fix: Copy lockfiles into target directory before invoking `cargo metadata`
diff --git a/crates/project-model/src/cargo_workspace.rs b/crates/project-model/src/cargo_workspace.rs
index 392650e..5850741 100644
--- a/crates/project-model/src/cargo_workspace.rs
+++ b/crates/project-model/src/cargo_workspace.rs
@@ -7,7 +7,7 @@
 use base_db::Env;
 use cargo_metadata::{CargoOpt, MetadataCommand};
 use la_arena::{Arena, Idx};
-use paths::{AbsPath, AbsPathBuf, Utf8PathBuf};
+use paths::{AbsPath, AbsPathBuf, Utf8Path, Utf8PathBuf};
 use rustc_hash::{FxHashMap, FxHashSet};
 use serde_derive::Deserialize;
 use serde_json::from_value;
@@ -18,6 +18,14 @@
 use crate::{CfgOverrides, InvocationStrategy};
 use crate::{ManifestPath, Sysroot};
 
+const MINIMUM_TOOLCHAIN_VERSION_SUPPORTING_LOCKFILE_PATH: semver::Version = semver::Version {
+    major: 1,
+    minor: 82,
+    patch: 0,
+    pre: semver::Prerelease::EMPTY,
+    build: semver::BuildMetadata::EMPTY,
+};
+
 /// [`CargoWorkspace`] represents the logical structure of, well, a Cargo
 /// workspace. It pretty closely mirrors `cargo metadata` output.
 ///
@@ -291,6 +299,13 @@
     pub extra_args: Vec<String>,
     /// Extra env vars to set when invoking the cargo command
     pub extra_env: FxHashMap<String, Option<String>>,
+    /// The target dir for this workspace load.
+    pub target_dir: Utf8PathBuf,
+    /// What kind of metadata are we fetching: workspace, rustc, or sysroot.
+    pub kind: &'static str,
+    /// The toolchain version, if known.
+    /// Used to conditionally enable unstable cargo features.
+    pub toolchain_version: Option<semver::Version>,
 }
 
 // Deserialize helper for the cargo metadata
@@ -383,18 +398,54 @@
                 config.targets.iter().flat_map(|it| ["--filter-platform".to_owned(), it.clone()]),
             );
         }
-        // The manifest is a rust file, so this means its a script manifest
-        if cargo_toml.is_rust_manifest() {
-            // Deliberately don't set up RUSTC_BOOTSTRAP or a nightly override here, the user should
-            // opt into it themselves.
-            other_options.push("-Zscript".to_owned());
-        }
-        if locked {
-            other_options.push("--locked".to_owned());
-        }
         if no_deps {
             other_options.push("--no-deps".to_owned());
         }
+
+        let mut using_lockfile_copy = false;
+        // The manifest is a rust file, so this means its a script manifest
+        if cargo_toml.is_rust_manifest() {
+            other_options.push("-Zscript".to_owned());
+        } else if config
+            .toolchain_version
+            .as_ref()
+            .is_some_and(|v| *v >= MINIMUM_TOOLCHAIN_VERSION_SUPPORTING_LOCKFILE_PATH)
+        {
+            let lockfile = <_ as AsRef<Utf8Path>>::as_ref(cargo_toml).with_extension("lock");
+            let target_lockfile = config
+                .target_dir
+                .join("rust-analyzer")
+                .join("metadata")
+                .join(config.kind)
+                .join("Cargo.lock");
+            match std::fs::copy(&lockfile, &target_lockfile) {
+                Ok(_) => {
+                    using_lockfile_copy = true;
+                    other_options.push("--lockfile-path".to_owned());
+                    other_options.push(target_lockfile.to_string());
+                }
+                Err(e) if e.kind() == std::io::ErrorKind::NotFound => {
+                    // There exists no lockfile yet
+                    using_lockfile_copy = true;
+                    other_options.push("--lockfile-path".to_owned());
+                    other_options.push(target_lockfile.to_string());
+                }
+                Err(e) => {
+                    tracing::warn!(
+                        "Failed to copy lock file from `{lockfile}` to `{target_lockfile}`: {e}",
+                    );
+                }
+            }
+        }
+        if using_lockfile_copy {
+            other_options.push("-Zunstable-options".to_owned());
+            meta.env("RUSTC_BOOTSTRAP", "1");
+        }
+        // No need to lock it if we copied the lockfile, we won't modify the original after all/
+        // This way cargo cannot error out on us if the lockfile requires updating.
+        if !using_lockfile_copy && locked {
+            other_options.push("--locked".to_owned());
+        }
         meta.other_options(other_options);
 
