feat: Support escaped string literals (PostgreSQL) (#502)

* feat: Support escaped string literals (PostgreSQL)

Signed-off-by: Dmitry Patsura <talk@dmtry.me>

* lint

* escape ', \r, \t

* Update src/ast/value.rs

Co-authored-by: Andrew Lamb <andrew@nerdnetworks.org>

* Update src/tokenizer.rs

Co-authored-by: Andrew Lamb <andrew@nerdnetworks.org>

* test: two slashes

* remove dead code

* test: parsing error

* support generic dialect too (for DF)

Co-authored-by: Andrew Lamb <andrew@nerdnetworks.org>

src/ast/value.rs

@@ -30,6 +30,9 @@ pub enum Value {
     Number(BigDecimal, bool),
     /// 'string value'
     SingleQuotedString(String),
+    /// e'string value' (postgres extension)
+    /// <https://www.postgresql.org/docs/8.3/sql-syntax-lexical.html#SQL-SYNTAX-STRINGS
+    EscapedStringLiteral(String),
     /// N'string value'
     NationalStringLiteral(String),
     /// X'hex value'
@@ -69,6 +72,7 @@ impl fmt::Display for Value {
             Value::Number(v, l) => write!(f, "{}{long}", v, long = if *l { "L" } else { "" }),
             Value::DoubleQuotedString(v) => write!(f, "\"{}\"", v),
             Value::SingleQuotedString(v) => write!(f, "'{}'", escape_single_quote_string(v)),
+            Value::EscapedStringLiteral(v) => write!(f, "E'{}'", escape_escaped_string(v)),
             Value::NationalStringLiteral(v) => write!(f, "N'{}'", v),
             Value::HexStringLiteral(v) => write!(f, "X'{}'", v),
             Value::Boolean(v) => write!(f, "{}", v),
@@ -193,6 +197,40 @@ pub fn escape_single_quote_string(s: &str) -> EscapeSingleQuoteString<'_> {
     EscapeSingleQuoteString(s)
 }
 
+pub struct EscapeEscapedStringLiteral<'a>(&'a str);
+
+impl<'a> fmt::Display for EscapeEscapedStringLiteral<'a> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        for c in self.0.chars() {
+            match c {
+                '\'' => {
+                    write!(f, r#"\'"#)?;
+                }
+                '\\' => {
+                    write!(f, r#"\\"#)?;
+                }
+                '\n' => {
+                    write!(f, r#"\n"#)?;
+                }
+                '\t' => {
+                    write!(f, r#"\t"#)?;
+                }
+                '\r' => {
+                    write!(f, r#"\r"#)?;
+                }
+                _ => {
+                    write!(f, "{}", c)?;
+                }
+            }
+        }
+        Ok(())
+    }
+}
+
+pub fn escape_escaped_string(s: &str) -> EscapeEscapedStringLiteral<'_> {
+    EscapeEscapedStringLiteral(s)
+}
+
 #[derive(Debug, Clone, PartialEq, Eq, Hash)]
 #[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
 pub enum TrimWhereField {

src/parser.rs

@@ -497,6 +497,11 @@ impl<'a> Parser<'a> {
                     expr: Box::new(self.parse_subexpr(Self::PLUS_MINUS_PREC)?),
                 })
             }
+            Token::EscapedStringLiteral(_) if dialect_of!(self is PostgreSqlDialect | GenericDialect) =>
+            {
+                self.prev_token();
+                Ok(Expr::Value(self.parse_value()?))
+            }
             Token::Number(_, _)
             | Token::SingleQuotedString(_)
             | Token::NationalStringLiteral(_)
@@ -902,6 +907,7 @@ impl<'a> Parser<'a> {
                         None
                     }
                     Token::SingleQuotedString(_)
+                    | Token::EscapedStringLiteral(_)
                     | Token::NationalStringLiteral(_)
                     | Token::HexStringLiteral(_) => Some(Box::new(self.parse_expr()?)),
                     unexpected => {
@@ -2576,6 +2582,7 @@ impl<'a> Parser<'a> {
             },
             Token::SingleQuotedString(ref s) => Ok(Value::SingleQuotedString(s.to_string())),
             Token::NationalStringLiteral(ref s) => Ok(Value::NationalStringLiteral(s.to_string())),
+            Token::EscapedStringLiteral(ref s) => Ok(Value::EscapedStringLiteral(s.to_string())),
             Token::HexStringLiteral(ref s) => Ok(Value::HexStringLiteral(s.to_string())),
             Token::Placeholder(ref s) => Ok(Value::Placeholder(s.to_string())),
             unexpected => self.expected("a value", unexpected),
@@ -2607,6 +2614,9 @@ impl<'a> Parser<'a> {
         match self.next_token() {
             Token::Word(Word { value, keyword, .. }) if keyword == Keyword::NoKeyword => Ok(value),
             Token::SingleQuotedString(s) => Ok(s),
+            Token::EscapedStringLiteral(s) if dialect_of!(self is PostgreSqlDialect | GenericDialect) => {
+                Ok(s)
+            }
             unexpected => self.expected("literal string", unexpected),
         }
     }

