Auto merge of #47098 - estebank:immutable-field, r=nagisa

Reword trying to operate in immutable fields

The previous message ("cannot assign/mutably borrow immutable field")
when trying to modify a field of an immutable binding gave the
(incorrect) impression that fields can be mutable independently of their
ADT's binding. Slightly reword the message to read "cannot
assign/mutably borrow field of immutable binding".

Re #35937.

10 files changed, 44 insertions, 41 deletions

diff --git a/src/test/compile-fail/issue-5500-1.rs b/src/test/compile-fail/issue-5500-1.rs
index 75ff0a12101..4bd147a5e1c 100644
--- a/src/test/compile-fail/issue-5500-1.rs
+++ b/src/test/compile-fail/issue-5500-1.rs
@@ -18,8 +18,8 @@ struct TrieMapIterator<'a> {
 fn main() {
     let a = 5;
     let _iter = TrieMapIterator{node: &a};
-    _iter.node = & //[ast]~ ERROR cannot assign to immutable field `_iter.node`
-                   //[mir]~^ ERROR cannot assign to immutable field `_iter.node` (Ast)
+    _iter.node = & //[ast]~ ERROR cannot assign to field `_iter.node` of immutable binding
+                   //[mir]~^ ERROR cannot assign to field `_iter.node` of immutable binding (Ast)
                    // MIR doesn't generate an error because the code isn't reachable. This is OK
                    // because the test is here to check that the compiler doesn't ICE (cf. #5500).
     panic!()
diff --git a/src/test/ui/did_you_mean/issue-35937.stderr b/src/test/ui/did_you_mean/issue-35937.stderr
index ec44755cb7c..cfaff973170 100644
--- a/src/test/ui/did_you_mean/issue-35937.stderr
+++ b/src/test/ui/did_you_mean/issue-35937.stderr
@@ -1,26 +1,26 @@
-error[E0596]: cannot borrow immutable field `f.v` as mutable
+error[E0596]: cannot borrow field `f.v` of immutable binding as mutable
   --> $DIR/issue-35937.rs:17:5
    |
 16 |     let f = Foo { v: Vec::new() };
    |         - consider changing this to `mut f`
 17 |     f.v.push("cat".to_string()); //~ ERROR cannot borrow
-   |     ^^^ cannot mutably borrow immutable field
+   |     ^^^ cannot mutably borrow field of immutable binding
 
-error[E0594]: cannot assign to immutable field `s.x`
+error[E0594]: cannot assign to field `s.x` of immutable binding
   --> $DIR/issue-35937.rs:26:5
    |
 25 |     let s = S { x: 42 };
    |         - consider changing this to `mut s`
 26 |     s.x += 1; //~ ERROR cannot assign
-   |     ^^^^^^^^ cannot mutably borrow immutable field
+   |     ^^^^^^^^ cannot mutably borrow field of immutable binding
 
-error[E0594]: cannot assign to immutable field `s.x`
+error[E0594]: cannot assign to field `s.x` of immutable binding
   --> $DIR/issue-35937.rs:30:5
    |
 29 | fn bar(s: S) {
    |        - consider changing this to `mut s`
 30 |     s.x += 1; //~ ERROR cannot assign
-   |     ^^^^^^^^ cannot mutably borrow immutable field
+   |     ^^^^^^^^ cannot mutably borrow field of immutable binding
 
 error: aborting due to 3 previous errors
 
diff --git a/src/test/ui/did_you_mean/issue-38147-2.rs b/src/test/ui/did_you_mean/issue-38147-2.rs
index cc6be98bcf8..1a24f471f08 100644
--- a/src/test/ui/did_you_mean/issue-38147-2.rs
+++ b/src/test/ui/did_you_mean/issue-38147-2.rs
@@ -14,7 +14,8 @@ struct Bar<'a> {
 
 impl<'a> Bar<'a> {
     fn f(&mut self) {
-        self.s.push('x'); //~ ERROR cannot borrow immutable borrowed
+        self.s.push('x');
+        //~^ ERROR cannot borrow borrowed content `*self.s` of immutable binding as mutable
     }
 }
 
