Allow qualified type names in cast_as_quoted (#922)

As discussed here:
#827 (comment)

## PR Info

- Closes #827

- Dependencies:
  - #921
  - #953

## Changes

The PR has been updated. The up-to-date description is in the changelog
in the diff.

---

**Original, outdated note:**

Merge after #921. Marking as draft until then. The first commit comes as
a dependency from that PR. If you want to review the diff before merging
that PR, review only the second commit.

Author: Expurple

CHANGELOG.md

@@ -52,6 +52,8 @@ pub struct TableName(pub Option<SchemaName>, pub DynIden);
 
 * Enable `clippy::nursery` https://github.com/SeaQL/sea-query/pull/938
 * Removed unnecessary `'static` bounds from type signatures https://github.com/SeaQL/sea-query/pull/921
+* `cast_as_quoted` now allows you to [qualify the type
+  name](https://github.com/SeaQL/sea-query/issues/827).
 * Most `Value` variants are now unboxed (except `BigDecimal` and `Array`). Previously the size is 24 bytes. https://github.com/SeaQL/sea-query/pull/925
 ```rust
 assert_eq!(std::mem::size_of::<Value>(), 32);
@@ -96,6 +98,11 @@ assert_eq!(
 
 ### Breaking Changes
 
+* Changed `Expr::TypeName(DynIden)` to `Expr::TypeName(TypeName)`, which can be
+  [qualified](https://github.com/SeaQL/sea-query/issues/827).
+
+  If you manually construct this variant and it no longer compiles, just add
+  `.into()`.
 * Removed inherent `SimpleExpr` methods that duplicate `ExprTrait`. If you encounter the following error, please add `use sea_query::ExprTrait` in scope https://github.com/SeaQL/sea-query/pull/890
 ```rust
 error[E0599]: no method named `like` found for enum `sea_query::Expr` in the current scope

src/backend/query_builder.rs

@@ -454,8 +454,8 @@ pub trait QueryBuilder:
             Expr::Constant(val) => {
                 self.prepare_constant(val, sql);
             }
-            Expr::TypeName(iden) => {
-                self.prepare_iden(iden, sql);
+            Expr::TypeName(type_name) => {
+                self.prepare_type_name(type_name, sql);
             }
         }
     }
@@ -910,6 +910,16 @@ pub trait QueryBuilder:
         self.prepare_function_name_common(function, sql)
     }
 
+    /// Translate [`TypeName`] into an SQL statement.
+    fn prepare_type_name(&self, type_name: &TypeName, sql: &mut dyn SqlWriter) {
+        let TypeName(schema_name, r#type) = type_name;
+        if let Some(schema_name) = schema_name {
+            self.prepare_schema_name(schema_name, sql);
+            write!(sql, ".").unwrap();
+        }
+        self.prepare_iden(r#type, sql);
+    }
+
     /// Translate [`JoinType`] into SQL statement.
     fn prepare_join_type(&self, join_type: &JoinType, sql: &mut dyn SqlWriter) {
         self.prepare_join_type_common(join_type, sql)

src/backend/table_ref_builder.rs

@@ -19,14 +19,20 @@ pub trait TableRefBuilder: QuotedBuilder {
     /// Translate [`TableName`] into an SQL statement.
     fn prepare_table_name(&self, table_name: &TableName, sql: &mut dyn SqlWriter) {
         let TableName(schema_name, table) = table_name;
-        if let Some(SchemaName(database_name, schema)) = schema_name {
-            if let Some(DatabaseName(database)) = database_name {
-                self.prepare_iden(database, sql);
-                write!(sql, ".").unwrap();
-            }
-            self.prepare_iden(schema, sql);
+        if let Some(schema_name) = schema_name {
+            self.prepare_schema_name(schema_name, sql);
             write!(sql, ".").unwrap();
         }
         self.prepare_iden(table, sql);
     }
+
+    /// Translate [`SchemaName`] into an SQL statement.
+    fn prepare_schema_name(&self, schema_name: &SchemaName, sql: &mut dyn SqlWriter) {
+        let SchemaName(database_name, schema) = schema_name;
+        if let Some(DatabaseName(database)) = database_name {
+            self.prepare_iden(database, sql);
+            write!(sql, ".").unwrap();
+        }
+        self.prepare_iden(schema, sql);
+    }
 }

src/expr.rs

@@ -43,7 +43,7 @@ pub enum Expr {
     AsEnum(DynIden, Box<Expr>),
     Case(Box<CaseStatement>),
     Constant(Value),
-    TypeName(DynIden),
+    TypeName(TypeName),
 }
 
