Rollup merge of #40841 - arielb1:immutable-blame, r=pnkfelix

borrowck: consolidate `mut` suggestions

This converts all of borrowck's `mut` suggestions to a new
`mc::ImmutabilityBlame` API instead of the current mix of various hacks.

Fixes #35937.
Fixes #40823.
Fixes #40859.

cc @estebank
r? @pnkfelix

src/test/compile-fail/augmented-assignments.rs

@@ -27,7 +27,7 @@ fn main() {
     x;  //~ value moved here
 
     let y = Int(2);
-    //~^use `mut y` here to make mutable
+    //~^ consider changing this to `mut y`
     y   //~ error: cannot borrow immutable local variable `y` as mutable
         //~| cannot borrow
     +=

src/test/compile-fail/borrowck/borrowck-issue-14498.rs

@@ -23,7 +23,7 @@ fn indirect_write_to_imm_box() {
     let mut x: isize = 1;
     let y: Box<_> = box &mut x;
     let p = &y;
-    ***p = 2; //~ ERROR cannot assign to data in an immutable container
+    ***p = 2; //~ ERROR cannot assign to data in a `&` reference
     drop(p);
 }
 
@@ -43,7 +43,6 @@ fn borrow_in_var_from_var_via_imm_box() {
     let p = &y;
     let q = &***p;
     **y = 2; //~ ERROR cannot assign to `**y` because it is borrowed
-    //~^         ERROR cannot assign to data in an immutable container
     drop(p);
     drop(q);
 }
@@ -64,7 +63,6 @@ fn borrow_in_var_from_field_via_imm_box() {
     let p = &y;
     let q = &***p;
     **y = 2; //~ ERROR cannot assign to `**y` because it is borrowed
-    //~^         ERROR cannot assign to data in an immutable container
     drop(p);
     drop(q);
 }
@@ -85,7 +83,6 @@ fn borrow_in_field_from_var_via_imm_box() {
     let p = &y.a;
     let q = &***p;
     **y.a = 2; //~ ERROR cannot assign to `**y.a` because it is borrowed
-    //~^           ERROR cannot assign to data in an immutable container
     drop(p);
     drop(q);
 }
@@ -106,7 +103,6 @@ fn borrow_in_field_from_field_via_imm_box() {
     let p = &y.a;
     let q = &***p;
     **y.a = 2; //~ ERROR cannot assign to `**y.a` because it is borrowed
-    //~^           ERROR cannot assign to data in an immutable container
     drop(p);
     drop(q);
 }

src/test/compile-fail/issue-33819.rs

@@ -12,7 +12,7 @@ fn main() {
     match op {
         Some(ref v) => { let a = &mut v; },
         //~^ ERROR:cannot borrow immutable
-        //~| use `ref mut v` here to make mutable
+        //~| cannot borrow mutably
         None => {},
     }
 }

src/test/compile-fail/mut-suggestion.rs

@@ -17,7 +17,7 @@ impl S {
 }
 
 fn func(arg: S) {
-    //~^ here to make mutable
+    //~^ consider changing this to `mut arg`
     arg.mutate();
     //~^ ERROR cannot borrow immutable argument
     //~| cannot borrow mutably
@@ -25,7 +25,7 @@ fn func(arg: S) {
 
 fn main() {
     let local = S;
-    //~^ here to make mutable
+    //~^ consider changing this to `mut local`
     local.mutate();
     //~^ ERROR cannot borrow immutable local variable
     //~| cannot borrow mutably

src/test/ui/codemap_tests/huge_multispan_highlight.stderr

@@ -2,7 +2,7 @@ error: cannot borrow immutable local variable `x` as mutable
    --> $DIR/huge_multispan_highlight.rs:100:18
     |
 12  |     let x = "foo";
-    |         - use `mut x` here to make mutable
+    |         - consider changing this to `mut x`
 ...
 100 |     let y = &mut x;
     |                  ^ cannot borrow mutably

src/test/ui/did_you_mean/issue-31424.stderr

@@ -10,6 +10,8 @@ error: cannot borrow immutable argument `self` as mutable
 error: cannot borrow immutable argument `self` as mutable
   --> $DIR/issue-31424.rs:23:15
    |
+22 |     fn bar(self: &mut Self) {
+   |            ---- consider changing this to `mut self`
 23 |         (&mut self).bar();
    |               ^^^^ cannot borrow mutably
 

