Reduce double errors for invalid let expressions

Previously some invalid let expressions would result in both a feature
error and a parsing error. Avoid this and ensure that we only emit the
parsing error when this happens.

7 files changed, 1249 insertions, 140 deletions

diff --git a/compiler/rustc_parse/src/parser/expr.rs b/compiler/rustc_parse/src/parser/expr.rs
index 82701a8b5d5..43cd8fe55df 100644
--- a/compiler/rustc_parse/src/parser/expr.rs
+++ b/compiler/rustc_parse/src/parser/expr.rs
@@ -2485,9 +2485,6 @@ impl<'a> Parser<'a> {
         }
         let expr = self.parse_expr_assoc_with(1 + prec_let_scrutinee_needs_par(), None.into())?;
         let span = lo.to(expr.span);
-        if is_recovered.is_none() {
-            self.sess.gated_spans.gate(sym::let_chains, span);
-        }
         Ok(self.mk_expr(span, ExprKind::Let(pat, expr, span, is_recovered)))
     }
 
@@ -3460,6 +3457,8 @@ impl MutVisitor for CondChecker<'_> {
                             .sess
                             .emit_err(errors::ExpectedExpressionFoundLet { span, reason }),
                     );
+                } else {
+                    self.parser.sess.gated_spans.gate(sym::let_chains, span);
                 }
             }
             ExprKind::Binary(Spanned { node: BinOpKind::And, .. }, _, _) => {
diff --git a/tests/ui/expr/if/bad-if-let-suggestion.rs b/tests/ui/expr/if/bad-if-let-suggestion.rs
index 1ff9f3fa3d0..99d584ac7a5 100644
--- a/tests/ui/expr/if/bad-if-let-suggestion.rs
+++ b/tests/ui/expr/if/bad-if-let-suggestion.rs
@@ -4,7 +4,6 @@
 fn a() {
     if let x = 1 && i = 2 {}
     //~^ ERROR cannot find value `i` in this scope
-    //~| ERROR `let` expressions in this position are unstable
     //~| ERROR mismatched types
     //~| ERROR expected expression, found `let` statement
 }
diff --git a/tests/ui/expr/if/bad-if-let-suggestion.stderr b/tests/ui/expr/if/bad-if-let-suggestion.stderr
index a2367c59040..dc013155e81 100644
--- a/tests/ui/expr/if/bad-if-let-suggestion.stderr
+++ b/tests/ui/expr/if/bad-if-let-suggestion.stderr
@@ -11,7 +11,7 @@ LL |     if let x = 1 && i = 2 {}
    |                     ^ not found in this scope
 
 error[E0425]: cannot find value `i` in this scope
-  --> $DIR/bad-if-let-suggestion.rs:13:9
+  --> $DIR/bad-if-let-suggestion.rs:12:9
    |
 LL | fn a() {
    | ------ similarly named function `a` defined here
@@ -20,7 +20,7 @@ LL |     if (i + j) = i {}
    |         ^ help: a function with a similar name exists: `a`
 
 error[E0425]: cannot find value `j` in this scope
-  --> $DIR/bad-if-let-suggestion.rs:13:13
+  --> $DIR/bad-if-let-suggestion.rs:12:13
    |
 LL | fn a() {
    | ------ similarly named function `a` defined here
@@ -29,7 +29,7 @@ LL |     if (i + j) = i {}
    |             ^ help: a function with a similar name exists: `a`
 
 error[E0425]: cannot find value `i` in this scope
-  --> $DIR/bad-if-let-suggestion.rs:13:18
+  --> $DIR/bad-if-let-suggestion.rs:12:18
    |
 LL | fn a() {
    | ------ similarly named function `a` defined here
@@ -38,7 +38,7 @@ LL |     if (i + j) = i {}
    |                  ^ help: a function with a similar name exists: `a`
 
 error[E0425]: cannot find value `x` in this scope
-  --> $DIR/bad-if-let-suggestion.rs:20:8
+  --> $DIR/bad-if-let-suggestion.rs:19:8
    |
 LL | fn a() {
    | ------ similarly named function `a` defined here
@@ -46,15 +46,6 @@ LL | fn a() {
 LL |     if x[0] = 1 {}
    |        ^ help: a function with a similar name exists: `a`
 
-error[E0658]: `let` expressions in this position are unstable
-  --> $DIR/bad-if-let-suggestion.rs:5:8
-   |
-LL |     if let x = 1 && i = 2 {}
-   |        ^^^^^^^^^
-   |
-   = note: see issue #53667 <https://github.com/rust-lang/rust/issues/53667> for more information
-   = help: add `#![feature(let_chains)]` to the crate attributes to enable
-
 error[E0308]: mismatched types
   --> $DIR/bad-if-let-suggestion.rs:5:8
    |
@@ -66,7 +57,7 @@ help: you might have meant to compare for equality
 LL |     if let x = 1 && i == 2 {}
    |                        +
 
