Assert that Instance::try_resolve is only used on body-like things

2 files changed, 156 insertions, 0 deletions

diff --git a/compiler/rustc_trait_selection/src/error_reporting/traits/call_kind.rs b/compiler/rustc_trait_selection/src/error_reporting/traits/call_kind.rs
new file mode 100644
index 00000000000..1c3e570b676
--- /dev/null
+++ b/compiler/rustc_trait_selection/src/error_reporting/traits/call_kind.rs
@@ -0,0 +1,155 @@
+//! Common logic for borrowck use-after-move errors when moved into a `fn(self)`,
+//! as well as errors when attempting to call a non-const function in a const
+//! context.
+
+use rustc_hir::def::DefKind;
+use rustc_hir::def_id::DefId;
+use rustc_hir::{LangItem, lang_items};
+use rustc_middle::ty::{AssocItemContainer, GenericArgsRef, Instance, Ty, TyCtxt, TypingEnv};
+use rustc_span::{DesugaringKind, Ident, Span, sym};
+use tracing::debug;
+
+use crate::traits::specialization_graph;
+
+#[derive(Clone, Copy, PartialEq, Eq, Debug)]
+pub enum CallDesugaringKind {
+    /// for _ in x {} calls x.into_iter()
+    ForLoopIntoIter,
+    /// for _ in x {} calls iter.next()
+    ForLoopNext,
+    /// x? calls x.branch()
+    QuestionBranch,
+    /// x? calls type_of(x)::from_residual()
+    QuestionFromResidual,
+    /// try { ..; x } calls type_of(x)::from_output(x)
+    TryBlockFromOutput,
+    /// `.await` calls `IntoFuture::into_future`
+    Await,
+}
+
+impl CallDesugaringKind {
+    pub fn trait_def_id(self, tcx: TyCtxt<'_>) -> DefId {
+        match self {
+            Self::ForLoopIntoIter => tcx.get_diagnostic_item(sym::IntoIterator).unwrap(),
+            Self::ForLoopNext => tcx.require_lang_item(LangItem::Iterator, None),
+            Self::QuestionBranch | Self::TryBlockFromOutput => {
+                tcx.require_lang_item(LangItem::Try, None)
+            }
+            Self::QuestionFromResidual => tcx.get_diagnostic_item(sym::FromResidual).unwrap(),
+            Self::Await => tcx.get_diagnostic_item(sym::IntoFuture).unwrap(),
+        }
+    }
+}
+
+#[derive(Clone, Copy, PartialEq, Eq, Debug)]
+pub enum CallKind<'tcx> {
+    /// A normal method call of the form `receiver.foo(a, b, c)`
+    Normal {
+        self_arg: Option<Ident>,
+        desugaring: Option<(CallDesugaringKind, Ty<'tcx>)>,
+        method_did: DefId,
+        method_args: GenericArgsRef<'tcx>,
+    },
+    /// A call to `Fn(..)::call(..)`, desugared from `my_closure(a, b, c)`
+    FnCall { fn_trait_id: DefId, self_ty: Ty<'tcx> },
+    /// A call to an operator trait, desugared from operator syntax (e.g. `a << b`)
+    Operator { self_arg: Option<Ident>, trait_id: DefId, self_ty: Ty<'tcx> },
+    DerefCoercion {
+        /// The `Span` of the `Target` associated type
+        /// in the `Deref` impl we are using.
+        deref_target_span: Option<Span>,
+        /// The type `T::Deref` we are dereferencing to
+        deref_target_ty: Ty<'tcx>,
+        self_ty: Ty<'tcx>,
+    },
+}
+
+pub fn call_kind<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    typing_env: TypingEnv<'tcx>,
+    method_did: DefId,
+    method_args: GenericArgsRef<'tcx>,
+    fn_call_span: Span,
+    from_hir_call: bool,
+    self_arg: Option<Ident>,
+) -> CallKind<'tcx> {
+    let parent = tcx.opt_associated_item(method_did).and_then(|assoc| {
+        let container_id = assoc.container_id(tcx);
+        match assoc.container {
+            AssocItemContainer::Impl => tcx.trait_id_of_impl(container_id),
+            AssocItemContainer::Trait => Some(container_id),
+        }
+    });
+
+    let fn_call = parent.and_then(|p| {
+        lang_items::FN_TRAITS.iter().filter_map(|&l| tcx.lang_items().get(l)).find(|&id| id == p)
+    });
+
+    let operator = if !from_hir_call && let Some(p) = parent {
+        lang_items::OPERATORS.iter().filter_map(|&l| tcx.lang_items().get(l)).find(|&id| id == p)
+    } else {
+        None
+    };
+
+    // Check for a 'special' use of 'self' -
+    // an FnOnce call, an operator (e.g. `<<`), or a
+    // deref coercion.
