Merge #10785

10785: ide: show const value in hover r=jhgg a=jhgg

fixes #10783

I think my original attempt was incorrect, because it looks like `HirDisplay` is used in more places than just the hover.  

So, I've attempted it again in 312eafe, this time specifically just rendering the value in `hover::render`

pictoral:

![image](https://user-images.githubusercontent.com/5489149/142163890-b6aa2ab4-7bd0-4dd3-b35d-5eaa83fffb7f.png)


Co-authored-by: Jake Heinz <jh@discordapp.com>
Co-authored-by: Jake <jh@discordapp.com>

crates/hir/src/lib.rs

@@ -1457,6 +1457,10 @@ pub fn name(self, db: &dyn HirDatabase) -> Option<Name> {
         db.const_data(self.id).name.clone()
     }
 
+    pub fn value(self, db: &dyn HirDatabase) -> Option<ast::Expr> {
+        self.source(db)?.value.body()
+    }
+
     pub fn ty(self, db: &dyn HirDatabase) -> Type {
         let data = db.const_data(self.id);
         let resolver = self.id.resolver(db.upcast());

crates/ide/src/hover/render.rs

@@ -1,6 +1,6 @@
 //! Logic for rendering the different hover messages
 use either::Either;
-use hir::{AsAssocItem, HasAttrs, HasSource, HirDisplay, Semantics, TypeInfo};
+use hir::{AsAssocItem, Const, HasAttrs, HasSource, HirDisplay, Semantics, TypeInfo};
 use ide_db::{
     base_db::SourceDatabase,
     defs::Definition,
@@ -352,7 +352,7 @@ pub(super) fn definition(
         Definition::Function(it) => label_and_docs(db, it),
         Definition::Adt(it) => label_and_docs(db, it),
         Definition::Variant(it) => label_and_docs(db, it),
-        Definition::Const(it) => label_and_docs(db, it),
+        Definition::Const(it) => const_label_value_and_docs(db, it),
         Definition::Static(it) => label_and_docs(db, it),
         Definition::Trait(it) => label_and_docs(db, it),
         Definition::TypeAlias(it) => label_and_docs(db, it),
@@ -381,6 +381,21 @@ fn label_and_docs<D>(db: &RootDatabase, def: D) -> (String, Option<hir::Document
     (label, docs)
 }
 
+fn const_label_value_and_docs(
+    db: &RootDatabase,
+    konst: Const,
+) -> (String, Option<hir::Documentation>) {
+    let label = if let Some(expr) = konst.value(db) {
+        format!("{} = {}", konst.display(db), expr)
+    } else {
+        konst.display(db).to_string()
+    };
+
+    let docs = konst.attrs(db).docs();
+
+    (label, docs)
+}
+
 fn definition_mod_path(db: &RootDatabase, def: &Definition) -> Option<String> {
     if let Definition::GenericParam(_) = def {
         return None;

crates/ide/src/hover/tests.rs

@@ -510,10 +510,32 @@ fn hover_const_static() {
             ```
 
             ```rust
-                const foo: u32
+            const foo: u32 = 123
             ```
         "#]],
     );
+    check(
+        r#"
+const foo$0: u32 = {
+    let x = foo();
+    x + 100
+};"#,
+        expect![[r#"
+            *foo*
+
+            ```rust
+            test
+            ```
+
+            ```rust
+            const foo: u32 = {
+                let x = foo();
+                x + 100
+            }
+            ```
+        "#]],
+    );
+
     check(
         r#"static foo$0: u32 = 456;"#,
         expect![[r#"
@@ -795,7 +817,7 @@ fn main() {
             ```
 
             ```rust
-                const C: u32
+            const C: u32 = 1
             ```
         "#]],
     )
@@ -3183,7 +3205,7 @@ fn foo() {
             ```
 
             ```rust
-                const FOO: usize
+            const FOO: usize = 3
             ```
 
             ---