refactor(rust): align workspace with style rules

src/monorepo/BUILD

@@ -0,0 +1,17 @@
+load("@rules_rust//rust:defs.bzl", "rust_library", "rust_test")
+
+rust_library(
+    name = "monorepo",
+    crate_name = "monorepo",
+    srcs = [
+        "monorepo.rs",
+        "workspace.rs",
+    ],
+    visibility = ["//visibility:public"],
+)
+
+rust_test(
+    name = "workspace_test",
+    srcs = ["workspace_test.rs"],
+    deps = [":monorepo"],
+)

src/monorepo/Cargo.toml

@@ -0,0 +1,9 @@
+[package]
+name = "monorepo"
+version = "0.1.0"
+edition = "2024"
+
+[lib]
+path = "monorepo.rs"
+
+[dependencies]

src/monorepo/monorepo.rs

@@ -0,0 +1 @@
+pub mod workspace;

src/monorepo/workspace.rs

@@ -0,0 +1,20 @@
+use std::path::PathBuf;
+
+pub fn resolve_workspace_path(path: PathBuf) -> PathBuf {
+    resolve_workspace_path_impl(
+        path,
+        std::env::var_os("BUILD_WORKSPACE_DIRECTORY").map(PathBuf::from),
+    )
+}
+
+fn resolve_workspace_path_impl(path: PathBuf, workspace: Option<PathBuf>) -> PathBuf {
+    if path.is_absolute() {
+        return path;
+    }
+
+    if let Some(workspace) = workspace {
+        return workspace.join(path);
+    }
+
+    path
+}

src/monorepo/workspace_test.rs

@@ -0,0 +1,52 @@
+use std::path::PathBuf;
+
+use monorepo::workspace::resolve_workspace_path;
+
+const BUILD_WORKSPACE_DIRECTORY: &str = "BUILD_WORKSPACE_DIRECTORY";
+
+
+#[derive(Debug)]
+struct Case {
+    name: &'static str,
+    workspace: Option<&'static str>,
+    path: &'static str,
+    expected: &'static str,
+}
+
+#[test]
+fn resolve_workspace_path_cases() {
+    let cases = [
+        Case {
+            name: "absolute path returns unchanged path",
+            workspace: Some("/workspace"),
+            path: "/tmp/output",
+            expected: "/tmp/output",
+        },
+        Case {
+            name: "relative path joins workspace path",
+            workspace: Some("/workspace"),
+            path: "output/graph",
+            expected: "/workspace/output/graph",
+        },
+        Case {
+            name: "relative path without workspace returns unchanged path",
+            workspace: None,
+            path: "output/graph",
+            expected: "output/graph",
+        },
+    ];
+
+    for case in cases {
+        unsafe {
+            if let Some(workspace) = case.workspace {
+                std::env::set_var(BUILD_WORKSPACE_DIRECTORY, workspace);
+            } else {
+                std::env::remove_var(BUILD_WORKSPACE_DIRECTORY);
+            }
+        }
+
+        let resolved = resolve_workspace_path(PathBuf::from(case.path));
+
+        assert_eq!(resolved, PathBuf::from(case.expected), "{}", case.name);
+    }
+}