diff --git a/src/test/ui/did_you_mean/issue-38147-2.stderr b/src/test/ui/did_you_mean/issue-38147-2.stderr
index b09ecf9057c..569bfa11803 100644
--- a/src/test/ui/did_you_mean/issue-38147-2.stderr
+++ b/src/test/ui/did_you_mean/issue-38147-2.stderr
@@ -1,10 +1,10 @@
-error[E0596]: cannot borrow immutable borrowed content `*self.s` as mutable
+error[E0596]: cannot borrow borrowed content `*self.s` of immutable binding as mutable
   --> $DIR/issue-38147-2.rs:17:9
    |
 12 |     s: &'a String
    |        ---------- use `&'a mut String` here to make mutable
 ...
-17 |         self.s.push('x'); //~ ERROR cannot borrow immutable borrowed
+17 |         self.s.push('x');
    |         ^^^^^^ cannot borrow as mutable
 
 error: aborting due to previous error
diff --git a/src/test/ui/did_you_mean/issue-38147-3.rs b/src/test/ui/did_you_mean/issue-38147-3.rs
index 42b29100517..5e2bf06e5d9 100644
--- a/src/test/ui/did_you_mean/issue-38147-3.rs
+++ b/src/test/ui/did_you_mean/issue-38147-3.rs
@@ -14,7 +14,8 @@ struct Qux<'a> {
 
 impl<'a> Qux<'a> {
     fn f(&self) {
-        self.s.push('x'); //~ ERROR cannot borrow immutable borrowed
+        self.s.push('x');
+        //~^ ERROR cannot borrow borrowed content `*self.s` of immutable binding as mutable
     }
 }
 
diff --git a/src/test/ui/did_you_mean/issue-38147-3.stderr b/src/test/ui/did_you_mean/issue-38147-3.stderr
index ca721f133a4..75d904d394a 100644
--- a/src/test/ui/did_you_mean/issue-38147-3.stderr
+++ b/src/test/ui/did_you_mean/issue-38147-3.stderr
@@ -1,10 +1,10 @@
-error[E0596]: cannot borrow immutable borrowed content `*self.s` as mutable
+error[E0596]: cannot borrow borrowed content `*self.s` of immutable binding as mutable
   --> $DIR/issue-38147-3.rs:17:9
    |
 12 |     s: &'a String
    |        ---------- use `&'a mut String` here to make mutable
 ...
-17 |         self.s.push('x'); //~ ERROR cannot borrow immutable borrowed
+17 |         self.s.push('x');
    |         ^^^^^^ cannot borrow as mutable
 
 error: aborting due to previous error
diff --git a/src/test/ui/did_you_mean/issue-39544.rs b/src/test/ui/did_you_mean/issue-39544.rs
index 7cd7768078a..205cbce7094 100644
--- a/src/test/ui/did_you_mean/issue-39544.rs
+++ b/src/test/ui/did_you_mean/issue-39544.rs
@@ -55,5 +55,6 @@ pub fn with_arg(z: Z, w: &Z) {
 pub fn with_tuple() {
     let mut y = 0;
     let x = (&y,);
-    *x.0 = 1; //~ ERROR cannot assign to immutable borrowed content
+    *x.0 = 1;
+    //~^ ERROR cannot assign to borrowed content `*x.0` of immutable binding
 }
diff --git a/src/test/ui/did_you_mean/issue-39544.stderr b/src/test/ui/did_you_mean/issue-39544.stderr
index 1fcb05374f6..d8c089806cd 100644
--- a/src/test/ui/did_you_mean/issue-39544.stderr
+++ b/src/test/ui/did_you_mean/issue-39544.stderr
@@ -1,99 +1,99 @@
-error[E0596]: cannot borrow immutable field `z.x` as mutable
+error[E0596]: cannot borrow field `z.x` of immutable binding as mutable
   --> $DIR/issue-39544.rs:21:18
    |
 20 |     let z = Z { x: X::Y };
    |         - consider changing this to `mut z`
 21 |     let _ = &mut z.x; //~ ERROR cannot borrow
-   |                  ^^^ cannot mutably borrow immutable field
+   |                  ^^^ cannot mutably borrow field of immutable binding
 
