.
+#[derive(Clone, Debug)]
+enum MatcherSegment {
+    Text(&'static str),
+    Env(&'static str),
+}
+
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 #[non_exhaustive]
 pub enum MappingTarget<'a> {
@@ -34,6 +89,15 @@ pub enum MappingTarget<'a> {
     MapExtensionToUnknown,
 }
 
+fn make_glob_matcher(from: &str) -> Result<GlobMatcher> {
+    let matcher = GlobBuilder::new(from)
+        .case_insensitive(true)
+        .literal_separator(true)
+        .build()?
+        .compile_matcher();
+    Ok(matcher)
+}
+
 #[derive(Debug, Clone, Default)]
 pub struct SyntaxMapping<'a> {
     mappings: Vec<(GlobMatcher, MappingTarget<'a>)>,
@@ -217,11 +281,8 @@ impl<'a> SyntaxMapping<'a> {
     }
 
     pub fn insert(&mut self, from: &str, to: MappingTarget<'a>) -> Result<()> {
-        let glob = GlobBuilder::new(from)
-            .case_insensitive(true)
-            .literal_separator(true)
-            .build()?;
-        self.mappings.push((glob.compile_matcher(), to));
+        let matcher = make_glob_matcher(from)?;
+        self.mappings.push((matcher, to));
         Ok(())
     }