         // FIXME: Fetching metadata is a slow process, as it might require
@@ -427,8 +478,8 @@
                         current_dir,
                         config,
                         sysroot,
-                        locked,
                         true,
+                        locked,
                         progress,
                     ) {
                         return Ok((metadata, Some(error)));
diff --git a/crates/project-model/src/manifest_path.rs b/crates/project-model/src/manifest_path.rs
index 4f43be2..fba8cc9 100644
--- a/crates/project-model/src/manifest_path.rs
+++ b/crates/project-model/src/manifest_path.rs
@@ -1,7 +1,7 @@
 //! See [`ManifestPath`].
 use std::{borrow::Borrow, fmt, ops};
 
-use paths::{AbsPath, AbsPathBuf};
+use paths::{AbsPath, AbsPathBuf, Utf8Path};
 
 /// More or less [`AbsPathBuf`] with non-None parent.
 ///
@@ -78,6 +78,12 @@
     }
 }
 
+impl AsRef<Utf8Path> for ManifestPath {
+    fn as_ref(&self) -> &Utf8Path {
+        self.file.as_ref()
+    }
+}
+
 impl Borrow<AbsPath> for ManifestPath {
     fn borrow(&self) -> &AbsPath {
         self.file.borrow()
diff --git a/crates/project-model/src/sysroot.rs b/crates/project-model/src/sysroot.rs
index 29818ac..4b34fc0 100644
--- a/crates/project-model/src/sysroot.rs
+++ b/crates/project-model/src/sysroot.rs
@@ -4,6 +4,7 @@
 //! but we can't process `.rlib` and need source code instead. The source code
 //! is typically installed with `rustup component add rust-src` command.
 
+use core::fmt;
 use std::{env, fs, ops::Not, path::Path, process::Command};
 
 use anyhow::{Result, format_err};
@@ -34,6 +35,19 @@
     Empty,
 }
 
+impl fmt::Display for RustLibSrcWorkspace {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            RustLibSrcWorkspace::Workspace(ws) => write!(f, "workspace {}", ws.workspace_root()),
+            RustLibSrcWorkspace::Json(json) => write!(f, "json {}", json.manifest_or_root()),
+            RustLibSrcWorkspace::Stitched(stitched) => {
+                write!(f, "stitched with {} crates", stitched.crates.len())
+            }
+            RustLibSrcWorkspace::Empty => write!(f, "empty"),
+        }
+    }
+}
+
 impl Sysroot {
     pub const fn empty() -> Sysroot {
         Sysroot {
@@ -195,6 +209,7 @@
     pub fn load_workspace(
         &self,
         sysroot_source_config: &RustSourceWorkspaceConfig,
+        current_dir: &AbsPath,
         progress: &dyn Fn(String),
     ) -> Option<RustLibSrcWorkspace> {
         assert!(matches!(self.workspace, RustLibSrcWorkspace::Empty), "workspace already loaded");
@@ -205,10 +220,16 @@
         if let RustSourceWorkspaceConfig::CargoMetadata(cargo_config) = sysroot_source_config {
             let library_manifest = ManifestPath::try_from(src_root.join("Cargo.toml")).unwrap();
             if fs::metadata(&library_manifest).is_ok() {
-                if let Some(loaded) =
-                    self.load_library_via_cargo(library_manifest, src_root, cargo_config, progress)
-                {
-                    return Some(loaded);
+                match self.load_library_via_cargo(
+                    &library_manifest,
+                    current_dir,
+                    cargo_config,
+                    progress,
+                ) {
+                    Ok(loaded) => return Some(loaded),
+                    Err(e) => {
+                        tracing::error!("`cargo metadata` failed on `{library_manifest}` : {e}")
+                    }
                 }
             }
             tracing::debug!("Stitching sysroot library: {src_root}");
@@ -294,11 +315,11 @@
 
