Rollup merge of #67538 - varkor:lhs-assign-diagnostics, r=Centril

Improve diagnostics for invalid assignment

- Improve wording and span information for invalid assignment diagnostics.
- Link to https://github.com/rust-lang/rfcs/issues/372 when it appears the user is trying a destructuring assignment.
- Make the equality constraint in `where` clauses error consistent with the invalid assignment error.

18 files changed, 254 insertions, 58 deletions

diff --git a/src/test/ui-fulldeps/pprust-expr-roundtrip.rs b/src/test/ui-fulldeps/pprust-expr-roundtrip.rs
index 0c050e31413..36d47cea13b 100644
--- a/src/test/ui-fulldeps/pprust-expr-roundtrip.rs
+++ b/src/test/ui-fulldeps/pprust-expr-roundtrip.rs
@@ -126,8 +126,8 @@ fn iter_exprs(depth: usize, f: &mut dyn FnMut(P<Expr>)) {
                                           DUMMY_SP)));
             },
             12 => {
-                iter_exprs(depth - 1, &mut |e| g(ExprKind::Assign(e, make_x())));
-                iter_exprs(depth - 1, &mut |e| g(ExprKind::Assign(make_x(), e)));
+                iter_exprs(depth - 1, &mut |e| g(ExprKind::Assign(e, make_x(), DUMMY_SP)));
+                iter_exprs(depth - 1, &mut |e| g(ExprKind::Assign(make_x(), e, DUMMY_SP)));
             },
             13 => {
                 iter_exprs(depth - 1, &mut |e| g(ExprKind::Field(e, Ident::from_str("f"))));
diff --git a/src/test/ui/bad/bad-expr-lhs.rs b/src/test/ui/bad/bad-expr-lhs.rs
index 2cd8bc9d473..d7cf1b77005 100644
--- a/src/test/ui/bad/bad-expr-lhs.rs
+++ b/src/test/ui/bad/bad-expr-lhs.rs
@@ -1,10 +1,10 @@
 fn main() {
-    1 = 2; //~ ERROR invalid left-hand side expression
-    1 += 2; //~ ERROR invalid left-hand side expression
-    (1, 2) = (3, 4); //~ ERROR invalid left-hand side expression
+    1 = 2; //~ ERROR invalid left-hand side of assignment
+    1 += 2; //~ ERROR invalid left-hand side of assignment
+    (1, 2) = (3, 4); //~ ERROR invalid left-hand side of assignment
 
     let (a, b) = (1, 2);
-    (a, b) = (3, 4); //~ ERROR invalid left-hand side expression
+    (a, b) = (3, 4); //~ ERROR invalid left-hand side of assignment
 
-    None = Some(3); //~ ERROR invalid left-hand side expression
+    None = Some(3); //~ ERROR invalid left-hand side of assignment
 }
diff --git a/src/test/ui/bad/bad-expr-lhs.stderr b/src/test/ui/bad/bad-expr-lhs.stderr
index a0de6a73797..a195e1054d0 100644
--- a/src/test/ui/bad/bad-expr-lhs.stderr
+++ b/src/test/ui/bad/bad-expr-lhs.stderr
@@ -1,32 +1,45 @@
-error[E0070]: invalid left-hand side expression
-  --> $DIR/bad-expr-lhs.rs:2:5
+error[E0070]: invalid left-hand side of assignment
+  --> $DIR/bad-expr-lhs.rs:2:7
    |
 LL |     1 = 2;
-   |     ^^^^^ left-hand of expression not valid
+   |     - ^
+   |     |
+   |     cannot assign to this expression
 
-error[E0067]: invalid left-hand side expression
-  --> $DIR/bad-expr-lhs.rs:3:5
+error[E0067]: invalid left-hand side of assignment
+  --> $DIR/bad-expr-lhs.rs:3:7
    |
 LL |     1 += 2;
-   |     ^ invalid expression for left-hand side
+   |     - ^^
+   |     |
+   |     cannot assign to this expression
 
