Compiler error messages: reduce assertiveness of message E0384

This message is emitted as guidance by the compiler when a developer attempts to reassign a value to an immutable variable.  Following the message will always currently work, but it may not always be the best course of action; following the 'consider ...' messaging pattern provides a hint to the developer that it could be wise to explore other alternatives.

compiler/rustc_mir/src/borrow_check/diagnostics/conflict_errors.rs

@@ -1681,7 +1681,7 @@ pub(in crate::borrow_check) fn report_illegal_reassignment(
                 if decl.can_be_made_mutable() {
                     err.span_suggestion(
                         decl.source_info.span,
-                        "make this binding mutable",
+                        "consider making this binding mutable",
                         format!("mut {}", name),
                         Applicability::MachineApplicable,
                     );

src/test/ui/assign-imm-local-twice.rs

@@ -1,6 +1,6 @@
 fn test() {
     let v: isize;
-    //~^ HELP make this binding mutable
+    //~^ HELP consider making this binding mutable
     //~| SUGGESTION mut v
     v = 1; //~ NOTE first assignment
     println!("v={}", v);

src/test/ui/assign-imm-local-twice.stderr

@@ -2,7 +2,7 @@ error[E0384]: cannot assign twice to immutable variable `v`
   --> $DIR/assign-imm-local-twice.rs:7:5
    |
 LL |     let v: isize;
-   |         - help: make this binding mutable: `mut v`
+   |         - help: consider making this binding mutable: `mut v`
 ...
 LL |     v = 1;
    |     ----- first assignment to `v`

src/test/ui/async-await/issue-61452.stderr

@@ -13,7 +13,7 @@ LL | pub async fn g(x: usize) {
    |                -
    |                |
    |                first assignment to `x`
-   |                help: make this binding mutable: `mut x`
+   |                help: consider making this binding mutable: `mut x`
 LL |     x += 1;
    |     ^^^^^^ cannot assign twice to immutable variable
 

src/test/ui/borrowck/borrowck-asm.stderr

@@ -29,7 +29,7 @@ LL |         let x = 3;
    |             -
    |             |
    |             first assignment to `x`
-   |             help: make this binding mutable: `mut x`
+   |             help: consider making this binding mutable: `mut x`
 LL |         unsafe {
 LL |             llvm_asm!("nop" : "=r"(x));
    |                                    ^ cannot assign twice to immutable variable
@@ -41,7 +41,7 @@ LL |         let x = 3;
    |             -
    |             |
    |             first assignment to `x`
-   |             help: make this binding mutable: `mut x`
+   |             help: consider making this binding mutable: `mut x`
 LL |         unsafe {
 LL |             llvm_asm!("nop" : "+r"(x));
    |                                    ^ cannot assign twice to immutable variable

src/test/ui/borrowck/borrowck-match-binding-is-assignment.stderr

@@ -5,7 +5,7 @@ LL |         x => {
    |         -
    |         |
    |         first assignment to `x`
-   |         help: make this binding mutable: `mut x`
+   |         help: consider making this binding mutable: `mut x`
 LL |             x += 1;
    |             ^^^^^^ cannot assign twice to immutable variable
 
@@ -16,7 +16,7 @@ LL |         E::Foo(x) => {
    |                -
    |                |
    |                first assignment to `x`
-   |                help: make this binding mutable: `mut x`
+   |                help: consider making this binding mutable: `mut x`
 LL |             x += 1;
    |             ^^^^^^ cannot assign twice to immutable variable
 
@@ -27,7 +27,7 @@ LL |         S { bar: x } => {
    |                  -
    |                  |
    |                  first assignment to `x`
-   |                  help: make this binding mutable: `mut x`
+   |                  help: consider making this binding mutable: `mut x`
 LL |             x += 1;
    |             ^^^^^^ cannot assign twice to immutable variable
 
@@ -38,7 +38,7 @@ LL |         (x,) => {
    |          -
    |          |
    |          first assignment to `x`
-   |          help: make this binding mutable: `mut x`
+   |          help: consider making this binding mutable: `mut x`
 LL |             x += 1;
    |             ^^^^^^ cannot assign twice to immutable variable
 
@@ -49,7 +49,7 @@ LL |         [x,_,_] => {
    |          -
    |          |
    |          first assignment to `x`
-   |          help: make this binding mutable: `mut x`
+   |          help: consider making this binding mutable: `mut x`
 LL |             x += 1;
    |             ^^^^^^ cannot assign twice to immutable variable
 

src/test/ui/borrowck/immutable-arg.stderr

@@ -2,7 +2,7 @@ error[E0384]: cannot assign to immutable argument `_x`
   --> $DIR/immutable-arg.rs:2:5
    |
 LL | fn foo(_x: u32) {
-   |        -- help: make this binding mutable: `mut _x`
+   |        -- help: consider making this binding mutable: `mut _x`
 LL |     _x = 4;
    |     ^^^^^^ cannot assign to immutable argument
 

src/test/ui/borrowck/issue-45199.rs

@@ -1,6 +1,6 @@
 fn test_drop_replace() {
     let b: Box<isize>;
-    //~^ HELP make this binding mutable
+    //~^ HELP consider making this binding mutable
     //~| SUGGESTION mut b
     b = Box::new(1);    //~ NOTE first assignment
     b = Box::new(2);    //~ ERROR cannot assign twice to immutable variable `b`
@@ -9,13 +9,13 @@ fn test_drop_replace() {
 
 fn test_call() {
     let b = Box::new(1);    //~ NOTE first assignment
-                            //~| HELP make this binding mutable
+                            //~| HELP consider making this binding mutable
                             //~| SUGGESTION mut b
     b = Box::new(2);        //~ ERROR cannot assign twice to immutable variable `b`
                             //~| NOTE cannot assign twice to immutable
 }
 