     fn load_library_via_cargo(
         &self,
-        library_manifest: ManifestPath,
-        rust_lib_src_dir: &AbsPathBuf,
+        library_manifest: &ManifestPath,
+        current_dir: &AbsPath,
         cargo_config: &CargoMetadataConfig,
         progress: &dyn Fn(String),
-    ) -> Option<RustLibSrcWorkspace> {
+    ) -> Result<RustLibSrcWorkspace> {
         tracing::debug!("Loading library metadata: {library_manifest}");
         let mut cargo_config = cargo_config.clone();
         // the sysroot uses `public-dependency`, so we make cargo think it's a nightly
@@ -307,22 +328,16 @@
             Some("nightly".to_owned()),
         );
 
-        let (mut res, _) = match CargoWorkspace::fetch_metadata(
-            &library_manifest,
-            rust_lib_src_dir,
+        let (mut res, _) = CargoWorkspace::fetch_metadata(
+            library_manifest,
+            current_dir,
             &cargo_config,
             self,
             false,
             // Make sure we never attempt to write to the sysroot
             true,
             progress,
-        ) {
-            Ok(it) => it,
-            Err(e) => {
-                tracing::error!("`cargo metadata` failed on `{library_manifest}` : {e}");
-                return None;
-            }
-        };
+        )?;
 
         // Patch out `rustc-std-workspace-*` crates to point to the real crates.
         // This is done prior to `CrateGraph` construction to prevent de-duplication logic from failing.
@@ -373,8 +388,9 @@
             res.packages.remove(idx);
         });
 
-        let cargo_workspace = CargoWorkspace::new(res, library_manifest, Default::default(), true);
-        Some(RustLibSrcWorkspace::Workspace(cargo_workspace))
+        let cargo_workspace =
+            CargoWorkspace::new(res, library_manifest.clone(), Default::default(), true);
+        Ok(RustLibSrcWorkspace::Workspace(cargo_workspace))
     }
 }
 