-error[E0070]: invalid left-hand side expression
-  --> $DIR/bad-expr-lhs.rs:4:5
+error[E0070]: invalid left-hand side of assignment
+  --> $DIR/bad-expr-lhs.rs:4:12
    |
 LL |     (1, 2) = (3, 4);
-   |     ^^^^^^^^^^^^^^^ left-hand of expression not valid
+   |     ------ ^
+   |     |
+   |     cannot assign to this expression
 
-error[E0070]: invalid left-hand side expression
-  --> $DIR/bad-expr-lhs.rs:7:5
+error[E0070]: invalid left-hand side of assignment
+  --> $DIR/bad-expr-lhs.rs:7:12
    |
 LL |     (a, b) = (3, 4);
-   |     ^^^^^^^^^^^^^^^ left-hand of expression not valid
+   |     ------ ^
+   |     |
+   |     cannot assign to this expression
+   |
+   = note: destructuring assignments are not currently supported
+   = note: for more information, see https://github.com/rust-lang/rfcs/issues/372
 
-error[E0070]: invalid left-hand side expression
-  --> $DIR/bad-expr-lhs.rs:9:5
+error[E0070]: invalid left-hand side of assignment
+  --> $DIR/bad-expr-lhs.rs:9:10
    |
 LL |     None = Some(3);
-   |     ^^^^^^^^^^^^^^ left-hand of expression not valid
+   |     ---- ^
+   |     |
+   |     cannot assign to this expression
 
