From 814d617d348c23507fd444e58515c9bff6b73105 Mon Sep 17 00:00:00 2001
From: Lukas Wirth <lukastw97@gmail.com>
Date: Tue, 9 Mar 2021 16:33:41 +0100
Subject: Show whether a binding is mutable or not on hover

---
 crates/hir/src/lib.rs                           |  8 +---
 crates/ide/src/hover.rs                         | 62 +++++++++++++++++--------
 crates/ide/src/syntax_highlighting/highlight.rs |  5 +-
 3 files changed, 47 insertions(+), 28 deletions(-)

diff --git a/crates/hir/src/lib.rs b/crates/hir/src/lib.rs
index d5a3d9034..caf4c3395 100644
--- a/crates/hir/src/lib.rs
+++ b/crates/hir/src/lib.rs
@@ -1296,13 +1296,7 @@ impl Local {
 
     pub fn is_mut(self, db: &dyn HirDatabase) -> bool {
         let body = db.body(self.parent.into());
-        match &body[self.pat_id] {
-            Pat::Bind { mode, .. } => match mode {
-                BindingAnnotation::Mutable | BindingAnnotation::RefMut => true,
-                _ => false,
-            },
-            _ => false,
-        }
+        matches!(&body[self.pat_id], Pat::Bind { mode: BindingAnnotation::Mutable, .. })
     }
 
     pub fn parent(self, _db: &dyn HirDatabase) -> DefWithBody {
diff --git a/crates/ide/src/hover.rs b/crates/ide/src/hover.rs
index 5d1cc2052..ea45086ce 100644
--- a/crates/ide/src/hover.rs
+++ b/crates/ide/src/hover.rs
@@ -1,3 +1,4 @@
+use either::Either;
 use hir::{
     Adt, AsAssocItem, AssocItemContainer, FieldSource, GenericParam, HasAttrs, HasSource,
     HirDisplay, Module, ModuleDef, ModuleSource, Semantics,
@@ -366,7 +367,7 @@ fn hover_for_definition(
                 .and_then(|fd| hover_for_builtin(fd, it))
                 .or_else(|| Some(Markup::fenced_block(&it.name()))),
         },
-        Definition::Local(it) => Some(Markup::fenced_block(&it.ty(db).display(db))),
+        Definition::Local(it) => hover_for_local(it, db),
         Definition::SelfType(impl_def) => {
             impl_def.target_ty(db).as_adt().and_then(|adt| match adt {
                 Adt::Struct(it) => from_def_source(db, it, mod_path),
@@ -405,6 +406,29 @@ fn hover_for_definition(
     }
 }
 
+fn hover_for_local(it: hir::Local, db: &RootDatabase) -> Option<Markup> {
+    let ty = it.ty(db);
+    let ty = ty.display(db);
+    let is_mut = if it.is_mut(db) { "mut " } else { "" };
+    let desc = match it.source(db).value {
+        Either::Left(ident) => {
+            let name = it.name(db).unwrap();
+            let let_kw = if ident
+                .syntax()
+                .parent()
+                .map_or(false, |p| p.kind() == LET_STMT || p.kind() == CONDITION)
+            {
+                "let "
+            } else {
+                ""
+            };
+            format!("{}{}{}: {}", let_kw, is_mut, name, ty)
+        }
+        Either::Right(_) => format!("{}self: {}", is_mut, ty),
+    };
+    hover_markup(None, Some(desc), None)
+}
+
 fn hover_for_keyword(
     sema: &Semantics<RootDatabase>,
     links_in_hover: bool,
@@ -574,7 +598,7 @@ fn main() {
                 *iter*
 
                 ```rust
-                Iter<Scan<OtherStruct<OtherStruct<i32>>, |&mut u32, &u32, &mut u32| -> Option<u32>, u32>>
+                let mut iter: Iter<Scan<OtherStruct<OtherStruct<i32>>, |&mut u32, &u32, &mut u32| -> Option<u32>, u32>>
                 ```
             "#]],
         );
@@ -798,7 +822,7 @@ fn main() {
                 ```
 
                 ```rust
-                const foo: u32 = 123
+                const foo: u32
                 ```
             "#]],
         );
@@ -831,7 +855,7 @@ fn main() {
                 *zz*
 
