Add ability for dialects to override prefix, infix, and statement parsing (#581)

src/dialect/mod.rs

@@ -22,6 +22,7 @@ mod redshift;
 mod snowflake;
 mod sqlite;
 
+use crate::ast::{Expr, Statement};
 use core::any::{Any, TypeId};
 use core::fmt::Debug;
 use core::iter::Peekable;
@@ -39,6 +40,7 @@ pub use self::redshift::RedshiftSqlDialect;
 pub use self::snowflake::SnowflakeDialect;
 pub use self::sqlite::SQLiteDialect;
 pub use crate::keywords;
+use crate::parser::{Parser, ParserError};
 
 /// `dialect_of!(parser is SQLiteDialect |  GenericDialect)` evaluates
 /// to `true` if `parser.dialect` is one of the `Dialect`s specified.
@@ -65,6 +67,31 @@ pub trait Dialect: Debug + Any {
     fn is_identifier_start(&self, ch: char) -> bool;
     /// Determine if a character is a valid unquoted identifier character
     fn is_identifier_part(&self, ch: char) -> bool;
+    /// Dialect-specific prefix parser override
+    fn parse_prefix(&self, _parser: &mut Parser) -> Option<Result<Expr, ParserError>> {
+        // return None to fall back to the default behavior
+        None
+    }
+    /// Dialect-specific infix parser override
+    fn parse_infix(
+        &self,
+        _parser: &mut Parser,
+        _expr: &Expr,
+        _precendence: u8,
+    ) -> Option<Result<Expr, ParserError>> {
+        // return None to fall back to the default behavior
+        None
+    }
+    /// Dialect-specific precedence override
+    fn get_next_precedence(&self, _parser: &Parser) -> Option<Result<u8, ParserError>> {
+        // return None to fall back to the default behavior
+        None
+    }
+    /// Dialect-specific statement parser override
+    fn parse_statement(&self, _parser: &mut Parser) -> Option<Result<Statement, ParserError>> {
+        // return None to fall back to the default behavior
+        None
+    }
 }
 
 impl dyn Dialect {

src/dialect/postgresql.rs

@@ -10,7 +10,11 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+use crate::ast::{CommentObject, Statement};
 use crate::dialect::Dialect;
+use crate::keywords::Keyword;
+use crate::parser::{Parser, ParserError};
+use crate::tokenizer::Token;
 
 #[derive(Debug)]
 pub struct PostgreSqlDialect {}
@@ -30,4 +34,41 @@ impl Dialect for PostgreSqlDialect {
             || ch == '$'
             || ch == '_'
     }
+
+    fn parse_statement(&self, parser: &mut Parser) -> Option<Result<Statement, ParserError>> {
+        if parser.parse_keyword(Keyword::COMMENT) {
+            Some(parse_comment(parser))
+        } else {
+            None
+        }
+    }
+}
+
+pub fn parse_comment(parser: &mut Parser) -> Result<Statement, ParserError> {
+    parser.expect_keyword(Keyword::ON)?;
+    let token = parser.next_token();
+
+    let (object_type, object_name) = match token {
+        Token::Word(w) if w.keyword == Keyword::COLUMN => {
+            let object_name = parser.parse_object_name()?;
+            (CommentObject::Column, object_name)
+        }
+        Token::Word(w) if w.keyword == Keyword::TABLE => {
+            let object_name = parser.parse_object_name()?;
+            (CommentObject::Table, object_name)
+        }
+        _ => parser.expected("comment object_type", token)?,
+    };
+
+    parser.expect_keyword(Keyword::IS)?;
+    let comment = if parser.parse_keyword(Keyword::NULL) {
+        None
+    } else {
+        Some(parser.parse_literal_string()?)
+    };
+    Ok(Statement::Comment {
+        object_type,
+        object_name,
+        comment,
+    })
 }

src/dialect/sqlite.rs

@@ -10,7 +10,10 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+use crate::ast::Statement;
 use crate::dialect::Dialect;
+use crate::keywords::Keyword;
+use crate::parser::{Parser, ParserError};
 