-error: aborting due to 8 previous errors
+error: aborting due to 7 previous errors
 
-Some errors have detailed explanations: E0308, E0425, E0658.
+Some errors have detailed explanations: E0308, E0425.
 For more information about an error, try `rustc --explain E0308`.
diff --git a/tests/ui/rfcs/rfc-2294-if-let-guard/feature-gate.rs b/tests/ui/rfcs/rfc-2294-if-let-guard/feature-gate.rs
index 21f2a41cb1b..b8c0eb3e6d6 100644
--- a/tests/ui/rfcs/rfc-2294-if-let-guard/feature-gate.rs
+++ b/tests/ui/rfcs/rfc-2294-if-let-guard/feature-gate.rs
@@ -9,11 +9,9 @@ fn _if_let_guard() {
 
         () if (let 0 = 1) => {}
         //~^ ERROR expected expression, found `let` statement
-        //~| ERROR `let` expressions in this position are unstable
 
         () if (((let 0 = 1))) => {}
         //~^ ERROR expected expression, found `let` statement
-        //~| ERROR `let` expressions in this position are unstable
 
         () if true && let 0 = 1 => {}
         //~^ ERROR `if let` guards are experimental
@@ -25,25 +23,18 @@ fn _if_let_guard() {
 
         () if (let 0 = 1) && true => {}
         //~^ ERROR expected expression, found `let` statement
-        //~| ERROR `let` expressions in this position are unstable
 
         () if true && (let 0 = 1) => {}
         //~^ ERROR expected expression, found `let` statement
-        //~| ERROR `let` expressions in this position are unstable
 
         () if (let 0 = 1) && (let 0 = 1) => {}
         //~^ ERROR expected expression, found `let` statement
         //~| ERROR expected expression, found `let` statement
-        //~| ERROR `let` expressions in this position are unstable
-        //~| ERROR `let` expressions in this position are unstable
 
         () if let 0 = 1 && let 1 = 2 && (let 2 = 3 && let 3 = 4 && let 4 = 5) => {}
         //~^ ERROR `if let` guards are experimental
         //~| ERROR `let` expressions in this position are unstable
         //~| ERROR `let` expressions in this position are unstable
-        //~| ERROR `let` expressions in this position are unstable
-        //~| ERROR `let` expressions in this position are unstable
-        //~| ERROR `let` expressions in this position are unstable
         //~| ERROR expected expression, found `let` statement
         //~| ERROR expected expression, found `let` statement
         //~| ERROR expected expression, found `let` statement
diff --git a/tests/ui/rfcs/rfc-2294-if-let-guard/feature-gate.stderr b/tests/ui/rfcs/rfc-2294-if-let-guard/feature-gate.stderr
index d5187ba1afc..a21ecae4eae 100644
--- a/tests/ui/rfcs/rfc-2294-if-let-guard/feature-gate.stderr
+++ b/tests/ui/rfcs/rfc-2294-if-let-guard/feature-gate.stderr
@@ -11,115 +11,115 @@ LL |         () if (let 0 = 1) => {}
    |                ^^^^^^^^^
 
 error: expected expression, found `let` statement
-  --> $DIR/feature-gate.rs:14:18
+  --> $DIR/feature-gate.rs:13:18
    |
 LL |         () if (((let 0 = 1))) => {}
    |                  ^^^^^^^^^
    |
 note: `let`s wrapped in parentheses are not supported in a context with let chains
-  --> $DIR/feature-gate.rs:14:18
+  --> $DIR/feature-gate.rs:13:18
    |
 LL |         () if (((let 0 = 1))) => {}
    |                  ^^^^^^^^^
 
 error: expected expression, found `let` statement
-  --> $DIR/feature-gate.rs:26:16
+  --> $DIR/feature-gate.rs:24:16
    |
 LL |         () if (let 0 = 1) && true => {}
    |                ^^^^^^^^^
    |
 note: `let`s wrapped in parentheses are not supported in a context with let chains
-  --> $DIR/feature-gate.rs:26:16
+  --> $DIR/feature-gate.rs:24:16
    |
 LL |         () if (let 0 = 1) && true => {}
    |                ^^^^^^^^^
 
 error: expected expression, found `let` statement
-  --> $DIR/feature-gate.rs:30:24
+  --> $DIR/feature-gate.rs:27:24
    |
 LL |         () if true && (let 0 = 1) => {}
    |                        ^^^^^^^^^
    |
 note: `let`s wrapped in parentheses are not supported in a context with let chains
-  --> $DIR/feature-gate.rs:30:24
+  --> $DIR/feature-gate.rs:27:24
    |
 LL |         () if true && (let 0 = 1) => {}
    |                        ^^^^^^^^^
 