diff --git a/crates/project-model/src/tests.rs b/crates/project-model/src/tests.rs
index 426aa58..4f11af2 100644
--- a/crates/project-model/src/tests.rs
+++ b/crates/project-model/src/tests.rs
@@ -1,3 +1,5 @@
+use std::env::temp_dir;
+
 use base_db::{CrateGraphBuilder, ProcMacroPaths};
 use cargo_metadata::Metadata;
 use cfg::{CfgAtom, CfgDiff};
@@ -235,12 +237,18 @@
         AbsPath::assert(Utf8Path::new(env!("CARGO_MANIFEST_DIR"))),
         &Default::default(),
     );
+    let cwd = AbsPathBuf::assert_utf8(temp_dir().join("smoke_test_real_sysroot_cargo"));
+    std::fs::create_dir_all(&cwd).unwrap();
     let loaded_sysroot =
-        sysroot.load_workspace(&RustSourceWorkspaceConfig::default_cargo(), &|_| ());
+        sysroot.load_workspace(&RustSourceWorkspaceConfig::default_cargo(), &cwd, &|_| ());
     if let Some(loaded_sysroot) = loaded_sysroot {
         sysroot.set_workspace(loaded_sysroot);
     }
-    assert!(matches!(sysroot.workspace(), RustLibSrcWorkspace::Workspace(_)));
+    assert!(
+        matches!(sysroot.workspace(), RustLibSrcWorkspace::Workspace(_)),
+        "got {}",
+        sysroot.workspace()
+    );
     let project_workspace = ProjectWorkspace {
         kind: ProjectWorkspaceKind::Cargo {
             cargo: cargo_workspace,
diff --git a/crates/project-model/src/workspace.rs b/crates/project-model/src/workspace.rs
index 9366c0a..a6743a3 100644
--- a/crates/project-model/src/workspace.rs
+++ b/crates/project-model/src/workspace.rs
@@ -12,7 +12,7 @@
 };
 use cfg::{CfgAtom, CfgDiff, CfgOptions};
 use intern::{Symbol, sym};
-use paths::{AbsPath, AbsPathBuf};
+use paths::{AbsPath, AbsPathBuf, Utf8PathBuf};
 use rustc_hash::{FxHashMap, FxHashSet};
 use semver::Version;
 use span::{Edition, FileId};
@@ -209,6 +209,7 @@
         progress: &(dyn Fn(String) + Sync),
     ) -> Result<ProjectWorkspace, anyhow::Error> {
         progress("Discovering sysroot".to_owned());
+        let workspace_dir = cargo_toml.parent();
         let CargoConfig {
             features,
             rustc_source,
@@ -224,15 +225,9 @@
             ..
         } = config;
         let mut sysroot = match (sysroot, sysroot_src) {
-            (Some(RustLibSource::Discover), None) => {
-                Sysroot::discover(cargo_toml.parent(), extra_env)
-            }
+            (Some(RustLibSource::Discover), None) => Sysroot::discover(workspace_dir, extra_env),
             (Some(RustLibSource::Discover), Some(sysroot_src)) => {
-                Sysroot::discover_with_src_override(
-                    cargo_toml.parent(),
-                    extra_env,
-                    sysroot_src.clone(),
-                )
+                Sysroot::discover_with_src_override(workspace_dir, extra_env, sysroot_src.clone())
             }
             (Some(RustLibSource::Path(path)), None) => {
                 Sysroot::discover_rust_lib_src_dir(path.clone())
@@ -248,24 +243,23 @@
         let toolchain_config = QueryConfig::Cargo(&sysroot, cargo_toml);
         let targets =
             target_tuple::get(toolchain_config, target.as_deref(), extra_env).unwrap_or_default();
+        let toolchain = version::get(toolchain_config, extra_env)
+            .inspect_err(|e| {
+                tracing::error!(%e,
+                    "failed fetching toolchain version for {cargo_toml:?} workspace"
+                )
+            })
+            .ok()
+            .flatten();
+
+        let target_dir =
+            config.target_dir.clone().unwrap_or_else(|| workspace_dir.join("target").into());
 
         // We spawn a bunch of processes to query various information about the workspace's
         // toolchain and sysroot
         // We can speed up loading a bit by spawning all of these processes in parallel (especially
         // on systems were process spawning is delayed)
         let join = thread::scope(|s| {
-            let workspace_dir = cargo_toml.parent();
-            let toolchain = s.spawn(|| {
-                version::get(toolchain_config, extra_env)
-                    .inspect_err(|e| {
-                        tracing::error!(%e,
-                            "failed fetching toolchain version for {cargo_toml:?} workspace"
-                        )
-                    })
-                    .ok()
-                    .flatten()
-            });
-
             let rustc_cfg = s.spawn(|| {
                 rustc_cfg::get(toolchain_config, targets.first().map(Deref::deref), extra_env)
             });
@@ -300,10 +294,13 @@
                             targets: targets.clone(),
                             extra_args: extra_args.clone(),
                             extra_env: extra_env.clone(),
+                            target_dir: target_dir.clone(),
+                            toolchain_version: toolchain.clone(),
+                            kind: "rustc-dev"
                         },
                         &sysroot,
                         *no_deps,
-                        false,
+                        true,
                         progress,
                     ) {
                         Ok((meta, _error)) => {
@@ -343,6 +340,9 @@
                         targets: targets.clone(),
                         extra_args: extra_args.clone(),
                         extra_env: extra_env.clone(),
+                        target_dir: target_dir.clone(),
+                        toolchain_version: toolchain.clone(),
+                        kind: "workspace",
                     },
                     &sysroot,
                     *no_deps,
@@ -353,15 +353,18 @@
             let loaded_sysroot = s.spawn(|| {
                 sysroot.load_workspace(
                     &RustSourceWorkspaceConfig::CargoMetadata(sysroot_metadata_config(
-                        extra_env, &targets,
+                        config,
+                        &targets,
+                        toolchain.clone(),
+                        target_dir.clone(),
                     )),
+                    workspace_dir,
                     progress,
                 )
             });
             let cargo_config_extra_env =
                 s.spawn(|| cargo_config_env(cargo_toml, extra_env, &sysroot));
             thread::Result::Ok((
-                toolchain.join()?,
                 rustc_cfg.join()?,
                 data_layout.join()?,
                 rustc_dir.join()?,
@@ -371,18 +374,11 @@
             ))
         });
 
