track proc-macro expansions in the self-profiler

Use the proc-macro descr to track their individual expansions with
self-profiling events. This will help diagnose performance issues
with slow proc-macros.

compiler/rustc_expand/src/base.rs

@@ -1047,6 +1047,12 @@ impl<'a> ExtCtxt<'a> {
         self.current_expansion.id.expn_data().call_site
     }
 
+    /// Returns the current expansion kind's description.
+    pub(crate) fn expansion_descr(&self) -> String {
+        let expn_data = self.current_expansion.id.expn_data();
+        expn_data.kind.descr()
+    }
+
     /// Equivalent of `Span::def_site` from the proc macro API,
     /// except that the location is taken from the span passed as an argument.
     pub fn with_def_site_ctxt(&self, span: Span) -> Span {

compiler/rustc_expand/src/proc_macro.rs

@@ -24,6 +24,8 @@ impl base::ProcMacro for BangProcMacro {
         span: Span,
         input: TokenStream,
     ) -> Result<TokenStream, ErrorGuaranteed> {
+        let _timer =
+            ecx.sess.prof.generic_activity_with_arg("expand_proc_macro", ecx.expansion_descr());
         let proc_macro_backtrace = ecx.ecfg.proc_macro_backtrace;
         let server = proc_macro_server::Rustc::new(ecx);
         self.client.run(&EXEC_STRATEGY, server, input, proc_macro_backtrace).map_err(|e| {
@@ -48,6 +50,8 @@ impl base::AttrProcMacro for AttrProcMacro {
         annotation: TokenStream,
         annotated: TokenStream,
     ) -> Result<TokenStream, ErrorGuaranteed> {
+        let _timer =
+            ecx.sess.prof.generic_activity_with_arg("expand_proc_macro", ecx.expansion_descr());
         let proc_macro_backtrace = ecx.ecfg.proc_macro_backtrace;
         let server = proc_macro_server::Rustc::new(ecx);
         self.client
@@ -97,9 +101,12 @@ impl MultiItemModifier for ProcMacroDerive {
             nt_to_tokenstream(&item, &ecx.sess.parse_sess, CanSynthesizeMissingTokens::No)
         };
 
+        let stream = {
+            let _timer =
+                ecx.sess.prof.generic_activity_with_arg("expand_proc_macro", ecx.expansion_descr());
             let proc_macro_backtrace = ecx.ecfg.proc_macro_backtrace;
             let server = proc_macro_server::Rustc::new(ecx);
-        let stream = match self.client.run(&EXEC_STRATEGY, server, input, proc_macro_backtrace) {
+            match self.client.run(&EXEC_STRATEGY, server, input, proc_macro_backtrace) {
                 Ok(stream) => stream,
                 Err(e) => {
                     let mut err = ecx.struct_span_err(span, "proc-macro derive panicked");
@@ -109,6 +116,7 @@ impl MultiItemModifier for ProcMacroDerive {
                     err.emit();
                     return ExpandResult::Ready(vec![]);
                 }
+            }
         };
 
         let error_count_before = ecx.sess.parse_sess.span_diagnostic.err_count();