From b70020aceb48b4ecf1ddce0145aed80b9f6bd915 Mon Sep 17 00:00:00 2001
From: Anna Henningsen <anna@addaleax.net>
Date: Mon, 21 Jul 2025 18:17:45 +0200
Subject: [PATCH 1/2] src: use C++20 `consteval` for `FastStringKey`

This makes it easier to avoid unintentional mis-usage of the API.
---
 src/util-inl.h | 9 ++++++++-
 src/util.h     | 8 +++++++-
 2 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/src/util-inl.h b/src/util-inl.h
index 3493732471fd95..778cc57537a966 100644
--- a/src/util-inl.h
+++ b/src/util-inl.h
@@ -618,7 +618,14 @@ constexpr bool FastStringKey::operator==(const FastStringKey& other) const {
   return name_ == other.name_;
 }
 
-constexpr FastStringKey::FastStringKey(std::string_view name)
+consteval FastStringKey::FastStringKey(std::string_view name)
+    : FastStringKey(name, 0) {}
+
+constexpr FastStringKey FastStringKey::AllowDynamic(std::string_view name) {
+  return FastStringKey(name, 0);
+}
+
+constexpr FastStringKey::FastStringKey(std::string_view name, int dummy)
     : name_(name), cached_hash_(HashImpl(name)) {}
 
 constexpr std::string_view FastStringKey::as_string_view() const {
diff --git a/src/util.h b/src/util.h
index 5d4be8c90ade86..0719f7370fe64a 100644
--- a/src/util.h
+++ b/src/util.h
@@ -822,7 +822,11 @@ class PersistentToLocal {
 // computations.
 class FastStringKey {
  public:
-  constexpr explicit FastStringKey(std::string_view name);
+  // consteval ensures that the argument is a compile-time constant.
+  consteval explicit FastStringKey(std::string_view name);
+  // passing something that is not a compile-time constant needs explicit
+  // opt-in via this helper, as it defeats the purpose of FastStringKey.
+  static constexpr FastStringKey AllowDynamic(std::string_view name);
 
   struct Hash {
     constexpr size_t operator()(const FastStringKey& key) const;
@@ -832,6 +836,8 @@ class FastStringKey {
   constexpr std::string_view as_string_view() const;
 
  private:
+  constexpr explicit FastStringKey(std::string_view name, int dummy);
+
   static constexpr size_t HashImpl(std::string_view str);
 
   const std::string_view name_;

From b8f684714834ac6e53cd986b3ea190a4cbf9a112 Mon Sep 17 00:00:00 2001
From: Anna Henningsen <anna@addaleax.net>
Date: Mon, 21 Jul 2025 18:18:44 +0200
Subject: [PATCH 2/2] src: use `FastStringKey` for `TrackV8FastApiCall`

This is the exact intended use case of `FastStringKey`.
---
 src/node_debug.cc | 10 ++++++----
 src/node_debug.h  |  9 +++++----
 2 files changed, 11 insertions(+), 8 deletions(-)

diff --git a/src/node_debug.cc b/src/node_debug.cc
index 0f254b1fbfe820..bb0e11747e418c 100644
--- a/src/node_debug.cc
+++ b/src/node_debug.cc
@@ -23,13 +23,14 @@ using v8::Number;
 using v8::Object;
 using v8::Value;
 
-thread_local std::unordered_map<std::string_view, int> v8_fast_api_call_counts;
+thread_local std::unordered_map<FastStringKey, int, FastStringKey::Hash>
+    v8_fast_api_call_counts;
 
-void TrackV8FastApiCall(std::string_view key) {
+void TrackV8FastApiCall(FastStringKey key) {
   v8_fast_api_call_counts[key]++;
 }
 
-int GetV8FastApiCallCount(std::string_view key) {
+int GetV8FastApiCallCount(FastStringKey key) {
   return v8_fast_api_call_counts[key];
 }
 
@@ -40,7 +41,8 @@ void GetV8FastApiCallCount(const FunctionCallbackInfo<Value>& args) {
     return;
   }
   Utf8Value utf8_key(env->isolate(), args[0]);
-  args.GetReturnValue().Set(GetV8FastApiCallCount(utf8_key.ToStringView()));
+  args.GetReturnValue().Set(GetV8FastApiCallCount(
+      FastStringKey::AllowDynamic(utf8_key.ToStringView())));
 }
 
 void SlowIsEven(const FunctionCallbackInfo<Value>& args) {
diff --git a/src/node_debug.h b/src/node_debug.h
index f42aeb8ba01162..32fbf21c813366 100644
--- a/src/node_debug.h
+++ b/src/node_debug.h
@@ -3,17 +3,18 @@
 #if defined(NODE_WANT_INTERNALS) && NODE_WANT_INTERNALS
 
 #ifdef DEBUG
-#include <string_view>
+#include "util.h"
 #endif  // DEBUG
 
 namespace node {
 namespace debug {
 
 #ifdef DEBUG
-void TrackV8FastApiCall(std::string_view key);
-int GetV8FastApiCallCount(std::string_view key);
+void TrackV8FastApiCall(FastStringKey key);
+int GetV8FastApiCallCount(FastStringKey key);
 
-#define TRACK_V8_FAST_API_CALL(key) node::debug::TrackV8FastApiCall(key)
+#define TRACK_V8_FAST_API_CALL(key)                                            \
+  node::debug::TrackV8FastApiCall(FastStringKey(key))
 #else  // !DEBUG
 #define TRACK_V8_FAST_API_CALL(key)
 #endif  // DEBUG