 error: aborting due to 5 previous errors
 
diff --git a/src/test/ui/destructuring-assignment/note-unsupported.rs b/src/test/ui/destructuring-assignment/note-unsupported.rs
new file mode 100644
index 00000000000..876c9efea26
--- /dev/null
+++ b/src/test/ui/destructuring-assignment/note-unsupported.rs
@@ -0,0 +1,25 @@
+struct S { x: u8, y: u8 }
+
+fn main() {
+    let (a, b) = (1, 2);
+
+    (a, b) = (3, 4); //~ ERROR invalid left-hand side of assignment
+    (a, b) += (3, 4); //~ ERROR invalid left-hand side of assignment
+    //~^ ERROR binary assignment operation `+=` cannot be applied
+
+    [a, b] = [3, 4]; //~ ERROR invalid left-hand side of assignment
+    [a, b] += [3, 4]; //~ ERROR invalid left-hand side of assignment
+    //~^ ERROR binary assignment operation `+=` cannot be applied
+
+    let s = S { x: 3, y: 4 };
+
+    S { x: a, y: b } = s; //~ ERROR invalid left-hand side of assignment
+    S { x: a, y: b } += s; //~ ERROR invalid left-hand side of assignment
+    //~^ ERROR binary assignment operation `+=` cannot be applied
+
+    S { x: a, ..s } = S { x: 3, y: 4 }; //~ ERROR invalid left-hand side of assignment
+
+    let c = 3;
+
+    ((a, b), c) = ((3, 4), 5); //~ ERROR invalid left-hand side of assignment
+}
diff --git a/src/test/ui/destructuring-assignment/note-unsupported.stderr b/src/test/ui/destructuring-assignment/note-unsupported.stderr
new file mode 100644
index 00000000000..a6805c32a6e
--- /dev/null
+++ b/src/test/ui/destructuring-assignment/note-unsupported.stderr
@@ -0,0 +1,122 @@
+error[E0070]: invalid left-hand side of assignment
+  --> $DIR/note-unsupported.rs:6:12
+   |
+LL |     (a, b) = (3, 4);
+   |     ------ ^
+   |     |
+   |     cannot assign to this expression
+   |
+   = note: destructuring assignments are not currently supported
+   = note: for more information, see https://github.com/rust-lang/rfcs/issues/372
+
+error[E0368]: binary assignment operation `+=` cannot be applied to type `({integer}, {integer})`
+  --> $DIR/note-unsupported.rs:7:5
+   |
+LL |     (a, b) += (3, 4);
+   |     ------^^^^^^^^^^
+   |     |
+   |     cannot use `+=` on type `({integer}, {integer})`
+   |
+   = note: an implementation of `std::ops::AddAssign` might be missing for `({integer}, {integer})`
+
+error[E0067]: invalid left-hand side of assignment
+  --> $DIR/note-unsupported.rs:7:12
+   |
+LL |     (a, b) += (3, 4);
+   |     ------ ^^
+   |     |
+   |     cannot assign to this expression
+   |
+   = note: destructuring assignments are not currently supported
+   = note: for more information, see https://github.com/rust-lang/rfcs/issues/372
+
+error[E0070]: invalid left-hand side of assignment
+  --> $DIR/note-unsupported.rs:10:12
+   |
+LL |     [a, b] = [3, 4];
+   |     ------ ^
+   |     |
+   |     cannot assign to this expression
+   |
+   = note: destructuring assignments are not currently supported
+   = note: for more information, see https://github.com/rust-lang/rfcs/issues/372
+
+error[E0368]: binary assignment operation `+=` cannot be applied to type `[{integer}; 2]`
+  --> $DIR/note-unsupported.rs:11:5
+   |
+LL |     [a, b] += [3, 4];
+   |     ------^^^^^^^^^^
+   |     |
+   |     cannot use `+=` on type `[{integer}; 2]`
+   |
+   = note: an implementation of `std::ops::AddAssign` might be missing for `[{integer}; 2]`
+
+error[E0067]: invalid left-hand side of assignment
+  --> $DIR/note-unsupported.rs:11:12
+   |
+LL |     [a, b] += [3, 4];
+   |     ------ ^^
+   |     |
+   |     cannot assign to this expression
+   |
+   = note: destructuring assignments are not currently supported
+   = note: for more information, see https://github.com/rust-lang/rfcs/issues/372
+
+error[E0070]: invalid left-hand side of assignment
+  --> $DIR/note-unsupported.rs:16:22
+   |
+LL |     S { x: a, y: b } = s;
+   |     ---------------- ^
+   |     |
+   |     cannot assign to this expression
+   |
+   = note: destructuring assignments are not currently supported
+   = note: for more information, see https://github.com/rust-lang/rfcs/issues/372
+
+error[E0368]: binary assignment operation `+=` cannot be applied to type `S`
+  --> $DIR/note-unsupported.rs:17:5
+   |
+LL |     S { x: a, y: b } += s;
+   |     ----------------^^^^^
+   |     |
+   |     cannot use `+=` on type `S`
+   |
+   = note: an implementation of `std::ops::AddAssign` might be missing for `S`
+
+error[E0067]: invalid left-hand side of assignment
+  --> $DIR/note-unsupported.rs:17:22
+   |
+LL |     S { x: a, y: b } += s;
+   |     ---------------- ^^
+   |     |
+   |     cannot assign to this expression
+   |
+   = note: destructuring assignments are not currently supported
+   = note: for more information, see https://github.com/rust-lang/rfcs/issues/372
+
+error[E0070]: invalid left-hand side of assignment
+  --> $DIR/note-unsupported.rs:20:21
+   |
+LL |     S { x: a, ..s } = S { x: 3, y: 4 };
+   |     --------------- ^
+   |     |
+   |     cannot assign to this expression
+   |
+   = note: destructuring assignments are not currently supported
+   = note: for more information, see https://github.com/rust-lang/rfcs/issues/372
+
+error[E0070]: invalid left-hand side of assignment
+  --> $DIR/note-unsupported.rs:24:17
+   |
+LL |     ((a, b), c) = ((3, 4), 5);
+   |     ----------- ^
+   |     |
+   |     cannot assign to this expression
+   |
+   = note: destructuring assignments are not currently supported
+   = note: for more information, see https://github.com/rust-lang/rfcs/issues/372
+
+error: aborting due to 11 previous errors
+
+Some errors have detailed explanations: E0067, E0070, E0368.
+For more information about an error, try `rustc --explain E0067`.
diff --git a/src/test/ui/error-codes/E0067.stderr b/src/test/ui/error-codes/E0067.stderr
index 0334565840f..526503798b3 100644
--- a/src/test/ui/error-codes/E0067.stderr
+++ b/src/test/ui/error-codes/E0067.stderr
@@ -8,11 +8,13 @@ LL |     LinkedList::new() += 1;
    |
    = note: an implementation of `std::ops::AddAssign` might be missing for `std::collections::LinkedList<_>`
 
