Auto merge of #95739 - lqd:proc-macro-expansions, r=wesleywiser

self-profiler: record spans for proc-macro expansions

This PR is a follow-up to #95473, using the arg recorder feature from #95689:
- it adds support code to easily record spans in the event's arguments, when using `generic_activity_with_arg_recorder`.
- uses that to record the spans where proc-macro expansions happen in addition to their name.

As for the other 2 PRs, the goal here is to provide visibility into proc-macro expansion performance, so that users can diagnose which uses of proc-macros in their code could be causing compile time issues.

Some areas where I'd love feedback:
- [x] the API and names: the `SpannedEventArgRecorder` trait and its method, much like #95689 had the same question about the `EventArgRecorder` naming
- [x] we don't currently have a way to record the names of the event arguments, so should `record_arg_spanned` record the span as "location: {}" or similar ?

2 files changed, 37 insertions, 0 deletions

diff --git a/compiler/rustc_span/src/lib.rs b/compiler/rustc_span/src/lib.rs
index b0307cc20d1..f22faef2580 100644
--- a/compiler/rustc_span/src/lib.rs
+++ b/compiler/rustc_span/src/lib.rs
@@ -59,6 +59,8 @@ pub use symbol::{sym, Symbol};
 mod analyze_source_file;
 pub mod fatal_error;
 
+pub mod profiling;
+
 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
 use rustc_data_structures::sync::{Lock, Lrc};
 
diff --git a/compiler/rustc_span/src/profiling.rs b/compiler/rustc_span/src/profiling.rs
new file mode 100644
index 00000000000..f169007fab4
--- /dev/null
+++ b/compiler/rustc_span/src/profiling.rs
@@ -0,0 +1,35 @@
+use std::borrow::Borrow;
+
+use rustc_data_structures::profiling::EventArgRecorder;
+
+/// Extension trait for self-profiling purposes: allows to record spans within a generic activity's
+/// event arguments.
+pub trait SpannedEventArgRecorder {
+    /// Records the following event arguments within the current generic activity being profiled:
+    /// - the provided `event_arg`
+    /// - a string representation of the provided `span`
+    ///
+    /// Note: when self-profiling with costly event arguments, at least one argument
+    /// needs to be recorded. A panic will be triggered if that doesn't happen.
+    fn record_arg_with_span<A>(&mut self, event_arg: A, span: crate::Span)
+    where
+        A: Borrow<str> + Into<String>;
+}
+
+impl SpannedEventArgRecorder for EventArgRecorder<'_> {
+    fn record_arg_with_span<A>(&mut self, event_arg: A, span: crate::Span)
+    where
+        A: Borrow<str> + Into<String>,
+    {
+        self.record_arg(event_arg);
+
+        let span_arg = crate::with_session_globals(|session_globals| {
+            if let Some(source_map) = &*session_globals.source_map.borrow() {
+                source_map.span_to_embeddable_string(span)
+            } else {
+                format!("{:?}", span)
+            }
+        });
+        self.record_arg(span_arg);
+    }
+}