 /// "Operator" methods for building expressions.

src/func.rs

@@ -476,6 +476,8 @@ impl Func {
 
     /// Call `CAST` function with a case-sensitive custom type.
     ///
+    /// Type can be qualified with a schema name.
+    ///
     /// # Examples
     ///
     /// ```
@@ -497,15 +499,33 @@ impl Func {
     ///     query.to_string(SqliteQueryBuilder),
     ///     r#"SELECT CAST('hello' AS "MyType")"#
     /// );
+    ///
+    /// // Also works with a schema-qualified type name:
+    ///
+    /// let query = Query::select()
+    ///     .expr(Func::cast_as_quoted("hello", ("MySchema", "MyType")))
+    ///     .to_owned();
+    ///
+    /// assert_eq!(
+    ///     query.to_string(MysqlQueryBuilder),
+    ///     r#"SELECT CAST('hello' AS `MySchema`.`MyType`)"#
+    /// );
+    /// assert_eq!(
+    ///     query.to_string(PostgresQueryBuilder),
+    ///     r#"SELECT CAST('hello' AS "MySchema"."MyType")"#
+    /// );
+    /// assert_eq!(
+    ///     query.to_string(SqliteQueryBuilder),
+    ///     r#"SELECT CAST('hello' AS "MySchema"."MyType")"#
+    /// );
     /// ```
-    pub fn cast_as_quoted<V, I>(expr: V, iden: I) -> FunctionCall
+    pub fn cast_as_quoted<V, I>(expr: V, r#type: I) -> FunctionCall
     where
         V: Into<Expr>,
-        I: IntoIden,
+        I: Into<TypeName>,
     {
         let expr: Expr = expr.into();
-        FunctionCall::new(Func::Cast)
-            .arg(expr.binary(BinOper::As, Expr::TypeName(iden.into_iden())))
+        FunctionCall::new(Func::Cast).arg(expr.binary(BinOper::As, Expr::TypeName(r#type.into())))
     }
 
     /// Call `COALESCE` function.

src/types/mod.rs

@@ -146,6 +146,10 @@ pub struct DatabaseName(pub DynIden);
 #[derive(Debug, Clone, PartialEq, Eq, Hash)]
 pub struct SchemaName(pub Option<DatabaseName>, pub DynIden);
 
+/// An SQL type name, potentially qualified as `(database.)(schema.)type`.
+#[derive(Debug, Clone, PartialEq, Eq, Hash)]
+pub struct TypeName(pub Option<SchemaName>, pub DynIden);
+
 /// A table name, potentially qualified as `(database.)(schema.)table`.
 #[derive(Debug, Clone, PartialEq, Eq, Hash)]
 pub struct TableName(pub Option<SchemaName>, pub DynIden);

src/types/qualification.rs

@@ -87,6 +87,21 @@ where
     }
 }
 
+/// Construct a [`TypeName`] from 1-3 parts (`(database?).(schema?).type`)
+impl<T> From<T> for TypeName
+where
+    T: MaybeQualifiedTwice,
+{
+    fn from(value: T) -> Self {
+        let (schema_parts, r#type) = value.into_3_parts();
+        let schema_name = schema_parts.map(|schema_parts| match schema_parts {
+            (Some(db), schema) => SchemaName(Some(DatabaseName(db)), schema),
+            (None, schema) => SchemaName(None, schema),
+        });
+        TypeName(schema_name, r#type)
+    }
+}
+
 /// Construct a [`TableName`] from 1-3 parts (`(database?).(schema?).table`)
 impl<T> From<T> for TableName
 where