Handle more cases of value suggestions

compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

@@ -652,6 +652,55 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
         err
     }
 
+    fn ty_kind_suggestion(&self, ty: Ty<'tcx>) -> Option<String> {
+        // Keep in sync with `rustc_hir_analysis/src/check/mod.rs:ty_kind_suggestion`.
+        // FIXME: deduplicate the above.
+        let implements_default = |ty| {
+            let Some(default_trait) = self.infcx.tcx.get_diagnostic_item(sym::Default) else {
+                return false;
+            };
+            self.infcx
+                .type_implements_trait(default_trait, [ty], self.param_env)
+                .must_apply_modulo_regions()
+        };
+
+        Some(match ty.kind() {
+            ty::Never | ty::Error(_) => return None,
+            ty::Bool => "false".to_string(),
+            ty::Char => "\'x\'".to_string(),
+            ty::Int(_) | ty::Uint(_) => "42".into(),
+            ty::Float(_) => "3.14159".into(),
+            ty::Slice(_) => "[]".to_string(),
+            ty::Adt(def, _) if Some(def.did()) == self.infcx.tcx.get_diagnostic_item(sym::Vec) => {
+                "vec![]".to_string()
+            }
+            ty::Adt(_, _) if implements_default(ty) => "Default::default()".to_string(),
+            ty::Ref(_, ty, mutability) => {
+                if let (ty::Str, hir::Mutability::Not) = (ty.kind(), mutability) {
+                    "\"\"".to_string()
+                } else {
+                    let Some(ty) = self.ty_kind_suggestion(*ty) else {
+                        return None;
+                    };
+                    format!("&{}{ty}", mutability.prefix_str())
+                }
+            }
+            ty::Array(ty, len) => format!(
+                "[{}; {}]",
+                self.ty_kind_suggestion(*ty)?,
+                len.eval_target_usize(self.infcx.tcx, ty::ParamEnv::reveal_all()),
+            ),
+            ty::Tuple(tys) => format!(
+                "({})",
+                tys.iter()
+                    .map(|ty| self.ty_kind_suggestion(ty))
+                    .collect::<Option<Vec<String>>>()?
+                    .join(", ")
+            ),
+            _ => "value".to_string(),
+        })
+    }
+
     fn suggest_assign_value(
         &self,
         err: &mut Diag<'_>,
@@ -661,24 +710,8 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
         let ty = moved_place.ty(self.body, self.infcx.tcx).ty;
         debug!("ty: {:?}, kind: {:?}", ty, ty.kind());
 
-        let tcx = self.infcx.tcx;
+        let Some(assign_value) = self.ty_kind_suggestion(ty) else {
-        let implements_default = |ty, param_env| {
+            return;
-            let Some(default_trait) = tcx.get_diagnostic_item(sym::Default) else {
-                return false;
-            };
-            self.infcx
-                .type_implements_trait(default_trait, [ty], param_env)
-                .must_apply_modulo_regions()
-        };
-
-        let assign_value = match ty.kind() {
-            ty::Never | ty::Error(_) => return,
-            ty::Bool => "false",
-            ty::Float(_) => "0.0",
-            ty::Int(_) | ty::Uint(_) => "0",
-            ty::Adt(def, _) if Some(def.did()) == tcx.get_diagnostic_item(sym::Vec) => "vec![]",
-            ty::Adt(_, _) if implements_default(ty, self.param_env) => "Default::default()",
-            _ => "value",
         };
 
         err.span_suggestion_verbose(

compiler/rustc_hir_analysis/src/check/mod.rs

@@ -81,6 +81,7 @@ use rustc_errors::ErrorGuaranteed;
 use rustc_errors::{pluralize, struct_span_code_err, Diag};
 use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_hir::intravisit::Visitor;
+use rustc_hir::Mutability;
 use rustc_index::bit_set::BitSet;
 use rustc_infer::infer::error_reporting::ObligationCauseExt as _;
 use rustc_infer::infer::outlives::env::OutlivesEnvironment;
@@ -467,7 +468,9 @@ fn fn_sig_suggestion<'tcx>(
     )
 }
 
