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.

1 files changed, 5 insertions, 6 deletions

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")
         })