-error[E0067]: invalid left-hand side expression
-  --> $DIR/E0067.rs:4:5
+error[E0067]: invalid left-hand side of assignment
+  --> $DIR/E0067.rs:4:23
    |
 LL |     LinkedList::new() += 1;
-   |     ^^^^^^^^^^^^^^^^^ invalid expression for left-hand side
+   |     ----------------- ^^
+   |     |
+   |     cannot assign to this expression
 
 error: aborting due to 2 previous errors
 
diff --git a/src/test/ui/error-codes/E0070.stderr b/src/test/ui/error-codes/E0070.stderr
index 845833bc82f..d809bb18dee 100644
--- a/src/test/ui/error-codes/E0070.stderr
+++ b/src/test/ui/error-codes/E0070.stderr
@@ -1,14 +1,18 @@
-error[E0070]: invalid left-hand side expression
-  --> $DIR/E0070.rs:6:5
+error[E0070]: invalid left-hand side of assignment
+  --> $DIR/E0070.rs:6:16
    |
 LL |     SOME_CONST = 14;
-   |     ^^^^^^^^^^^^^^^ left-hand of expression not valid
+   |     ---------- ^
+   |     |
+   |     cannot assign to this expression
 
-error[E0070]: invalid left-hand side expression
-  --> $DIR/E0070.rs:7:5
+error[E0070]: invalid left-hand side of assignment
+  --> $DIR/E0070.rs:7:7
    |
 LL |     1 = 3;
-   |     ^^^^^ left-hand of expression not valid
+   |     - ^
+   |     |
+   |     cannot assign to this expression
 
 error[E0308]: mismatched types
   --> $DIR/E0070.rs:8:25
@@ -16,11 +20,13 @@ error[E0308]: mismatched types
 LL |     some_other_func() = 4;
    |                         ^ expected `()`, found integer
 
-error[E0070]: invalid left-hand side expression
-  --> $DIR/E0070.rs:8:5
+error[E0070]: invalid left-hand side of assignment
+  --> $DIR/E0070.rs:8:23
    |
 LL |     some_other_func() = 4;
-   |     ^^^^^^^^^^^^^^^^^^^^^ left-hand of expression not valid
+   |     ----------------- ^
+   |     |
+   |     cannot assign to this expression
 
 error: aborting due to 4 previous errors
 
diff --git a/src/test/ui/issues/issue-13407.rs b/src/test/ui/issues/issue-13407.rs
index 322e67cc131..fa53d55f5b3 100644
--- a/src/test/ui/issues/issue-13407.rs
+++ b/src/test/ui/issues/issue-13407.rs
@@ -4,7 +4,7 @@ mod A {
 
 fn main() {
     A::C = 1;
-    //~^ ERROR: invalid left-hand side expression
+    //~^ ERROR: invalid left-hand side of assignment
     //~| ERROR: mismatched types
     //~| ERROR: struct `C` is private
 }
diff --git a/src/test/ui/issues/issue-13407.stderr b/src/test/ui/issues/issue-13407.stderr
index 5a465cc533b..b280de3158f 100644
--- a/src/test/ui/issues/issue-13407.stderr
+++ b/src/test/ui/issues/issue-13407.stderr
@@ -10,11 +10,13 @@ error[E0308]: mismatched types
 LL |     A::C = 1;
    |            ^ expected struct `A::C`, found integer
 
