1. fix jobserver GLOBAL_CLIENT_CHECKED uninitialized before use

2. jobserver::initialize_checked should call before build_session, still should use EarlyErrorHandler, so revert stderr change in #118635

compiler/rustc_data_structures/src/jobserver.rs

@@ -52,7 +52,7 @@ fn default_client() -> Client {
 
 static GLOBAL_CLIENT_CHECKED: OnceLock<Client> = OnceLock::new();
 
-pub fn check(report_warning: impl FnOnce(&'static str)) {
+pub fn initialize_checked(report_warning: impl FnOnce(&'static str)) {
     let client_checked = match &*GLOBAL_CLIENT {
         Ok(client) => client.clone(),
         Err(e) => {

compiler/rustc_interface/src/interface.rs

@@ -316,6 +316,10 @@ pub fn run_compiler<R: Send>(config: Config, f: impl FnOnce(&Compiler) -> R + Se
     // Set parallel mode before thread pool creation, which will create `Lock`s.
     rustc_data_structures::sync::set_dyn_thread_safe_mode(config.opts.unstable_opts.threads > 1);
 
+    // Check jobserver before run_in_thread_pool_with_globals, which call jobserver::acquire_thread
+    let early_handler = EarlyErrorHandler::new(config.opts.error_format);
+    early_handler.initialize_checked_jobserver();
+
     util::run_in_thread_pool_with_globals(
         config.opts.edition,
         config.opts.unstable_opts.threads,

compiler/rustc_interface/src/tests.rs

@@ -27,6 +27,8 @@ use std::sync::Arc;
 
 fn mk_session(matches: getopts::Matches) -> (Session, Cfg) {
     let mut early_handler = EarlyErrorHandler::new(ErrorOutputType::default());
+    early_handler.initialize_checked_jobserver();
+
     let registry = registry::Registry::new(&[]);
     let sessopts = build_session_options(&mut early_handler, &matches);
     let temps_dir = sessopts.unstable_opts.temps_dir.as_deref().map(PathBuf::from);

compiler/rustc_session/src/session.rs

@@ -1474,17 +1474,6 @@ pub fn build_session(
     let asm_arch =
         if target_cfg.allow_asm { InlineAsmArch::from_str(&target_cfg.arch).ok() } else { None };
 
-    // Check jobserver before getting `jobserver::client`.
-    jobserver::check(|err| {
-        #[allow(rustc::untranslatable_diagnostic)]
-        #[allow(rustc::diagnostic_outside_of_impl)]
-        parse_sess
-            .span_diagnostic
-            .struct_warn(err)
-            .note("the build environment is likely misconfigured")
-            .emit()
-    });
-
     let sess = Session {
         target: target_cfg,
         host,
@@ -1792,6 +1781,18 @@ impl EarlyErrorHandler {
     pub fn early_warn(&self, msg: impl Into<DiagnosticMessage>) {
         self.handler.struct_warn(msg).emit()
     }
+
+    pub fn initialize_checked_jobserver(&self) {
+        // initialize jobserver before getting `jobserver::client` and `build_session`.
+        jobserver::initialize_checked(|err| {
+            #[allow(rustc::untranslatable_diagnostic)]
+            #[allow(rustc::diagnostic_outside_of_impl)]
+            self.handler
+                .struct_warn(err)
+                .note("the build environment is likely misconfigured")
+                .emit()
+        });
+    }
 }
 
 fn mk_emitter(output: ErrorOutputType) -> Box<DynEmitter> {

tests/run-make/jobserver-error/cannot_open_fd.stderr

@@ -4,5 +4,3 @@ warning: failed to connect to jobserver from environment variable `MAKEFLAGS="--
 
 error: no input filename given
 
-warning: 1 warning emitted
-

tests/run-make/jobserver-error/not_a_pipe.stderr

@@ -2,5 +2,3 @@ warning: failed to connect to jobserver from environment variable `MAKEFLAGS="--
   |
   = note: the build environment is likely misconfigured
 
-warning: 1 warning emitted
-