fix(lib): use precise capturing on 1.82+ (#435)

* feat: add build cfg

* feat: test precise capturing

* fix: typo

* fix: indentation

* chore: add documentation about cfg flag

* fix: raise MSRV

* chore: change msrv for cargo-msrv

* fix: add rustfmt component

.github/workflows/rustlib.yml

@@ -29,6 +29,8 @@ jobs:
     strategy:
       matrix:
         rust:
+        - 1.74.0 # current MSRV
+        - 1.82.0 # precise capturing
         - stable
         - beta
         - nightly
@@ -47,6 +49,9 @@ jobs:
 
     - name: Install stable toolchain
       uses: dtolnay/rust-toolchain@stable
+      with:
+        toolchain: ${{ matrix.rust }}
+        components: rustfmt
 
     - name: Cache dependencies
       uses: Swatinem/rust-cache@v2

Cargo.toml

@@ -3,7 +3,10 @@ members = ["logos-cli", "logos-codegen", "logos-derive", "tests", "fuzz"]
 resolver = "2"
 
 [workspace.package]
-authors = ["Maciej Hirsz <[email protected]>", "Jérome Eertmans (maintainer) <[email protected]>"]
+authors = [
+    "Maciej Hirsz <[email protected]>",
+    "Jérome Eertmans (maintainer) <[email protected]>",
+]
 categories = ["parsing", "text-processing"]
 description = "Create ridiculously fast Lexers"
 edition = "2021"
@@ -12,7 +15,7 @@ keywords = ["lexer", "lexical", "tokenizer", "parser", "no_std"]
 license = "MIT OR Apache-2.0"
 readme = "README.md"
 repository = "https://github.com/maciejhirsz/logos"
-rust-version = "1.70.0"
+rust-version = "1.74.0"
 version = "0.14.2"
 
 [package]
@@ -30,7 +33,7 @@ rust-version.workspace = true
 version.workspace = true
 
 [package.metadata]
-msrv = "1.70.0"  # Needed to duplicate, because cargo-msrv does not support workspace
+msrv = "1.74.0" # Needed to duplicate, because cargo-msrv does not support workspace
 
 [package.metadata.release]
 pre-release-replacements = [

logos-codegen/Cargo.toml

@@ -11,6 +11,9 @@ syn = { version = "2.0.13", features = ["full"] }
 pretty_assertions = "1.4.0"
 rstest = "0.23.0"
 
+[build-dependencies]
+rustc_version = "0.4.1"
+
 [features]
 # Enables debug messages
 debug = []

logos-codegen/build.rs

@@ -0,0 +1,21 @@
+use rustc_version::{version_meta, Version};
+
+fn main() {
+    let version_meta = version_meta().expect("Could not get Rust version");
+
+    let rustc_version = version_meta.semver;
+    let trimmed_rustc_version = Version::new(
+        rustc_version.major,
+        rustc_version.minor,
+        rustc_version.patch,
+    );
+
+    // Add cfg flag for Rust >= 1.82
+    // Required for precise capturing in edition 2024
+    // Due to changes in lifetime and type capture behavior for impl trait
+    // see: https://github.com/maciejhirsz/logos/issues/434, https://github.com/rust-lang/rfcs/pull/3498
+    println!("cargo:rustc-check-cfg=cfg(rust_1_82)");
+    if trimmed_rustc_version >= Version::new(1, 82, 0) {
+        println!("cargo:rustc-cfg=rust_1_82");
+    }
+}

logos-codegen/src/generator/leaf.rs

@@ -28,11 +28,17 @@ impl<'a> Generator<'a> {
                 let arg = &inline.arg;
                 let body = &inline.body;
 
+                #[cfg(not(rust_1_82))]
+                let ret = quote!(impl CallbackResult<'s, #ty, #this>);
+
+                #[cfg(rust_1_82)]
+                let ret = quote!(impl CallbackResult<'s, #ty, #this> + use<'s>);
+
                 quote! {
                     #bump
 
                     #[inline]
-                    fn callback<'s>(#arg: &mut Lexer<'s>) -> impl CallbackResult<'s, #ty, #this> {
+                    fn callback<'s>(#arg: &mut Lexer<'s>) -> #ret {
                         #body
                     }