-pub fn ty_kind_suggestion<'tcx>(ty: Ty<'tcx>, tcx: TyCtxt<'tcx>) -> Option<&'static str> {
+pub fn ty_kind_suggestion<'tcx>(ty: Ty<'tcx>, tcx: TyCtxt<'tcx>) -> Option<String> {
+    // Keep in sync with `rustc_borrowck/src/diagnostics/conflict_errors.rs:ty_kind_suggestion`.
+    // FIXME: deduplicate the above.
     let implements_default = |ty| {
         let Some(default_trait) = tcx.get_diagnostic_item(sym::Default) else {
             return false;
@@ -478,14 +481,39 @@ pub fn ty_kind_suggestion<'tcx>(ty: Ty<'tcx>, tcx: TyCtxt<'tcx>) -> Option<&'sta
             .must_apply_modulo_regions()
     };
     Some(match ty.kind() {
-        ty::Bool => "true",
+        ty::Never | ty::Error(_) => return None,
-        ty::Char => "'a'",
+        ty::Bool => "false".to_string(),
-        ty::Int(_) | ty::Uint(_) => "42",
+        ty::Char => "\'x\'".to_string(),
-        ty::Float(_) => "3.14159",
+        ty::Int(_) | ty::Uint(_) => "42".into(),
-        ty::Error(_) | ty::Never => return None,
+        ty::Float(_) => "3.14159".into(),
-        ty::Adt(def, _) if Some(def.did()) == tcx.get_diagnostic_item(sym::Vec) => "vec![]",
+        ty::Slice(_) => "[]".to_string(),
-        ty::Adt(_, _) if implements_default(ty) => "Default::default()",
+        ty::Adt(def, _) if Some(def.did()) == tcx.get_diagnostic_item(sym::Vec) => {
-        _ => "value",
+            "vec![]".to_string()
+        }
+        ty::Adt(_, _) if implements_default(ty) => "Default::default()".to_string(),
+        ty::Ref(_, ty, mutability) => {
+            if let (ty::Str, Mutability::Not) = (ty.kind(), mutability) {
+                "\"\"".to_string()
+            } else {
+                let Some(ty) = ty_kind_suggestion(*ty, tcx) else {
+                    return None;
+                };
+                format!("&{}{ty}", mutability.prefix_str())
+            }
+        }
+        ty::Array(ty, len) => format!(
+            "[{}; {}]",
+            ty_kind_suggestion(*ty, tcx)?,
+            len.eval_target_usize(tcx, ty::ParamEnv::reveal_all()),
+        ),
+        ty::Tuple(tys) => format!(
+            "({})",
+            tys.iter()
+                .map(|ty| ty_kind_suggestion(ty, tcx))
+                .collect::<Option<Vec<String>>>()?
+                .join(", ")
+        ),
+        _ => "value".to_string(),
     })
 }
 
@@ -523,7 +551,7 @@ fn suggestion_signature<'tcx>(
         }
         ty::AssocKind::Const => {
             let ty = tcx.type_of(assoc.def_id).instantiate_identity();
-            let val = ty_kind_suggestion(ty, tcx).unwrap_or("todo!()");
+            let val = ty_kind_suggestion(ty, tcx).unwrap_or_else(|| "value".to_string());
             format!("const {}: {} = {};", assoc.name, ty, val)
         }
     }

tests/ui/asm/x86_64/type-check-5.stderr

@@ -8,8 +8,8 @@ LL |         asm!("{}", in(reg) x);
    |
 help: consider assigning a value
    |
-LL |         let x: u64 = 0;
+LL |         let x: u64 = 42;
-   |                    +++
+   |                    ++++
 
 error[E0381]: used binding `y` isn't initialized
   --> $DIR/type-check-5.rs:18:9
@@ -21,8 +21,8 @@ LL |         asm!("{}", inout(reg) y);
    |
 help: consider assigning a value
    |
-LL |         let mut y: u64 = 0;
+LL |         let mut y: u64 = 42;
-   |                        +++
+   |                        ++++
 
