Move initialize_checked_jobserver.

Currently it's a method on `EarlyDiagCtxt`, which is not the right place
for it at all -- `EarlyDiagCtxt` is used to issue diagnostics, but
shouldn't be doing any of the actual checking.

This commit moves it into a standalone function that takes an
`EarlyDiagCtxt` as an argument, which is more sensible. This does
require adding `EarlyDiagCtxt::early_struct_warn`, so a warning can be
returned and then modified with a note. (And that likely explains why
somebody put `initialize_checked_jobserver` into `EarlyDiagCtxt` in the
first place.)

compiler/rustc_interface/src/interface.rs

@@ -5,6 +5,7 @@ use rustc_ast::{LitKind, MetaItemKind};
 use rustc_codegen_ssa::traits::CodegenBackend;
 use rustc_data_structures::defer;
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
+use rustc_data_structures::jobserver;
 use rustc_data_structures::stable_hasher::StableHasher;
 use rustc_data_structures::sync::Lrc;
 use rustc_errors::registry::Registry;
@@ -318,6 +319,18 @@ pub struct Config {
     pub expanded_args: Vec<String>,
 }
 
+/// Initialize jobserver before getting `jobserver::client` and `build_session`.
+pub(crate) fn initialize_checked_jobserver(early_dcx: &EarlyDiagCtxt) {
+    jobserver::initialize_checked(|err| {
+        #[allow(rustc::untranslatable_diagnostic)]
+        #[allow(rustc::diagnostic_outside_of_impl)]
+        early_dcx
+            .early_struct_warn(err)
+            .with_note("the build environment is likely misconfigured")
+            .emit()
+    });
+}
+
 // JUSTIFICATION: before session exists, only config
 #[allow(rustc::bad_opt_access)]
 #[allow(rustc::untranslatable_diagnostic)] // FIXME: make this translatable
@@ -329,7 +342,7 @@ pub fn run_compiler<R: Send>(config: Config, f: impl FnOnce(&Compiler) -> R + Se
 
     // Check jobserver before run_in_thread_pool_with_globals, which call jobserver::acquire_thread
     let early_dcx = EarlyDiagCtxt::new(config.opts.error_format);
-    early_dcx.initialize_checked_jobserver();
+    initialize_checked_jobserver(&early_dcx);
 
     crate::callbacks::setup_callbacks();
 

compiler/rustc_interface/src/tests.rs

@@ -1,5 +1,5 @@
 #![allow(rustc::bad_opt_access)]
-use crate::interface::parse_cfg;
+use crate::interface::{initialize_checked_jobserver, parse_cfg};
 use rustc_data_structures::profiling::TimePassesFormat;
 use rustc_errors::{emitter::HumanReadableErrorType, registry, ColorConfig};
 use rustc_session::config::{
@@ -31,7 +31,7 @@ where
     F: FnOnce(Session, Cfg),
 {
     let mut early_dcx = EarlyDiagCtxt::new(ErrorOutputType::default());
-    early_dcx.initialize_checked_jobserver();
+    initialize_checked_jobserver(&early_dcx);
 
     let matches = optgroups().parse(args).unwrap();
     let sessopts = build_session_options(&mut early_dcx, &matches);

compiler/rustc_session/src/session.rs

@@ -1411,16 +1411,10 @@ impl EarlyDiagCtxt {
         self.dcx.warn(msg)
     }
 
-    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.dcx
-                .struct_warn(err)
-                .with_note("the build environment is likely misconfigured")
-                .emit()
-        });
+    #[allow(rustc::untranslatable_diagnostic)]
+    #[allow(rustc::diagnostic_outside_of_impl)]
+    pub fn early_struct_warn(&self, msg: impl Into<DiagMessage>) -> Diag<'_, ()> {
+        self.dcx.struct_warn(msg)
     }
 }