Fix issue #1032

README.md

@@ -242,6 +242,24 @@ this feature is now considered deprecated in favor of a lower-overhead interop.
 You may still request implementations of `TryFrom<time::Type> for pgx::MatchingType`
 and `From<time::Type> for pgx::MatchingType` by enabling the `"time-crate"` feature.
 
+### "unsafe-postgres": Allow compilation for Postgres forks that have a different ABI
+
+As of Postgres v15, forks are allowed to specify they use a different ABI than canonical Postgres.
+Since pgx makes countless assumptions about Postgres' internal ABI it is not possible for it to 
+guarantee that a compiled pgx extension will probably execute within such a Postgres fork.  You,
+dear compiler runner, can make this guarantee for yourself by specifying the `unsafe-postgres` 
+feature flag.  Otherwise, a pgx extension will fail to compile with an error similar to:
+
+```
+error: Unrecognized Postgres ABI.  Perhaps you need `--features unsafe-postgres`?
+   --> pgx/src/lib.rs:139:9
+    |
+139 | /         compile_error!(
+140 | |             "Unrecognized Postgres ABI.  Perhaps you need `--features unsafe-postgres`?"
+141 | |         );
+    | |_________^
+```
+
 ### Experimental Features
 
 Adding `pgx = { version = "0.5.0", features = ["postgrestd"] }` to your Cargo.toml

pgx/Cargo.toml

@@ -27,6 +27,7 @@ pg14 = [ "pgx-pg-sys/pg14" ]
 pg15 = [ "pgx-pg-sys/pg15" ]
 time-crate = ["dep:time"]
 no-schema-generation = ["pgx-macros/no-schema-generation", "pgx-sql-entity-graph/no-schema-generation"]
+unsafe-postgres = []     # when trying to compile against something that looks like Postgres but claims to be diffent
 
 [package.metadata.docs.rs]
 features = ["pg14", "cshim"]

pgx/src/lib.rs

@@ -128,6 +128,20 @@ pub use pg_sys::{
 #[doc(hidden)]
 pub use pgx_sql_entity_graph;
 
+// Postgres v15 has the concept of an ABI "name".  The default is `b"PostgreSQL\0"` and this is the
+// ABI that pgx extensions expect to be running under.  We will refuse to compile if it is detected
+// that we're trying to be built against some other kind of "postgres" that has its own ABI name.
+//
+// Unless the compiling user explicitly told us that they're aware of this via `--features unsafe-postgres`.
+#[cfg(all(feature = "pg15", not(feature = "unsafe-postgres")))]
+const _: () = {
+    if crate::pg_sys::FMGR_ABI_EXTRA.iter().zip(b"PostgreSQL\0".iter()).all(|(a, b)| a == b) {
+        compile_error!(
+            "Unrecognized Postgres ABI.  Perhaps you need `--features unsafe-postgres`?"
+        );
+    }
+};
+
 /// A macro for marking a library compatible with [`pgx`][crate].
 ///
 /// <div class="example-wrap" style="display:inline-block">
@@ -220,8 +234,9 @@ macro_rules! pg_magic_func {
                 namedatalen: pgx::pg_sys::NAMEDATALEN as i32,
                 float8byval: cfg!(target_pointer_width = "64") as i32,
                 abi_extra: {
-                    // array::from_fn isn't const yet, boohoo, so const-copy a bstr
-                    let magic = b"PostgreSQL";
+                    // we'll use what the bindings tell us, but if it ain't "PostgreSQL" then we'll
+                    // raise a compilation error unless the `unsafe-postgres` feature is set
+                    let magic = pgx::pg_sys::FMGR_ABI_EXTRA;
                     let mut abi = [0 as ::pgx::ffi::c_char; 32];
                     let mut i = 0;
                     while i < magic.len() {