-error[E0070]: invalid left-hand side expression
-  --> $DIR/issue-13407.rs:6:5
+error[E0070]: invalid left-hand side of assignment
+  --> $DIR/issue-13407.rs:6:10
    |
 LL |     A::C = 1;
-   |     ^^^^^^^^ left-hand of expression not valid
+   |     ---- ^
+   |     |
+   |     cannot assign to this expression
 
 error: aborting due to 3 previous errors
 
diff --git a/src/test/ui/issues/issue-26093.rs b/src/test/ui/issues/issue-26093.rs
index 7895c90068f..c838515caf9 100644
--- a/src/test/ui/issues/issue-26093.rs
+++ b/src/test/ui/issues/issue-26093.rs
@@ -1,7 +1,9 @@
 macro_rules! not_a_place {
     ($thing:expr) => {
         $thing = 42;
-        //~^ ERROR invalid left-hand side expression
+        //~^ ERROR invalid left-hand side of assignment
+        $thing += 42;
+        //~^ ERROR invalid left-hand side of assignment
     }
 }
 
diff --git a/src/test/ui/issues/issue-26093.stderr b/src/test/ui/issues/issue-26093.stderr
index 947c52f08d2..c96228b518a 100644
--- a/src/test/ui/issues/issue-26093.stderr
+++ b/src/test/ui/issues/issue-26093.stderr
@@ -1,12 +1,28 @@
-error[E0070]: invalid left-hand side expression
-  --> $DIR/issue-26093.rs:3:9
+error[E0070]: invalid left-hand side of assignment
+  --> $DIR/issue-26093.rs:3:16
    |
 LL |         $thing = 42;
-   |         ^^^^^^^^^^^ left-hand of expression not valid
+   |                ^
 ...
 LL |     not_a_place!(99);
-   |     ----------------- in this macro invocation
+   |     -----------------
+   |     |            |
+   |     |            cannot assign to this expression
+   |     in this macro invocation
 
-error: aborting due to previous error
+error[E0067]: invalid left-hand side of assignment
+  --> $DIR/issue-26093.rs:5:16
+   |
+LL |         $thing += 42;
+   |                ^^
+...
+LL |     not_a_place!(99);
+   |     -----------------
+   |     |            |
+   |     |            cannot assign to this expression
+   |     in this macro invocation
+
+error: aborting due to 2 previous errors
 
-For more information about this error, try `rustc --explain E0070`.
+Some errors have detailed explanations: E0067, E0070.
+For more information about an error, try `rustc --explain E0067`.
diff --git a/src/test/ui/issues/issue-34334.rs b/src/test/ui/issues/issue-34334.rs
index 4457d71cbb4..e34b5c9a0f4 100644
--- a/src/test/ui/issues/issue-34334.rs
+++ b/src/test/ui/issues/issue-34334.rs
@@ -3,7 +3,7 @@ fn main () {
     //~^ ERROR expected one of `,` or `>`, found `=`
     //~| ERROR expected value, found struct `Vec`
     //~| ERROR mismatched types
-    //~| ERROR invalid left-hand side expression
+    //~| ERROR invalid left-hand side of assignment
     //~| ERROR expected expression, found reserved identifier `_`
     //~| ERROR expected expression, found reserved identifier `_`
     let sr2: Vec<(u32, _, _)> = sr.iter().map(|(faction, th_sender, th_receiver)| {}).collect();
diff --git a/src/test/ui/issues/issue-34334.stderr b/src/test/ui/issues/issue-34334.stderr
index fc90e0674cf..3055e316a08 100644
--- a/src/test/ui/issues/issue-34334.stderr
+++ b/src/test/ui/issues/issue-34334.stderr
@@ -35,11 +35,13 @@ LL |     let sr: Vec<(u32, _, _) = vec![];
             found struct `std::vec::Vec<_>`
    = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
 
-error[E0070]: invalid left-hand side expression
-  --> $DIR/issue-34334.rs:2:13
+error[E0070]: invalid left-hand side of assignment
+  --> $DIR/issue-34334.rs:2:29
    |
 LL |     let sr: Vec<(u32, _, _) = vec![];
-   |             ^^^^^^^^^^^^^^^^^^^^^^^^ left-hand of expression not valid
+   |             --------------- ^
+   |             |
+   |             cannot assign to this expression
 