 error[E0596]: cannot borrow `v` as mutable, as it is not declared as mutable
   --> $DIR/type-check-5.rs:24:13

tests/ui/binop/issue-77910-1.stderr

@@ -32,8 +32,8 @@ LL |     xs
    |
 help: consider assigning a value
    |
-LL |     let xs = value;
+LL |     let xs = &42;
-   |            +++++++
+   |            +++++
 
 error: aborting due to 3 previous errors
 

tests/ui/binop/issue-77910-2.stderr

@@ -21,8 +21,8 @@ LL |     xs
    |
 help: consider assigning a value
    |
-LL |     let xs = value;
+LL |     let xs = &42;
-   |            +++++++
+   |            +++++
 
 error: aborting due to 2 previous errors
 

tests/ui/borrowck/borrowck-block-uninit.stderr

@@ -10,8 +10,8 @@ LL |         println!("{}", x);
    |
 help: consider assigning a value
    |
-LL |     let x: isize = 0;
+LL |     let x: isize = 42;
-   |                  +++
+   |                  ++++
 
 error: aborting due to 1 previous error
 

tests/ui/borrowck/borrowck-break-uninit-2.stderr

@@ -10,8 +10,8 @@ LL |     println!("{}", x);
    = note: this error originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info)
 help: consider assigning a value
    |
-LL |     let x: isize = 0;
+LL |     let x: isize = 42;
-   |                  +++
+   |                  ++++
 
 error: aborting due to 1 previous error
 

tests/ui/borrowck/borrowck-break-uninit.stderr

@@ -10,8 +10,8 @@ LL |     println!("{}", x);
    = note: this error originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info)
 help: consider assigning a value
    |
-LL |     let x: isize = 0;
+LL |     let x: isize = 42;
-   |                  +++
+   |                  ++++
 
 error: aborting due to 1 previous error
 

tests/ui/borrowck/borrowck-init-in-called-fn-expr.stderr

@@ -8,8 +8,8 @@ LL |         i
    |
 help: consider assigning a value
    |
-LL |         let i: isize = 0;
+LL |         let i: isize = 42;
-   |                      +++
+   |                      ++++
 
 error: aborting due to 1 previous error
 

tests/ui/borrowck/borrowck-init-in-fn-expr.stderr

@@ -8,8 +8,8 @@ LL |         i
    |
 help: consider assigning a value
    |
-LL |         let i: isize = 0;
+LL |         let i: isize = 42;
-   |                      +++
+   |                      ++++
 
 error: aborting due to 1 previous error
 

tests/ui/borrowck/borrowck-init-op-equal.stderr

@@ -8,8 +8,8 @@ LL |     v += 1;
    |
 help: consider assigning a value
    |
-LL |     let v: isize = 0;
+LL |     let v: isize = 42;
-   |                  +++
+   |                  ++++
 
 error: aborting due to 1 previous error
 

tests/ui/borrowck/borrowck-init-plus-equal.stderr

@@ -8,8 +8,8 @@ LL |     v = v + 1;
    |
 help: consider assigning a value
    |
-LL |     let mut v: isize = 0;
+LL |     let mut v: isize = 42;
-   |                      +++
+   |                      ++++
 
 error: aborting due to 1 previous error
 

tests/ui/borrowck/borrowck-return.stderr

@@ -8,8 +8,8 @@ LL |     return x;
    |
 help: consider assigning a value
    |
-LL |     let x: isize = 0;
+LL |     let x: isize = 42;
-   |                  +++
+   |                  ++++
 
 error: aborting due to 1 previous error
 

tests/ui/borrowck/borrowck-storage-dead.stderr

@@ -8,8 +8,8 @@ LL |         let _ = x + 1;
    |
 help: consider assigning a value
    |
-LL |         let x: i32 = 0;
+LL |         let x: i32 = 42;
-   |                    +++
+   |                    ++++
 
 error: aborting due to 1 previous error
 

tests/ui/borrowck/borrowck-uninit-after-item.stderr

@@ -9,8 +9,8 @@ LL |     baz(bar);
    |
 help: consider assigning a value
    |
-LL |     let bar = 0;
+LL |     let bar = 42;
-   |             +++
+   |             ++++
 
