WIP: Add support for PostgreSQL 12 (except FDW)

PostgreSQL 12 brings changes to FunctionCallInfoData (the way arguments
are passed to functions) and the FDW API.

This pull request:
* Implements support for the new call interface (keeping backwards
  compatibility).
* Disables FDW support in PostgreSQL 12.

Upstream commit:
postgres/postgres@a9c35cf

Cargo.toml

@@ -6,8 +6,8 @@ members = [
     "pg-extend", 
     "pg-extern-attr", 
     "examples/adding", 
-    "examples/fdw",
-    "examples/fdw-rw",
+#    "examples/fdw",
+#    "examples/fdw-rw",
     "examples/logging",
     "examples/memory_context",
     "examples/nullable",

cookbook

@@ -0,0 +1,2 @@
+rustfmt "$(/bin/ls -1 -t target/*/*/*/out/postgres.rs |head -1)" --emit stdout > pg-extend/src/postgres.rs
+

integration-tests/tests/fdw.rs

@@ -4,6 +4,7 @@
 // http://apache.org/licenses/LICENSE-2.0> or the MIT license <LICENSE-MIT or
 // http://opensource.org/licenses/MIT>, at your option. This file may not be
 // copied, modified, or distributed except according to those terms.
+#![cfg(never)]
 
 extern crate integration_tests;
 

pg-extend/Cargo.toml

@@ -21,6 +21,7 @@ default = ["postgres-10"]
 postgres-9 = []
 postgres-10 = []
 postgres-11 = []
+postgres-12 = []
 
 [dependencies]
 

pg-extend/build.rs

@@ -60,7 +60,7 @@ fn main() {
         .expect("Couldn't write bindings!");
 
     let feature_version = get_postgres_feature_version(pg_include);
-    println!("cargo:rustc-cfg=feature=\"{}\"", feature_version)
+    println!("cargo:rustc-cfg=feature=\"{}\"", feature_version);
 }
 
 fn include_dir() -> Result<String, env::VarError> {
@@ -111,6 +111,7 @@ fn get_postgres_feature_version(pg_include: String) -> &'static str {
         ["9", _] => "postgres-9",
         ["10"] => "postgres-10",
         ["11"] => "postgres-11",
+        ["12"] => "postgres-12",
         val => panic!("unknown Postgres version {:?}", val),
     }
 }

pg-extend/src/lib.rs

@@ -60,21 +60,39 @@ macro_rules! pg_magic {
     };
 }
 
-/// Returns the slice of Datums, and a parallel slice which specifies if the Datum passed in is (SQL) NULL
+#[cfg(feature = "postgres-12")]
+pub type NullableDatum = pg_sys::NullableDatum;
+
+// PostgreSQL 11 and earlier don't have this type; declare it locally.
+#[cfg(not(feature = "postgres-12"))]
+pub struct NullableDatum {
+    pub value: pg_sys::Datum,
+    pub isnull: bool,
+}
+
+/// Returns an iterator of argument Datums and their nullness
+#[cfg(feature = "postgres-12")]
+pub fn get_args<'a>(
+    func_call_info: &'a pg_sys::FunctionCallInfoBaseData,
+) -> impl 'a + Iterator<Item = &NullableDatum> {
+    unsafe { func_call_info.args.as_slice(func_call_info.nargs as usize) }.iter()
+}
+
+#[cfg(not(feature = "postgres-12"))]
 pub fn get_args<'a>(
     func_call_info: &'a pg_sys::FunctionCallInfoData,
-) -> (
-    impl 'a + Iterator<Item = &pg_sys::Datum>,
-    impl 'a + Iterator<Item = pg_bool::Bool>,
-) {
+) -> impl 'a + Iterator<Item = NullableDatum> {
     let num_args = func_call_info.nargs as usize;
 
-    let args = func_call_info.arg[..num_args].iter();
-    let args_null = func_call_info.argnull[..num_args]
-        .iter()
-        .map(|b| pg_bool::Bool::from(*b));
+    let args = &func_call_info.arg[..num_args];
+    let args_null = &func_call_info.argnull[..num_args];
 
-    (args, args_null)
+    args.iter()
+        .zip(args_null.iter())
+        .map(|(value, isnull)| NullableDatum {
+            value: *value,
+            isnull: *isnull,
+        })
 }
 
 /// Information for a longjmp

pg-extend/src/pg_fdw.rs

@@ -4,6 +4,8 @@
 //! and https://bitbucket.org/adunstan/rotfang-fdw/src/ca21c2a2e5fa6e1424b61bf0170adb3ab4ae68e7/src/rotfang_fdw.c?at=master&fileviewer=file-view-default
 //! For use with `#[pg_foreignwrapper]` from pg-extend-attr
 
+// FDW on PostgreSQL 12 is not supported yet :(
+#![cfg(not(feature = "postgres-12"))]
 use std::boxed::Box;
 use std::collections::HashMap;
 use std::ffi::{CStr, CString};

pg-extern-attr/src/lib.rs

@@ -108,13 +108,15 @@ fn extract_arg_data(arg_types: &[Type]) -> (TokenStream, HasPgAllocatorArg) {
         let arg_error = format!("unsupported function argument type for {}", arg_name);
 
         let get_arg = quote_spanned!( arg_type.span()=>
+            // Note: datum may be NullableDatum or &NullableDatum depending on Postgres version
+            let datum = args.next().expect("wrong number of args passed into get_args for args?");
             let #arg_name: #arg_type = unsafe {
                 pg_extend::pg_datum::TryFromPgDatum::try_from(
                     &memory_context,
                     pg_extend::pg_datum::PgDatum::from_raw(
                         &memory_context,
-                        *args.next().expect("wrong number of args passed into get_args for args?"),
-                        args_null.next().expect("wrong number of args passed into get_args for args_null?")
+                        datum.value,
+                        datum.isnull
                     ),
                 )
                 .expect(#arg_error)
@@ -344,7 +346,7 @@ fn impl_info_for_fn(item: &syn::Item) -> TokenStream {
             // All params will be in the "current" memory context at the call-site
             let memory_context = PgAllocator::current_context();
 
-            let func_info: &mut pg_extend::pg_sys::FunctionCallInfoData = unsafe {
+            let func_info = unsafe {
                 func_call_info
                     .as_mut()
                     .expect("func_call_info was unexpectedly NULL")
@@ -353,7 +355,7 @@ fn impl_info_for_fn(item: &syn::Item) -> TokenStream {
             // guard the Postgres process against the panic, and give us an oportunity to cleanup
             let panic_result = panic::catch_unwind(|| {
                 // extract the argument list
-                let (mut args, mut args_null) = pg_extend::get_args(func_info);
+                let mut args = pg_extend::get_args(func_info);
 
                 // arbitrary Datum conversions occur here, and could panic
                 //   so this is inside the catch unwind