Use CARGO_MANIFEST_DIR variable for bootimage runner

For doctests it's not possible to derive the manifest path from the executable path and the cargo metadata since doctests live under temp and all use the same name ('rust-out'). Fortunately, cargo sets a `CARGO_MANIFEST_DIR` environment variable for runner executables that points to the manifest path of the executable (which can be different from the root manifest path for workpace projects.)

Author: phil-opp

src/main.rs

@@ -85,8 +85,17 @@ pub(crate) fn runner(args: RunnerArgs) -> Result<i32> {
             args.executable.display(),
         )
     })?;
+
+    // Cargo sets a CARGO_MANIFEST_DIR environment variable for all runner
+    // executables. This variable contains the path to the Cargo.toml of the
+    // crate that the executable belongs to (i.e. not the project root
+    // manifest for workspace projects)
+    let manifest_dir = env::var("CARGO_MANIFEST_DIR")
+        .context("Failed to read CARGO_MANIFEST_DIR environment variable")?;
+    let kernel_manifest_path = Path::new(&manifest_dir).join("Cargo.toml");
+
     builder.create_bootimage(
-        bin_name,
+        &kernel_manifest_path,
         &executable_canonicalized,
         &output_bin_path,
         args.quiet,