feat(hygiene): Collect loaded proc macros using all_proc_macro_def_ids

The recently introduced CStore::all_proc_macro_def_ids function exposes the information on the loaded proc macos we were trying to access, for which we had to use custom workarounds before. The previous workaround relied on enumerating the def indices of each proc macro crate, and then attempting to read the def entries of each of the def indices within to find the proc macro entries. This wasn't much of a performance concern due to the general size of proc macro crates and the reads being made to previously cached metadata. However, because proc macro crates have a different rmeta representation which removes lots of unnecessary def entries, and because the publicly accessible interfaces (CStore::def_kind_untracked, CStore::load_proc_macro_untracked) all panicked upon a missing def entry, we had to catch panics and even remove the panic hook for the duration of these lookups to gather the information on loaded proc macros that this new publicly-available interface now provides.

We primarily use information on loaded proc macros to clean up residual helper attributes which are left behind after proc macro expansion, and are not interpretable without the call to the proc macro.

Author: zalanlevai

mutest-emit/src/codegen/hygiene.rs

@@ -1,7 +1,6 @@
 use std::iter;
 use std::mem;
 use std::ops::DerefMut;
-use std::panic;
 use std::sync::Arc;
 
 use rustc_data_structures::flat_map_in_place::FlatMapInPlace;
@@ -1807,36 +1806,8 @@ pub fn sanitize_macro_expansions<'tcx>(tcx: TyCtxt<'tcx>, crate_res: &res::Crate
 
     let cstore = CStore::from_tcx(tcx);
 
-    // HACK: The only way to enumerate the definitions of an external crate though the public API is
-    //       by enumerating the def indices up to `CStore::num_def_ids_untracked`.
-    //       See https://github.com/rust-lang/rust/pull/85889.
-    let crate_def_indices = |cnum: hir::CrateNum| {
-        const BASE_DEF_IDX: usize = hir::CRATE_DEF_INDEX.as_usize();
-        let max_def_idx = cstore.num_def_ids_untracked(cnum);
-
-        (BASE_DEF_IDX..max_def_idx).map(hir::DefIndex::from_usize)
-    };
-
     // Find all loaded proc macro syntax extensions.
-    tcx.crates(()).iter()
-        // Ensure that we are only looking at crates with `CrateKind::ProcMacro`.
-        .filter(|&&cnum| tcx.dep_kind(cnum).macros_only())
-        .flat_map(|&cnum| crate_def_indices(cnum).map(move |index| hir::DefId { krate: cnum, index }))
-        .filter(|&def_id| {
-            // HACK: Not all def indices are encoded for proc macro crates, only the macro definitions themselves.
-            //       To avoid crashes due to missing def index lookups, we must only generate "valid" indices,
-            //       however, there is no stable mechanism for this.
-            //       Instead, we use a def kind query to trigger a crate metadata lookup, and
-            //       catch the panic, if it occurs.
-            //       We also disable printing of panic messages with an empty hook.
-            //       See https://github.com/rust-lang/rust/pull/76897.
-            let builtin_panic_hook = panic::take_hook();
-            panic::set_hook(Box::new(|_panic_info| {}));
-            let Ok(def_kind) = panic::catch_unwind(panic::AssertUnwindSafe(|| cstore.def_kind_untracked(def_id))) else { return false; };
-            panic::set_hook(builtin_panic_hook);
-
-            matches!(def_kind, hir::DefKind::Macro(_))
-        })
+    cstore.all_proc_macro_def_ids()
         .filter_map(|def_id| {
             match cstore.load_macro_untracked(def_id, tcx) {
                 LoadedMacro::ProcMacro(syntax_extension) => Some(syntax_extension),