Auto merge of rust-lang#17984 - ShoyuVanilla:cast, r=Veykril

feat: Implement cast typecheck and diagnostics

Fixes  rust-lang#17897 and fixes rust-lang#16564
Mainly adopted from https://github.com/rust-lang/rust/blob/100fde5246bf56f22fb5cc85374dd841296fce0e/compiler/rustc_hir_typeck/src/cast.rs

Author: bors

src/tools/rust-analyzer/crates/hir-def/src/data/adt.rs

@@ -14,6 +14,7 @@ use triomphe::Arc;
 use crate::{
     builtin_type::{BuiltinInt, BuiltinUint},
     db::DefDatabase,
+    hir::Expr,
     item_tree::{
         AttrOwner, Field, FieldParent, FieldsShape, ItemTree, ModItem, RawVisibilityId, TreeId,
     },
@@ -317,6 +318,27 @@ impl EnumData {
             _ => IntegerType::Pointer(true),
         }
     }
+
+    // [Adopted from rustc](https://github.com/rust-lang/rust/blob/bd53aa3bf7a24a70d763182303bd75e5fc51a9af/compiler/rustc_middle/src/ty/adt.rs#L446-L448)
+    pub fn is_payload_free(&self, db: &dyn DefDatabase) -> bool {
+        self.variants.iter().all(|(v, _)| {
+            // The condition check order is slightly modified from rustc
+            // to improve performance by early returning with relatively fast checks
+            let variant = &db.enum_variant_data(*v).variant_data;
+            if !variant.fields().is_empty() {
+                return false;
+            }
+            // The outer if condition is whether this variant has const ctor or not
+            if !matches!(variant.kind(), StructKind::Unit) {
+                let body = db.body((*v).into());
+                // A variant with explicit discriminant
+                if body.exprs[body.body_expr] != Expr::Missing {
+                    return false;
+                }
+            }
+            true
+        })
+    }
 }
 
 impl EnumVariantData {

src/tools/rust-analyzer/crates/hir-ty/src/consteval/tests.rs

@@ -186,7 +186,13 @@ fn floating_point() {
 
 #[test]
 fn casts() {
-    check_number(r#"const GOAL: usize = 12 as *const i32 as usize"#, 12);
+    check_number(
+        r#"
+    //- minicore: sized
+    const GOAL: usize = 12 as *const i32 as usize
+        "#,
+        12,
+    );
     check_number(
         r#"
     //- minicore: coerce_unsized, index, slice
@@ -204,7 +210,7 @@ fn casts() {
         r#"
     //- minicore: coerce_unsized, index, slice
     const GOAL: i16 = {
-        let a = &mut 5;
+        let a = &mut 5_i16;
         let z = a as *mut _;
         unsafe { *z }
     };
@@ -244,7 +250,13 @@ fn casts() {
         "#,
         4,
     );
-    check_number(r#"const GOAL: i32 = -12i8 as i32"#, -12);
+    check_number(
+        r#"
+    //- minicore: sized
+    const GOAL: i32 = -12i8 as i32
+        "#,
+        -12,
+    );
 }
 
 #[test]
@@ -1911,6 +1923,7 @@ fn function_pointer() {
     );
     check_number(
         r#"
+    //- minicore: sized
     fn add2(x: u8) -> u8 {
         x + 2
     }
@@ -2422,6 +2435,7 @@ fn statics() {
 fn extern_weak_statics() {
     check_number(
         r#"
+    //- minicore: sized
     extern "C" {
         #[linkage = "extern_weak"]
         static __dso_handle: *mut u8;
@@ -2716,6 +2730,7 @@ fn const_trait_assoc() {
     );
     check_number(
         r#"
+    //- minicore: sized
     struct S<T>(*mut T);
 
     trait MySized: Sized {

src/tools/rust-analyzer/crates/hir-ty/src/consteval/tests/intrinsics.rs

@@ -311,6 +311,7 @@ fn saturating() {
 fn allocator() {
     check_number(
         r#"
+        //- minicore: sized
         extern "Rust" {
             #[rustc_allocator]
             fn __rust_alloc(size: usize, align: usize) -> *mut u8;

src/tools/rust-analyzer/crates/hir-ty/src/infer.rs

@@ -13,7 +13,7 @@
 //! to certain types. To record this, we use the union-find implementation from
 //! the `ena` crate, which is extracted from rustc.
 
-mod cast;
+pub(crate) mod cast;
 pub(crate) mod closure;
 mod coerce;
 mod expr;
@@ -76,7 +76,7 @@ pub use coerce::could_coerce;
 #[allow(unreachable_pub)]
 pub use unify::{could_unify, could_unify_deeply};
 
-use cast::CastCheck;
+use cast::{CastCheck, CastError};
 pub(crate) use closure::{CaptureKind, CapturedItem, CapturedItemWithoutTy};
 
 /// The entry point of type inference.
@@ -254,6 +254,16 @@ pub enum InferenceDiagnostic {
         expr: ExprId,
         expected: Ty,
     },
+    CastToUnsized {
+        expr: ExprId,
+        cast_ty: Ty,
+    },
+    InvalidCast {
+        expr: ExprId,
+        error: CastError,
+        expr_ty: Ty,
+        cast_ty: Ty,
+    },
 }
 
 /// A mismatch between an expected and an inferred type.
@@ -456,6 +466,7 @@ pub struct InferenceResult {
     pub(crate) closure_info: FxHashMap<ClosureId, (Vec<CapturedItem>, FnTrait)>,
     // FIXME: remove this field
     pub mutated_bindings_in_closure: FxHashSet<BindingId>,
+    pub coercion_casts: FxHashSet<ExprId>,
 }
 
 impl InferenceResult {
@@ -666,7 +677,7 @@ impl<'a> InferenceContext<'a> {
         let InferenceContext {
             mut table,
             mut result,
-            deferred_cast_checks,
+            mut deferred_cast_checks,
             tuple_field_accesses_rev,
             ..
         } = self;
@@ -695,15 +706,26 @@ impl<'a> InferenceContext<'a> {
             closure_info: _,
             mutated_bindings_in_closure: _,
             tuple_field_access_types: _,
+            coercion_casts,
         } = &mut result;
 
         table.fallback_if_possible();
 
         // Comment from rustc:
         // Even though coercion casts provide type hints, we check casts after fallback for
         // backwards compatibility. This makes fallback a stronger type hint than a cast coercion.
-        for cast in deferred_cast_checks {
-            cast.check(&mut table);
+        let mut apply_adjustments = |expr, adj| {
+            expr_adjustments.insert(expr, adj);
+        };
+        let mut set_coercion_cast = |expr| {
+            coercion_casts.insert(expr);
+        };
+        for cast in deferred_cast_checks.iter_mut() {
+            if let Err(diag) =
+                cast.check(&mut table, &mut apply_adjustments, &mut set_coercion_cast)
+            {
+                diagnostics.push(diag);
+            }
         }
 
         // FIXME resolve obligations as well (use Guidance if necessary)