 error: aborting due to 1 previous error
 

tests/ui/borrowck/borrowck-uninit-in-assignop.stderr

@@ -8,8 +8,8 @@ LL |     x += 1;
    |
 help: consider assigning a value
    |
-LL |     let x: isize = 0;
+LL |     let x: isize = 42;
-   |                  +++
+   |                  ++++
 
 error[E0381]: used binding `x` isn't initialized
   --> $DIR/borrowck-uninit-in-assignop.rs:9:5
@@ -21,8 +21,8 @@ LL |     x -= 1;
    |
 help: consider assigning a value
    |
-LL |     let x: isize = 0;
+LL |     let x: isize = 42;
-   |                  +++
+   |                  ++++
 
 error[E0381]: used binding `x` isn't initialized
   --> $DIR/borrowck-uninit-in-assignop.rs:12:5
@@ -34,8 +34,8 @@ LL |     x *= 1;
    |
 help: consider assigning a value
    |
-LL |     let x: isize = 0;
+LL |     let x: isize = 42;
-   |                  +++
+   |                  ++++
 
 error[E0381]: used binding `x` isn't initialized
   --> $DIR/borrowck-uninit-in-assignop.rs:15:5
@@ -47,8 +47,8 @@ LL |     x /= 1;
    |
 help: consider assigning a value
    |
-LL |     let x: isize = 0;
+LL |     let x: isize = 42;
-   |                  +++
+   |                  ++++
 
 error[E0381]: used binding `x` isn't initialized
   --> $DIR/borrowck-uninit-in-assignop.rs:18:5
@@ -60,8 +60,8 @@ LL |     x %= 1;
    |
 help: consider assigning a value
    |
-LL |     let x: isize = 0;
+LL |     let x: isize = 42;
-   |                  +++
+   |                  ++++
 
 error[E0381]: used binding `x` isn't initialized
   --> $DIR/borrowck-uninit-in-assignop.rs:21:5
@@ -73,8 +73,8 @@ LL |     x ^= 1;
    |
 help: consider assigning a value
    |
-LL |     let x: isize = 0;
+LL |     let x: isize = 42;
-   |                  +++
+   |                  ++++
 
 error[E0381]: used binding `x` isn't initialized
   --> $DIR/borrowck-uninit-in-assignop.rs:24:5
@@ -86,8 +86,8 @@ LL |     x &= 1;
    |
 help: consider assigning a value
    |
-LL |     let x: isize = 0;
+LL |     let x: isize = 42;
-   |                  +++
+   |                  ++++
 
 error[E0381]: used binding `x` isn't initialized
   --> $DIR/borrowck-uninit-in-assignop.rs:27:5
@@ -99,8 +99,8 @@ LL |     x |= 1;
    |
 help: consider assigning a value
    |
-LL |     let x: isize = 0;
+LL |     let x: isize = 42;
-   |                  +++
+   |                  ++++
 
 error[E0381]: used binding `x` isn't initialized
   --> $DIR/borrowck-uninit-in-assignop.rs:30:5
@@ -112,8 +112,8 @@ LL |     x <<= 1;
    |
 help: consider assigning a value
    |
-LL |     let x: isize = 0;
+LL |     let x: isize = 42;
-   |                  +++
+   |                  ++++
 
 error[E0381]: used binding `x` isn't initialized
   --> $DIR/borrowck-uninit-in-assignop.rs:33:5
@@ -125,8 +125,8 @@ LL |     x >>= 1;
    |
 help: consider assigning a value
    |
-LL |     let x: isize = 0;
+LL |     let x: isize = 42;
-   |                  +++
+   |                  ++++
 
 error: aborting due to 10 previous errors
 

tests/ui/borrowck/borrowck-uninit-ref-chain.stderr

@@ -8,8 +8,8 @@ LL |     let _y = &**x;
    |
 help: consider assigning a value
    |
-LL |     let x: &&Box<i32> = value;
+LL |     let x: &&Box<i32> = &&Default::default();
-   |                       +++++++
+   |                       ++++++++++++++++++++++
 
