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>

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"
+    );
+}