 #[derive(Debug)]
 pub struct SQLiteDialect {}
@@ -35,4 +38,13 @@ impl Dialect for SQLiteDialect {
     fn is_identifier_part(&self, ch: char) -> bool {
         self.is_identifier_start(ch) || ('0'..='9').contains(&ch)
     }
+
+    fn parse_statement(&self, parser: &mut Parser) -> Option<Result<Statement, ParserError>> {
+        if parser.parse_keyword(Keyword::REPLACE) {
+            parser.prev_token();
+            Some(parser.parse_insert())
+        } else {
+            None
+        }
+    }
 }

src/parser.rs

@@ -152,6 +152,11 @@ impl<'a> Parser<'a> {
     /// Parse a single top-level statement (such as SELECT, INSERT, CREATE, etc.),
     /// stopping before the statement separator, if any.
     pub fn parse_statement(&mut self) -> Result<Statement, ParserError> {
+        // allow the dialect to override statement parsing
+        if let Some(statement) = self.dialect.parse_statement(self) {
+            return statement;
+        }
+
         match self.next_token() {
             Token::Word(w) => match w.keyword {
                 Keyword::KILL => Ok(self.parse_kill()?),
@@ -195,13 +200,6 @@ impl<'a> Parser<'a> {
                 Keyword::EXECUTE => Ok(self.parse_execute()?),
                 Keyword::PREPARE => Ok(self.parse_prepare()?),
                 Keyword::MERGE => Ok(self.parse_merge()?),
-                Keyword::REPLACE if dialect_of!(self is SQLiteDialect ) => {
-                    self.prev_token();
-                    Ok(self.parse_insert()?)
-                }
-                Keyword::COMMENT if dialect_of!(self is PostgreSqlDialect) => {
-                    Ok(self.parse_comment()?)
-                }
                 _ => self.expected("an SQL statement", Token::Word(w)),
             },
             Token::LParen => {
@@ -381,6 +379,11 @@ impl<'a> Parser<'a> {
 
     /// Parse an expression prefix
     pub fn parse_prefix(&mut self) -> Result<Expr, ParserError> {
+        // allow the dialect to override prefix parsing
+        if let Some(prefix) = self.dialect.parse_prefix(self) {
+            return prefix;
+        }
+
         // PostgreSQL allows any string literal to be preceded by a type name, indicating that the
         // string literal represents a literal of that type. Some examples:
         //
@@ -1164,6 +1167,11 @@ impl<'a> Parser<'a> {
 
     /// Parse an operator following an expression
     pub fn parse_infix(&mut self, expr: Expr, precedence: u8) -> Result<Expr, ParserError> {
+        // allow the dialect to override infix parsing
+        if let Some(infix) = self.dialect.parse_infix(self, &expr, precedence) {
+            return infix;
+        }
+
         let tok = self.next_token();
 
         let regular_binary_operator = match &tok {
@@ -1491,6 +1499,11 @@ impl<'a> Parser<'a> {
 
     /// Get the precedence of the next token
     pub fn get_next_precedence(&self) -> Result<u8, ParserError> {
+        // allow the dialect to override precedence logic
+        if let Some(precedence) = self.dialect.get_next_precedence(self) {
+            return precedence;
+        }
+
         let token = self.peek_token();
         debug!("get_next_precedence() {:?}", token);
         let token_0 = self.peek_nth_token(0);
@@ -1618,7 +1631,7 @@ impl<'a> Parser<'a> {
     }
 
     /// Report unexpected token
-    fn expected<T>(&self, expected: &str, found: Token) -> Result<T, ParserError> {
+    pub fn expected<T>(&self, expected: &str, found: Token) -> Result<T, ParserError> {
         parser_err!(format!("Expected {}, found: {}", expected, found))
     }
 
@@ -4735,35 +4748,6 @@ impl<'a> Parser<'a> {
         })
     }
 
-    pub fn parse_comment(&mut self) -> Result<Statement, ParserError> {
-        self.expect_keyword(Keyword::ON)?;
-        let token = self.next_token();
-
-        let (object_type, object_name) = match token {
-            Token::Word(w) if w.keyword == Keyword::COLUMN => {
-                let object_name = self.parse_object_name()?;
-                (CommentObject::Column, object_name)
-            }
-            Token::Word(w) if w.keyword == Keyword::TABLE => {
-                let object_name = self.parse_object_name()?;
-                (CommentObject::Table, object_name)
-            }
-            _ => self.expected("comment object_type", token)?,
-        };
-
-        self.expect_keyword(Keyword::IS)?;
-        let comment = if self.parse_keyword(Keyword::NULL) {
-            None
-        } else {
-            Some(self.parse_literal_string()?)
-        };
-        Ok(Statement::Comment {
-            object_type,
-            object_name,
-            comment,
-        })
-    }
-
     pub fn parse_merge_clauses(&mut self) -> Result<Vec<MergeClause>, ParserError> {
         let mut clauses: Vec<MergeClause> = vec![];
         loop {

