From d3e3f4e519e6bd556c529f260d0ad6c90944f071 Mon Sep 17 00:00:00 2001
From: Aria Desires <aria.desires@gmail.com>
Date: Fri, 20 Jun 2025 15:17:02 -0400
Subject: [PATCH] Add better diagnostic for lock --check

---
 crates/uv/src/commands/project/lock.rs | 19 +++++++++++++++++--
 crates/uv/src/commands/project/mod.rs  |  2 +-
 crates/uv/src/commands/project/sync.rs | 10 +++++-----
 crates/uv/tests/it/lock.rs             |  9 +++++++--
 4 files changed, 30 insertions(+), 10 deletions(-)

diff --git a/crates/uv/src/commands/project/lock.rs b/crates/uv/src/commands/project/lock.rs
index 97ee01767..429ce3d98 100644
--- a/crates/uv/src/commands/project/lock.rs
+++ b/crates/uv/src/commands/project/lock.rs
@@ -232,6 +232,18 @@ pub(crate) async fn lock(
 
             Ok(ExitStatus::Success)
         }
+        Err(ProjectError::LockMismatch(previous, lock)) => {
+            // we're --locked and there was a mismatch, show all changes and exit as Failure
+            for event in LockEvent::detect_changes(previous.as_deref(), &lock, dry_run) {
+                writeln!(printer.stderr(), "{event}")?;
+            }
+            writeln!(
+                printer.stderr(),
+                "{}",
+                "The lockfile is outdated; run `uv lock` to update it".bold()
+            )?;
+            Ok(ExitStatus::Failure)
+        }
         Err(ProjectError::Operation(err)) => {
             diagnostics::OperationDiagnostic::native_tls(network_settings.native_tls)
                 .report(err)
@@ -340,8 +352,11 @@ impl<'env> LockOperation<'env> {
                 .await?;
 
                 // If the lockfile changed, return an error.
-                if matches!(result, LockResult::Changed(_, _)) {
-                    return Err(ProjectError::LockMismatch(Box::new(result.into_lock())));
+                if let LockResult::Changed(prev, cur) = result {
+                    return Err(ProjectError::LockMismatch(
+                        prev.map(Box::new),
+                        Box::new(cur),
+                    ));
                 }
 
                 Ok(result)
diff --git a/crates/uv/src/commands/project/mod.rs b/crates/uv/src/commands/project/mod.rs
index a3249b11a..02823e036 100644
--- a/crates/uv/src/commands/project/mod.rs
+++ b/crates/uv/src/commands/project/mod.rs
@@ -75,7 +75,7 @@ pub(crate) enum ProjectError {
     #[error(
         "The lockfile at `uv.lock` needs to be updated, but `--locked` was provided. To update the lockfile, run `uv lock`."
     )]
-    LockMismatch(Box<Lock>),
+    LockMismatch(Option<Box<Lock>>, Box<Lock>),
 
     #[error(
         "Unable to find lockfile at `uv.lock`. To create a lockfile, run `uv lock` or `uv sync`."
diff --git a/crates/uv/src/commands/project/sync.rs b/crates/uv/src/commands/project/sync.rs
index f1a73b8c8..12bf3caae 100644
--- a/crates/uv/src/commands/project/sync.rs
+++ b/crates/uv/src/commands/project/sync.rs
@@ -422,10 +422,10 @@ pub(crate) async fn sync(
                 .report(err)
                 .map_or(Ok(ExitStatus::Failure), |err| Err(err.into()));
         }
-        Err(ProjectError::LockMismatch(lock)) if dry_run.enabled() => {
+        Err(ProjectError::LockMismatch(prev, cur)) if dry_run.enabled() => {
             // The lockfile is mismatched, but we're in dry-run mode. We should proceed with the
             // sync operation, but exit with a non-zero status.
-            Outcome::LockMismatch(lock)
+            Outcome::LockMismatch(prev, cur)
         }
         Err(err) => return Err(err.into()),
     };
@@ -469,7 +469,7 @@ pub(crate) async fn sync(
 
     match outcome {
         Outcome::Success(..) => Ok(ExitStatus::Success),
-        Outcome::LockMismatch(lock) => Err(ProjectError::LockMismatch(lock).into()),
+        Outcome::LockMismatch(prev, cur) => Err(ProjectError::LockMismatch(prev, cur).into()),
     }
 }
 
@@ -480,7 +480,7 @@ enum Outcome {
     /// The `lock` operation was successful.
     Success(Lock),
     /// The `lock` operation successfully resolved, but failed due to a mismatch (e.g., with `--locked`).
-    LockMismatch(Box<Lock>),
+    LockMismatch(Option<Box<Lock>>, Box<Lock>),
 }
 
 impl Outcome {
@@ -488,7 +488,7 @@ impl Outcome {
     fn lock(&self) -> &Lock {
         match self {
             Self::Success(lock) => lock,
-            Self::LockMismatch(lock) => lock,
+            Self::LockMismatch(_prev, cur) => cur,
         }
     }
 }
diff --git a/crates/uv/tests/it/lock.rs b/crates/uv/tests/it/lock.rs
index 1144674a8..03afb3a0b 100644
--- a/crates/uv/tests/it/lock.rs
+++ b/crates/uv/tests/it/lock.rs
@@ -11826,12 +11826,17 @@ fn check_outdated_lock() -> Result<()> {
     uv_snapshot!(context.filters(), context.lock()
         .arg("--check"), @r"
     success: false
-    exit_code: 2
+    exit_code: 1
     ----- stdout -----
 
     ----- stderr -----
     Resolved 2 packages in [TIME]
-    error: The lockfile at `uv.lock` needs to be updated, but `--locked` was provided. To update the lockfile, run `uv lock`.
+    Added iniconfig v2.0.0
+    Removed myproject v0.1.0
+    Added project v0.1.0
+    Removed sortedcollections v2.1.0
+    Removed sortedcontainers v2.4.0
+    The lockfile is outdated; run `uv lock` to update it
     ");
     Ok(())
 }