Auto merge of #13545 - Veykril:adjustment-hints, r=Veykril

Generalize reborrow hints as adjustment hints

Like reborrow hints, these are still mainly useful for teaching/learning

![image](https://user-images.githubusercontent.com/3757771/200073606-b5cd3b95-a9ad-454d-a3c4-d4d89bf45928.png)

Author: bors

crates/hir-ty/src/lib.rs

@@ -53,7 +53,7 @@ pub use builder::{ParamKind, TyBuilder};
 pub use chalk_ext::*;
 pub use infer::{
     could_coerce, could_unify, Adjust, Adjustment, AutoBorrow, BindingMode, InferenceDiagnostic,
-    InferenceResult,
+    InferenceResult, OverloadedDeref, PointerCast,
 };
 pub use interner::Interner;
 pub use lower::{

crates/hir/src/lib.rs

@@ -117,7 +117,7 @@ pub use {
         name::{known, Name},
         ExpandResult, HirFileId, InFile, MacroFile, Origin,
     },
-    hir_ty::display::HirDisplay,
+    hir_ty::{display::HirDisplay, PointerCast, Safety},
 };
 
 // These are negative re-exports: pub using these names is forbidden, they
@@ -3651,6 +3651,28 @@ impl From<ItemInNs> for ScopeDef {
     }
 }
 
+#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
+pub enum Adjust {
+    /// Go from ! to any type.
+    NeverToAny,
+    /// Dereference once, producing a place.
+    Deref(Option<OverloadedDeref>),
+    /// Take the address and produce either a `&` or `*` pointer.
+    Borrow(AutoBorrow),
+    Pointer(PointerCast),
+}
+
+#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
+pub enum AutoBorrow {
+    /// Converts from T to &T.
+    Ref(Mutability),
+    /// Converts from T to *T.
+    RawPtr(Mutability),
+}
+
+#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
+pub struct OverloadedDeref(pub Mutability);
+
 pub trait HasVisibility {
     fn visibility(&self, db: &dyn HirDatabase) -> Visibility;
     fn is_visible_from(&self, db: &dyn HirDatabase, module: Module) -> bool {

crates/hir/src/semantics.rs

@@ -29,9 +29,10 @@ use crate::{
     db::HirDatabase,
     semantics::source_to_def::{ChildContainer, SourceToDefCache, SourceToDefCtx},
     source_analyzer::{resolve_hir_path, SourceAnalyzer},
-    Access, BindingMode, BuiltinAttr, Callable, ConstParam, Crate, DeriveHelper, Field, Function,
-    HasSource, HirFileId, Impl, InFile, Label, LifetimeParam, Local, Macro, Module, ModuleDef,
-    Name, Path, ScopeDef, ToolModule, Trait, Type, TypeAlias, TypeParam, VariantDef,
+    Access, Adjust, AutoBorrow, BindingMode, BuiltinAttr, Callable, ConstParam, Crate,
+    DeriveHelper, Field, Function, HasSource, HirFileId, Impl, InFile, Label, LifetimeParam, Local,
+    Macro, Module, ModuleDef, Name, OverloadedDeref, Path, ScopeDef, ToolModule, Trait, Type,
+    TypeAlias, TypeParam, VariantDef,
 };
 
 #[derive(Debug, Clone, PartialEq, Eq)]
@@ -333,9 +334,8 @@ impl<'db, DB: HirDatabase> Semantics<'db, DB> {
         self.imp.resolve_trait(trait_)
     }
 
-    // FIXME: Figure out a nice interface to inspect adjustments
-    pub fn is_implicit_reborrow(&self, expr: &ast::Expr) -> Option<Mutability> {
-        self.imp.is_implicit_reborrow(expr)
+    pub fn expr_adjustments(&self, expr: &ast::Expr) -> Option<Vec<Adjust>> {
+        self.imp.expr_adjustments(expr)
     }
 
     pub fn type_of_expr(&self, expr: &ast::Expr) -> Option<TypeInfo> {
@@ -1067,8 +1067,29 @@ impl<'db> SemanticsImpl<'db> {
         }
     }
 
-    fn is_implicit_reborrow(&self, expr: &ast::Expr) -> Option<Mutability> {
-        self.analyze(expr.syntax())?.is_implicit_reborrow(self.db, expr)
+    fn expr_adjustments(&self, expr: &ast::Expr) -> Option<Vec<Adjust>> {
+        let mutability = |m| match m {
+            hir_ty::Mutability::Not => Mutability::Shared,
+            hir_ty::Mutability::Mut => Mutability::Mut,
+        };
+        self.analyze(expr.syntax())?.expr_adjustments(self.db, expr).map(|it| {
+            it.iter()
+                .map(|adjust| match adjust.kind {
+                    hir_ty::Adjust::NeverToAny => Adjust::NeverToAny,
+                    hir_ty::Adjust::Deref(Some(hir_ty::OverloadedDeref(m))) => {
+                        Adjust::Deref(Some(OverloadedDeref(mutability(m))))
+                    }
+                    hir_ty::Adjust::Deref(None) => Adjust::Deref(None),
+                    hir_ty::Adjust::Borrow(hir_ty::AutoBorrow::RawPtr(m)) => {
+                        Adjust::Borrow(AutoBorrow::RawPtr(mutability(m)))
+                    }
+                    hir_ty::Adjust::Borrow(hir_ty::AutoBorrow::Ref(m)) => {
+                        Adjust::Borrow(AutoBorrow::Ref(mutability(m)))
+                    }
+                    hir_ty::Adjust::Pointer(pc) => Adjust::Pointer(pc),
+                })
+                .collect()
+        })
     }
 
     fn type_of_expr(&self, expr: &ast::Expr) -> Option<TypeInfo> {

crates/hir/src/source_analyzer.rs

@@ -38,8 +38,7 @@ use hir_ty::{
         UnsafeExpr,
     },
     method_resolution::{self, lang_names_for_bin_op},
-    Adjust, Adjustment, AutoBorrow, InferenceResult, Interner, Substitution, Ty, TyExt, TyKind,
-    TyLoweringContext,
+    Adjustment, InferenceResult, Interner, Substitution, Ty, TyExt, TyKind, TyLoweringContext,
 };
 use itertools::Itertools;
 use smallvec::SmallVec;
@@ -156,21 +155,14 @@ impl SourceAnalyzer {
         Some(res)
     }
 
-    pub(crate) fn is_implicit_reborrow(
+    pub(crate) fn expr_adjustments(
         &self,
         db: &dyn HirDatabase,
         expr: &ast::Expr,
-    ) -> Option<Mutability> {
+    ) -> Option<&[Adjustment]> {
         let expr_id = self.expr_id(db, expr)?;
         let infer = self.infer.as_ref()?;
-        let adjustments = infer.expr_adjustments.get(&expr_id)?;
-        adjustments.windows(2).find_map(|slice| match slice {
-            &[Adjustment {kind: Adjust::Deref(None), ..}, Adjustment {kind: Adjust::Borrow(AutoBorrow::Ref(m)), ..}] => Some(match m {
-                hir_ty::Mutability::Mut => Mutability::Mut,
-                hir_ty::Mutability::Not => Mutability::Shared,
-            }),
-            _ => None,
-        })
+        infer.expr_adjustments.get(&expr_id).map(|v| &**v)
     }
 
     pub(crate) fn type_of_expr(