feat(turbopack_core): define trait for diagnostics (#5503)

### Description

Extracting trait definition from
vercel/next.js#52356, renamed it for more
generic usage that turbopack can emit any kind of arbitary metadata, but
next-swc can use it as telemetry for its subset.

crates/turbopack-core/src/diagnostics/mod.rs

@@ -0,0 +1,84 @@
+use std::collections::HashMap;
+
+use anyhow::Result;
+use async_trait::async_trait;
+use turbo_tasks::{emit, CollectiblesSource, Upcast, Vc};
+
+#[turbo_tasks::value(serialization = "none")]
+#[derive(Clone, Debug)]
+pub struct PlainDiagnostic {
+    pub category: String,
+    pub name: String,
+    pub payload: HashMap<String, String>,
+}
+
+#[turbo_tasks::value(transparent)]
+pub struct DiagnosticPayload(pub HashMap<String, String>);
+
+/// An arbitrary payload can be used to analyze, diagnose
+/// Turbopack's behavior.
+#[turbo_tasks::value_trait]
+pub trait Diagnostic {
+    /// [NOTE]: Psuedo-reserved; this is not being used currently.
+    /// The `type` of the diagnostics that can be used selectively filtered by
+    /// consumers. For example, this could be `telemetry`, or
+    /// `slow_perf_event`, or something else. This is not strongly typed
+    /// though; since consumer or implementation may need to define own
+    /// category.
+    fn category(&self) -> Vc<String>;
+    /// Name of the specific diagnostic event.
+    fn name(&self) -> Vc<String>;
+    /// Arbitarary payload included in the diagnostic event.
+    fn payload(&self) -> Vc<DiagnosticPayload>;
+
+    async fn into_plain(self: Vc<Self>) -> Result<Vc<PlainDiagnostic>> {
+        Ok(PlainDiagnostic {
+            category: self.category().await?.clone_value(),
+            name: self.name().await?.clone_value(),
+            payload: self.payload().await?.clone_value(),
+        }
+        .cell())
+    }
+}
+
+pub trait DiagnosticExt {
+    fn emit(self);
+}
+
+impl<T> DiagnosticExt for Vc<T>
+where
+    T: Upcast<Box<dyn Diagnostic>>,
+{
+    fn emit(self) {
+        let diagnostic = Vc::upcast::<Box<dyn Diagnostic>>(self);
+        emit(diagnostic);
+    }
+}
+
+#[async_trait]
+pub trait DiagnosticContextExt
+where
+    Self: Sized,
+{
+    async fn peek_diagnostics(self) -> Result<Vc<CapturedDiagnostics>>;
+}
+
+#[async_trait]
+impl<T> DiagnosticContextExt for T
+where
+    T: CollectiblesSource + Copy + Send,
+{
+    async fn peek_diagnostics(self) -> Result<Vc<CapturedDiagnostics>> {
+        Ok(CapturedDiagnostics::cell(CapturedDiagnostics {
+            diagnostics: self.peek_collectibles().strongly_consistent().await?,
+        }))
+    }
+}
+
+/// A list of diagnostics captured with
+/// [`DiagnosticsVc::peek_diagnostics_with_path`] and
+#[derive(Debug)]
+#[turbo_tasks::value]
+pub struct CapturedDiagnostics {
+    pub diagnostics: auto_hash_map::AutoSet<Vc<Box<dyn Diagnostic>>>,
+}

crates/turbopack-core/src/lib.rs

@@ -13,6 +13,7 @@ pub mod chunk;
 pub mod code_builder;
 pub mod compile_time_info;
 pub mod context;
+pub mod diagnostics;
 pub mod environment;
 pub mod error;
 pub mod file_source;