Rollup merge of rust-lang#141253 - azhogin:azhogin/async-drop-feature-inconsistency-warning, r=oli-obk

Warning added when dependency crate has async drop types, and the feature is disabled

In continue of rust-lang#141031.

When dependency crate has non-empty `adt_async_destructor` table in metadata, and `async_drop` feature is disabled for local crate, warning will be emitted.

Test `dependency-dropped` has two revisions - with and without feature enabled. With feature enabled, async drop for dropee is executed ("Async drop" printed). Without the feature enabled, sync drop is executed ("Sync drop" printed) and warning is emitted.

Warning example:
```
warning: found async drop types in dependecy `async_drop_dep`, but async_drop feature is disabled for `dependency_dropped`
  --> $DIR/dependency-dropped.rs:7:1
   |
LL | #![cfg_attr(with_feature, feature(async_drop))]
   | ^
   |
   = help: if async drop type will be dropped in a crate without `feature(async_drop)`, sync Drop will be used
```

Author: matthiaskrgr

compiler/rustc_interface/src/passes.rs

@@ -282,6 +282,7 @@ fn configure_and_expand(
     resolver.resolve_crate(&krate);
 
     CStore::from_tcx(tcx).report_incompatible_target_modifiers(tcx, &krate);
+    CStore::from_tcx(tcx).report_incompatible_async_drop_feature(tcx, &krate);
     krate
 }
 

compiler/rustc_metadata/messages.ftl

@@ -1,6 +1,10 @@
 metadata_as_needed_compatibility =
     linking modifier `as-needed` is only compatible with `dylib` and `framework` linking kinds
 
+metadata_async_drop_types_in_dependency =
+    found async drop types in dependecy `{$extern_crate}`, but async_drop feature is disabled for `{$local_crate}`
+    .help = if async drop type will be dropped in a crate without `feature(async_drop)`, sync Drop will be used
+
 metadata_bad_panic_strategy =
     the linked panic runtime `{$runtime}` is not compiled with this crate's panic strategy `{$strategy}`
 

compiler/rustc_metadata/src/creader.rs

@@ -473,6 +473,27 @@ impl CStore {
         }
     }
 
+    // Report about async drop types in dependency if async drop feature is disabled
+    pub fn report_incompatible_async_drop_feature(&self, tcx: TyCtxt<'_>, krate: &Crate) {
+        if tcx.features().async_drop() {
+            return;
+        }
+        for (_cnum, data) in self.iter_crate_data() {
+            if data.is_proc_macro_crate() {
+                continue;
+            }
+            if data.has_async_drops() {
+                let extern_crate = data.name();
+                let local_crate = tcx.crate_name(LOCAL_CRATE);
+                tcx.dcx().emit_warn(errors::AsyncDropTypesInDependency {
+                    span: krate.spans.inner_span.shrink_to_lo(),
+                    extern_crate,
+                    local_crate,
+                });
+            }
+        }
+    }
+
     pub fn new(metadata_loader: Box<MetadataLoaderDyn>) -> CStore {
         CStore {
             metadata_loader,

compiler/rustc_metadata/src/errors.rs

@@ -811,3 +811,13 @@ pub struct UnknownTargetModifierUnsafeAllowed {
     pub span: Span,
     pub flag_name: String,
 }
+
+#[derive(Diagnostic)]
+#[diag(metadata_async_drop_types_in_dependency)]
+#[help]
+pub struct AsyncDropTypesInDependency {
+    #[primary_span]
+    pub span: Span,
+    pub extern_crate: Symbol,
+    pub local_crate: Symbol,
+}

compiler/rustc_metadata/src/rmeta/decoder.rs

@@ -1984,6 +1984,10 @@ impl CrateMetadata {
         self.root.header.hash
     }
 
+    pub(crate) fn has_async_drops(&self) -> bool {
+        self.root.tables.adt_async_destructor.len > 0
+    }
+
     fn num_def_ids(&self) -> usize {
         self.root.tables.def_keys.size()
     }

tests/ui/async-await/async-drop/dependency-dropped.rs

@@ -1,9 +1,12 @@
 //@ run-pass
 //@ check-run-results
+//@ revisions: with_feature without_feature
 //@ aux-build:async-drop-dep.rs
 //@ edition:2021
 
-#![feature(async_drop)]
+#![cfg_attr(with_feature, feature(async_drop))]
+//[without_feature]~^ WARN found async drop types in dependecy `async_drop_dep`, but async_drop feature is disabled for `dependency_dropped`
+
 #![allow(incomplete_features)]
 
 extern crate async_drop_dep;

tests/ui/async-await/async-drop/dependency-dropped.run.stdout renamed to tests/ui/async-await/async-drop/dependency-dropped.with_feature.run.stdout

@@ -0,0 +1 @@
+Sync drop

tests/ui/async-await/async-drop/dependency-dropped.without_feature.run.stdout

@@ -0,0 +1,10 @@
+warning: found async drop types in dependecy `async_drop_dep`, but async_drop feature is disabled for `dependency_dropped`
+  --> $DIR/dependency-dropped.rs:7:1
+   |
+LL | #![cfg_attr(with_feature, feature(async_drop))]
+   | ^
+   |
+   = help: if async drop type will be dropped in a crate without `feature(async_drop)`, sync Drop will be used
+
+warning: 1 warning emitted
+