-        let (
-            toolchain,
-            rustc_cfg,
-            data_layout,
-            rustc,
-            loaded_sysroot,
-            cargo_metadata,
-            cargo_config_extra_env,
-        ) = match join {
-            Ok(it) => it,
-            Err(e) => std::panic::resume_unwind(e),
-        };
+        let (rustc_cfg, data_layout, rustc, loaded_sysroot, cargo_metadata, cargo_config_extra_env) =
+            match join {
+                Ok(it) => it,
+                Err(e) => std::panic::resume_unwind(e),
+            };
 
         let (meta, error) = cargo_metadata.with_context(|| {
             format!(
@@ -391,6 +387,7 @@
         })?;
         let cargo = CargoWorkspace::new(meta, cargo_toml.clone(), cargo_config_extra_env, false);
         if let Some(loaded_sysroot) = loaded_sysroot {
+            tracing::info!(src_root = ?sysroot.rust_lib_src_root(), root = %loaded_sysroot, "Loaded sysroot");
             sysroot.set_workspace(loaded_sysroot);
         }
 
@@ -426,14 +423,13 @@
         let query_config = QueryConfig::Rustc(&sysroot, project_json.path().as_ref());
         let targets = target_tuple::get(query_config, config.target.as_deref(), &config.extra_env)
             .unwrap_or_default();
+        let toolchain = version::get(query_config, &config.extra_env).ok().flatten();
 
         // We spawn a bunch of processes to query various information about the workspace's
         // toolchain and sysroot
         // We can speed up loading a bit by spawning all of these processes in parallel (especially
         // on systems were process spawning is delayed)
         let join = thread::scope(|s| {
-            let toolchain =
-                s.spawn(|| version::get(query_config, &config.extra_env).ok().flatten());
             let rustc_cfg = s.spawn(|| {
                 rustc_cfg::get(query_config, targets.first().map(Deref::deref), &config.extra_env)
             });
@@ -445,31 +441,35 @@
                 )
             });
             let loaded_sysroot = s.spawn(|| {
+                let project_root = project_json.project_root();
                 if let Some(sysroot_project) = sysroot_project {
                     sysroot.load_workspace(
                         &RustSourceWorkspaceConfig::Json(*sysroot_project),
+                        project_root,
                         progress,
                     )
                 } else {
+                    let target_dir = config
+                        .target_dir
+                        .clone()
+                        .unwrap_or_else(|| project_root.join("target").into());
                     sysroot.load_workspace(
                         &RustSourceWorkspaceConfig::CargoMetadata(sysroot_metadata_config(
-                            &config.extra_env,
+                            config,
                             &targets,
+                            toolchain.clone(),
+                            target_dir,
                         )),
+                        project_root,
                         progress,
                     )
                 }
             });
 
-            thread::Result::Ok((
-                toolchain.join()?,
-                rustc_cfg.join()?,
-                data_layout.join()?,
-                loaded_sysroot.join()?,
-            ))
+            thread::Result::Ok((rustc_cfg.join()?, data_layout.join()?, loaded_sysroot.join()?))
         });
 