src/tokenizer.rs

@@ -51,6 +51,8 @@ pub enum Token {
     SingleQuotedString(String),
     /// "National" string literal: i.e: N'string'
     NationalStringLiteral(String),
+    /// "escaped" string literal, which are an extension to the SQL standard: i.e: e'first \n second' or E 'first \n second'
+    EscapedStringLiteral(String),
     /// Hexadecimal string literal: i.e.: X'deadbeef'
     HexStringLiteral(String),
     /// Comma
@@ -160,6 +162,7 @@ impl fmt::Display for Token {
             Token::Char(ref c) => write!(f, "{}", c),
             Token::SingleQuotedString(ref s) => write!(f, "'{}'", s),
             Token::NationalStringLiteral(ref s) => write!(f, "N'{}'", s),
+            Token::EscapedStringLiteral(ref s) => write!(f, "E'{}'", s),
             Token::HexStringLiteral(ref s) => write!(f, "X'{}'", s),
             Token::Comma => f.write_str(","),
             Token::Whitespace(ws) => write!(f, "{}", ws),
@@ -392,6 +395,21 @@ impl<'a> Tokenizer<'a> {
                         }
                     }
                 }
+                // PostgreSQL accepts "escape" string constants, which are an extension to the SQL standard.
+                x @ 'e' | x @ 'E' => {
+                    chars.next(); // consume, to check the next char
+                    match chars.peek() {
+                        Some('\'') => {
+                            let s = self.tokenize_escaped_single_quoted_string(chars)?;
+                            Ok(Some(Token::EscapedStringLiteral(s)))
+                        }
+                        _ => {
+                            // regular identifier starting with an "E" or "e"
+                            let s = self.tokenize_word(x, chars);
+                            Ok(Some(Token::make_word(&s, None)))
+                        }
+                    }
+                }
                 // The spec only allows an uppercase 'X' to introduce a hex
                 // string, but PostgreSQL, at least, allows a lowercase 'x' too.
                 x @ 'x' | x @ 'X' => {
@@ -690,6 +708,66 @@ impl<'a> Tokenizer<'a> {
         s
     }
 
+    /// Read a single quoted string, starting with the opening quote.
+    fn tokenize_escaped_single_quoted_string(
+        &self,
+        chars: &mut Peekable<Chars<'_>>,
+    ) -> Result<String, TokenizerError> {
+        let mut s = String::new();
+        chars.next(); // consume the opening quote
+
+        // slash escaping
+        let mut is_escaped = false;
+        while let Some(&ch) = chars.peek() {
+            macro_rules! escape_control_character {
+                ($ESCAPED:expr) => {{
+                    if is_escaped {
+                        s.push($ESCAPED);
+                        is_escaped = false;
+                    } else {
+                        s.push(ch);
+                    }
+
+                    chars.next();
+                }};
+            }
+
+            match ch {
+                '\'' => {
+                    chars.next(); // consume
+                    if is_escaped {
+                        s.push(ch);
+                        is_escaped = false;
+                    } else if chars.peek().map(|c| *c == '\'').unwrap_or(false) {
+                        s.push(ch);
+                        chars.next();
+                    } else {
+                        return Ok(s);
+                    }
+                }
+                '\\' => {
+                    if is_escaped {
+                        s.push('\\');
+                        is_escaped = false;
+                    } else {
+                        is_escaped = true;
+                    }
+
+                    chars.next();
+                }
+                'r' => escape_control_character!('\r'),
+                'n' => escape_control_character!('\n'),
+                't' => escape_control_character!('\t'),
+                _ => {
+                    is_escaped = false;
+                    chars.next(); // consume
+                    s.push(ch);
+                }
+            }
+        }
+        self.tokenizer_error("Unterminated encoded string literal")
+    }
+
     /// Read a single quoted string, starting with the opening quote.
     fn tokenize_single_quoted_string(
         &self,

tests/sqlparser_postgres.rs

@@ -1467,3 +1467,44 @@ fn pg_and_generic() -> TestedDialects {
         dialects: vec![Box::new(PostgreSqlDialect {}), Box::new(GenericDialect {})],
     }
 }
+
+#[test]
+fn parse_escaped_literal_string() {
+    let sql =
+        r#"SELECT E's1 \n s1', E's2 \\n s2', E's3 \\\n s3', E's4 \\\\n s4', E'\'', E'foo \\'"#;
+    let select = pg_and_generic().verified_only_select(sql);
+    assert_eq!(6, select.projection.len());
+    assert_eq!(
+        &Expr::Value(Value::EscapedStringLiteral("s1 \n s1".to_string())),
+        expr_from_projection(&select.projection[0])
+    );
+    assert_eq!(
+        &Expr::Value(Value::EscapedStringLiteral("s2 \\n s2".to_string())),
+        expr_from_projection(&select.projection[1])
+    );
+    assert_eq!(
+        &Expr::Value(Value::EscapedStringLiteral("s3 \\\n s3".to_string())),
+        expr_from_projection(&select.projection[2])
+    );
+    assert_eq!(
+        &Expr::Value(Value::EscapedStringLiteral("s4 \\\\n s4".to_string())),
+        expr_from_projection(&select.projection[3])
+    );
+    assert_eq!(
+        &Expr::Value(Value::EscapedStringLiteral("'".to_string())),
+        expr_from_projection(&select.projection[4])
+    );
+    assert_eq!(
+        &Expr::Value(Value::EscapedStringLiteral("foo \\".to_string())),
+        expr_from_projection(&select.projection[5])
+    );
+
+    let sql = r#"SELECT E'\'"#;
+    assert_eq!(
+        pg_and_generic()
+            .parse_sql_statements(sql)
+            .unwrap_err()
+            .to_string(),
+        "sql parser error: Unterminated encoded string literal at Line: 1, Column 8"
+    );
+}