 error[E0381]: used binding `x` isn't initialized
   --> $DIR/borrowck-uninit-ref-chain.rs:11:14
@@ -21,8 +21,8 @@ LL |     let _y = &**x;
    |
 help: consider assigning a value
    |
-LL |     let x: &&S<i32, i32> = value;
+LL |     let x: &&S<i32, i32> = &&value;
-   |                          +++++++
+   |                          +++++++++
 
 error[E0381]: used binding `x` isn't initialized
   --> $DIR/borrowck-uninit-ref-chain.rs:14:14
@@ -34,8 +34,8 @@ LL |     let _y = &**x;
    |
 help: consider assigning a value
    |
-LL |     let x: &&i32 = value;
+LL |     let x: &&i32 = &&42;
-   |                  +++++++
+   |                  ++++++
 
 error[E0381]: partially assigned binding `a` isn't fully initialized
   --> $DIR/borrowck-uninit-ref-chain.rs:18:5

tests/ui/borrowck/borrowck-uninit.stderr

@@ -8,8 +8,8 @@ LL |     foo(x);
    |
 help: consider assigning a value
    |
-LL |     let x: isize = 0;
+LL |     let x: isize = 42;
-   |                  +++
+   |                  ++++
 
 error[E0381]: used binding `a` isn't initialized
   --> $DIR/borrowck-uninit.rs:14:32

tests/ui/borrowck/borrowck-use-in-index-lvalue.fixed

@@ -0,0 +1,11 @@
+//@ run-rustfix
+#[allow(unused_mut)]
+fn test() {
+    let w: &mut [isize] = &mut [];
+    w[5] = 0; //~ ERROR [E0381]
+
+    let mut w: &mut [isize] = &mut [];
+    w[5] = 0; //~ ERROR [E0381]
+}
+
+fn main() { test(); }

tests/ui/borrowck/borrowck-use-in-index-lvalue.rs

@@ -1,3 +1,5 @@
+//@ run-rustfix
+#[allow(unused_mut)]
 fn test() {
     let w: &mut [isize];
     w[5] = 0; //~ ERROR [E0381]

tests/ui/borrowck/borrowck-use-in-index-lvalue.stderr

@@ -1,5 +1,5 @@
 error[E0381]: used binding `w` isn't initialized
-  --> $DIR/borrowck-use-in-index-lvalue.rs:3:5
+  --> $DIR/borrowck-use-in-index-lvalue.rs:5:5
    |
 LL |     let w: &mut [isize];
    |         - binding declared here but left uninitialized
@@ -8,11 +8,11 @@ LL |     w[5] = 0;
    |
 help: consider assigning a value
    |
-LL |     let w: &mut [isize] = value;
+LL |     let w: &mut [isize] = &mut [];
-   |                         +++++++
+   |                         +++++++++
 
 error[E0381]: used binding `w` isn't initialized
-  --> $DIR/borrowck-use-in-index-lvalue.rs:6:5
+  --> $DIR/borrowck-use-in-index-lvalue.rs:8:5
    |
 LL |     let mut w: &mut [isize];
    |         ----- binding declared here but left uninitialized
@@ -21,8 +21,8 @@ LL |     w[5] = 0;
    |
 help: consider assigning a value
    |
-LL |     let mut w: &mut [isize] = value;
+LL |     let mut w: &mut [isize] = &mut [];
-   |                             +++++++
+   |                             +++++++++
 
 error: aborting due to 2 previous errors
 

tests/ui/borrowck/borrowck-use-uninitialized-in-cast-trait.fixed

@@ -0,0 +1,12 @@
+// Variation on `borrowck-use-uninitialized-in-cast` in which we do a
+// trait cast from an uninitialized source. Issue #20791.
+//@ run-rustfix
+#![allow(unused_variables, dead_code)]
+
+trait Foo { fn dummy(&self) { } }
+impl Foo for i32 { }
+
+fn main() {
+    let x: &i32 = &42;
+    let y = x as *const dyn Foo; //~ ERROR [E0381]
+}