src/test/ui/did_you_mean/issue-35937.rs

@@ -0,0 +1,31 @@
+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+struct Foo {
+    pub v: Vec<String>
+}
+
+fn main() {
+    let f = Foo { v: Vec::new() };
+    f.v.push("cat".to_string());
+}
+
+
+struct S {
+    x: i32,
+}
+fn foo() {
+    let s = S { x: 42 };
+    s.x += 1;
+}
+
+fn bar(s: S) {
+    s.x += 1;
+}

src/test/ui/did_you_mean/issue-35937.stderr

@@ -0,0 +1,26 @@
+error: cannot borrow immutable field `f.v` 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());
+   |     ^^^ cannot mutably borrow immutable field
+
+error: cannot assign to immutable field `s.x`
+  --> $DIR/issue-35937.rs:26:5
+   |
+25 |     let s = S { x: 42 };
+   |         - consider changing this to `mut s`
+26 |     s.x += 1;
+   |     ^^^^^^^^ cannot mutably borrow immutable field
+
+error: cannot assign to immutable field `s.x`
+  --> $DIR/issue-35937.rs:30:5
+   |
+29 | fn bar(s: S) {
+   |        - consider changing this to `mut s`
+30 |     s.x += 1;
+   |     ^^^^^^^^ cannot mutably borrow immutable field
+
+error: aborting due to 3 previous errors
+

src/test/ui/did_you_mean/issue-38147-2.stderr

@@ -2,7 +2,7 @@ error: cannot borrow immutable borrowed content `*self.s` as mutable
   --> $DIR/issue-38147-2.rs:17:9
    |
 12 |     s: &'a String
-   |     ------------- use `&'a mut String` here to make mutable
+   |        ---------- use `&'a mut String` here to make mutable
 ...
 17 |         self.s.push('x');
    |         ^^^^^^ cannot borrow as mutable

src/test/ui/did_you_mean/issue-38147-3.stderr

@@ -2,10 +2,8 @@ error: cannot borrow immutable borrowed content `*self.s` as mutable
   --> $DIR/issue-38147-3.rs:17:9
    |
 12 |     s: &'a String
-   |     ------------- use `&'a mut String` here to make mutable
+   |        ---------- use `&'a mut String` here to make mutable
 ...
-16 |     fn f(&self) {
-   |          ----- use `&mut self` here to make mutable
 17 |         self.s.push('x');
    |         ^^^^^^ cannot borrow as mutable
 

src/test/ui/did_you_mean/issue-39544.rs

@@ -8,11 +8,11 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-enum X {
+pub enum X {
     Y
 }
 
-struct Z {
+pub struct Z {
     x: X
 }
 
@@ -20,3 +20,34 @@ fn main() {
     let z = Z { x: X::Y };
     let _ = &mut z.x;
 }
+
+impl Z {
+    fn foo<'z>(&'z self) {
+        let _ = &mut self.x;
+    }
+
+    fn foo1(&self, other: &Z) {
+        let _ = &mut self.x;
+        let _ = &mut other.x;
+    }
+
+    fn foo2<'a>(&'a self, other: &Z) {
+        let _ = &mut self.x;
+        let _ = &mut other.x;
+    }
+
+    fn foo3<'a>(self: &'a Self, other: &Z) {
+        let _ = &mut self.x;
+        let _ = &mut other.x;
+    }
+
+    fn foo4(other: &Z) {
+        let _ = &mut other.x;
+    }
+
+}
+
+pub fn with_arg(z: Z, w: &Z) {
+    let _ = &mut z.x;
+    let _ = &mut w.x;
+}

src/test/ui/did_you_mean/issue-39544.stderr

@@ -6,5 +6,89 @@ error: cannot borrow immutable field `z.x` as mutable
 21 |     let _ = &mut z.x;
    |                  ^^^ cannot mutably borrow immutable field
 
-error: aborting due to previous error
+error: cannot borrow immutable field `self.x` 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;
+   |                      ^^^^^^ cannot mutably borrow immutable field
+
+error: cannot borrow immutable field `self.x` 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;
+   |                      ^^^^^^ cannot mutably borrow immutable field
+
+error: cannot borrow immutable field `other.x` 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;
+31 |         let _ = &mut other.x;
+   |                      ^^^^^^^ cannot mutably borrow immutable field
+
+error: cannot borrow immutable field `self.x` 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;
+   |                      ^^^^^^ cannot mutably borrow immutable field
+
+error: cannot borrow immutable field `other.x` 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;
+36 |         let _ = &mut other.x;
+   |                      ^^^^^^^ cannot mutably borrow immutable field
+
+error: cannot borrow immutable field `self.x` 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;
+   |                      ^^^^^^ cannot mutably borrow immutable field
+
+error: cannot borrow immutable field `other.x` 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;
+41 |         let _ = &mut other.x;
+   |                      ^^^^^^^ cannot mutably borrow immutable field
+
+error: cannot borrow immutable field `other.x` 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;
+   |                      ^^^^^^^ cannot mutably borrow immutable field
+
+error: cannot borrow immutable field `z.x` 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;
+   |                  ^^^ cannot mutably borrow immutable field
+
+error: cannot borrow immutable field `w.x` 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;
+52 |     let _ = &mut w.x;
+   |                  ^^^ cannot mutably borrow immutable field
+
+error: aborting due to 11 previous errors
 

