Fixes lockfile checksum for non-root repo

crate_universe/src/lockfile.rs

@@ -8,6 +8,8 @@ use std::process::Command;
 
 use anyhow::{bail, Context as AnyhowContext, Result};
 use hex::ToHex;
+use once_cell::sync::OnceCell;
+use regex::Regex;
 use serde::{Deserialize, Serialize};
 use sha2::{Digest as Sha2Digest, Sha256};
 
@@ -103,6 +105,33 @@ impl Digest {
         hash
     }
 
+    /// Normalize canonical Bazel labels in a JSON string for stable digest computation.
+    ///
+    /// The canonical name of a repository changes depending on whether it is used as the
+    /// root workspace/module or as a dependency:
+    ///
+    /// - bzlmod root:     `@@//package:target`
+    /// - bzlmod non-root: `@@module_name+//package:target`
+    /// - WORKSPACE root:  `@@//package:target` (or `//package:target`)
+    /// - WORKSPACE dep:   `@@repo_name//package:target`
+    ///
+    /// To ensure the lockfile digest is stable across these contexts (so that a lockfile
+    /// generated when a module is root remains valid when the module is used as a
+    /// non-root dependency), we normalize all canonical labels by stripping the
+    /// repository name component, treating `@@repo_name//` the same as `@@//`.
+    fn normalize_labels_for_digest(json: &str) -> std::borrow::Cow<'_, str> {
+        static RE: OnceCell<Regex> = OnceCell::new();
+        let re = RE.get_or_init(|| {
+            // Match canonical labels (@@...) with a non-empty repository name followed by //.
+            // The repository name is matched by [^/"]+ (one or more chars that are not / or ").
+            // This handles both bzlmod (@@module_name+//) and WORKSPACE (@@repo_name//) forms.
+            // This does NOT match @@// (root form, empty repo name) since [^/"]+ requires at
+            // least one character.
+            Regex::new(r#"@@[^/"]+//"#).expect("valid regex")
+        });
+        re.replace_all(json, "@@//")
+    }
+
     fn compute(
         context: &Context,
         config: &Config,
@@ -132,8 +161,10 @@ impl Digest {
         hasher.update(b"\0");
 
         // This content is generated by various attributes in Bazel rules and written to a file behind the scenes.
+        // Labels are normalized to strip bzlmod canonical repository names so the digest is stable
+        // regardless of whether the module is used as a root module or a non-root dependency.
         hasher.update(Digest::compute_single_hash(
-            &serde_json::to_string(config).unwrap(),
+            &Self::normalize_labels_for_digest(&serde_json::to_string(config).unwrap()),
             "workspace config",
         ));
         hasher.update(b"\0");
@@ -429,4 +460,103 @@ mod test {
             "Digests should be identical regardless of CRLF vs LF line endings in cargo_config"
         );
     }
+
+    #[test]
+    fn digest_stable_for_root_vs_non_root_module() {
+        // Verifies that the digest is stable when labels in the config use different
+        // canonical forms depending on whether the module is root (@@//) or a non-root
+        // dependency (@@module_name+//). See: https://github.com/bazelbuild/rules_rust/issues/3521
+        let context = Context::default();
+        let splicing_metadata = SplicingMetadata::default();
+
+        let make_config = |patch_label: &str| -> Config {
+            Config {
+                annotations: BTreeMap::from([(
+                    CrateNameAndVersionReq::new("some_crate".to_owned(), "1.0.0".parse().unwrap()),
+                    CrateAnnotations {
+                        patches: Some(BTreeSet::from([patch_label.to_owned()])),
+                        ..CrateAnnotations::default()
+                    },
+                )]),
+                ..Config::default()
+            }
+        };
+
+        // Same patch label in root vs non-root bzlmod context
+        let config_root = make_config("@@//patches/my_crate.patch");
+        let config_non_root = make_config("@@module1+//patches/my_crate.patch");
+
+        let digest_root = Digest::compute(
+            &context,
+            &config_root,
+            &splicing_metadata,
+            "0.1.0",
+            "cargo 1.57.0 (b2e52d7ca 2021-10-21)",
+            "rustc 1.57.0 (f1edd0429 2021-11-29)",
+        );
+
+        let digest_non_root = Digest::compute(
+            &context,
+            &config_non_root,
+            &splicing_metadata,
+            "0.1.0",
+            "cargo 1.57.0 (b2e52d7ca 2021-10-21)",
+            "rustc 1.57.0 (f1edd0429 2021-11-29)",
+        );
+
+        assert_eq!(
+            digest_root, digest_non_root,
+            "Digests should be identical for root (@@//...) and non-root (@@module_name+//...) module contexts"
+        );
+    }
+
+    #[test]
+    fn digest_stable_for_workspace_root_vs_dep() {
+        // Verifies that the digest is stable in legacy WORKSPACE mode, where labels also
+        // change canonical form when the workspace transitions from root to an external dep:
+        // - Root workspace:    @@//package:target
+        // - External workspace dep: @@repo_name//package:target  (no "+" suffix unlike bzlmod)
+        let context = Context::default();
+        let splicing_metadata = SplicingMetadata::default();
+
+        let make_config = |patch_label: &str| -> Config {
+            Config {
+                annotations: BTreeMap::from([(
+                    CrateNameAndVersionReq::new("some_crate".to_owned(), "1.0.0".parse().unwrap()),
+                    CrateAnnotations {
+                        patches: Some(BTreeSet::from([patch_label.to_owned()])),
+                        ..CrateAnnotations::default()
+                    },
+                )]),
+                ..Config::default()
+            }
+        };
+
+        // Same patch label in WORKSPACE root vs external dep context (no "+" in repo name)
+        let config_root = make_config("@@//patches/my_crate.patch");
+        let config_dep = make_config("@@my_workspace//patches/my_crate.patch");
+
+        let digest_root = Digest::compute(
+            &context,
+            &config_root,
+            &splicing_metadata,
+            "0.1.0",
+            "cargo 1.57.0 (b2e52d7ca 2021-10-21)",
+            "rustc 1.57.0 (f1edd0429 2021-11-29)",
+        );
+
+        let digest_dep = Digest::compute(
+            &context,
+            &config_dep,
+            &splicing_metadata,
+            "0.1.0",
+            "cargo 1.57.0 (b2e52d7ca 2021-10-21)",
+            "rustc 1.57.0 (f1edd0429 2021-11-29)",
+        );
+
+        assert_eq!(
+            digest_root, digest_dep,
+            "Digests should be identical for WORKSPACE root (@@//...) and dep (@@repo_name//...) contexts"
+        );
+    }
 }