Collect multiple optimizer hints per statement and extract comment prefix

Two orthogonal improvements to optimizer hint parsing:

1. `Option<OptimizerHint>` -> `Vec<OptimizerHint>`: the old Option silently
   dropped all but the first hint-style comment. Vec preserves all hint
   comments the parser encounters, letting consumers decide which to use.
   This is backwards compatible: `optimizer_hint: None` becomes
   `optimizer_hints: vec![]`, and `optimizer_hint.unwrap()` becomes
   `optimizer_hints[0]`.

2. Generic prefix extraction: the `/*+...*/` pattern is an established
   convention. Various systems extend it with `/*prefix+...*/` where the
   prefix is opaque alphanumeric text before `+`. Rather than adding a new
   dialect flag or struct for each system, the parser now captures any
   `[a-zA-Z0-9]*` run before `+` as a `prefix` field. Standard hints have
   `prefix: ""`. No new dialect surface -- same `supports_comment_optimizer_hint()`
   gate. This makes OptimizerHint a generic extension point: downstream
   consumers can define their own prefixed hint conventions and filter hints
   by prefix, without requiring any changes to the parser or dialect
   configuration.

Author: altmannmarcelo

src/ast/dml.rs

@@ -43,11 +43,11 @@ use super::{
 pub struct Insert {
     /// Token for the `INSERT` keyword (or its substitutes)
     pub insert_token: AttachedToken,
-    /// A query optimizer hint
+    /// Query optimizer hints
     ///
     /// [MySQL](https://dev.mysql.com/doc/refman/8.4/en/optimizer-hints.html)
     /// [Oracle](https://docs.oracle.com/en/database/oracle/oracle-database/21/sqlrf/Comments.html#GUID-D316D545-89E2-4D54-977F-FC97815CD62E)
-    pub optimizer_hint: Option<OptimizerHint>,
+    pub optimizer_hints: Vec<OptimizerHint>,
     /// Only for Sqlite
     pub or: Option<SqliteOnConflict>,
     /// Only for mysql
@@ -133,7 +133,7 @@ impl Display for Insert {
 
         if let Some(on_conflict) = self.or {
             f.write_str("INSERT")?;
-            if let Some(hint) = self.optimizer_hint.as_ref() {
+            for hint in &self.optimizer_hints {
                 write!(f, " {hint}")?;
             }
             write!(f, " {on_conflict} INTO {table_name} ")?;
@@ -147,7 +147,7 @@ impl Display for Insert {
                     "INSERT"
                 }
             )?;
-            if let Some(hint) = self.optimizer_hint.as_ref() {
+            for hint in &self.optimizer_hints {
                 write!(f, " {hint}")?;
             }
             if let Some(priority) = self.priority {
@@ -267,11 +267,11 @@ impl Display for Insert {
 pub struct Delete {
     /// Token for the `DELETE` keyword
     pub delete_token: AttachedToken,
-    /// A query optimizer hint
+    /// Query optimizer hints
     ///
     /// [MySQL](https://dev.mysql.com/doc/refman/8.4/en/optimizer-hints.html)
     /// [Oracle](https://docs.oracle.com/en/database/oracle/oracle-database/21/sqlrf/Comments.html#GUID-D316D545-89E2-4D54-977F-FC97815CD62E)
-    pub optimizer_hint: Option<OptimizerHint>,
+    pub optimizer_hints: Vec<OptimizerHint>,
     /// Multi tables delete are supported in mysql
     pub tables: Vec<ObjectName>,
     /// FROM
@@ -291,7 +291,7 @@ pub struct Delete {
 impl Display for Delete {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         f.write_str("DELETE")?;
-        if let Some(hint) = self.optimizer_hint.as_ref() {
+        for hint in &self.optimizer_hints {
             f.write_str(" ")?;
             hint.fmt(f)?;
         }
@@ -345,11 +345,11 @@ impl Display for Delete {
 pub struct Update {
     /// Token for the `UPDATE` keyword
     pub update_token: AttachedToken,
-    /// A query optimizer hint
+    /// Query optimizer hints
     ///
     /// [MySQL](https://dev.mysql.com/doc/refman/8.4/en/optimizer-hints.html)
     /// [Oracle](https://docs.oracle.com/en/database/oracle/oracle-database/21/sqlrf/Comments.html#GUID-D316D545-89E2-4D54-977F-FC97815CD62E)
-    pub optimizer_hint: Option<OptimizerHint>,
+    pub optimizer_hints: Vec<OptimizerHint>,
     /// TABLE
     pub table: TableWithJoins,
     /// Column assignments
@@ -368,11 +368,12 @@ pub struct Update {
 
 impl Display for Update {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        f.write_str("UPDATE ")?;
-        if let Some(hint) = self.optimizer_hint.as_ref() {
-            hint.fmt(f)?;
+        f.write_str("UPDATE")?;
+        for hint in &self.optimizer_hints {
             f.write_str(" ")?;
+            hint.fmt(f)?;
         }
+        f.write_str(" ")?;
         if let Some(or) = &self.or {
             or.fmt(f)?;
             f.write_str(" ")?;
@@ -419,10 +420,10 @@ impl Display for Update {
 pub struct Merge {
     /// The `MERGE` token that starts the statement.
     pub merge_token: AttachedToken,
-    /// A query optimizer hint
+    /// Query optimizer hints
     ///
     /// [Oracle](https://docs.oracle.com/en/database/oracle/oracle-database/21/sqlrf/Comments.html#GUID-D316D545-89E2-4D54-977F-FC97815CD62E)
-    pub optimizer_hint: Option<OptimizerHint>,
+    pub optimizer_hints: Vec<OptimizerHint>,
     /// optional INTO keyword
     pub into: bool,
     /// Specifies the table to merge
@@ -440,7 +441,7 @@ pub struct Merge {
 impl Display for Merge {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         f.write_str("MERGE")?;
-        if let Some(hint) = self.optimizer_hint.as_ref() {
+        for hint in &self.optimizer_hints {
             write!(f, " {hint}")?;
         }
         if self.into {