                 ```rust
-                Test<i32, u8>
+                let zz: Test<i32, u8>
                 ```
             "#]],
         );
@@ -870,7 +894,7 @@ fn main() { let b$0ar = Some(12); }
                 *bar*
 
                 ```rust
-                Option<i32>
+                let bar: Option<i32>
                 ```
             "#]],
         );
@@ -938,7 +962,7 @@ fn main() {
                 *foo*
 
                 ```rust
-                i32
+                foo: i32
                 ```
             "#]],
         )
@@ -952,7 +976,7 @@ fn main() {
                 *foo*
 
                 ```rust
-                i32
+                foo: i32
                 ```
             "#]],
         )
@@ -966,7 +990,7 @@ fn main() {
                 *foo*
 
                 ```rust
-                i32
+                foo: i32
                 ```
             "#]],
         )
@@ -980,7 +1004,7 @@ fn main() {
                 *foo*
 
                 ```rust
-                i32
+                foo: i32
                 ```
             "#]],
         )
@@ -1000,7 +1024,7 @@ fn main() {
                 *_x*
 
                 ```rust
-                impl Deref<Target = u8> + DerefMut<Target = u8>
+                _x: impl Deref<Target = u8> + DerefMut<Target = u8>
                 ```
             "#]],
         )
@@ -1022,7 +1046,7 @@ fn main() { let foo_$0test = Thing::new(); }
                 *foo_test*
 
                 ```rust
-                Thing
+                let foo_test: Thing
                 ```
             "#]],
         )
@@ -1081,7 +1105,7 @@ fn main() {
                 ```
 
                 ```rust
-                const C: u32 = 1
+                const C: u32
                 ```
             "#]],
         )
@@ -1182,7 +1206,7 @@ fn y() {
                 *x*
 
                 ```rust
-                i32
+                let x: i32
                 ```
             "#]],
         )
@@ -1259,7 +1283,7 @@ fn foo(bar:u32) { let a = id!(ba$0r); }
                 *bar*
 
                 ```rust
-                u32
+                bar: u32
                 ```
             "#]],
         );
@@ -1277,7 +1301,7 @@ fn foo(bar:u32) { let a = id!(ba$0r); }
                 *bar*
 
                 ```rust
-                u32
+                bar: u32
                 ```
             "#]],
         );
@@ -3302,7 +3326,7 @@ fn main() {
                 *f*
 
                 ```rust
-                &i32
+                f: &i32
                 ```
             "#]],
         );
@@ -3321,7 +3345,7 @@ impl Foo {
                 *self*
 
                 ```rust
-                &Foo
+                self: &Foo
                 ```
             "#]],
         );
@@ -3341,7 +3365,7 @@ impl Foo {
                 *self*
 
                 ```rust
-                Arc<Foo>
+                self: Arc<Foo>
                 ```
             "#]],
         );
@@ -3537,7 +3561,7 @@ fn foo() {
                 ```
 
                 ```rust
-                const FOO: usize = 3
+                const FOO: usize
                 ```
 
                 ---
diff --git a/crates/ide/src/syntax_highlighting/highlight.rs b/crates/ide/src/syntax_highlighting/highlight.rs
index 24fcbb584..b0cfdd8b7 100644
--- a/crates/ide/src/syntax_highlighting/highlight.rs
+++ b/crates/ide/src/syntax_highlighting/highlight.rs
@@ -330,10 +330,11 @@ fn highlight_def(db: &RootDatabase, def: Definition) -> Highlight {
                 HlTag::Symbol(SymbolKind::Local)
             };
             let mut h = Highlight::new(tag);
-            if local.is_mut(db) || local.ty(db).is_mutable_reference() {
+            let ty = local.ty(db);
+            if local.is_mut(db) || ty.is_mutable_reference() {
                 h |= HlMod::Mutable;
             }
-            if local.ty(db).as_callable(db).is_some() || local.ty(db).impls_fnonce(db) {
+            if ty.as_callable(db).is_some() || ty.impls_fnonce(db) {
                 h |= HlMod::Callable;
             }
             return h;
-- 
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