-error[E0596]: cannot borrow immutable field `self.x` as mutable
+error[E0596]: cannot borrow field `self.x` of immutable binding as mutable
   --> $DIR/issue-39544.rs:26:22
    |
 25 |     fn foo<'z>(&'z self) {
    |                -------- use `&'z mut self` here to make mutable
 26 |         let _ = &mut self.x; //~ ERROR cannot borrow
-   |                      ^^^^^^ cannot mutably borrow immutable field
+   |                      ^^^^^^ cannot mutably borrow field of immutable binding
 
-error[E0596]: cannot borrow immutable field `self.x` as mutable
+error[E0596]: cannot borrow field `self.x` of immutable binding as mutable
   --> $DIR/issue-39544.rs:30:22
    |
 29 |     fn foo1(&self, other: &Z) {
    |             ----- use `&mut self` here to make mutable
 30 |         let _ = &mut self.x; //~ ERROR cannot borrow
-   |                      ^^^^^^ cannot mutably borrow immutable field
+   |                      ^^^^^^ cannot mutably borrow field of immutable binding
 
-error[E0596]: cannot borrow immutable field `other.x` as mutable
+error[E0596]: cannot borrow field `other.x` of immutable binding as mutable
   --> $DIR/issue-39544.rs:31:22
    |
 29 |     fn foo1(&self, other: &Z) {
    |                           -- use `&mut Z` here to make mutable
 30 |         let _ = &mut self.x; //~ ERROR cannot borrow
 31 |         let _ = &mut other.x; //~ ERROR cannot borrow
-   |                      ^^^^^^^ cannot mutably borrow immutable field
+   |                      ^^^^^^^ cannot mutably borrow field of immutable binding
 
-error[E0596]: cannot borrow immutable field `self.x` as mutable
+error[E0596]: cannot borrow field `self.x` of immutable binding as mutable
   --> $DIR/issue-39544.rs:35:22
    |
 34 |     fn foo2<'a>(&'a self, other: &Z) {
    |                 -------- use `&'a mut self` here to make mutable
 35 |         let _ = &mut self.x; //~ ERROR cannot borrow
-   |                      ^^^^^^ cannot mutably borrow immutable field
+   |                      ^^^^^^ cannot mutably borrow field of immutable binding
 
-error[E0596]: cannot borrow immutable field `other.x` as mutable
+error[E0596]: cannot borrow field `other.x` of immutable binding as mutable
   --> $DIR/issue-39544.rs:36:22
    |
 34 |     fn foo2<'a>(&'a self, other: &Z) {
    |                                  -- use `&mut Z` here to make mutable
 35 |         let _ = &mut self.x; //~ ERROR cannot borrow
 36 |         let _ = &mut other.x; //~ ERROR cannot borrow
-   |                      ^^^^^^^ cannot mutably borrow immutable field
+   |                      ^^^^^^^ cannot mutably borrow field of immutable binding
 
-error[E0596]: cannot borrow immutable field `self.x` as mutable
+error[E0596]: cannot borrow field `self.x` of immutable binding as mutable
   --> $DIR/issue-39544.rs:40:22
    |
 39 |     fn foo3<'a>(self: &'a Self, other: &Z) {
    |                       -------- use `&'a mut Self` here to make mutable
 40 |         let _ = &mut self.x; //~ ERROR cannot borrow
-   |                      ^^^^^^ cannot mutably borrow immutable field
+   |                      ^^^^^^ cannot mutably borrow field of immutable binding
 
-error[E0596]: cannot borrow immutable field `other.x` as mutable
+error[E0596]: cannot borrow field `other.x` of immutable binding as mutable
   --> $DIR/issue-39544.rs:41:22
    |
 39 |     fn foo3<'a>(self: &'a Self, other: &Z) {
    |                                        -- use `&mut Z` here to make mutable
 40 |         let _ = &mut self.x; //~ ERROR cannot borrow
 41 |         let _ = &mut other.x; //~ ERROR cannot borrow
-   |                      ^^^^^^^ cannot mutably borrow immutable field
+   |                      ^^^^^^^ cannot mutably borrow field of immutable binding
 
