Query parser: encode ?? as ?

src/query.rs

@@ -45,7 +45,7 @@ impl Query {
     /// during query execution (`execute()`, `fetch()` etc).
     ///
     /// WARNING: This means that the query must not have any extra `?`, even if
-    /// they are in a string literal!
+    /// they are in a string literal! Use `??` to have plain `?` in query.
     ///
     /// [`Serialize`]: serde::Serialize
     /// [`Identifier`]: crate::sql::Identifier

src/sql/mod.rs

@@ -21,6 +21,7 @@ pub(crate) enum SqlBuilder {
 pub(crate) enum Part {
     Arg,
     Fields,
+    Str(&'static str),
     Text(String),
 }
 
@@ -45,20 +46,28 @@ impl fmt::Display for SqlBuilder {
 
 impl SqlBuilder {
     pub(crate) fn new(template: &str) -> Self {
-        let mut iter = template.split('?');
-        let prefix = String::from(iter.next().unwrap());
-        let mut parts = vec![Part::Text(prefix)];
+        let mut parts = Vec::new();
+        let mut rest = template;
+        while let Some(idx) = rest.find('?') {
+            if rest[idx + 1..].starts_with('?') {
+                parts.push(Part::Text(rest[..idx + 1].to_string()));
+                rest = &rest[idx + 2..];
+                continue;
+            } else if idx != 0 {
+                parts.push(Part::Text(rest[..idx].to_string()));
+            }
 
-        for s in iter {
-            let text = if let Some(text) = s.strip_prefix("fields") {
+            rest = &rest[idx + 1..];
+            if let Some(restfields) = rest.strip_prefix("fields") {
                 parts.push(Part::Fields);
-                text
+                rest = restfields;
             } else {
                 parts.push(Part::Arg);
-                s
-            };
+            }
+        }
 
-            parts.push(Part::Text(text.into()));
+        if !rest.is_empty() {
+            parts.push(Part::Text(rest.to_string()));
         }
 
         SqlBuilder::InProgress(parts)
@@ -96,16 +105,12 @@ impl SqlBuilder {
         }
     }
 
-    pub(crate) fn append(&mut self, suffix: &str) {
+    pub(crate) fn append(&mut self, suffix: &'static str) {
         let Self::InProgress(parts) = self else {
             return;
         };
 
-        if let Some(Part::Text(text)) = parts.last_mut() {
-            text.push_str(suffix);
-        } else {
-            // Do nothing, it will fail in `finish()`.
-        }
+        parts.push(Part::Str(suffix));
     }
 
     pub(crate) fn finish(mut self) -> Result<String> {
@@ -114,6 +119,7 @@ impl SqlBuilder {
         if let Self::InProgress(parts) = &self {
             for part in parts {
                 match part {
+                    Part::Str(text) => sql.push_str(text),
                     Part::Text(text) => sql.push_str(text),
                     Part::Arg => {
                         self.error("unbound query argument");
@@ -223,6 +229,15 @@ mod tests {
         );
     }
 
+    #[test]
+    fn question_escape() {
+        let sql = SqlBuilder::new("SELECT 1 FROM test WHERE a IN 'a??b'");
+        assert_eq!(
+            sql.finish().unwrap(),
+            r"SELECT 1 FROM test WHERE a IN 'a?b'"
+        );
+    }
+
     #[test]
     fn option_as_null() {
         let mut sql = SqlBuilder::new("SELECT 1 FROM test WHERE a = ?");