Replace all uses of sysroot_candidates with get_or_default_sysroot

Before this change we had two different ways to attempt to locate the
sysroot which are inconsistently used:
* get_or_default_sysroot which tries to locate based on the 0th cli
  argument and if that doesn't work falls back to locating it using the
  librustc_driver.so location and returns a single path.,
* sysroot_candidates which takes the former and additionally does
  another attempt at locating using librustc_driver.so except without
  linux multiarch handling and then returns both paths.,

The latter was originally introduced to be able to locate the codegen
backend back when cg_llvm was dynamically linked even for a custom
driver when the --sysroot passed in does not contain a copy of cg_llvm.
Back then get_or_default_sysroot did not attempt to locate the sysroot
based on the location of librustc_driver.so yet. Because that is now
done, the only case where removing sysroot_candidates can break things
is if you have a custom driver inside what looks like a sysroot
including the lib/rustlib directory, but which is missing some parts of
the full sysroot like eg rust-lld.

5 files changed, 17 insertions, 44 deletions

diff --git a/compiler/rustc_error_messages/src/lib.rs b/compiler/rustc_error_messages/src/lib.rs
index 3c6df147b1b..a1f787b00d9 100644
--- a/compiler/rustc_error_messages/src/lib.rs
+++ b/compiler/rustc_error_messages/src/lib.rs
@@ -107,7 +107,7 @@ impl From<Vec<FluentError>> for TranslationBundleError {
 #[instrument(level = "trace")]
 pub fn fluent_bundle(
     sysroot: PathBuf,
-    sysroot_candidates: Vec<PathBuf>,
+    default_sysroot: PathBuf,
     requested_locale: Option<LanguageIdentifier>,
     additional_ftl_path: Option<&Path>,
     with_directionality_markers: bool,
@@ -141,7 +141,7 @@ pub fn fluent_bundle(
     // If the user requests the default locale then don't try to load anything.
     if let Some(requested_locale) = requested_locale {
         let mut found_resources = false;
-        for mut sysroot in Some(sysroot).into_iter().chain(sysroot_candidates.into_iter()) {
+        for mut sysroot in [sysroot, default_sysroot] {
             sysroot.push("share");
             sysroot.push("locale");
             sysroot.push(requested_locale.to_string());
diff --git a/compiler/rustc_interface/src/interface.rs b/compiler/rustc_interface/src/interface.rs
index cf494f8d686..068b8c6d044 100644
--- a/compiler/rustc_interface/src/interface.rs
+++ b/compiler/rustc_interface/src/interface.rs
@@ -18,7 +18,7 @@ use rustc_parse::parser::attr::AllowLeadingUnsafe;
 use rustc_query_impl::QueryCtxt;
 use rustc_query_system::query::print_query_stack;
 use rustc_session::config::{self, Cfg, CheckCfg, ExpectedValues, Input, OutFileName};
-use rustc_session::filesearch::sysroot_candidates;
+use rustc_session::filesearch::get_or_default_sysroot;
 use rustc_session::parse::ParseSess;
 use rustc_session::{CompilerIO, EarlyDiagCtxt, Session, lint};
 use rustc_span::source_map::{FileLoader, RealFileLoader, SourceMapInputs};
@@ -443,7 +443,7 @@ pub fn run_compiler<R: Send>(config: Config, f: impl FnOnce(&Compiler) -> R + Se
 
             let bundle = match rustc_errors::fluent_bundle(
                 config.opts.sysroot.clone(),
-                sysroot_candidates().to_vec(),
+                get_or_default_sysroot(),
                 config.opts.unstable_opts.translate_lang.clone(),
                 config.opts.unstable_opts.translate_additional_ftl.as_deref(),
                 config.opts.unstable_opts.translate_directionality_markers,
diff --git a/compiler/rustc_interface/src/util.rs b/compiler/rustc_interface/src/util.rs
index 087b11fdf9d..f769c6156ae 100644
--- a/compiler/rustc_interface/src/util.rs
+++ b/compiler/rustc_interface/src/util.rs
@@ -2,7 +2,7 @@ use std::env::consts::{DLL_PREFIX, DLL_SUFFIX};
 use std::path::{Path, PathBuf};
 use std::sync::atomic::{AtomicBool, Ordering};
 use std::sync::{Arc, OnceLock};
-use std::{env, iter, thread};
+use std::{env, thread};
 
 use rustc_ast as ast;
 use rustc_codegen_ssa::traits::CodegenBackend;
@@ -12,7 +12,6 @@ use rustc_metadata::{DylibError, load_symbol_from_dylib};
 use rustc_middle::ty::CurrentGcx;
 use rustc_parse::validate_attr;
 use rustc_session::config::{Cfg, OutFileName, OutputFilenames, OutputTypes, host_tuple};
-use rustc_session::filesearch::sysroot_candidates;
 use rustc_session::lint::{self, BuiltinLintDiag, LintBuffer};
 use rustc_session::output::{CRATE_TYPES, categorize_crate_type};
 use rustc_session::{EarlyDiagCtxt, Session, filesearch};
@@ -346,7 +345,7 @@ pub fn rustc_path<'a>() -> Option<&'a Path> {
 }
 
