rustc_session: Add a structure for keeping both explicit and default sysroots

Also avoid creating and cloning sysroot unnecessarily.

4 files changed, 36 insertions, 31 deletions

diff --git a/compiler/rustc_session/src/config.rs b/compiler/rustc_session/src/config.rs
index 87e4b0a17aa..c62e4ac30ea 100644
--- a/compiler/rustc_session/src/config.rs
+++ b/compiler/rustc_session/src/config.rs
@@ -1296,6 +1296,28 @@ bitflags::bitflags! {
     }
 }
 
+#[derive(Clone, Debug)]
+pub struct Sysroot {
+    pub explicit: Option<PathBuf>,
+    pub default: PathBuf,
+}
+
+impl Sysroot {
+    pub fn new(explicit: Option<PathBuf>) -> Sysroot {
+        Sysroot { explicit, default: filesearch::default_sysroot() }
+    }
+
+    /// Return explicit sysroot if it was passed with `--sysroot`, or default sysroot otherwise.
+    pub fn path(&self) -> &Path {
+        self.explicit.as_deref().unwrap_or(&self.default)
+    }
+
+    /// Returns both explicit sysroot if it was passed with `--sysroot` and the default sysroot.
+    pub fn all_paths(&self) -> impl Iterator<Item = &Path> {
+        self.explicit.as_deref().into_iter().chain(iter::once(&*self.default))
+    }
+}
+
 pub fn host_tuple() -> &'static str {
     // Get the host triple out of the build environment. This ensures that our
     // idea of the host triple is the same as for the set of libraries we've
@@ -1342,7 +1364,7 @@ impl Default for Options {
             describe_lints: false,
             output_types: OutputTypes(BTreeMap::new()),
             search_paths: vec![],
-            sysroot: filesearch::materialize_sysroot(None),
+            sysroot: Sysroot::new(None),
             target_triple: TargetTuple::from_tuple(host_tuple()),
             test: false,
             incremental: None,
@@ -2673,7 +2695,6 @@ pub fn build_session_options(early_dcx: &mut EarlyDiagCtxt, matches: &getopts::M
 
     let cg = cg;
 
-    let sysroot_opt = matches.opt_str("sysroot").map(|m| PathBuf::from(&m));
     let target_triple = parse_target_triple(early_dcx, matches);
     let opt_level = parse_opt_level(early_dcx, matches, &cg);
     // The `-g` and `-C debuginfo` flags specify the same setting, so we want to be able
@@ -2712,10 +2733,10 @@ pub fn build_session_options(early_dcx: &mut EarlyDiagCtxt, matches: &getopts::M
 
     let logical_env = parse_logical_env(early_dcx, matches);
 
-    let sysroot = filesearch::materialize_sysroot(sysroot_opt);
+    let sysroot = Sysroot::new(matches.opt_str("sysroot").map(PathBuf::from));
 
     let real_source_base_dir = |suffix: &str, confirm: &str| {
-        let mut candidate = sysroot.join(suffix);
+        let mut candidate = sysroot.path().join(suffix);
         if let Ok(metadata) = candidate.symlink_metadata() {
             // Replace the symlink bootstrap creates, with its destination.
             // We could try to use `fs::canonicalize` instead, but that might
@@ -2742,7 +2763,7 @@ pub fn build_session_options(early_dcx: &mut EarlyDiagCtxt, matches: &getopts::M
     let mut search_paths = vec![];
     for s in &matches.opt_strs("L") {
         search_paths.push(SearchPath::from_cli_opt(
-            &sysroot,
+            sysroot.path(),
             &target_triple,
             early_dcx,
             s,
diff --git a/compiler/rustc_session/src/filesearch.rs b/compiler/rustc_session/src/filesearch.rs
index 4f8c3926207..f64fa86948c 100644
--- a/compiler/rustc_session/src/filesearch.rs
+++ b/compiler/rustc_session/src/filesearch.rs
@@ -5,7 +5,6 @@ use std::{env, fs};
 
 use rustc_fs_util::try_canonicalize;
 use rustc_target::spec::Target;
-use smallvec::{SmallVec, smallvec};
 
 use crate::search_paths::{PathKind, SearchPath};
 
@@ -182,24 +181,9 @@ fn current_dll_path() -> Result<PathBuf, String> {
     Err("current_dll_path is not supported on WASI".to_string())
 }
 