tests/ui/borrowck/borrowck-use-uninitialized-in-cast-trait.rs

@@ -1,5 +1,7 @@
 // Variation on `borrowck-use-uninitialized-in-cast` in which we do a
 // trait cast from an uninitialized source. Issue #20791.
+//@ run-rustfix
+#![allow(unused_variables, dead_code)]
 
 trait Foo { fn dummy(&self) { } }
 impl Foo for i32 { }

tests/ui/borrowck/borrowck-use-uninitialized-in-cast-trait.stderr

@@ -1,5 +1,5 @@
 error[E0381]: used binding `x` isn't initialized
-  --> $DIR/borrowck-use-uninitialized-in-cast-trait.rs:9:13
+  --> $DIR/borrowck-use-uninitialized-in-cast-trait.rs:11:13
    |
 LL |     let x: &i32;
    |         - binding declared here but left uninitialized
@@ -8,8 +8,8 @@ LL |     let y = x as *const dyn Foo;
    |
 help: consider assigning a value
    |
-LL |     let x: &i32 = value;
+LL |     let x: &i32 = &42;
-   |                 +++++++
+   |                 +++++
 
 error: aborting due to 1 previous error
 

tests/ui/borrowck/borrowck-use-uninitialized-in-cast.fixed

@@ -0,0 +1,10 @@
+// Check that we detect unused values that are cast to other things.
+// The problem was specified to casting to `*`, as creating unsafe
+// pointers was not being fully checked. Issue #20791.
+//@ run-rustfix
+#![allow(unused_variables)]
+
+fn main() {
+    let x: &i32 = &42;
+    let y = x as *const i32; //~ ERROR [E0381]
+}

tests/ui/borrowck/borrowck-use-uninitialized-in-cast.rs

@@ -1,6 +1,8 @@
 // Check that we detect unused values that are cast to other things.
 // The problem was specified to casting to `*`, as creating unsafe
 // pointers was not being fully checked. Issue #20791.
+//@ run-rustfix
+#![allow(unused_variables)]
 
 fn main() {
     let x: &i32;

tests/ui/borrowck/borrowck-use-uninitialized-in-cast.stderr

@@ -1,5 +1,5 @@
 error[E0381]: used binding `x` isn't initialized
-  --> $DIR/borrowck-use-uninitialized-in-cast.rs:7:13
+  --> $DIR/borrowck-use-uninitialized-in-cast.rs:9:13
    |
 LL |     let x: &i32;
    |         - binding declared here but left uninitialized
@@ -8,8 +8,8 @@ LL |     let y = x as *const i32;
    |
 help: consider assigning a value
    |
-LL |     let x: &i32 = value;
+LL |     let x: &i32 = &42;
-   |                 +++++++
+   |                 +++++
 
 error: aborting due to 1 previous error
 

tests/ui/borrowck/issue-24267-flow-exit.stderr

@@ -10,8 +10,8 @@ LL |     println!("{}", x);
    = note: this error originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info)
 help: consider assigning a value
    |
-LL |     let x: i32 = 0;
+LL |     let x: i32 = 42;
-   |                +++
+   |                ++++
 
 error[E0381]: used binding `x` isn't initialized
   --> $DIR/issue-24267-flow-exit.rs:18:20
@@ -25,8 +25,8 @@ LL |     println!("{}", x);
    = note: this error originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info)
 help: consider assigning a value
    |
-LL |     let x: i32 = 0;
+LL |     let x: i32 = 42;
-   |                +++
+   |                ++++
 
 error: aborting due to 2 previous errors
 

tests/ui/borrowck/issue-62107-match-arm-scopes.stderr

@@ -9,8 +9,8 @@ LL |         ref u if true => {}
    |
 help: consider assigning a value
    |
-LL |     let e: i32 = 0;
+LL |     let e: i32 = 42;
-   |                +++
+   |                ++++
 
