Rewrite implementation of `#[alloc_error_handler]`

The new implementation doesn't use weak lang items and instead changes
`#[alloc_error_handler]` to an attribute macro just like
`#[global_allocator]`.

The attribute will generate the `__rg_oom` function which is called by
the compiler-generated `__rust_alloc_error_handler`. If no `__rg_oom`
function is defined in any crate then the compiler shim will call
`__rdl_oom` in the alloc crate which will simply panic.

This also fixes link errors with `-C link-dead-code` with
`default_alloc_error_handler`: `__rg_oom` was previously defined in the
alloc crate and would attempt to reference the `oom` lang item, even if
it didn't exist. This worked as long as `__rg_oom` was excluded from
linking since it was not called.

This is a prerequisite for the stabilization of
`default_alloc_error_handler` (#102318).

1 files changed, 11 insertions, 0 deletions

diff --git a/compiler/rustc_middle/src/query/mod.rs b/compiler/rustc_middle/src/query/mod.rs
index a098e570305..33acaed435b 100644
--- a/compiler/rustc_middle/src/query/mod.rs
+++ b/compiler/rustc_middle/src/query/mod.rs
@@ -1391,6 +1391,13 @@ rustc_queries! {
         desc { "checking if the crate has_global_allocator" }
         separate_provide_extern
     }
+    query has_alloc_error_handler(_: CrateNum) -> bool {
+        // This query depends on untracked global state in CStore
+        eval_always
+        fatal_cycle
+        desc { "checking if the crate has_alloc_error_handler" }
+        separate_provide_extern
+    }
     query has_panic_handler(_: CrateNum) -> bool {
         fatal_cycle
         desc { "checking if the crate has_panic_handler" }
@@ -1761,6 +1768,10 @@ rustc_queries! {
         eval_always
         desc { "getting the allocator kind for the current crate" }
     }
+    query alloc_error_handler_kind(_: ()) -> Option<AllocatorKind> {
+        eval_always
+        desc { "alloc error handler kind for the current crate" }
+    }
 
     query upvars_mentioned(def_id: DefId) -> Option<&'tcx FxIndexMap<hir::HirId, hir::Upvar>> {
         desc { |tcx| "collecting upvars mentioned in `{}`", tcx.def_path_str(def_id) }