refactor: lift type mappings into driver crates

Motivated by #2917

sqlx-core/src/lib.rs

@@ -77,6 +77,7 @@ pub mod query_scalar;
 pub mod row;
 pub mod rt;
 pub mod sync;
+pub mod type_checking;
 pub mod type_info;
 pub mod value;
 

sqlx-core/src/type_checking.rs

@@ -0,0 +1,188 @@
+use crate::database::Database;
+use crate::decode::Decode;
+use crate::type_info::TypeInfo;
+use crate::value::Value;
+use std::any::Any;
+use std::fmt;
+use std::fmt::{Debug, Formatter};
+
+/// The type of query parameter checking done by a SQL database.
+#[derive(PartialEq, Eq)]
+pub enum ParamChecking {
+    /// Parameter checking is weak or nonexistent (uses coercion or allows mismatches).
+    Weak,
+    /// Parameter checking is strong (types must match exactly).
+    Strong,
+}
+
+/// Type-checking extensions for the `Database` trait.
+///
+/// Mostly supporting code for the macros, and for `Debug` impls.
+pub trait TypeChecking: Database {
+    /// Describes how the database in question typechecks query parameters.
+    const PARAM_CHECKING: ParamChecking;
+
+    /// Get the full path of the Rust type that corresponds to the given `TypeInfo`, if applicable.
+    ///
+    /// If the type has a borrowed equivalent suitable for query parameters,
+    /// this is that borrowed type.
+    fn param_type_for_id(id: &Self::TypeInfo) -> Option<&'static str>;
+
+    /// Get the full path of the Rust type that corresponds to the given `TypeInfo`, if applicable.
+    ///
+    /// Always returns the owned version of the type, suitable for decoding from `Row`.
+    fn return_type_for_id(id: &Self::TypeInfo) -> Option<&'static str>;
+
+    /// Get the name of the Cargo feature gate that must be enabled to process the given `TypeInfo`,
+    /// if applicable.
+    fn get_feature_gate(info: &Self::TypeInfo) -> Option<&'static str>;
+
+    /// If `value` is a well-known type, decode and format it using `Debug`.
+    ///
+    /// If `value` is not a well-known type or could not be decoded, the reason is printed instead.
+    fn fmt_value_debug(value: &<Self as Database>::Value) -> FmtValue<'_, Self>;
+}
+
+/// An adapter for [`Value`] which attempts to decode the value and format it when printed using [`Debug`].
+pub struct FmtValue<'v, DB>
+where
+    DB: Database,
+{
+    value: &'v <DB as Database>::Value,
+    fmt: fn(&'v <DB as Database>::Value, &mut Formatter<'_>) -> fmt::Result,
+}
+
+impl<'v, DB> FmtValue<'v, DB>
+where
+    DB: Database,
+{
+    // This API can't take `ValueRef` directly as it would need to pass it to `Decode` by-value,
+    // which means taking ownership of it. We cannot rely on a `Clone` impl because `SqliteValueRef` doesn't have one.
+    /// When printed with [`Debug`], attempt to decode `value` as the given type `T` and format it using [`Debug`].
+    ///
+    /// If `value` could not be decoded as `T`, the reason is printed instead.
+    pub fn debug<T>(value: &'v <DB as Database>::Value) -> Self
+    where
+        T: Decode<'v, DB> + Debug + Any,
+    {
+        Self {
+            value,
+            fmt: |value, f| {
+                let info = value.type_info();
+
+                match T::decode(value.as_ref()) {
+                    Ok(value) => Debug::fmt(&value, f),
+                    Err(e) => f.write_fmt(format_args!(
+                        "(error decoding SQL type {} as {}: {e:?})",
+                        info.name(),
+                        std::any::type_name::<T>()
+                    )),
+                }
+            },
+        }
+    }
+
+    /// If the type to be decoded is not known or not supported, print the SQL type instead,
+    /// as well as any applicable SQLx feature that needs to be enabled.
+    pub fn unknown(value: &'v <DB as Database>::Value) -> Self
+    where
+        DB: TypeChecking,
+    {
+        Self {
+            value,
+            fmt: |value, f| {
+                let info = value.type_info();
+
+                if let Some(feature_gate) = <DB as TypeChecking>::get_feature_gate(&info) {
+                    return f.write_fmt(format_args!(
+                        "(unknown SQL type {}: SQLx feature {feature_gate} not enabled)",
+                        info.name()
+                    ));
+                }
+
+                f.write_fmt(format_args!("(unknown SQL type {})", info.name()))
+            },
+        }
+    }
+}
+
+impl<'v, DB> Debug for FmtValue<'v, DB>
+where
+    DB: Database,
+{
+    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
+        (self.fmt)(&self.value, f)
+    }
+}
+
+#[doc(hidden)]
+#[macro_export]
+macro_rules! select_input_type {
+    ($ty:ty, $input:ty) => {
+        stringify!($input)
+    };
+    ($ty:ty) => {
+        stringify!($ty)
+    };
+}
+
+#[macro_export]
+macro_rules! impl_type_checking {
+    (
+        $database:path {
+            $($(#[$meta:meta])? $ty:ty $(| $input:ty)?),*$(,)?
+        },
+        ParamChecking::$param_checking:ident,
+        feature-types: $ty_info:ident => $get_gate:expr,
+    ) => {
+        impl $crate::type_checking::TypeChecking for $database {
+            const PARAM_CHECKING: $crate::type_checking::ParamChecking = $crate::type_checking::ParamChecking::$param_checking;
+
+            fn param_type_for_id(info: &Self::TypeInfo) -> Option<&'static str> {
+                match () {
+                    $(
+                        $(#[$meta])?
+                        _ if <$ty as sqlx_core::types::Type<$database>>::type_info() == *info => Some($crate::select_input_type!($ty $(, $input)?)),
+                    )*
+                    $(
+                        $(#[$meta])?
+                        _ if <$ty as sqlx_core::types::Type<$database>>::compatible(info) => Some(select_input_type!($ty $(, $input)?)),
+                    )*
+                    _ => None
+                }
+            }
+
+            fn return_type_for_id(info: &Self::TypeInfo) -> Option<&'static str> {
+                match () {
+                    $(
+                        $(#[$meta])?
+                        _ if <$ty as sqlx_core::types::Type<$database>>::type_info() == *info => Some(stringify!($ty)),
+                    )*
+                    $(
+                        $(#[$meta])?
+                        _ if <$ty as sqlx_core::types::Type<$database>>::compatible(info) => Some(stringify!($ty)),
+                    )*
+                    _ => None
+                }
+            }
+
+            fn get_feature_gate($ty_info: &Self::TypeInfo) -> Option<&'static str> {
+                $get_gate
+            }
+
+            fn fmt_value_debug(value: &Self::Value) -> $crate::type_checking::FmtValue<Self> {
+                use $crate::value::Value;
+
+                let info = value.type_info();
+
+                match () {
+                    $(
+                        $(#[$meta])?
+                        _ if <$ty as sqlx_core::types::Type<$database>>::compatible(&info) => $crate::type_checking::FmtValue::debug::<$ty>(value),
+                    )*
+                    _ => $crate::type_checking::FmtValue::unknown(value),
+                }
+            }
+        }
+    };
+}

