Add config for supplying sysroot path

crates/project-model/src/cargo_workspace.rs

@@ -94,9 +94,8 @@ pub struct CargoConfig {
     pub features: CargoFeatures,
     /// rustc target
     pub target: Option<String>,
-    /// Don't load sysroot crates (`std`, `core` & friends). Might be useful
-    /// when debugging isolated issues.
-    pub no_sysroot: bool,
+    /// Sysroot loading behavior
+    pub sysroot: Option<RustcSource>,
     /// rustc private crate source
     pub rustc_source: Option<RustcSource>,
     /// crates to disable `#[cfg(test)]` on

crates/project-model/src/sysroot.rs

@@ -67,11 +67,14 @@ impl Sysroot {
     pub fn crates<'a>(&'a self) -> impl Iterator<Item = SysrootCrate> + ExactSizeIterator + 'a {
         self.crates.iter().map(|(id, _data)| id)
     }
+}
 
+impl Sysroot {
     pub fn discover(dir: &AbsPath, extra_env: &FxHashMap<String, String>) -> Result<Sysroot> {
         tracing::debug!("Discovering sysroot for {}", dir.display());
         let sysroot_dir = discover_sysroot_dir(dir, extra_env)?;
-        let sysroot_src_dir = discover_sysroot_src_dir(&sysroot_dir, dir, extra_env)?;
+        let sysroot_src_dir =
+            discover_sysroot_src_dir_or_add_component(&sysroot_dir, dir, extra_env)?;
         let res = Sysroot::load(sysroot_dir, sysroot_src_dir)?;
         Ok(res)
     }
@@ -87,6 +90,14 @@ impl Sysroot {
             .and_then(|sysroot_dir| get_rustc_src(&sysroot_dir))
     }
 
+    pub fn with_sysroot_dir(sysroot_dir: AbsPathBuf) -> Result<Sysroot> {
+        let sysroot_src_dir = discover_sysroot_src_dir(&sysroot_dir).ok_or_else(|| {
+            format_err!("can't load standard library from sysroot {}", sysroot_dir.display())
+        })?;
+        let res = Sysroot::load(sysroot_dir, sysroot_src_dir)?;
+        Ok(res)
+    }
+
     pub fn load(sysroot_dir: AbsPathBuf, sysroot_src_dir: AbsPathBuf) -> Result<Sysroot> {
         let mut sysroot =
             Sysroot { root: sysroot_dir, src_root: sysroot_src_dir, crates: Arena::default() };
@@ -162,23 +173,28 @@ fn discover_sysroot_dir(
     Ok(AbsPathBuf::assert(PathBuf::from(stdout)))
 }
 
-fn discover_sysroot_src_dir(
+fn discover_sysroot_src_dir(sysroot_path: &AbsPathBuf) -> Option<AbsPathBuf> {
+    if let Ok(path) = env::var("RUST_SRC_PATH") {
+        if let Ok(path) = AbsPathBuf::try_from(path.as_str()) {
+            let core = path.join("core");
+            if fs::metadata(&core).is_ok() {
+                tracing::debug!("Discovered sysroot by RUST_SRC_PATH: {}", path.display());
+                return Some(path);
+            }
+            tracing::debug!("RUST_SRC_PATH is set, but is invalid (no core: {:?}), ignoring", core);
+        } else {
+            tracing::debug!("RUST_SRC_PATH is set, but is invalid, ignoring");
+        }
+    }
+
+    get_rust_src(sysroot_path)
+}
+fn discover_sysroot_src_dir_or_add_component(
     sysroot_path: &AbsPathBuf,
     current_dir: &AbsPath,
     extra_env: &FxHashMap<String, String>,
 ) -> Result<AbsPathBuf> {
-    if let Ok(path) = env::var("RUST_SRC_PATH") {
-        let path = AbsPathBuf::try_from(path.as_str())
-            .map_err(|path| format_err!("RUST_SRC_PATH must be absolute: {}", path.display()))?;
-        let core = path.join("core");
-        if fs::metadata(&core).is_ok() {
-            tracing::debug!("Discovered sysroot by RUST_SRC_PATH: {}", path.display());
-            return Ok(path);
-        }
-        tracing::debug!("RUST_SRC_PATH is set, but is invalid (no core: {:?}), ignoring", core);
-    }
-
-    get_rust_src(sysroot_path)
+    discover_sysroot_src_dir(sysroot_path)
         .or_else(|| {
             let mut rustup = Command::new(toolchain::rustup());
             rustup.envs(extra_env);

crates/project-model/src/workspace.rs

@@ -188,17 +188,26 @@ impl ProjectWorkspace {
                 })?;
                 let cargo = CargoWorkspace::new(meta);
 
-                let sysroot = if config.no_sysroot {
-                    None
-                } else {
-                    Some(Sysroot::discover(cargo_toml.parent(), &config.extra_env).with_context(
-                        || {
+                let sysroot = match &config.sysroot {
+                    Some(RustcSource::Path(path)) => {
+                        Some(Sysroot::with_sysroot_dir(path.clone()).with_context(|| {
                             format!(
+                                "Failed to find sysroot for Cargo.toml file {}.",
+                                cargo_toml.display()
+                            )
+                        })?)
+                    }
+                    Some(RustcSource::Discover) => Some(
+                        Sysroot::discover(cargo_toml.parent(), &config.extra_env).with_context(
+                            || {
+                                format!(
                             "Failed to find sysroot for Cargo.toml file {}. Is rust-src installed?",
                             cargo_toml.display()
                         )
-                        },
-                    )?)
+                            },
+                        )?,
+                    ),
+                    None => None,
                 };
 
                 let rustc_dir = match &config.rustc_source {