 error[E0599]: no method named `iter` found for type `()` in the current scope
   --> $DIR/issue-34334.rs:9:36
diff --git a/src/test/ui/type/type-check/assignment-expected-bool.rs b/src/test/ui/type/type-check/assignment-expected-bool.rs
index 03830fea062..191939bdb70 100644
--- a/src/test/ui/type/type-check/assignment-expected-bool.rs
+++ b/src/test/ui/type/type-check/assignment-expected-bool.rs
@@ -30,5 +30,5 @@ fn main() {
     // A test to check that not expecting `bool` behaves well:
     let _: usize = 0 = 0;
     //~^ ERROR mismatched types [E0308]
-    //~| ERROR invalid left-hand side expression [E0070]
+    //~| ERROR invalid left-hand side of assignment [E0070]
 }
diff --git a/src/test/ui/type/type-check/assignment-expected-bool.stderr b/src/test/ui/type/type-check/assignment-expected-bool.stderr
index 9a1cf5b2562..3f1caddf728 100644
--- a/src/test/ui/type/type-check/assignment-expected-bool.stderr
+++ b/src/test/ui/type/type-check/assignment-expected-bool.stderr
@@ -97,11 +97,13 @@ LL |         || (0 = 0);
    |            expected `bool`, found `()`
    |            help: try comparing for equality: `0 == 0`
 
-error[E0070]: invalid left-hand side expression
-  --> $DIR/assignment-expected-bool.rs:31:20
+error[E0070]: invalid left-hand side of assignment
+  --> $DIR/assignment-expected-bool.rs:31:22
    |
 LL |     let _: usize = 0 = 0;
-   |                    ^^^^^ left-hand of expression not valid
+   |                    - ^
+   |                    |
+   |                    cannot assign to this expression
 
 error[E0308]: mismatched types
   --> $DIR/assignment-expected-bool.rs:31:20
diff --git a/src/test/ui/type/type-check/assignment-in-if.rs b/src/test/ui/type/type-check/assignment-in-if.rs
index 77b122b0a79..8da7b32b47b 100644
--- a/src/test/ui/type/type-check/assignment-in-if.rs
+++ b/src/test/ui/type/type-check/assignment-in-if.rs
@@ -26,7 +26,7 @@ fn main() {
         //~^ ERROR mismatched types
         println!("{}", x);
     }
-    // "invalid left-hand side expression" error is suppresed
+    // "invalid left-hand side of assignment" error is suppresed
     if 3 = x {
         //~^ ERROR mismatched types
         println!("{}", x);
diff --git a/src/test/ui/where-clauses/where-equality-constraints.rs b/src/test/ui/where-clauses/where-equality-constraints.rs
index f2349144b88..8828f09d92d 100644
--- a/src/test/ui/where-clauses/where-equality-constraints.rs
+++ b/src/test/ui/where-clauses/where-equality-constraints.rs
@@ -1,6 +1,6 @@
 fn f() where u8 = u16 {}
-//~^ ERROR equality constraints are not yet supported in where clauses
+//~^ ERROR equality constraints are not yet supported in `where` clauses
 fn g() where for<'a> &'static (u8,) == u16, {}
-//~^ ERROR equality constraints are not yet supported in where clauses
+//~^ ERROR equality constraints are not yet supported in `where` clauses
 
 fn main() {}
diff --git a/src/test/ui/where-clauses/where-equality-constraints.stderr b/src/test/ui/where-clauses/where-equality-constraints.stderr
index 220447079c6..c0241fe708f 100644
--- a/src/test/ui/where-clauses/where-equality-constraints.stderr
+++ b/src/test/ui/where-clauses/where-equality-constraints.stderr
@@ -1,14 +1,18 @@
-error: equality constraints are not yet supported in where clauses (see #20041)
+error: equality constraints are not yet supported in `where` clauses
   --> $DIR/where-equality-constraints.rs:1:14
    |
 LL | fn f() where u8 = u16 {}
    |              ^^^^^^^^
+   |
+   = note: for more information, see https://github.com/rust-lang/rust/issues/20041
 
-error: equality constraints are not yet supported in where clauses (see #20041)
+error: equality constraints are not yet supported in `where` clauses
   --> $DIR/where-equality-constraints.rs:3:14
    |
 LL | fn g() where for<'a> &'static (u8,) == u16, {}
    |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: for more information, see https://github.com/rust-lang/rust/issues/20041
 
 error: aborting due to 2 previous errors