sqlx-macros-core/src/database/impls.rs

@@ -0,0 +1,71 @@
+macro_rules! impl_database_ext {
+    (
+        $database:path,
+        row: $row:path,
+        $(describe-blocking: $describe:path,)?
+    ) => {
+        impl $crate::database::DatabaseExt for $database {
+            const DATABASE_PATH: &'static str = stringify!($database);
+            const ROW_PATH: &'static str = stringify!($row);
+            impl_describe_blocking!($database, $($describe)?);
+        }
+    }
+}
+
+macro_rules! impl_describe_blocking {
+    ($database:path $(,)?) => {
+        fn describe_blocking(
+            query: &str,
+            database_url: &str,
+        ) -> sqlx_core::Result<sqlx_core::describe::Describe<Self>> {
+            use $crate::database::CachingDescribeBlocking;
+
+            // This can't be a provided method because the `static` can't reference `Self`.
+            static CACHE: CachingDescribeBlocking<$database> = CachingDescribeBlocking::new();
+
+            CACHE.describe(query, database_url)
+        }
+    };
+    ($database:path, $describe:path) => {
+        fn describe_blocking(
+            query: &str,
+            database_url: &str,
+        ) -> sqlx_core::Result<sqlx_core::describe::Describe<Self>> {
+            $describe(query, database_url)
+        }
+    };
+}
+
+// The paths below will also be emitted from the macros, so they need to match the final facade.
+mod sqlx {
+    #[cfg(feature = "mysql")]
+    pub use sqlx_mysql as mysql;
+
+    #[cfg(feature = "postgres")]
+    pub use sqlx_postgres as postgres;
+
+    #[cfg(feature = "sqlite")]
+    pub use sqlx_sqlite as sqlite;
+}
+
+// NOTE: type mappings have been moved to `src/type_checking.rs` in their respective driver crates.
+#[cfg(feature = "mysql")]
+impl_database_ext! {
+    sqlx::mysql::MySql,
+    row: sqlx::mysql::MySqlRow,
+}
+
+#[cfg(feature = "postgres")]
+impl_database_ext! {
+    sqlx::postgres::Postgres,
+    row: sqlx::postgres::PgRow,
+}
+
+#[cfg(feature = "sqlite")]
+impl_database_ext! {
+    sqlx::sqlite::Sqlite,
+    row: sqlx::sqlite::SqliteRow,
+    // Since proc-macros don't benefit from async, we can make a describe call directly
+    // which also ensures that the database is closed afterwards, regardless of errors.
+    describe-blocking: sqlx_sqlite::describe_blocking,
+}