src/test/ui/did_you_mean/issue-40823.rs

@@ -0,0 +1,14 @@
+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+fn main() {
+    let mut buf = &[1, 2, 3, 4];
+    buf.iter_mut();
+}

src/test/ui/did_you_mean/issue-40823.stderr

@@ -0,0 +1,8 @@
+error: cannot borrow immutable borrowed content `*buf` as mutable
+  --> $DIR/issue-40823.rs:13:5
+   |
+13 |     buf.iter_mut();
+   |     ^^^ cannot borrow as mutable
+
+error: aborting due to previous error
+

src/test/ui/span/borrowck-borrow-overloaded-auto-deref-mut.stderr

@@ -2,7 +2,7 @@ error: cannot borrow immutable argument `x` as mutable
   --> $DIR/borrowck-borrow-overloaded-auto-deref-mut.rs:63:24
    |
 62 | fn deref_mut_field1(x: Own<Point>) {
-   |                     - use `mut x` here to make mutable
+   |                     - consider changing this to `mut x`
 63 |     let __isize = &mut x.y; //~ ERROR cannot borrow
    |                        ^ cannot borrow mutably
 
@@ -28,7 +28,7 @@ error: cannot borrow immutable argument `x` as mutable
   --> $DIR/borrowck-borrow-overloaded-auto-deref-mut.rs:98:5
    |
 97 | fn assign_field1<'a>(x: Own<Point>) {
-   |                      - use `mut x` here to make mutable
+   |                      - consider changing this to `mut x`
 98 |     x.y = 3; //~ ERROR cannot borrow
    |     ^ cannot borrow mutably
 
@@ -54,7 +54,7 @@ error: cannot borrow immutable argument `x` as mutable
    --> $DIR/borrowck-borrow-overloaded-auto-deref-mut.rs:119:5
     |
 118 | fn deref_mut_method1(x: Own<Point>) {
-    |                      - use `mut x` here to make mutable
+    |                      - consider changing this to `mut x`
 119 |     x.set(0, 0); //~ ERROR cannot borrow
     |     ^ cannot borrow mutably
 
@@ -70,7 +70,7 @@ error: cannot borrow immutable argument `x` as mutable
    --> $DIR/borrowck-borrow-overloaded-auto-deref-mut.rs:139:6
     |
 138 | fn assign_method1<'a>(x: Own<Point>) {
-    |                       - use `mut x` here to make mutable
+    |                       - consider changing this to `mut x`
 139 |     *x.y_mut() = 3; //~ ERROR cannot borrow
     |      ^ cannot borrow mutably
 

src/test/ui/span/borrowck-borrow-overloaded-deref-mut.stderr

@@ -2,7 +2,7 @@ error: cannot borrow immutable argument `x` as mutable
   --> $DIR/borrowck-borrow-overloaded-deref-mut.rs:39:25
    |
 38 | fn deref_mut1(x: Own<isize>) {
-   |               - use `mut x` here to make mutable
+   |               - consider changing this to `mut x`
 39 |     let __isize = &mut *x; //~ ERROR cannot borrow
    |                         ^ cannot borrow mutably
 
@@ -18,7 +18,7 @@ error: cannot borrow immutable argument `x` as mutable
   --> $DIR/borrowck-borrow-overloaded-deref-mut.rs:59:6
    |
 58 | fn assign1<'a>(x: Own<isize>) {
-   |                - use `mut x` here to make mutable
+   |                - consider changing this to `mut x`
 59 |     *x = 3; //~ ERROR cannot borrow
    |      ^ cannot borrow mutably
 

src/test/ui/span/borrowck-object-mutability.stderr

@@ -10,6 +10,9 @@ error: cannot borrow immutable borrowed content `*x` as mutable
 error: cannot borrow immutable `Box` content `*x` as mutable
   --> $DIR/borrowck-object-mutability.rs:29:5
    |
+27 | fn owned_receiver(x: Box<Foo>) {
+   |                   - consider changing this to `mut x`
+28 |     x.borrowed();
 29 |     x.borrowed_mut(); //~ ERROR cannot borrow
    |     ^ cannot borrow as mutable