4 files changed, 130 insertions, 2 deletions
diff --git a/compiler/rustc_errors/src/emitter.rs b/compiler/rustc_errors/src/emitter.rs
index fe01e289334..6ab6f96079e 100644
--- a/compiler/rustc_errors/src/emitter.rs
+++ b/compiler/rustc_errors/src/emitter.rs
@@ -34,6 +34,7 @@ use crate::snippet::{
     Annotation, AnnotationColumn, AnnotationType, Line, MultilineAnnotation, Style, StyledString,
 };
 use crate::styled_buffer::StyledBuffer;
+use crate::timings::TimingRecord;
 use crate::translation::{Translate, to_fluent_args};
 use crate::{
     CodeSuggestion, DiagInner, DiagMessage, ErrCode, FluentBundle, LazyFallbackBundle, Level,
@@ -164,11 +165,16 @@ impl Margin {
     }
 }
 
+pub enum TimingEvent {
+    Start,
+    End,
+}
+
 const ANONYMIZED_LINE_NUM: &str = "LL";
 
 pub type DynEmitter = dyn Emitter + DynSend;
 
-/// Emitter trait for emitting errors.
+/// Emitter trait for emitting errors and other structured information.
 pub trait Emitter: Translate {
     /// Emit a structured diagnostic.
     fn emit_diagnostic(&mut self, diag: DiagInner, registry: &Registry);
@@ -177,6 +183,10 @@ pub trait Emitter: Translate {
     /// Currently only supported for the JSON format.
     fn emit_artifact_notification(&mut self, _path: &Path, _artifact_type: &str) {}
 
+    /// Emit a timestamp with start/end of a timing section.
+    /// Currently only supported for the JSON format.
+    fn emit_timing_section(&mut self, _record: TimingRecord, _event: TimingEvent) {}
+
     /// Emit a report about future breakage.
     /// Currently only supported for the JSON format.
     fn emit_future_breakage_report(&mut self, _diags: Vec<DiagInner>, _registry: &Registry) {}
diff --git a/compiler/rustc_errors/src/json.rs b/compiler/rustc_errors/src/json.rs
index a6583407b7e..d67e2ba2d60 100644
--- a/compiler/rustc_errors/src/json.rs
+++ b/compiler/rustc_errors/src/json.rs
@@ -28,9 +28,10 @@ use termcolor::{ColorSpec, WriteColor};
 use crate::diagnostic::IsLint;
 use crate::emitter::{
     ColorConfig, Destination, Emitter, HumanEmitter, HumanReadableErrorType, OutputTheme,
-    should_show_source_code,
+    TimingEvent, should_show_source_code,
 };
 use crate::registry::Registry;
+use crate::timings::{TimingRecord, TimingSection};
 use crate::translation::{Translate, to_fluent_args};
 use crate::{
     CodeSuggestion, FluentBundle, LazyFallbackBundle, MultiSpan, SpanLabel, Subdiag, Suggestions,
@@ -104,6 +105,7 @@ impl JsonEmitter {
 enum EmitTyped<'a> {
     Diagnostic(Diagnostic),
     Artifact(ArtifactNotification<'a>),
+    SectionTiming(SectionTimestamp<'a>),
     FutureIncompat(FutureIncompatReport<'a>),
     UnusedExtern(UnusedExterns<'a>),
 }
@@ -135,6 +137,21 @@ impl Emitter for JsonEmitter {
         }
     }
 
+    fn emit_timing_section(&mut self, record: TimingRecord, event: TimingEvent) {
+        let event = match event {
+            TimingEvent::Start => "start",
+            TimingEvent::End => "end",
+        };
+        let name = match record.section {
+            TimingSection::Linking => "link",
+        };
+        let data = SectionTimestamp { name, event, timestamp: record.timestamp };
+        let result = self.emit(EmitTyped::SectionTiming(data));
+        if let Err(e) = result {
+            panic!("failed to print timing section: {e:?}");
+        }
+    }
+
     fn emit_future_breakage_report(&mut self, diags: Vec<crate::DiagInner>, registry: &Registry) {
         let data: Vec<FutureBreakageItem<'_>> = diags
             .into_iter()
@@ -264,6 +281,16 @@ struct ArtifactNotification<'a> {
 }
 