+    if let Some(trait_id) = fn_call {
+        return CallKind::FnCall { fn_trait_id: trait_id, self_ty: method_args.type_at(0) };
+    } else if let Some(trait_id) = operator {
+        return CallKind::Operator { self_arg, trait_id, self_ty: method_args.type_at(0) };
+    } else if !from_hir_call && tcx.is_diagnostic_item(sym::deref_method, method_did) {
+        let deref_target_def_id =
+            tcx.get_diagnostic_item(sym::deref_target).expect("deref method but no deref target");
+        let deref_target_ty = tcx.normalize_erasing_regions(
+            typing_env,
+            Ty::new_projection(tcx, deref_target_def_id, method_args),
+        );
+        let deref_target_span = if let Ok(Some(instance)) =
+            Instance::try_resolve(tcx, typing_env, method_did, method_args)
+            && let instance_parent_def_id = tcx.parent(instance.def_id())
+            && matches!(tcx.def_kind(instance_parent_def_id), DefKind::Impl { .. })
+            && let Ok(instance) =
+                specialization_graph::assoc_def(tcx, instance_parent_def_id, deref_target_def_id)
+            && instance.is_final()
+        {
+            Some(tcx.def_span(instance.item.def_id))
+        } else {
+            None
+        };
+        return CallKind::DerefCoercion {
+            deref_target_ty,
+            deref_target_span,
+            self_ty: method_args.type_at(0),
+        };
+    }
+
+    // This isn't a 'special' use of `self`
+    debug!(?method_did, ?fn_call_span);
+    let desugaring = if tcx.is_lang_item(method_did, LangItem::IntoIterIntoIter)
+        && fn_call_span.desugaring_kind() == Some(DesugaringKind::ForLoop)
+    {
+        Some((CallDesugaringKind::ForLoopIntoIter, method_args.type_at(0)))
+    } else if tcx.is_lang_item(method_did, LangItem::IteratorNext)
+        && fn_call_span.desugaring_kind() == Some(DesugaringKind::ForLoop)
+    {
+        Some((CallDesugaringKind::ForLoopNext, method_args.type_at(0)))
+    } else if fn_call_span.desugaring_kind() == Some(DesugaringKind::QuestionMark) {
+        if tcx.is_lang_item(method_did, LangItem::TryTraitBranch) {
+            Some((CallDesugaringKind::QuestionBranch, method_args.type_at(0)))
+        } else if tcx.is_lang_item(method_did, LangItem::TryTraitFromResidual) {
+            Some((CallDesugaringKind::QuestionFromResidual, method_args.type_at(0)))
+        } else {
+            None
+        }
+    } else if tcx.is_lang_item(method_did, LangItem::TryTraitFromOutput)
+        && fn_call_span.desugaring_kind() == Some(DesugaringKind::TryBlock)
+    {
+        Some((CallDesugaringKind::TryBlockFromOutput, method_args.type_at(0)))
+    } else if fn_call_span.is_desugaring(DesugaringKind::Await) {
+        Some((CallDesugaringKind::Await, method_args.type_at(0)))
+    } else {
+        None
+    };
+    CallKind::Normal { self_arg, desugaring, method_did, method_args }
+}
diff --git a/compiler/rustc_trait_selection/src/error_reporting/traits/mod.rs b/compiler/rustc_trait_selection/src/error_reporting/traits/mod.rs
index b108a9352a5..cd4f77bb4cf 100644
--- a/compiler/rustc_trait_selection/src/error_reporting/traits/mod.rs
+++ b/compiler/rustc_trait_selection/src/error_reporting/traits/mod.rs
@@ -1,4 +1,5 @@
 pub mod ambiguity;
+pub mod call_kind;
 mod fulfillment_errors;
 pub mod on_unimplemented;
 mod overflow;