fix: Handle double quotes inside quoted identifiers correctly

This fixes apache#410 for standard SQL, however I don't know enough about other dialects to know if they
handle this differently. May need more extensive testing as well.

Author: Markus Westerlind

src/ast/mod.rs

@@ -23,7 +23,7 @@ use alloc::{
     string::{String, ToString},
     vec::Vec,
 };
-use core::fmt;
+use core::fmt::{self, Write};
 
 #[cfg(feature = "serde")]
 use serde::{Deserialize, Serialize};
@@ -127,7 +127,18 @@ impl From<&str> for Ident {
 impl fmt::Display for Ident {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match self.quote_style {
-            Some(q) if q == '"' || q == '\'' || q == '`' => write!(f, "{}{}{}", q, self.value, q),
+            Some(q) if q == '"' || q == '\'' || q == '`' => {
+                f.write_char(q)?;
+                let mut first = true;
+                for s in self.value.split_inclusive(q) {
+                    if !first {
+                        f.write_char(q)?;
+                    }
+                    first = false;
+                    f.write_str(s)?;
+                }
+                f.write_char(q)
+            }
             Some(q) if q == '[' => write!(f, "[{}]", self.value),
             None => f.write_str(&self.value),
             _ => panic!("unexpected quote style"),

src/tokenizer.rs

@@ -418,8 +418,26 @@ impl<'a> Tokenizer<'a> {
                 quote_start if self.dialect.is_delimited_identifier_start(quote_start) => {
                     chars.next(); // consume the opening quote
                     let quote_end = Word::matching_end_quote(quote_start);
-                    let s = peeking_take_while(chars, |ch| ch != quote_end);
-                    if chars.next() == Some(quote_end) {
+                    let mut last_char = None;
+                    let s = {
+                        let mut s = String::new();
+                        while let Some(ch) = chars.next() {
+                            if ch == quote_end {
+                                if chars.peek() == Some(&quote_end) {
+                                    chars.next();
+                                    s.push(ch);
+                                } else {
+                                    last_char = Some(quote_end);
+                                    break;
+                                }
+                            } else {
+                                s.push(ch);
+                            }
+                        }
+                        s
+                    };
+
+                    if last_char == Some(quote_end) {
                         Ok(Some(Token::make_word(&s, Some(quote_start))))
                     } else {
                         self.tokenizer_error(format!(

tests/sqlparser_postgres.rs

@@ -834,6 +834,11 @@ fn parse_comments() {
     }
 }
 
+#[test]
+fn parse_quoted_identifier() {
+    pg_and_generic().verified_stmt(r#"SELECT "quoted "" ident""#);
+}
+
 fn pg() -> TestedDialects {
     TestedDialects {
         dialects: vec![Box::new(PostgreSqlDialect {})],