suggest type annotation for local statement initialed by ref expression

src/test/ui/suggestions/format-borrow.stderr

@@ -11,6 +11,10 @@ help: consider removing the borrow
 LL -     let a: String = &String::from("a");
 LL +     let a: String = String::from("a");
    |
+help: alternatively, consider changing the type annotation
+   |
+LL |     let a: &String = &String::from("a");
+   |            +
 
 error[E0308]: mismatched types
   --> $DIR/format-borrow.rs:4:21
@@ -25,6 +29,10 @@ help: consider removing the borrow
 LL -     let b: String = &format!("b");
 LL +     let b: String = format!("b");
    |
+help: alternatively, consider changing the type annotation
+   |
+LL |     let b: &String = &format!("b");
+   |            +
 
 error[E0308]: mismatched types
   --> $DIR/format-borrow.rs:6:21
@@ -39,6 +47,10 @@ help: consider removing the borrow
 LL -     let c: String = &mut format!("c");
 LL +     let c: String = format!("c");
    |
+help: alternatively, consider changing the type annotation
+   |
+LL |     let c: &mut String = &mut format!("c");
+   |            ++++
 
 error[E0308]: mismatched types
   --> $DIR/format-borrow.rs:8:21
@@ -53,6 +65,10 @@ help: consider removing the borrow
 LL -     let d: String = &mut (format!("d"));
 LL +     let d: String = format!("d"));
    |
+help: alternatively, consider changing the type annotation
+   |
+LL |     let d: &mut String = &mut (format!("d"));
+   |            ++++
 
 error: aborting due to 4 previous errors
 

src/test/ui/suggestions/issue-102892.rs

@@ -0,0 +1,25 @@
+#![allow(dead_code, unused_variables)]
+
+use std::sync::Arc;
+
+#[derive(Debug)]
+struct A;
+#[derive(Debug)]
+struct B;
+
+fn process_without_annot(arc: &Arc<(A, B)>) {
+    let (a, b) = **arc; // suggests putting `&**arc` here; with that, fixed!
+}
+
+fn process_with_annot(arc: &Arc<(A, B)>) {
+    let (a, b): (A, B) = &**arc; // suggests putting `&**arc` here too
+    //~^ ERROR mismatched types
+}
+
+fn process_with_tuple_annot(mutation: &mut (A, B), arc: &Arc<(A, B)>) {
+    let (a, b): ((A, B), A) = (&mut *mutation, &(**arc).0); // suggests putting `&**arc` here too
+    //~^ ERROR mismatched types
+    //~| ERROR mismatched types
+}
+
+fn main() {}

src/test/ui/suggestions/issue-102892.stderr

@@ -0,0 +1,57 @@
+error[E0308]: mismatched types
+  --> $DIR/issue-102892.rs:15:26
+   |
+LL |     let (a, b): (A, B) = &**arc; // suggests putting `&**arc` here too
+   |                 ------   ^^^^^^ expected tuple, found `&(A, B)`
+   |                 |
+   |                 expected due to this
+   |
+   = note:  expected tuple `(A, B)`
+           found reference `&(A, B)`
+help: consider removing the borrow
+   |
+LL -     let (a, b): (A, B) = &**arc; // suggests putting `&**arc` here too
+LL +     let (a, b): (A, B) = **arc; // suggests putting `&**arc` here too
+   |
+help: alternatively, consider changing the type annotation
+   |
+LL |     let (a, b): &(A, B) = &**arc; // suggests putting `&**arc` here too
+   |                 +
+
+error[E0308]: mismatched types
+  --> $DIR/issue-102892.rs:20:32
+   |
+LL |     let (a, b): ((A, B), A) = (&mut *mutation, &(**arc).0); // suggests putting `&**arc` here too
+   |                                ^^^^^^^^^^^^^^ expected tuple, found `&mut (A, B)`
+   |
+   = note:          expected tuple `(A, B)`
+           found mutable reference `&mut (A, B)`
+help: consider removing the borrow
+   |
+LL -     let (a, b): ((A, B), A) = (&mut *mutation, &(**arc).0); // suggests putting `&**arc` here too
+LL +     let (a, b): ((A, B), A) = (*mutation, &(**arc).0); // suggests putting `&**arc` here too
+   |
+help: alternatively, consider changing the type annotation
+   |
+LL |     let (a, b): (&mut (A, B), A) = (&mut *mutation, &(**arc).0); // suggests putting `&**arc` here too
+   |                  ++++
+
+error[E0308]: mismatched types
+  --> $DIR/issue-102892.rs:20:48
+   |
+LL |     let (a, b): ((A, B), A) = (&mut *mutation, &(**arc).0); // suggests putting `&**arc` here too
+   |                                                ^^^^^^^^^^ expected struct `A`, found `&A`
+   |
+help: consider removing the borrow
+   |
+LL -     let (a, b): ((A, B), A) = (&mut *mutation, &(**arc).0); // suggests putting `&**arc` here too
+LL +     let (a, b): ((A, B), A) = (&mut *mutation, (**arc).0); // suggests putting `&**arc` here too
+   |
+help: alternatively, consider changing the type annotation
+   |
+LL |     let (a, b): ((A, B), &A) = (&mut *mutation, &(**arc).0); // suggests putting `&**arc` here too
+   |                          +
+
+error: aborting due to 3 previous errors
+
+For more information about this error, try `rustc --explain E0308`.