Add identifier quote style to Dialect trait (#1170)

src/dialect/mod.rs

@@ -108,6 +108,10 @@ pub trait Dialect: Debug + Any {
     fn is_delimited_identifier_start(&self, ch: char) -> bool {
         ch == '"' || ch == '`'
     }
+    /// Return the character used to quote identifiers.
+    fn identifier_quote_style(&self, _identifier: &str) -> Option<char> {
+        None
+    }
     /// Determine if quoted characters are proper for identifier
     fn is_proper_identifier_inside_quotes(&self, mut _chars: Peekable<Chars<'_>>) -> bool {
         true
@@ -262,6 +266,21 @@ mod tests {
         dialect_from_str(v).unwrap()
     }
 
+    #[test]
+    fn identifier_quote_style() {
+        let tests: Vec<(&dyn Dialect, &str, Option<char>)> = vec![
+            (&GenericDialect {}, "id", None),
+            (&SQLiteDialect {}, "id", Some('`')),
+            (&PostgreSqlDialect {}, "id", Some('"')),
+        ];
+
+        for (dialect, ident, expected) in tests {
+            let actual = dialect.identifier_quote_style(ident);
+
+            assert_eq!(actual, expected);
+        }
+    }
+
     #[test]
     fn parse_with_wrapped_dialect() {
         /// Wrapper for a dialect. In a real-world example, this wrapper
@@ -283,6 +302,10 @@ mod tests {
                 self.0.is_delimited_identifier_start(ch)
             }
 
+            fn identifier_quote_style(&self, identifier: &str) -> Option<char> {
+                self.0.identifier_quote_style(identifier)
+            }
+
             fn is_proper_identifier_inside_quotes(
                 &self,
                 chars: std::iter::Peekable<std::str::Chars<'_>>,

src/dialect/mysql.rs

@@ -44,6 +44,10 @@ impl Dialect for MySqlDialect {
         ch == '`'
     }
 
+    fn identifier_quote_style(&self, _identifier: &str) -> Option<char> {
+        Some('`')
+    }
+
     fn parse_infix(
         &self,
         parser: &mut crate::parser::Parser,

src/dialect/postgresql.rs

@@ -21,6 +21,10 @@ use crate::tokenizer::Token;
 pub struct PostgreSqlDialect {}
 
 impl Dialect for PostgreSqlDialect {
+    fn identifier_quote_style(&self, _identifier: &str) -> Option<char> {
+        Some('"')
+    }
+
     fn is_identifier_start(&self, ch: char) -> bool {
         // See https://www.postgresql.org/docs/11/sql-syntax-lexical.html#SQL-SYNTAX-IDENTIFIERS
         // We don't yet support identifiers beginning with "letters with

src/dialect/sqlite.rs

@@ -32,6 +32,10 @@ impl Dialect for SQLiteDialect {
         ch == '`' || ch == '"' || ch == '['
     }
 
+    fn identifier_quote_style(&self, _identifier: &str) -> Option<char> {
+        Some('`')
+    }
+
     fn is_identifier_start(&self, ch: char) -> bool {
         // See https://www.sqlite.org/draft/tokenreq.html
         ch.is_ascii_lowercase()