src/ast/mod.rs

@@ -11579,12 +11579,19 @@ pub struct ResetStatement {
 /// `SELECT`, `INSERT`, `UPDATE`, `REPLACE`, `MERGE`, and `DELETE` keywords in
 /// the corresponding statements.
 ///
-/// See [Select::optimizer_hint]
+/// See [Select::optimizer_hints]
 #[derive(Debug, Clone, PartialEq, PartialOrd, Eq, Ord, Hash)]
 #[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
 #[cfg_attr(feature = "visitor", derive(Visit, VisitMut))]
 pub struct OptimizerHint {
-    /// the raw test of the optimizer hint without its markers
+    /// An optional prefix between the comment marker and `+`.
+    ///
+    /// Standard optimizer hints like `/*+ ... */` have an empty prefix,
+    /// while system-specific hints like `/*abc+ ... */` have `prefix = "abc"`.
+    /// The prefix is any sequence of ASCII alphanumeric characters
+    /// immediately before the `+` marker.
+    pub prefix: String,
+    /// the raw text of the optimizer hint without its markers
     pub text: String,
     /// the style of the comment which `text` was extracted from,
     /// e.g. `/*+...*/` or `--+...`
@@ -11614,11 +11621,14 @@ impl fmt::Display for OptimizerHint {
         match &self.style {
             OptimizerHintStyle::SingleLine { prefix } => {
                 f.write_str(prefix)?;
+                f.write_str(&self.prefix)?;
                 f.write_str("+")?;
                 f.write_str(&self.text)
             }
             OptimizerHintStyle::MultiLine => {
-                f.write_str("/*+")?;
+                f.write_str("/*")?;
+                f.write_str(&self.prefix)?;
+                f.write_str("+")?;
                 f.write_str(&self.text)?;
                 f.write_str("*/")
             }

src/ast/query.rs

@@ -445,11 +445,11 @@ impl SelectModifiers {
 pub struct Select {
     /// Token for the `SELECT` keyword
     pub select_token: AttachedToken,
-    /// A query optimizer hint
+    /// Query optimizer hints
     ///
     /// [MySQL](https://dev.mysql.com/doc/refman/8.4/en/optimizer-hints.html)
     /// [Oracle](https://docs.oracle.com/en/database/oracle/oracle-database/21/sqlrf/Comments.html#GUID-D316D545-89E2-4D54-977F-FC97815CD62E)
-    pub optimizer_hint: Option<OptimizerHint>,
+    pub optimizer_hints: Vec<OptimizerHint>,
     /// `SELECT [DISTINCT] ...`
     pub distinct: Option<Distinct>,
     /// MySQL-specific SELECT modifiers.
@@ -521,7 +521,7 @@ impl fmt::Display for Select {
             }
         }
 
-        if let Some(hint) = self.optimizer_hint.as_ref() {
+        for hint in &self.optimizer_hints {
             f.write_str(" ")?;
             hint.fmt(f)?;
         }

src/ast/spans.rs

@@ -897,7 +897,7 @@ impl Spanned for Delete {
     fn span(&self) -> Span {
         let Delete {
             delete_token,
-            optimizer_hint: _,
+            optimizer_hints: _,
             tables,
             from,
             using,
@@ -931,7 +931,7 @@ impl Spanned for Update {
     fn span(&self) -> Span {
         let Update {
             update_token,
-            optimizer_hint: _,
+            optimizer_hints: _,
             table,
             assignments,
             from,
@@ -1295,7 +1295,7 @@ impl Spanned for Insert {
     fn span(&self) -> Span {
         let Insert {
             insert_token,
-            optimizer_hint: _,
+            optimizer_hints: _,
             or: _,     // enum, sqlite specific
             ignore: _, // bool
             into: _,   // bool
@@ -2243,7 +2243,7 @@ impl Spanned for Select {
     fn span(&self) -> Span {
         let Select {
             select_token,
-            optimizer_hint: _,
+            optimizer_hints: _,
             distinct: _, // todo
             select_modifiers: _,
             top: _, // todo, mysql specific
@@ -2837,7 +2837,7 @@ WHERE id = 1
         // ~ individual tokens within the statement
         let Statement::Merge(Merge {
             merge_token,
-            optimizer_hint: _,
+            optimizer_hints: _,
             into: _,
             table: _,
             source: _,

src/dialect/snowflake.rs

@@ -1752,7 +1752,7 @@ fn parse_multi_table_insert(
 
     Ok(Statement::Insert(Insert {
         insert_token: insert_token.into(),
-        optimizer_hint: None,
+        optimizer_hints: vec![],
         or: None,
         ignore: false,
         into: false,

src/parser/merge.rs

@@ -43,7 +43,7 @@ impl Parser<'_> {
 
     /// Parse a `MERGE` statement
     pub fn parse_merge(&mut self, merge_token: TokenWithSpan) -> Result<Merge, ParserError> {
-        let optimizer_hint = self.maybe_parse_optimizer_hint()?;
+        let optimizer_hints = self.maybe_parse_optimizer_hints()?;
         let into = self.parse_keyword(Keyword::INTO);
 
         let table = self.parse_table_factor()?;
@@ -60,7 +60,7 @@ impl Parser<'_> {
 
         Ok(Merge {
             merge_token: merge_token.into(),
-            optimizer_hint,
+            optimizer_hints,
             into,
             table,
             source,