Rollup merge of #142089 - bjorn3:sysroot_handling_cleanup3, r=petrochenkov

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.

Follow up to https://github.com/rust-lang/rust/pull/138404

2 files changed, 10 insertions, 16 deletions

diff --git a/compiler/rustc_interface/src/interface.rs b/compiler/rustc_interface/src/interface.rs
index cf494f8d686..e824e9d4aa9 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::sysroot_with_fallback;
 use rustc_session::parse::ParseSess;
 use rustc_session::{CompilerIO, EarlyDiagCtxt, Session, lint};
 use rustc_span::source_map::{FileLoader, RealFileLoader, SourceMapInputs};
@@ -442,8 +442,7 @@ pub fn run_compiler<R: Send>(config: Config, f: impl FnOnce(&Compiler) -> R + Se
             let temps_dir = config.opts.unstable_opts.temps_dir.as_deref().map(PathBuf::from);
 
             let bundle = match rustc_errors::fluent_bundle(
-                config.opts.sysroot.clone(),
-                sysroot_candidates().to_vec(),
+                sysroot_with_fallback(&config.opts.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..8bdc24d47d9 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};
@@ -346,14 +345,10 @@ pub fn rustc_path<'a>() -> Option<&'a Path> {
 }
 
 fn get_rustc_path_inner(bin_path: &str) -> Option<PathBuf> {
-    sysroot_candidates().iter().find_map(|sysroot| {
-        let candidate = sysroot.join(bin_path).join(if cfg!(target_os = "windows") {
-            "rustc.exe"
-        } else {
-            "rustc"
-        });
-        candidate.exists().then_some(candidate)
-    })
+    let candidate = filesearch::get_or_default_sysroot()
+        .join(bin_path)
+        .join(if cfg!(target_os = "windows") { "rustc.exe" } else { "rustc" });
+    candidate.exists().then_some(candidate)
 }
 
 #[allow(rustc::untranslatable_diagnostic)] // FIXME: make this translatable
@@ -374,10 +369,10 @@ 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")
         })