-pub fn sysroot_with_fallback(sysroot: &Path) -> SmallVec<[PathBuf; 2]> {
-    let mut candidates = smallvec![sysroot.to_owned()];
-    let default_sysroot = get_or_default_sysroot();
-    if default_sysroot != sysroot {
-        candidates.push(default_sysroot);
-    }
-    candidates
-}
-
-/// Returns the provided sysroot or calls [`get_or_default_sysroot`] if it's none.
-/// Panics if [`get_or_default_sysroot`]  returns an error.
-pub fn materialize_sysroot(maybe_sysroot: Option<PathBuf>) -> PathBuf {
-    maybe_sysroot.unwrap_or_else(|| get_or_default_sysroot())
-}
-
 /// This function checks if sysroot is found using env::args().next(), and if it
 /// is not found, finds sysroot from current rustc_driver dll.
-pub fn get_or_default_sysroot() -> PathBuf {
+pub(crate) fn default_sysroot() -> PathBuf {
     fn default_from_rustc_driver_dll() -> Result<PathBuf, String> {
         let dll = current_dll_path()?;
 
diff --git a/compiler/rustc_session/src/options.rs b/compiler/rustc_session/src/options.rs
index 7fef942525b..232531dc673 100644
--- a/compiler/rustc_session/src/options.rs
+++ b/compiler/rustc_session/src/options.rs
@@ -337,7 +337,7 @@ top_level_options!(
         output_types: OutputTypes [TRACKED],
         search_paths: Vec<SearchPath> [UNTRACKED],
         libs: Vec<NativeLib> [TRACKED],
-        sysroot: PathBuf [UNTRACKED],
+        sysroot: Sysroot [UNTRACKED],
 
         target_triple: TargetTuple [TRACKED],
 
diff --git a/compiler/rustc_session/src/session.rs b/compiler/rustc_session/src/session.rs
index ad58c3c8f7d..bad2581ae31 100644
--- a/compiler/rustc_session/src/session.rs
+++ b/compiler/rustc_session/src/session.rs
@@ -149,7 +149,6 @@ pub struct Session {
     pub opts: config::Options,
     pub target_tlib_path: Arc<SearchPath>,
     pub psess: ParseSess,
-    pub sysroot: PathBuf,
     /// Input, input file path and output file path to this compilation process.
     pub io: CompilerIO,
 
@@ -456,8 +455,10 @@ impl Session {
     /// directories are also returned, for example if `--sysroot` is used but tools are missing
     /// (#125246): we also add the bin directories to the sysroot where rustc is located.
     pub fn get_tools_search_paths(&self, self_contained: bool) -> Vec<PathBuf> {
-        let search_paths = filesearch::sysroot_with_fallback(&self.sysroot)
-            .into_iter()
+        let search_paths = self
+            .opts
+            .sysroot
+            .all_paths()
             .map(|sysroot| filesearch::make_target_bin_path(&sysroot, config::host_tuple()));
 
         if self_contained {
@@ -1028,7 +1029,6 @@ pub fn build_session(
     fluent_resources: Vec<&'static str>,
     driver_lint_caps: FxHashMap<lint::LintId, lint::Level>,
     target: Target,
-    sysroot: PathBuf,
     cfg_version: &'static str,
     ice_file: Option<PathBuf>,
     using_internal_features: &'static AtomicBool,
@@ -1063,7 +1063,7 @@ pub fn build_session(
     }
 
     let host_triple = TargetTuple::from_tuple(config::host_tuple());
-    let (host, target_warnings) = Target::search(&host_triple, &sysroot)
+    let (host, target_warnings) = Target::search(&host_triple, sopts.sysroot.path())
         .unwrap_or_else(|e| dcx.handle().fatal(format!("Error loading host specification: {e}")));
     for warning in target_warnings.warning_messages() {
         dcx.handle().warn(warning)
@@ -1096,13 +1096,14 @@ pub fn build_session(
     let host_triple = config::host_tuple();
     let target_triple = sopts.target_triple.tuple();
     // FIXME use host sysroot?
-    let host_tlib_path = Arc::new(SearchPath::from_sysroot_and_triple(&sysroot, host_triple));
+    let host_tlib_path =
+        Arc::new(SearchPath::from_sysroot_and_triple(sopts.sysroot.path(), host_triple));
     let target_tlib_path = if host_triple == target_triple {
         // Use the same `SearchPath` if host and target triple are identical to avoid unnecessary
         // rescanning of the target lib path and an unnecessary allocation.
         Arc::clone(&host_tlib_path)
     } else {
-        Arc::new(SearchPath::from_sysroot_and_triple(&sysroot, target_triple))
+        Arc::new(SearchPath::from_sysroot_and_triple(sopts.sysroot.path(), target_triple))
     };
 
     let prof = SelfProfilerRef::new(
@@ -1134,7 +1135,6 @@ pub fn build_session(
         opts: sopts,
         target_tlib_path,
         psess,
-        sysroot,
         io,
         incr_comp_session: RwLock::new(IncrCompSession::NotInitialized),
         prof,