Require FromDatum::from_polymorphic_datum (#749)

* Require `FromDatum::from_polymorphic_datum`

This also implies defaulting `FromDatum::from_datum` which just
calls `FromDatum::from_polymorphic_datum` with `pg_sys::InvalidOid`.
Polymorphic types like AnyElement should generally override this
on implementing, and non-polymorphic types should ignore
the third parameter, while others may want a pass-through behavior.

pgx-examples/bgworker/src/lib.rs

@@ -44,7 +44,7 @@ pub extern "C" fn _PG_init() {
 #[pg_guard]
 #[no_mangle]
 pub extern "C" fn background_worker_main(arg: pg_sys::Datum) {
-    let arg = unsafe { i32::from_datum(arg, false, pg_sys::INT4OID) };
+    let arg = unsafe { i32::from_polymorphic_datum(arg, false, pg_sys::INT4OID) };
 
     // these are the signals we want to receive.  If we don't attach the SIGTERM handler, then
     // we'll never be able to exit via an external notification

pgx-macros/src/lib.rs

@@ -621,7 +621,7 @@ fn impl_postgres_enum(ast: DeriveInput) -> proc_macro2::TokenStream {
     stream.extend(quote! {
         impl ::pgx::datum::FromDatum for #enum_ident {
             #[inline]
-            unsafe fn from_datum(datum: ::pgx::pg_sys::Datum, is_null: bool, typeoid: ::pgx::pg_sys::Oid) -> Option<#enum_ident> {
+            unsafe fn from_polymorphic_datum(datum: ::pgx::pg_sys::Datum, is_null: bool, typeoid: ::pgx::pg_sys::Oid) -> Option<#enum_ident> {
                 if is_null {
                     None
                 } else {

pgx/src/datum/anyarray.rs

@@ -29,20 +29,17 @@ impl AnyArray {
 
     #[inline]
     pub fn into<T: FromDatum>(&self) -> Option<T> {
-        unsafe { T::from_datum(self.datum(), false, self.oid()) }
+        unsafe { T::from_polymorphic_datum(self.datum(), false, self.oid()) }
     }
 }
 
 impl FromDatum for AnyArray {
     const GET_TYPOID: bool = true;
 
     #[inline]
-    unsafe fn from_datum(
-        datum: pg_sys::Datum,
-        is_null: bool,
-        typoid: pg_sys::Oid,
-    ) -> Option<AnyArray> {
-        FromDatum::from_polymorphic_datum(datum, is_null, typoid)
+    unsafe fn from_datum(_datum: pg_sys::Datum, _is_null: bool) -> Option<AnyArray> {
+        debug_assert!(false, "Can't create a polymorphic type using from_datum, call FromDatum::from_polymorphic_datum instead");
+        None
     }
 
     #[inline]

pgx/src/datum/anyelement.rs

@@ -29,20 +29,17 @@ impl AnyElement {
 
     #[inline]
     pub fn into<T: FromDatum>(&self) -> Option<T> {
-        unsafe { T::from_datum(self.datum(), false, self.oid()) }
+        unsafe { T::from_polymorphic_datum(self.datum(), false, self.oid()) }
     }
 }
 
 impl FromDatum for AnyElement {
     const GET_TYPOID: bool = true;
 
     #[inline]
-    unsafe fn from_datum(
-        datum: pg_sys::Datum,
-        is_null: bool,
-        typoid: pg_sys::Oid,
-    ) -> Option<AnyElement> {
-        FromDatum::from_polymorphic_datum(datum, is_null, typoid)
+    unsafe fn from_datum(_datum: pg_sys::Datum, _is_null: bool) -> Option<AnyElement> {
+        debug_assert!(false, "Can't create a polymorphic type using from_datum, call FromDatum::from_polymorphic_datum instead");
+        None
     }
 
     #[inline]

pgx/src/datum/array.rs

@@ -318,7 +318,7 @@ impl<'a, T: FromDatum> Array<'a, T> {
             None
         } else {
             Some(unsafe {
-                T::from_datum(
+                T::from_polymorphic_datum(
                     self.elem_slice[i],
                     self.null_slice.get(i)?,
                     self.raw.as_ref().map(|r| r.oid()).unwrap_or_default(),
@@ -502,18 +502,18 @@ impl<'a, T: FromDatum> Iterator for ArrayIntoIterator<'a, T> {
 
 impl<'a, T: FromDatum> FromDatum for VariadicArray<'a, T> {
     #[inline]
-    unsafe fn from_datum(
+    unsafe fn from_polymorphic_datum(
         datum: pg_sys::Datum,
         is_null: bool,
         oid: pg_sys::Oid,
     ) -> Option<VariadicArray<'a, T>> {
-        Array::from_datum(datum, is_null, oid).map(Self)
+        Array::from_polymorphic_datum(datum, is_null, oid).map(Self)
     }
 }
 
 impl<'a, T: FromDatum> FromDatum for Array<'a, T> {
     #[inline]
-    unsafe fn from_datum(
+    unsafe fn from_polymorphic_datum(
         datum: pg_sys::Datum,
         is_null: bool,
         _typoid: u32,
@@ -536,15 +536,15 @@ impl<'a, T: FromDatum> FromDatum for Array<'a, T> {
 
 impl<T: FromDatum> FromDatum for Vec<T> {
     #[inline]
-    unsafe fn from_datum(
+    unsafe fn from_polymorphic_datum(
         datum: pg_sys::Datum,
         is_null: bool,
         typoid: pg_sys::Oid,
     ) -> Option<Vec<T>> {
         if is_null {
             None
         } else {
-            let array = Array::<T>::from_datum(datum, is_null, typoid).unwrap();
+            let array = Array::<T>::from_polymorphic_datum(datum, is_null, typoid).unwrap();
             let mut v = Vec::with_capacity(array.len());
 
             for element in array.iter() {
@@ -557,15 +557,15 @@ impl<T: FromDatum> FromDatum for Vec<T> {
 
 impl<T: FromDatum> FromDatum for Vec<Option<T>> {
     #[inline]
-    unsafe fn from_datum(
+    unsafe fn from_polymorphic_datum(
         datum: pg_sys::Datum,
         is_null: bool,
         typoid: pg_sys::Oid,
     ) -> Option<Vec<Option<T>>> {
         if is_null || datum.is_null() {
             None
         } else {
-            let array = Array::<T>::from_datum(datum, is_null, typoid).unwrap();
+            let array = Array::<T>::from_polymorphic_datum(datum, is_null, typoid).unwrap();
             let mut v = Vec::with_capacity(array.len());
 
             for element in array.iter() {

pgx/src/datum/date.rs

@@ -38,7 +38,11 @@ impl IntoDatum for Date {
 }
 
 impl FromDatum for Date {
-    unsafe fn from_datum(datum: pg_sys::Datum, is_null: bool, _: pg_sys::Oid) -> Option<Self>
+    unsafe fn from_polymorphic_datum(
+        datum: pg_sys::Datum,
+        is_null: bool,
+        _: pg_sys::Oid,
+    ) -> Option<Self>
     where
         Self: Sized,
     {