-fn test_args(b: Box<i32>) {  //~ HELP make this binding mutable
+fn test_args(b: Box<i32>) {  //~ HELP consider making this binding mutable
                                 //~| SUGGESTION mut b
     b = Box::new(2);            //~ ERROR cannot assign to immutable argument `b`
                                 //~| NOTE cannot assign to immutable argument

src/test/ui/borrowck/issue-45199.stderr

@@ -2,7 +2,7 @@ error[E0384]: cannot assign twice to immutable variable `b`
   --> $DIR/issue-45199.rs:6:5
    |
 LL |     let b: Box<isize>;
-   |         - help: make this binding mutable: `mut b`
+   |         - help: consider making this binding mutable: `mut b`
 ...
 LL |     b = Box::new(1);
    |     - first assignment to `b`
@@ -16,7 +16,7 @@ LL |     let b = Box::new(1);
    |         -
    |         |
    |         first assignment to `b`
-   |         help: make this binding mutable: `mut b`
+   |         help: consider making this binding mutable: `mut b`
 ...
 LL |     b = Box::new(2);
    |     ^ cannot assign twice to immutable variable
@@ -25,7 +25,7 @@ error[E0384]: cannot assign to immutable argument `b`
   --> $DIR/issue-45199.rs:20:5
    |
 LL | fn test_args(b: Box<i32>) {
-   |              - help: make this binding mutable: `mut b`
+   |              - help: consider making this binding mutable: `mut b`
 LL |
 LL |     b = Box::new(2);
    |     ^ cannot assign to immutable argument

src/test/ui/command-line-diagnostics.stderr

@@ -5,7 +5,7 @@ LL |     let x = 42;
    |         -
    |         |
    |         first assignment to `x`
-   |         help: make this binding mutable: `mut x`
+   |         help: consider making this binding mutable: `mut x`
 LL |     x = 43;
    |     ^^^^^^ cannot assign twice to immutable variable
 

src/test/ui/lifetimes/lifetime-errors/ex3-both-anon-regions-one-is-struct-2.nll.stderr

@@ -12,7 +12,7 @@ error[E0384]: cannot assign to immutable argument `y`
   --> $DIR/ex3-both-anon-regions-one-is-struct-2.rs:4:5
    |
 LL | fn foo(mut x: Ref, y: &u32) {
-   |                    - help: make this binding mutable: `mut y`
+   |                    - help: consider making this binding mutable: `mut y`
 LL |     y = x.b;
    |     ^^^^^^^ cannot assign to immutable argument
 

src/test/ui/lifetimes/lifetime-errors/liveness-assign-imm-local-notes.stderr

@@ -2,7 +2,7 @@ error[E0384]: cannot assign twice to immutable variable `x`
   --> $DIR/liveness-assign-imm-local-notes.rs:10:9
    |
 LL |     let x;
-   |         - help: make this binding mutable: `mut x`
+   |         - help: consider making this binding mutable: `mut x`
 ...
 LL |         x = 2;
    |         ----- first assignment to `x`
@@ -13,7 +13,7 @@ error[E0384]: cannot assign twice to immutable variable `x`
   --> $DIR/liveness-assign-imm-local-notes.rs:21:13
    |
 LL |         let x;
-   |             - help: make this binding mutable: `mut x`
+   |             - help: consider making this binding mutable: `mut x`
 ...
 LL |             x = 2;
    |             ----- first assignment to `x`
@@ -24,7 +24,7 @@ error[E0384]: cannot assign twice to immutable variable `x`
   --> $DIR/liveness-assign-imm-local-notes.rs:30:13
    |
 LL |     let x;
-   |         - help: make this binding mutable: `mut x`
+   |         - help: consider making this binding mutable: `mut x`
 ...
 LL |             x = 1;
    |             ^^^^^ cannot assign twice to immutable variable
@@ -33,7 +33,7 @@ error[E0384]: cannot assign twice to immutable variable `x`
   --> $DIR/liveness-assign-imm-local-notes.rs:32:13
    |
 LL |     let x;
-   |         - help: make this binding mutable: `mut x`
+   |         - help: consider making this binding mutable: `mut x`
 ...
 LL |             x = 1;
    |             ----- first assignment to `x`

src/test/ui/liveness/liveness-assign/liveness-assign-imm-local-in-loop.rs

@@ -1,6 +1,6 @@
 fn test() {
     let v: isize;
-    //~^ HELP make this binding mutable
+    //~^ HELP consider making this binding mutable
     //~| SUGGESTION mut v
     loop {
         v = 1; //~ ERROR cannot assign twice to immutable variable `v`