 error: aborting due to 1 previous error
 

tests/ui/borrowck/suggest-assign-rvalue.stderr

@@ -8,8 +8,8 @@ LL |     apple(chaenomeles);
    |
 help: consider assigning a value
    |
-LL |     let chaenomeles = 0;
+LL |     let chaenomeles = 42;
-   |                     +++
+   |                     ++++
 
 error[E0381]: used binding `my_float` isn't initialized
   --> $DIR/suggest-assign-rvalue.rs:23:30
@@ -22,8 +22,8 @@ LL |     println!("my_float: {}", my_float);
    = note: this error originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info)
 help: consider assigning a value
    |
-LL |     let my_float: f32 = 0.0;
+LL |     let my_float: f32 = 3.14159;
-   |                       +++++
+   |                       +++++++++
 
 error[E0381]: used binding `demo` isn't initialized
   --> $DIR/suggest-assign-rvalue.rs:26:28
@@ -64,8 +64,8 @@ LL |     println!("arr: {:?}", arr);
    = note: this error originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info)
 help: consider assigning a value
    |
-LL |     let arr: [i32; 5] = value;
+LL |     let arr: [i32; 5] = [42; 5];
-   |                       +++++++
+   |                       +++++++++
 
 error[E0381]: used binding `foo` isn't initialized
   --> $DIR/suggest-assign-rvalue.rs:37:27
@@ -106,8 +106,8 @@ LL |     println!("my_int: {}", *my_int);
    = note: this error originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info)
 help: consider assigning a value
    |
-LL |     let my_int: &i32 = value;
+LL |     let my_int: &i32 = &42;
-   |                      +++++++
+   |                      +++++
 
 error[E0381]: used binding `hello` isn't initialized
   --> $DIR/suggest-assign-rvalue.rs:49:27
@@ -120,8 +120,8 @@ LL |     println!("hello: {}", hello);
    = note: this error originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info)
 help: consider assigning a value
    |
-LL |     let hello: &str = value;
+LL |     let hello: &str = "";
-   |                     +++++++
+   |                     ++++
 
 error[E0381]: used binding `never` isn't initialized
   --> $DIR/suggest-assign-rvalue.rs:53:27

tests/ui/closures/2229_closure_analysis/match/pattern-matching-should-fail.stderr

@@ -79,8 +79,8 @@ LL |     let c1 = || match x { };
    |
 help: consider assigning a value
    |
-LL |     let x: u8 = 0;
+LL |     let x: u8 = 42;
-   |               +++
+   |               ++++
 
 error: aborting due to 8 previous errors
 

tests/ui/const-generics/const-generic-default-wont-borrowck.fixed

@@ -0,0 +1,6 @@
+//@ run-rustfix
+pub struct X<const N: usize = {
+    let s: &'static str = ""; s.len() //~ ERROR E0381
+}>;
+
+fn main() {}

tests/ui/const-generics/const-generic-default-wont-borrowck.rs

@@ -1,4 +1,5 @@
-struct X<const N: usize = {
+//@ run-rustfix
+pub struct X<const N: usize = {
     let s: &'static str; s.len() //~ ERROR E0381
 }>;
 

tests/ui/const-generics/const-generic-default-wont-borrowck.stderr

@@ -1,5 +1,5 @@
 error[E0381]: used binding `s` isn't initialized
-  --> $DIR/const-generic-default-wont-borrowck.rs:2:26
+  --> $DIR/const-generic-default-wont-borrowck.rs:3:26
    |
 LL |     let s: &'static str; s.len()
    |         -                ^ `*s` used here but it isn't initialized
@@ -8,8 +8,8 @@ LL |     let s: &'static str; s.len()
    |
 help: consider assigning a value
    |
-LL |     let s: &'static str = value; s.len()
+LL |     let s: &'static str = ""; s.len()
-   |                         +++++++
+   |                         ++++
 
 error: aborting due to 1 previous error
 

tests/ui/consts/issue-78655.stderr

@@ -8,8 +8,8 @@ LL |     &x
    |
 help: consider assigning a value
    |
-LL |     let x = 0;
+LL |     let x = 42;
-   |           +++
+   |           ++++
 