 #[derive(Serialize)]
+struct SectionTimestamp<'a> {
+    /// Name of the section
+    name: &'a str,
+    /// Start/end of the section
+    event: &'a str,
+    /// Opaque timestamp.
+    timestamp: u128,
+}
+
+#[derive(Serialize)]
 struct FutureBreakageItem<'a> {
     // Always EmitTyped::Diagnostic, but we want to make sure it gets serialized
     // with "$message_type".
diff --git a/compiler/rustc_errors/src/lib.rs b/compiler/rustc_errors/src/lib.rs
index 9f72fc4705a..b520eb353d6 100644
--- a/compiler/rustc_errors/src/lib.rs
+++ b/compiler/rustc_errors/src/lib.rs
@@ -74,7 +74,9 @@ pub use snippet::Style;
 pub use termcolor::{Color, ColorSpec, WriteColor};
 use tracing::debug;
 
+use crate::emitter::TimingEvent;
 use crate::registry::Registry;
+use crate::timings::TimingRecord;
 
 pub mod annotate_snippet_emitter_writer;
 pub mod codes;
@@ -90,6 +92,7 @@ mod snippet;
 mod styled_buffer;
 #[cfg(test)]
 mod tests;
+pub mod timings;
 pub mod translation;
 
 pub type PResult<'a, T> = Result<T, Diag<'a>>;
@@ -1156,6 +1159,14 @@ impl<'a> DiagCtxtHandle<'a> {
         self.inner.borrow_mut().emitter.emit_artifact_notification(path, artifact_type);
     }
 
+    pub fn emit_timing_section_start(&self, record: TimingRecord) {
+        self.inner.borrow_mut().emitter.emit_timing_section(record, TimingEvent::Start);
+    }
+
+    pub fn emit_timing_section_end(&self, record: TimingRecord) {
+        self.inner.borrow_mut().emitter.emit_timing_section(record, TimingEvent::End);
+    }
+
     pub fn emit_future_breakage_report(&self) {
         let inner = &mut *self.inner.borrow_mut();
         let diags = std::mem::take(&mut inner.future_breakage_diagnostics);
diff --git a/compiler/rustc_errors/src/timings.rs b/compiler/rustc_errors/src/timings.rs
new file mode 100644
index 00000000000..27fc9df8d79
--- /dev/null
+++ b/compiler/rustc_errors/src/timings.rs
@@ -0,0 +1,80 @@
+use std::time::Instant;
+
+use crate::DiagCtxtHandle;
+
+/// A high-level section of the compilation process.
+#[derive(Copy, Clone, Debug)]
+pub enum TimingSection {
+    /// Time spent linking.
+    Linking,
+}
+
+/// Section with attached timestamp
+#[derive(Copy, Clone, Debug)]
+pub struct TimingRecord {
+    pub section: TimingSection,
+    /// Microseconds elapsed since some predetermined point in time (~start of the rustc process).
+    pub timestamp: u128,
+}
+
+impl TimingRecord {
+    fn from_origin(origin: Instant, section: TimingSection) -> Self {
+        Self { section, timestamp: Instant::now().duration_since(origin).as_micros() }
+    }
+
+    pub fn section(&self) -> TimingSection {
+        self.section
+    }
+
+    pub fn timestamp(&self) -> u128 {
+        self.timestamp
+    }
+}
+
+/// Manages emission of start/end section timings, enabled through `--json=timings`.
+pub struct TimingSectionHandler {
+    /// Time when the compilation session started.
+    /// If `None`, timing is disabled.
+    origin: Option<Instant>,
+}
+
+impl TimingSectionHandler {
+    pub fn new(enabled: bool) -> Self {
+        let origin = if enabled { Some(Instant::now()) } else { None };
+        Self { origin }
+    }
+
+    /// Returns a RAII guard that will immediately emit a start the provided section, and then emit
+    /// its end when it is dropped.
+    pub fn start_section<'a>(
+        &self,
+        diag_ctxt: DiagCtxtHandle<'a>,
+        section: TimingSection,
+    ) -> TimingSectionGuard<'a> {
+        TimingSectionGuard::create(diag_ctxt, section, self.origin)
+    }
+}
+
+/// RAII wrapper for starting and ending section timings.
+pub struct TimingSectionGuard<'a> {
+    dcx: DiagCtxtHandle<'a>,
+    section: TimingSection,
+    origin: Option<Instant>,
+}
+
+impl<'a> TimingSectionGuard<'a> {
+    fn create(dcx: DiagCtxtHandle<'a>, section: TimingSection, origin: Option<Instant>) -> Self {
+        if let Some(origin) = origin {
+            dcx.emit_timing_section_start(TimingRecord::from_origin(origin, section));
+        }
+        Self { dcx, section, origin }
+    }
+}
+
+impl<'a> Drop for TimingSectionGuard<'a> {
+    fn drop(&mut self) {
+        if let Some(origin) = self.origin {
+            self.dcx.emit_timing_section_end(TimingRecord::from_origin(origin, self.section));
+        }
+    }
+}