src/test/ui/liveness/liveness-assign/liveness-assign-imm-local-in-loop.stderr

@@ -2,7 +2,7 @@ error[E0384]: cannot assign twice to immutable variable `v`
   --> $DIR/liveness-assign-imm-local-in-loop.rs:6:9
    |
 LL |     let v: isize;
-   |         - help: make this binding mutable: `mut v`
+   |         - help: consider making this binding mutable: `mut v`
 ...
 LL |         v = 1;
    |         ^^^^^ cannot assign twice to immutable variable

src/test/ui/liveness/liveness-assign/liveness-assign-imm-local-in-op-eq.rs

@@ -1,6 +1,6 @@
 fn test() {
     let v: isize;
-    //~^ HELP make this binding mutable
+    //~^ HELP consider making this binding mutable
     //~| SUGGESTION mut v
     v = 2;  //~ NOTE first assignment
     v += 1; //~ ERROR cannot assign twice to immutable variable `v`

src/test/ui/liveness/liveness-assign/liveness-assign-imm-local-in-op-eq.stderr

@@ -2,7 +2,7 @@ error[E0384]: cannot assign twice to immutable variable `v`
   --> $DIR/liveness-assign-imm-local-in-op-eq.rs:6:5
    |
 LL |     let v: isize;
-   |         - help: make this binding mutable: `mut v`
+   |         - help: consider making this binding mutable: `mut v`
 ...
 LL |     v = 2;
    |     ----- first assignment to `v`

src/test/ui/liveness/liveness-assign/liveness-assign-imm-local-with-drop.rs

@@ -1,6 +1,6 @@
 fn test() {
     let b = Box::new(1); //~ NOTE first assignment
-                         //~| HELP make this binding mutable
+                         //~| HELP consider making this binding mutable
                          //~| SUGGESTION mut b
     drop(b);
     b = Box::new(2); //~ ERROR cannot assign twice to immutable variable `b`

src/test/ui/liveness/liveness-assign/liveness-assign-imm-local-with-drop.stderr

@@ -5,7 +5,7 @@ LL |     let b = Box::new(1);
    |         -
    |         |
    |         first assignment to `b`
-   |         help: make this binding mutable: `mut b`
+   |         help: consider making this binding mutable: `mut b`
 ...
 LL |     b = Box::new(2);
    |     ^ cannot assign twice to immutable variable

src/test/ui/liveness/liveness-assign/liveness-assign-imm-local-with-init.rs

@@ -1,6 +1,6 @@
 fn test() {
     let v: isize = 1; //~ NOTE first assignment
-                      //~| HELP make this binding mutable
+                      //~| HELP consider making this binding mutable
                       //~| SUGGESTION mut v
     v.clone();
     v = 2; //~ ERROR cannot assign twice to immutable variable `v`

src/test/ui/liveness/liveness-assign/liveness-assign-imm-local-with-init.stderr

@@ -5,7 +5,7 @@ LL |     let v: isize = 1;
    |         -
    |         |
    |         first assignment to `v`
-   |         help: make this binding mutable: `mut v`
+   |         help: consider making this binding mutable: `mut v`
 ...
 LL |     v = 2;
    |     ^^^^^ cannot assign twice to immutable variable

src/test/ui/llvm-asm/llvm-asm-out-assign-imm.stderr

@@ -2,7 +2,7 @@ error[E0384]: cannot assign twice to immutable variable `x`
   --> $DIR/llvm-asm-out-assign-imm.rs:25:39
    |
 LL |     let x: isize;
-   |         - help: make this binding mutable: `mut x`
+   |         - help: consider making this binding mutable: `mut x`
 LL |     x = 1;
    |     ----- first assignment to `x`
 ...

src/test/ui/mut/mut-pattern-internal-mutability.stderr

@@ -5,7 +5,7 @@ LL |     let &mut x = foo;
    |              -
    |              |
    |              first assignment to `x`
-   |              help: make this binding mutable: `mut x`
+   |              help: consider making this binding mutable: `mut x`
 LL |     x += 1;
    |     ^^^^^^ cannot assign twice to immutable variable
 

src/test/ui/pattern/move-ref-patterns/borrowck-move-ref-pattern.stderr

@@ -16,7 +16,7 @@ LL |     let [ref _x0_hold, _x1, ref xs_hold @ ..] = arr;
    |                        ---
    |                        |
    |                        first assignment to `_x1`
-   |                        help: make this binding mutable: `mut _x1`
+   |                        help: consider making this binding mutable: `mut _x1`
 LL |     _x1 = U;
    |     ^^^^^^^ cannot assign twice to immutable variable
 
@@ -74,7 +74,7 @@ LL |     let (ref _x0, _x1, ref _x2, ..) = tup;
    |                   ---
    |                   |
    |                   first assignment to `_x1`
-   |                   help: make this binding mutable: `mut _x1`
+   |                   help: consider making this binding mutable: `mut _x1`
 LL |     _x1 = U;
    |     ^^^^^^^ cannot assign twice to immutable variable