Implement --locked for build-std

src/cargo/core/compiler/standard_lib.rs

@@ -78,6 +78,7 @@ pub fn resolve_std<'gctx>(
     // TODO: Consider doing something to enforce --locked? Or to prevent the
     // lock file from being written, such as setting ephemeral.
     let mut std_ws = Workspace::new(&std_ws_manifest_path, gctx)?;
+    std_ws.set_is_std(true);
     // Don't require optional dependencies in this workspace, aka std's own
     // `[dev-dependencies]`. No need for us to generate a `Resolve` which has
     // those included because we'll never use them anyway.

src/cargo/core/workspace.rs

@@ -120,6 +120,9 @@ pub struct Workspace<'gctx> {
 
     /// Local overlay configuration. See [`crate::sources::overlay`].
     local_overlays: HashMap<SourceId, PathBuf>,
+
+    /// Whether this is the workspace used for building the standard library
+    is_std: bool,
 }
 
 // Separate structure for tracking loaded packages (to avoid loading anything
@@ -250,6 +253,7 @@ impl<'gctx> Workspace<'gctx> {
             resolve_honors_rust_version: false,
             custom_metadata: None,
             local_overlays: HashMap::new(),
+            is_std: false,
         }
     }
 
@@ -1790,6 +1794,14 @@ impl<'gctx> Workspace<'gctx> {
 
         Ok(ret.into_iter())
     }
+
+    pub fn is_std(&self) -> bool {
+        self.is_std
+    }
+
+    pub fn set_is_std(&mut self, is_std: bool) {
+        self.is_std = is_std
+    }
 }
 
 impl<'gctx> Packages<'gctx> {

src/cargo/ops/lockfile.rs

@@ -66,6 +66,13 @@ pub fn write_pkg_lockfile(ws: &Workspace<'_>, resolve: &mut Resolve) -> CargoRes
         );
     }
 
+    if ws.is_std() {
+        anyhow::bail!(
+            "Attempted to write the standard library's lockfile.\n\
+            This most likely means the lockfile has been previously modified by mistake."
+        );
+    }
+
     // While we're updating the lock file anyway go ahead and update its
     // encoding to whatever the latest default is. That way we can slowly roll
     // out lock file updates as they're otherwise already updated, and changes