Remove unjustified dead-code expectation (#322)

crates/no_std_fs_operations/src/lib.rs

@@ -22,15 +22,3 @@ mod usage;
 pub use config::NoStdFsConfig;
 #[cfg(feature = "dylint-driver")]
 pub use driver::*;
-
-#[cfg(not(feature = "dylint-driver"))]
-mod stub {
-    //! Placeholder compiled when the `dylint-driver` feature is off, so the
-    //! crate still builds without the `rustc_private` toolchain internals.
-
-    #[expect(
-        dead_code,
-        reason = "Exposed only when built without the `dylint-driver` feature"
-    )]
-    pub fn no_std_fs_operations_disabled_stub() {}
-}

crates/no_std_fs_operations/tests/no_default_features_build.rs

@@ -0,0 +1,90 @@
+//! Compile-time regression guard for the `dylint-driver`-disabled build.
+//!
+//! The crate is a Dylint lint library: the lint logic lives behind the
+//! optional `dylint-driver` feature, while the default feature set is empty so
+//! the crate can be built by tools that only need a plain library. Issue #322
+//! removed the private stub that previously existed solely to keep that
+//! empty build warning-free. This test re-checks the configuration the stub
+//! existed for: `cargo check --no-default-features --lib` must still succeed
+//! with warnings denied, now without relying on that stub.
+//!
+//! The check is deliberately restricted to the library target: the crate's
+//! integration test binaries are dylint harnesses that require `cargo-dylint`
+//! and `dylint-link`, which must not be assumed here. The nested `cargo`
+//! invocation therefore inherits the outer `RUSTFLAGS` (so `-D warnings` from
+//! the Makefile gate applies) but uses an isolated target directory so it never
+//! contends with the outer build.
+
+use std::path::PathBuf;
+use std::process::Command;
+
+use anyhow::Context as _;
+use serde_json::Value;
+use tempfile::TempDir;
+
+/// Top-level name of the package under test.
+const CRATE: &str = "no_std_fs_operations";
+
+/// Runs `cargo check --no-default-features --lib` for this crate and asserts
+/// that the build succeeds with warnings denied (via inherited `RUSTFLAGS`).
+///
+/// The workspace manifest is located by walking up from this test crate's
+/// manifest directory, mirroring `integration_exclusion.rs`, so the nested
+/// invocation resolves the same workspace this test builds under.
+#[test]
+fn crate_builds_without_dylint_driver_feature() -> anyhow::Result<()> {
+    let workspace_root = workspace_root()?;
+    let target_dir = TempDir::new().context("failed to create isolated target directory")?;
+
+    let output = Command::new("cargo")
+        .arg("check")
+        .arg("--package")
+        .arg(CRATE)
+        .arg("--no-default-features")
+        .arg("--lib")
+        .arg("--message-format=json")
+        .current_dir(&workspace_root)
+        .env("CARGO_TARGET_DIR", target_dir.path())
+        .output()
+        .context("failed to execute nested cargo check")?;
+
+    let stdout = String::from_utf8_lossy(&output.stdout);
+    let stderr = String::from_utf8_lossy(&output.stderr);
+    assert!(
+        output.status.success(),
+        "`cargo check --no-default-features --lib` for `{CRATE}` failed \
+         (it must compile without the `dylint-driver` feature now that the \
+         no-driver stub is gone):\n{stderr}"
+    );
+
+    let diagnostics = stdout
+        .lines()
+        .filter_map(|line| serde_json::from_str::<Value>(line).ok())
+        .filter(|message| message["reason"] == "compiler-message")
+        .collect::<Vec<_>>();
+    assert!(
+        diagnostics.is_empty(),
+        "`cargo check --no-default-features --lib` for `{CRATE}` emitted \
+         compiler diagnostics under `-D warnings`: {diagnostics:#?}"
+    );
+
+    Ok(())
+}
+
+/// Returns the workspace root containing this crate's manifest.
+fn workspace_root() -> anyhow::Result<PathBuf> {
+    let manifest_dir = PathBuf::from(env!("CARGO_MANIFEST_DIR"));
+    let mut candidate = manifest_dir.as_path();
+    loop {
+        if candidate.join("Cargo.toml").is_file() {
+            let workspace = std::fs::read_to_string(candidate.join("Cargo.toml"))
+                .context("failed to read candidate workspace Cargo.toml")?;
+            if workspace.contains("[workspace]") {
+                return Ok(candidate.to_path_buf());
+            }
+        }
+        candidate = candidate
+            .parent()
+            .context("workspace root not found above CARGO_MANIFEST_DIR")?;
+    }
+}