Investigate and fix parallel grammar builds on Windows (#869)

* This should reproduce the problem

* Disable concurrent grammar building on Windows

* Update CHANGELOG

* Tidy up comments

.github/workflows/ci.yml

@@ -107,6 +107,9 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v4
 
+      - name: Prefetch grammars
+        run: cargo run --all-features -- prefetch
+
       - name: Run test suite
         run: cargo test --all-features
 

CHANGELOG.md

@@ -62,8 +62,9 @@ This name should be decided amongst the team before the release.
 
 ### Fixed
 - [#867](https://github.com/tweag/topiary/pull/867) Enable coverage check and add code samples for OpenSCAD
+- [#869](https://github.com/tweag/topiary/pull/869) Disable parallel grammar building on Windows
 
-<!-->
+<!--
 
 ### Security
 - <Vulnerabilities>

topiary-config/src/lib.rs

@@ -150,8 +150,11 @@ impl Configuration {
         let tmp_dir = tempdir()?;
         let tmp_dir_path = tmp_dir.path().to_owned();
 
-        // When "parallel" is enabled, we use rayon to fetch and compile all found grammars in parallel.
-        #[cfg(feature = "parallel")]
+        // When the `parallel` feature is enabled (which it is by default), we use Rayon to fetch
+        // and compile all found grammars concurrently.
+        // NOTE The MSVC linker does not seem to like concurrent builds, so concurrency is disabled
+        // on Windows (see https://github.com/tweag/topiary/issues/868)
+        #[cfg(all(feature = "parallel", not(windows)))]
         {
             use rayon::prelude::*;
             self.languages
@@ -160,7 +163,7 @@ impl Configuration {
                 .collect::<Result<Vec<_>, TopiaryConfigFetchingError>>()?;
         }
 
-        #[cfg(not(feature = "parallel"))]
+        #[cfg(any(not(feature = "parallel"), windows))]
         {
             self.languages
                 .iter()