Force WDK rebuild only for manifest with WDK metadata

[smichaku]

Hi,

We use windows-drivers-rs in our project for building a kernel mode driver. In our project's workspace we have quite a few crates:

1. The "real" driver crate with a [package.metadata.wdk] section
2. Crates which are dependencies of the driver crate.
3. Crates which are user mode libraries for interacting with the driver.

We noticed that modifying the manifest (Cargo.toml) for any crate in the workspace triggers a rebuild of wdk-sys. This is most unfortunate and increases build times.

Does it make sense to limit rebuilds to changes in WDK manifests i.e. manifest with a WDK metadata? If not, would it make sense to somehow tag a manifest as non-WDK related so it won't trigger rebuilds?

I have been using the following patch for a while now. It seems to do the job of removing unnecessary rebuilds. I would appreciate the opinion of more devs on this:

diff --git a/crates/wdk-build/src/lib.rs b/crates/wdk-build/src/lib.rs
index 967dc06..6bcd62e 100644
--- a/crates/wdk-build/src/lib.rs
+++ b/crates/wdk-build/src/lib.rs
@@ -11,7 +11,7 @@
 //! models (WDM, KMDF, UMDF).
 
 #![cfg_attr(nightly_toolchain, feature(assert_matches))]
-use std::{fmt, str::FromStr};
+use std::{collections::HashSet, fmt, str::FromStr};
 
 pub use bindgen::BuilderExt;
 use metadata::TryFromCargoMetadataError;
@@ -315,10 +315,20 @@ pub fn from_env_auto() -> Result<Self, ConfigError> {
             .exec()?;
         let wdk_metadata = metadata::Wdk::try_from(&cargo_metadata)?;
 
-        // Force rebuilds if any of the manifest files change (ex. if wdk metadata
-        // section is modified)
+        // Force rebuilds if any of the manifest files which has WDK metadata change.
+        let wdk_package_paths = cargo_metadata
+            .packages
+            .iter()
+            .filter_map(|package| {
+                package
+                    .metadata
+                    .get("wdk")
+                    .map(|_| package.manifest_path.clone())
+            })
+            .collect::<HashSet<_>>();
         for manifest_path in metadata::iter_manifest_paths(cargo_metadata)
             .into_iter()
+            .filter(|path| wdk_package_paths.contains(path))
             .chain(std::iter::once(
                 top_level_manifest
                     .try_into()

[wmmc88]

Does it make sense to limit rebuilds to changes in WDK manifests i.e. manifest with a WDK metadata? If not, would it make sense to somehow tag a manifest as non-WDK related so it won't trigger rebuilds?

Unfortunately, I think it really does still need to be all manifests. One example of a situation is when a library previously wasn't dependent on the WDK, but then the dependency was added in the manifest. Let's also assume that the WDK configuration conflicts with another crate in the workspace. Without scanning all manifests, you could run into the situation where the build works, until something triggers a rebuild of the wdk crates (ex. cargo clean or a manifest with existing wdk section changing). Now this situation may be rare, but we need to be conservative here to avoid possibly stale builds and flaky non-determinism in builds.