Allow injecting a profiler runtime into #![no_core] crates

Now that the profiler runtime is itself `#![no_core]`, it can be a dependency
of other no_core crates, including core.

Author: Zalathar

compiler/rustc_metadata/messages.ftl

@@ -233,9 +233,6 @@ metadata_prev_alloc_error_handler =
 metadata_prev_global_alloc =
     previous global allocator defined here
 
-metadata_profiler_builtins_needs_core =
-    `profiler_builtins` crate (required by compiler options) is not compatible with crate attribute `#![no_core]`
-
 metadata_raw_dylib_no_nul =
     link name must not contain NUL characters if link kind is `raw-dylib`
 

compiler/rustc_metadata/src/creader.rs

@@ -799,7 +799,7 @@ impl<'a, 'tcx> CrateLoader<'a, 'tcx> {
         self.inject_dependency_if(cnum, "a panic runtime", &|data| data.needs_panic_runtime());
     }
 
-    fn inject_profiler_runtime(&mut self, krate: &ast::Crate) {
+    fn inject_profiler_runtime(&mut self, _krate: &ast::Crate) {
         let needs_profiler_runtime =
             self.sess.instrument_coverage() || self.sess.opts.cg.profile_generate.enabled();
         if !needs_profiler_runtime || self.sess.opts.unstable_opts.no_profiler_runtime {
@@ -809,10 +809,6 @@ impl<'a, 'tcx> CrateLoader<'a, 'tcx> {
         info!("loading profiler");
 
         let name = Symbol::intern(&self.sess.opts.unstable_opts.profiler_runtime);
-        if name == sym::profiler_builtins && attr::contains_name(&krate.attrs, sym::no_core) {
-            self.dcx().emit_err(errors::ProfilerBuiltinsNeedsCore);
-        }
-
         let Some(cnum) = self.resolve_crate(name, DUMMY_SP, CrateDepKind::Implicit) else {
             return;
         };

compiler/rustc_metadata/src/errors.rs

@@ -339,10 +339,6 @@ pub struct NoPanicStrategy {
     pub strategy: PanicStrategy,
 }
 
-#[derive(Diagnostic)]
-#[diag(metadata_profiler_builtins_needs_core)]
-pub struct ProfilerBuiltinsNeedsCore;
-
 #[derive(Diagnostic)]
 #[diag(metadata_not_profiler_runtime)]
 pub struct NotProfilerRuntime {