-error[E0596]: cannot borrow immutable field `other.x` as mutable
+error[E0596]: cannot borrow field `other.x` of immutable binding as mutable
   --> $DIR/issue-39544.rs:45:22
    |
 44 |     fn foo4(other: &Z) {
    |                    -- use `&mut Z` here to make mutable
 45 |         let _ = &mut other.x; //~ ERROR cannot borrow
-   |                      ^^^^^^^ cannot mutably borrow immutable field
+   |                      ^^^^^^^ cannot mutably borrow field of immutable binding
 
-error[E0596]: cannot borrow immutable field `z.x` as mutable
+error[E0596]: cannot borrow field `z.x` of immutable binding as mutable
   --> $DIR/issue-39544.rs:51:18
    |
 50 | pub fn with_arg(z: Z, w: &Z) {
    |                 - consider changing this to `mut z`
 51 |     let _ = &mut z.x; //~ ERROR cannot borrow
-   |                  ^^^ cannot mutably borrow immutable field
+   |                  ^^^ cannot mutably borrow field of immutable binding
 
-error[E0596]: cannot borrow immutable field `w.x` as mutable
+error[E0596]: cannot borrow field `w.x` of immutable binding as mutable
   --> $DIR/issue-39544.rs:52:18
    |
 50 | pub fn with_arg(z: Z, w: &Z) {
    |                          -- use `&mut Z` here to make mutable
 51 |     let _ = &mut z.x; //~ ERROR cannot borrow
 52 |     let _ = &mut w.x; //~ ERROR cannot borrow
-   |                  ^^^ cannot mutably borrow immutable field
+   |                  ^^^ cannot mutably borrow field of immutable binding
 
-error[E0594]: cannot assign to immutable borrowed content `*x.0`
+error[E0594]: cannot assign to borrowed content `*x.0` of immutable binding
   --> $DIR/issue-39544.rs:58:5
    |
-58 |     *x.0 = 1; //~ ERROR cannot assign to immutable borrowed content
+58 |     *x.0 = 1;
    |     ^^^^^^^^ cannot borrow as mutable
 
 error: aborting due to 12 previous errors
diff --git a/src/test/ui/span/borrowck-call-is-borrow-issue-12224.rs b/src/test/ui/span/borrowck-call-is-borrow-issue-12224.rs
index 66673c152d5..8e03c303e54 100644
--- a/src/test/ui/span/borrowck-call-is-borrow-issue-12224.rs
+++ b/src/test/ui/span/borrowck-call-is-borrow-issue-12224.rs
@@ -42,7 +42,7 @@ fn test3<F>(f: &mut F) where F: FnMut() {
 
 fn test4(f: &Test) {
     f.f.call_mut(())
-    //~^ ERROR: cannot borrow immutable `Box` content `*f.f` as mutable
+    //~^ ERROR: cannot borrow `Box` content `*f.f` of immutable binding as mutable
 }
 
 fn test5(f: &mut Test) {
diff --git a/src/test/ui/span/borrowck-call-is-borrow-issue-12224.stderr b/src/test/ui/span/borrowck-call-is-borrow-issue-12224.stderr
index 542ee997046..581b366af1c 100644
--- a/src/test/ui/span/borrowck-call-is-borrow-issue-12224.stderr
+++ b/src/test/ui/span/borrowck-call-is-borrow-issue-12224.stderr
@@ -19,7 +19,7 @@ error[E0596]: cannot borrow immutable borrowed content `*f` as mutable
 35 |     (*f)();
    |     ^^^^ cannot borrow as mutable
 
-error[E0596]: cannot borrow immutable `Box` content `*f.f` as mutable
+error[E0596]: cannot borrow `Box` content `*f.f` of immutable binding as mutable
   --> $DIR/borrowck-call-is-borrow-issue-12224.rs:44:5
    |
 43 | fn test4(f: &Test) {