tests/sqlparser_custom_dialect.rs

@@ -0,0 +1,138 @@
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//! Test the ability for dialects to override parsing
+
+use sqlparser::{
+    ast::{BinaryOperator, Expr, Statement, Value},
+    dialect::Dialect,
+    keywords::Keyword,
+    parser::{Parser, ParserError},
+    tokenizer::Token,
+};
+
+#[test]
+fn custom_prefix_parser() -> Result<(), ParserError> {
+    #[derive(Debug)]
+    struct MyDialect {}
+
+    impl Dialect for MyDialect {
+        fn is_identifier_start(&self, ch: char) -> bool {
+            is_identifier_start(ch)
+        }
+
+        fn is_identifier_part(&self, ch: char) -> bool {
+            is_identifier_part(ch)
+        }
+
+        fn parse_prefix(&self, parser: &mut Parser) -> Option<Result<Expr, ParserError>> {
+            if parser.consume_token(&Token::Number("1".to_string(), false)) {
+                Some(Ok(Expr::Value(Value::Null)))
+            } else {
+                None
+            }
+        }
+    }
+
+    let dialect = MyDialect {};
+    let sql = "SELECT 1 + 2";
+    let ast = Parser::parse_sql(&dialect, sql)?;
+    let query = &ast[0];
+    assert_eq!("SELECT NULL + 2", &format!("{}", query));
+    Ok(())
+}
+
+#[test]
+fn custom_infix_parser() -> Result<(), ParserError> {
+    #[derive(Debug)]
+    struct MyDialect {}
+
+    impl Dialect for MyDialect {
+        fn is_identifier_start(&self, ch: char) -> bool {
+            is_identifier_start(ch)
+        }
+
+        fn is_identifier_part(&self, ch: char) -> bool {
+            is_identifier_part(ch)
+        }
+
+        fn parse_infix(
+            &self,
+            parser: &mut Parser,
+            expr: &Expr,
+            _precendence: u8,
+        ) -> Option<Result<Expr, ParserError>> {
+            if parser.consume_token(&Token::Plus) {
+                Some(Ok(Expr::BinaryOp {
+                    left: Box::new(expr.clone()),
+                    op: BinaryOperator::Multiply, // translate Plus to Multiply
+                    right: Box::new(parser.parse_expr().unwrap()),
+                }))
+            } else {
+                None
+            }
+        }
+    }
+
+    let dialect = MyDialect {};
+    let sql = "SELECT 1 + 2";
+    let ast = Parser::parse_sql(&dialect, sql)?;
+    let query = &ast[0];
+    assert_eq!("SELECT 1 * 2", &format!("{}", query));
+    Ok(())
+}
+
+#[test]
+fn custom_statement_parser() -> Result<(), ParserError> {
+    #[derive(Debug)]
+    struct MyDialect {}
+
+    impl Dialect for MyDialect {
+        fn is_identifier_start(&self, ch: char) -> bool {
+            is_identifier_start(ch)
+        }
+
+        fn is_identifier_part(&self, ch: char) -> bool {
+            is_identifier_part(ch)
+        }
+
+        fn parse_statement(&self, parser: &mut Parser) -> Option<Result<Statement, ParserError>> {
+            if parser.parse_keyword(Keyword::SELECT) {
+                for _ in 0..3 {
+                    let _ = parser.next_token();
+                }
+                Some(Ok(Statement::Commit { chain: false }))
+            } else {
+                None
+            }
+        }
+    }
+
+    let dialect = MyDialect {};
+    let sql = "SELECT 1 + 2";
+    let ast = Parser::parse_sql(&dialect, sql)?;
+    let query = &ast[0];
+    assert_eq!("COMMIT", &format!("{}", query));
+    Ok(())
+}
+
+fn is_identifier_start(ch: char) -> bool {
+    ('a'..='z').contains(&ch) || ('A'..='Z').contains(&ch) || ch == '_'
+}
+
+fn is_identifier_part(ch: char) -> bool {
+    ('a'..='z').contains(&ch)
+        || ('A'..='Z').contains(&ch)
+        || ('0'..='9').contains(&ch)
+        || ch == '$'
+        || ch == '_'
+}