Add live query feature flag (#3396)

lib/src/fflags.rs

@@ -0,0 +1,68 @@
+#[allow(dead_code)]
+pub(crate) static FFLAGS: FFlags = FFlags {
+    change_feed_live_queries: FFlagEnabledStatus {
+        enabled_release: false,
+        enabled_debug: false,
+        enabled_test: false,
+        env_override: "SURREALDB_CHANGE_FEED_LIVE_QUERIES",
+        owner: "Hugh Kaznowski",
+        description: "Disables live queries as a separate feature and moves to using change feeds as the underlying mechanism",
+        date_enabled_test: None,
+        date_enabled_debug: None,
+        date_enabled_release: None,
+        release_version: None,
+    }
+};
+
+#[derive(Clone, Copy, Debug, Eq, PartialEq, Ord, PartialOrd, Hash)]
+#[non_exhaustive]
+#[allow(dead_code)]
+pub(crate) struct FFlags {
+	pub(crate) change_feed_live_queries: FFlagEnabledStatus,
+}
+
+/// This struct is not used in the implementation;
+/// All the fields are here as information for people investigating the feature flag.
+#[allow(dead_code)]
+#[derive(Clone, Copy, Debug, Eq, PartialEq, Ord, PartialOrd, Hash)]
+pub(crate) struct FFlagEnabledStatus {
+	pub(crate) enabled_release: bool,
+	pub(crate) enabled_debug: bool,
+	pub(crate) enabled_test: bool,
+	pub(crate) owner: &'static str,
+	pub(crate) description: &'static str,
+	pub(crate) env_override: &'static str,
+	pub(crate) date_enabled_test: Option<&'static str>,
+	pub(crate) date_enabled_debug: Option<&'static str>,
+	pub(crate) date_enabled_release: Option<&'static str>,
+	pub(crate) release_version: Option<&'static str>,
+}
+
+impl FFlagEnabledStatus {
+	#[allow(dead_code)]
+	pub(crate) fn enabled(&self) -> bool {
+		let mut enabled = false;
+		if let Ok(env_var) = std::env::var(self.env_override) {
+			if env_var.trim() == "true" {
+				return true;
+			}
+			return false;
+		}
+		// Test check
+		#[cfg(test)]
+		{
+			enabled = enabled || self.enabled_test;
+		}
+		// Debug build check
+		#[cfg(debug_assertions)]
+		{
+			enabled = enabled || self.enabled_debug;
+		}
+		// Release build check
+		#[cfg(not(debug_assertions))]
+		{
+			enabled = enabled || self.enabled_release;
+		}
+		enabled
+	}
+}

lib/src/lib.rs

@@ -123,6 +123,7 @@ pub mod dbs;
 pub mod env;
 #[doc(hidden)]
 pub mod err;
+pub(crate) mod fflags;
 #[doc(hidden)]
 pub mod iam;
 #[doc(hidden)]

lib/src/syn/v2/lexer/reader.rs

@@ -72,7 +72,7 @@ impl<'a> BytesReader<'a> {
 
 	#[inline]
 	pub fn peek(&self) -> Option<u8> {
-		self.remaining().get(0).copied()
+		self.remaining().first().copied()
 	}
 	#[inline]
 	pub fn span(&self, span: Span) -> &[u8] {

lib/src/syn/v2/lexer/uuid.rs

@@ -115,7 +115,7 @@ impl<'a> Lexer<'a> {
 	/// otherwise.
 	pub fn lex_hex(&mut self, amount: u8) -> bool {
 		for _ in 0..amount {
-			if !self.eat_when(|x| matches!(x,b'0'..=b'9' | b'a'..=b'f' | b'A'..=b'F')) {
+			if !self.eat_when(|x| x.is_ascii_hexdigit()) {
 				return false;
 			}
 		}