 error: could not evaluate constant pattern
   --> $DIR/issue-78655.rs:7:9

tests/ui/drop/repeat-drop-2.stderr

@@ -32,8 +32,8 @@ LL |     let _ = [x; 0];
    |
 help: consider assigning a value
    |
-LL |     let x: u8 = 0;
+LL |     let x: u8 = 42;
-   |               +++
+   |               ++++
 
 error: aborting due to 3 previous errors
 

tests/ui/loops/loop-proper-liveness.stderr

@@ -10,8 +10,8 @@ LL |     println!("{:?}", x);
    = note: this error originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info)
 help: consider assigning a value
    |
-LL |     let x: i32 = 0;
+LL |     let x: i32 = 42;
-   |                +++
+   |                ++++
 
 error: aborting due to 1 previous error
 

tests/ui/moves/move-into-dead-array-1.stderr

@@ -8,8 +8,8 @@ LL |     a[i] = d();
    |
 help: consider assigning a value
    |
-LL |     let mut a: [D; 4] = value;
+LL |     let mut a: [D; 4] = [value; 4];
-   |                       +++++++
+   |                       ++++++++++++
 
 error: aborting due to 1 previous error
 

tests/ui/nll/match-cfg-fake-edges.stderr

@@ -126,8 +126,8 @@ LL |         _ if { x; false } => 2,
    |
 help: consider assigning a value
    |
-LL |     let x = 0;
+LL |     let x = 42;
-   |           +++
+   |           ++++
 
 error[E0381]: used binding `x` isn't initialized
   --> $DIR/match-cfg-fake-edges.rs:86:31
@@ -142,8 +142,8 @@ LL |         _ if let Some(()) = { x; None } => 2,
    |
 help: consider assigning a value
    |
-LL |     let x = 0;
+LL |     let x = 42;
-   |           +++
+   |           ++++
 
 error[E0382]: use of moved value: `x`
   --> $DIR/match-cfg-fake-edges.rs:99:22

tests/ui/uninhabited/privately-uninhabited-mir-call.fixed

@@ -0,0 +1,31 @@
+// Verifies that MIR building for a call expression respects
+// privacy when checking if a call return type is uninhabited.
+//@ run-rustfix
+#![allow(unreachable_code, unused_variables)]
+
+pub mod widget {
+    enum Unimplemented {}
+    pub struct Widget(Unimplemented);
+
+    impl Widget {
+        pub fn new() -> Widget {
+            todo!();
+        }
+    }
+
+    pub fn f() {
+        let x: &mut u32;
+        Widget::new();
+        // Ok. Widget type returned from new is known to be uninhabited
+        // and the following code is considered unreachable.
+        *x = 1;
+    }
+}
+
+fn main() {
+    let y: &mut u32 = &mut 42;
+    widget::Widget::new();
+    // Error. Widget type is not known to be uninhabited here,
+    // so the following code is considered reachable.
+    *y = 2; //~ ERROR E0381
+}

tests/ui/uninhabited/privately-uninhabited-mir-call.rs

@@ -1,5 +1,7 @@
 // Verifies that MIR building for a call expression respects
 // privacy when checking if a call return type is uninhabited.
+//@ run-rustfix
+#![allow(unreachable_code, unused_variables)]
 
 pub mod widget {
     enum Unimplemented {}

tests/ui/uninhabited/privately-uninhabited-mir-call.stderr

@@ -1,5 +1,5 @@
 error[E0381]: used binding `y` isn't initialized
-  --> $DIR/privately-uninhabited-mir-call.rs:28:5
+  --> $DIR/privately-uninhabited-mir-call.rs:30:5
    |
 LL |     let y: &mut u32;
    |         - binding declared here but left uninitialized
@@ -9,8 +9,8 @@ LL |     *y = 2;
    |
 help: consider assigning a value
    |
-LL |     let y: &mut u32 = value;
+LL |     let y: &mut u32 = &mut 42;
-   |                     +++++++
+   |                     +++++++++
 
 error: aborting due to 1 previous error