Add infrastructure for emitting timing sections

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));
+        }
+    }
+}