-        let (toolchain, rustc_cfg, target_layout, loaded_sysroot) = match join {
+        let (rustc_cfg, target_layout, loaded_sysroot) = match join {
             Ok(it) => it,
             Err(e) => std::panic::resume_unwind(e),
         };
@@ -507,11 +507,15 @@
             .unwrap_or_default();
         let rustc_cfg = rustc_cfg::get(query_config, None, &config.extra_env);
         let data_layout = target_data_layout::get(query_config, None, &config.extra_env);
+        let target_dir = config.target_dir.clone().unwrap_or_else(|| dir.join("target").into());
         let loaded_sysroot = sysroot.load_workspace(
             &RustSourceWorkspaceConfig::CargoMetadata(sysroot_metadata_config(
-                &config.extra_env,
+                config,
                 &targets,
+                toolchain.clone(),
+                target_dir.clone(),
             )),
+            dir,
             &|_| (),
         );
         if let Some(loaded_sysroot) = loaded_sysroot {
@@ -526,6 +530,9 @@
                 targets,
                 extra_args: config.extra_args.clone(),
                 extra_env: config.extra_env.clone(),
+                target_dir,
+                toolchain_version: toolchain.clone(),
+                kind: "detached-file",
             },
             &sysroot,
             config.no_deps,
@@ -1818,13 +1825,18 @@
 }
 
 fn sysroot_metadata_config(
-    extra_env: &FxHashMap<String, Option<String>>,
+    config: &CargoConfig,
     targets: &[String],
+    toolchain_version: Option<Version>,
+    target_dir: Utf8PathBuf,
 ) -> CargoMetadataConfig {
     CargoMetadataConfig {
         features: Default::default(),
         targets: targets.to_vec(),
         extra_args: Default::default(),
-        extra_env: extra_env.clone(),
+        extra_env: config.extra_env.clone(),
+        target_dir,
+        toolchain_version,
+        kind: "sysroot",
     }
 }
diff --git a/crates/rust-analyzer/src/cli/rustc_tests.rs b/crates/rust-analyzer/src/cli/rustc_tests.rs
index 0e8b918..740fcd8 100644
--- a/crates/rust-analyzer/src/cli/rustc_tests.rs
+++ b/crates/rust-analyzer/src/cli/rustc_tests.rs
@@ -9,7 +9,6 @@
 use ide::{AnalysisHost, DiagnosticCode, DiagnosticsConfig};
 use ide_db::base_db;
 use itertools::Either;
-use paths::Utf8PathBuf;
 use profile::StopWatch;
 use project_model::toolchain_info::{QueryConfig, target_data_layout};
 use project_model::{
@@ -64,9 +63,9 @@
 
 impl Tester {
     fn new() -> Result<Self> {
-        let mut path = std::env::temp_dir();
-        path.push("ra-rustc-test.rs");
-        let tmp_file = AbsPathBuf::try_from(Utf8PathBuf::from_path_buf(path).unwrap()).unwrap();
+        let mut path = AbsPathBuf::assert_utf8(std::env::temp_dir());
+        path.push("ra-rustc-test");
+        let tmp_file = path.join("ra-rustc-test.rs");
         std::fs::write(&tmp_file, "")?;
         let cargo_config = CargoConfig {
             sysroot: Some(RustLibSource::Discover),
@@ -77,7 +76,7 @@
 
         let mut sysroot = Sysroot::discover(tmp_file.parent().unwrap(), &cargo_config.extra_env);
         let loaded_sysroot =
-            sysroot.load_workspace(&RustSourceWorkspaceConfig::default_cargo(), &|_| ());
+            sysroot.load_workspace(&RustSourceWorkspaceConfig::default_cargo(), &path, &|_| ());
         if let Some(loaded_sysroot) = loaded_sysroot {
             sysroot.set_workspace(loaded_sysroot);
         }