Render niches on hover

crates/hir/src/lib.rs

@@ -62,7 +62,7 @@ use hir_ty::{
     consteval::{try_const_usize, unknown_const_as_generic, ConstEvalError, ConstExt},
     diagnostics::BodyValidationDiagnostic,
     display::HexifiedConst,
-    layout::{Layout, LayoutError, RustcEnumVariantIdx, TagEncoding},
+    layout::{LayoutError, RustcEnumVariantIdx, TagEncoding},
     method_resolution::{self, TyFingerprint},
     mir::{self, interpret_mir},
     primitive::UintTy,
@@ -133,8 +133,11 @@ pub use {
     },
     hir_ty::{
         display::{ClosureStyle, HirDisplay, HirDisplayError, HirWrite},
+        // FIXME: This just needs a HIR wrapper
+        layout::Layout,
         mir::MirEvalError,
-        PointerCast, Safety,
+        PointerCast,
+        Safety,
     },
 };
 
@@ -4506,6 +4509,12 @@ impl HasCrate for Union {
     }
 }
 
+impl HasCrate for Enum {
+    fn krate(&self, db: &dyn HirDatabase) -> Crate {
+        self.module(db).krate()
+    }
+}
+
 impl HasCrate for Field {
     fn krate(&self, db: &dyn HirDatabase) -> Crate {
         self.parent_def(db).module(db).krate()

crates/ide/src/hover/render.rs

@@ -3,8 +3,8 @@ use std::fmt::Display;
 
 use either::Either;
 use hir::{
-    Adt, AsAssocItem, AttributeTemplate, CaptureKind, HasAttrs, HasSource, HirDisplay, Semantics,
-    TypeInfo,
+    db::HirDatabase, Adt, AsAssocItem, AttributeTemplate, CaptureKind, HasAttrs, HasCrate,
+    HasSource, HirDisplay, Layout, Semantics, TypeInfo,
 };
 use ide_db::{
     base_db::SourceDatabase,
@@ -404,8 +404,9 @@ pub(super) fn definition(
                     .map(|layout| format!(", offset = {:#X}", layout.fields.offset(id).bytes())),
                 _ => None,
             };
+            let niches = niches(db, it, &layout).unwrap_or_default();
             Some(format!(
-                "size = {:#X}, align = {:#X}{}",
+                "size = {:#X}, align = {:#X}{}{niches}",
                 layout.size.bytes(),
                 layout.align.abi.bytes(),
                 offset.as_deref().unwrap_or_default()
@@ -415,8 +416,9 @@ pub(super) fn definition(
         Definition::Function(it) => label_and_docs(db, it),
         Definition::Adt(it) => label_and_layout_info_and_docs(db, it, config, |&it| {
             let layout = it.layout(db).ok()?;
+            let niches = niches(db, it, &layout).unwrap_or_default();
             Some(format!(
-                "size = {:#X}, align = {:#X}",
+                "size = {:#X}, align = {:#X}{niches}",
                 layout.size.bytes(),
                 layout.align.abi.bytes()
             ))
@@ -437,14 +439,15 @@ pub(super) fn definition(
                     None
                 }
             },
-            |it| {
+            |&it| {
                 let (layout, tag_size) = it.layout(db).ok()?;
                 let size = layout.size.bytes_usize() - tag_size;
                 if size == 0 {
                     // There is no value in showing layout info for fieldless variants
                     return None;
                 }
-                Some(format!("size = {:#X}", layout.size.bytes()))
+                let niches = niches(db, it, &layout).unwrap_or_default();
+                Some(format!("size = {:#X}{niches}", layout.size.bytes()))
             },
         ),
         Definition::Const(it) => label_value_and_docs(db, it, |it| {
@@ -473,10 +476,11 @@ pub(super) fn definition(
         Definition::TraitAlias(it) => label_and_docs(db, it),
         Definition::TypeAlias(it) => label_and_layout_info_and_docs(db, it, config, |&it| {
             let layout = it.ty(db).layout(db).ok()?;
+            let niches = niches(db, it, &layout).unwrap_or_default();
             Some(format!(
-                "size = {:#X}, align = {:#X}",
+                "size = {:#X}, align = {:#X}{niches}",
                 layout.size.bytes(),
-                layout.align.abi.bytes()
+                layout.align.abi.bytes(),
             ))
         }),
         Definition::BuiltinType(it) => {
@@ -513,6 +517,13 @@ pub(super) fn definition(
     markup(docs, label, mod_path)
 }
 
+fn niches(db: &RootDatabase, it: impl HasCrate, layout: &Layout) -> Option<String> {
+    Some(format!(
+        ", niches = {}",
+        layout.largest_niche?.available(&*db.target_data_layout(it.krate(db).into())?)
+    ))
+}
+
 fn type_info(
     sema: &Semantics<'_, RootDatabase>,
     config: &HoverConfig,

crates/ide/src/hover/tests.rs

@@ -1528,7 +1528,7 @@ fn test_hover_function_pointer_show_identifiers() {
             ```
 
             ```rust
-            type foo = fn(a: i32, b: i32) -> i32 // size = 0x8, align = 0x8
+            type foo = fn(a: i32, b: i32) -> i32 // size = 0x8, align = 0x8, niches = 1
             ```
         "#]],
     );
@@ -1546,7 +1546,7 @@ fn test_hover_function_pointer_no_identifier() {
             ```
 
             ```rust
-            type foo = fn(i32, i32) -> i32 // size = 0x8, align = 0x8
+            type foo = fn(i32, i32) -> i32 // size = 0x8, align = 0x8, niches = 1
             ```
         "#]],
     );
@@ -1904,7 +1904,7 @@ fn test_hover_layout_of_enum() {
             ```
 
             ```rust
-            enum Foo // size = 0x10, align = 0x8
+            enum Foo // size = 0x10, align = 0x8, niches = 254
             ```
         "#]],
     );