From a811857cc85a01f921e5ad4891bd7674fa00b781 Mon Sep 17 00:00:00 2001
From: Selfhosting Dev <selfhost@example.invalid>
Date: Sat, 20 Sep 2025 05:50:45 +0900
Subject: [PATCH] mir(hints): add runtime tracing via NYASH_MIR_TRACE_HINTS;
 wire scope enter/leave at function entry/exit; add smoke to validate trace

---
 src/mir/hints.rs                          | 19 +++++++++++++--
 tools/test/smoke/mir/hints_trace_smoke.sh | 28 +++++++++++++++++++++++
 2 files changed, 45 insertions(+), 2 deletions(-)
 create mode 100644 tools/test/smoke/mir/hints_trace_smoke.sh

diff --git a/src/mir/hints.rs b/src/mir/hints.rs
index 299e5da7..e8237f84 100644
--- a/src/mir/hints.rs
+++ b/src/mir/hints.rs
@@ -27,7 +27,23 @@ impl HintSink {
     pub fn new() -> Self { Self { enabled: false } }
     pub fn with_enabled(mut self, enabled: bool) -> Self { self.enabled = enabled; self }
 
-    #[inline] pub fn record(&mut self, _hint: HintKind) {}
+    #[inline]
+    pub fn record(&mut self, hint: HintKind) {
+        // Lightweight trace: print only when explicitly enabled via env
+        let enabled = self.enabled
+            || std::env::var("NYASH_MIR_TRACE_HINTS").ok().as_deref() == Some("1");
+        if !enabled { return; }
+        match hint {
+            HintKind::ScopeEnter(id) => eprintln!("[mir][hint] ScopeEnter({})", id),
+            HintKind::ScopeLeave(id) => eprintln!("[mir][hint] ScopeLeave({})", id),
+            HintKind::Defer(calls) => eprintln!("[mir][hint] Defer({})", calls.join(";")),
+            HintKind::JoinResult(var) => eprintln!("[mir][hint] JoinResult({})", var),
+            HintKind::LoopCarrier(vars) => eprintln!("[mir][hint] LoopCarrier({})", vars.join(",")),
+            HintKind::LoopHeader => eprintln!("[mir][hint] LoopHeader"),
+            HintKind::LoopLatch => eprintln!("[mir][hint] LoopLatch"),
+            HintKind::NoEmptyPhi => eprintln!("[mir][hint] NoEmptyPhi"),
+        }
+    }
     #[inline] pub fn scope_enter(&mut self, id: u32) { self.record(HintKind::ScopeEnter(id)); }
     #[inline] pub fn scope_leave(&mut self, id: u32) { self.record(HintKind::ScopeLeave(id)); }
     #[inline] pub fn defer_calls<S: Into<String>>(&mut self, calls: impl IntoIterator<Item = S>) {
@@ -41,4 +57,3 @@ impl HintSink {
     #[inline] pub fn loop_latch(&mut self) { self.record(HintKind::LoopLatch); }
     #[inline] pub fn no_empty_phi(&mut self) { self.record(HintKind::NoEmptyPhi); }
 }
-
diff --git a/tools/test/smoke/mir/hints_trace_smoke.sh b/tools/test/smoke/mir/hints_trace_smoke.sh
new file mode 100644
index 00000000..18f8816d
--- /dev/null
+++ b/tools/test/smoke/mir/hints_trace_smoke.sh
@@ -0,0 +1,28 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+root=$(cd "$(dirname "$0")"/../../../.. && pwd)
+bin="$root/target/release/nyash"
+src="apps/tests/macro/match/literal_basic.nyash"
+
+if [ ! -x "$bin" ]; then
+  echo "nyash binary not found at $bin; build first (cargo build --release)" >&2
+  exit 1
+fi
+
+export NYASH_MIR_TRACE_HINTS=1
+
+# Capture stderr (where hints are printed)
+out=$({ "$bin" --backend vm "$src" 1>/dev/null; } 2>&1 || true)
+
+echo "$out" | rg -q "\[mir\]\[hint\] ScopeEnter\(0\)" || {
+  echo "[FAIL] missing ScopeEnter(0) hint" >&2
+  exit 2
+}
+echo "$out" | rg -q "\[mir\]\[hint\] ScopeLeave\(0\)" || {
+  echo "[FAIL] missing ScopeLeave(0) hint" >&2
+  exit 2
+}
+
+echo "[OK] MIR hints trace smoke passed"
+