 fn get_rustc_path_inner(bin_path: &str) -> Option<PathBuf> {
-    sysroot_candidates().iter().find_map(|sysroot| {
+    Some(filesearch::get_or_default_sysroot()).iter().find_map(|sysroot| {
         let candidate = sysroot.join(bin_path).join(if cfg!(target_os = "windows") {
             "rustc.exe"
         } else {
@@ -374,10 +373,10 @@ fn get_codegen_sysroot(
     );
 
     let target = host_tuple();
-    let sysroot_candidates = sysroot_candidates();
+    let sysroot_candidates = filesearch::sysroot_with_fallback(&sysroot);
 
-    let sysroot = iter::once(sysroot)
-        .chain(sysroot_candidates.iter().map(<_>::as_ref))
+    let sysroot = sysroot_candidates
+        .iter()
         .map(|sysroot| {
             filesearch::make_target_lib_path(sysroot, target).with_file_name("codegen-backends")
         })
diff --git a/compiler/rustc_session/src/filesearch.rs b/compiler/rustc_session/src/filesearch.rs
index 1fd74c914b2..def2cc97f06 100644
--- a/compiler/rustc_session/src/filesearch.rs
+++ b/compiler/rustc_session/src/filesearch.rs
@@ -182,35 +182,13 @@ fn current_dll_path() -> Result<PathBuf, String> {
     Err("current_dll_path is not supported on WASI".to_string())
 }
 
-pub fn sysroot_candidates() -> SmallVec<[PathBuf; 2]> {
-    let mut sysroot_candidates: SmallVec<[PathBuf; 2]> = smallvec![get_or_default_sysroot()];
-    if let Ok(dll) = current_dll_path() {
-        // use `parent` twice to chop off the file name and then also the
-        // directory containing the dll which should be either `lib` or `bin`.
-        if let Some(path) = dll.parent().and_then(|p| p.parent()) {
-            // The original `path` pointed at the `rustc_driver` crate's dll.
-            // Now that dll should only be in one of two locations. The first is
-            // in the compiler's libdir, for example `$sysroot/lib/*.dll`. The
-            // other is the target's libdir, for example
-            // `$sysroot/lib/rustlib/$target/lib/*.dll`.
-            //
-            // We don't know which, so let's assume that if our `path` above
-            // ends in `$target` we *could* be in the target libdir, and always
-            // assume that we may be in the main libdir.
-            sysroot_candidates.push(path.to_owned());
-
-            if path.ends_with(crate::config::host_tuple()) {
-                sysroot_candidates.extend(
-                    path.parent() // chop off `$target`
-                        .and_then(|p| p.parent()) // chop off `rustlib`
-                        .and_then(|p| p.parent()) // chop off `lib`
-                        .map(|s| s.to_owned()),
-                );
-            }
-        }
+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);
     }
-
-    sysroot_candidates
+    candidates
 }
 
 /// Returns the provided sysroot or calls [`get_or_default_sysroot`] if it's none.
@@ -236,7 +214,7 @@ pub fn get_or_default_sysroot() -> PathBuf {
             dll.display()
         ))?;
 
-        // if `dir` points target's dir, move up to the sysroot
+        // if `dir` points to target's dir, move up to the sysroot
         let mut sysroot_dir = if dir.ends_with(crate::config::host_tuple()) {
             dir.parent() // chop off `$target`
                 .and_then(|p| p.parent()) // chop off `rustlib`
diff --git a/compiler/rustc_session/src/session.rs b/compiler/rustc_session/src/session.rs
index 010ae42c280..6b85e0abc86 100644
--- a/compiler/rustc_session/src/session.rs
+++ b/compiler/rustc_session/src/session.rs
@@ -458,13 +458,9 @@ 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 bin_path = filesearch::make_target_bin_path(&self.sysroot, config::host_tuple());
-        let fallback_sysroot_paths = filesearch::sysroot_candidates()
+        let search_paths = filesearch::sysroot_with_fallback(&self.sysroot)
             .into_iter()
-            // Ignore sysroot candidate if it was the same as the sysroot path we just used.
-            .filter(|sysroot| *sysroot != self.sysroot)
             .map(|sysroot| filesearch::make_target_bin_path(&sysroot, config::host_tuple()));
-        let search_paths = std::iter::once(bin_path).chain(fallback_sysroot_paths);
 
         if self_contained {
             // The self-contained tools are expected to be e.g. in `bin/self-contained` in the