 error: expected expression, found `let` statement
-  --> $DIR/feature-gate.rs:34:16
+  --> $DIR/feature-gate.rs:30:16
    |
 LL |         () if (let 0 = 1) && (let 0 = 1) => {}
    |                ^^^^^^^^^
    |
 note: `let`s wrapped in parentheses are not supported in a context with let chains
-  --> $DIR/feature-gate.rs:34:16
+  --> $DIR/feature-gate.rs:30:16
    |
 LL |         () if (let 0 = 1) && (let 0 = 1) => {}
    |                ^^^^^^^^^
 
 error: expected expression, found `let` statement
-  --> $DIR/feature-gate.rs:34:31
+  --> $DIR/feature-gate.rs:30:31
    |
 LL |         () if (let 0 = 1) && (let 0 = 1) => {}
    |                               ^^^^^^^^^
    |
 note: `let`s wrapped in parentheses are not supported in a context with let chains
-  --> $DIR/feature-gate.rs:34:31
+  --> $DIR/feature-gate.rs:30:31
    |
 LL |         () if (let 0 = 1) && (let 0 = 1) => {}
    |                               ^^^^^^^^^
 
 error: expected expression, found `let` statement
-  --> $DIR/feature-gate.rs:40:42
+  --> $DIR/feature-gate.rs:34:42
    |
 LL |         () if let 0 = 1 && let 1 = 2 && (let 2 = 3 && let 3 = 4 && let 4 = 5) => {}
    |                                          ^^^^^^^^^
    |
 note: `let`s wrapped in parentheses are not supported in a context with let chains
-  --> $DIR/feature-gate.rs:40:42
+  --> $DIR/feature-gate.rs:34:42
    |
 LL |         () if let 0 = 1 && let 1 = 2 && (let 2 = 3 && let 3 = 4 && let 4 = 5) => {}
    |                                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: expected expression, found `let` statement
-  --> $DIR/feature-gate.rs:40:55
+  --> $DIR/feature-gate.rs:34:55
    |
 LL |         () if let 0 = 1 && let 1 = 2 && (let 2 = 3 && let 3 = 4 && let 4 = 5) => {}
    |                                                       ^^^^^^^^^
    |
 note: `let`s wrapped in parentheses are not supported in a context with let chains
-  --> $DIR/feature-gate.rs:40:42
+  --> $DIR/feature-gate.rs:34:42
    |
 LL |         () if let 0 = 1 && let 1 = 2 && (let 2 = 3 && let 3 = 4 && let 4 = 5) => {}
    |                                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: expected expression, found `let` statement
-  --> $DIR/feature-gate.rs:40:68
+  --> $DIR/feature-gate.rs:34:68
    |
 LL |         () if let 0 = 1 && let 1 = 2 && (let 2 = 3 && let 3 = 4 && let 4 = 5) => {}
    |                                                                    ^^^^^^^^^
    |
 note: `let`s wrapped in parentheses are not supported in a context with let chains
-  --> $DIR/feature-gate.rs:40:42
+  --> $DIR/feature-gate.rs:34:42
    |
 LL |         () if let 0 = 1 && let 1 = 2 && (let 2 = 3 && let 3 = 4 && let 4 = 5) => {}
    |                                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: expected expression, found `let` statement
-  --> $DIR/feature-gate.rs:69:16
+  --> $DIR/feature-gate.rs:60:16
    |
 LL |     use_expr!((let 0 = 1 && 0 == 0));
    |                ^^^
 
 error: expected expression, found `let` statement
-  --> $DIR/feature-gate.rs:71:16
+  --> $DIR/feature-gate.rs:62:16
    |
 LL |     use_expr!((let 0 = 1));
    |                ^^^
 
 error: no rules expected the token `let`
-  --> $DIR/feature-gate.rs:79:15
+  --> $DIR/feature-gate.rs:70:15
    |
 LL |     macro_rules! use_expr {
    |     --------------------- when calling this macro
@@ -128,7 +128,7 @@ LL |     use_expr!(let 0 = 1);
    |               ^^^ no rules expected this token in macro call
    |
 note: while trying to match meta-variable `$e:expr`
-  --> $DIR/feature-gate.rs:62:10
+  --> $DIR/feature-gate.rs:53:10
    |
 LL |         ($e:expr) => {
    |          ^^^^^^^
@@ -144,7 +144,7 @@ LL |         () if let 0 = 1 => {}
    = help: you can write `if matches!(<expr>, <pattern>)` instead of `if let <pattern> = <expr>`
 
 error[E0658]: `if let` guards are experimental
-  --> $DIR/feature-gate.rs:18:12
+  --> $DIR/feature-gate.rs:16:12
    |
 LL |         () if true && let 0 = 1 => {}
    |            ^^^^^^^^^^^^^^^^^^^^
@@ -154,7 +154,7 @@ LL |         () if true && let 0 = 1 => {}
    = help: you can write `if matches!(<expr>, <pattern>)` instead of `if let <pattern> = <expr>`
 
 error[E0658]: `if let` guards are experimental
-  --> $DIR/feature-gate.rs:22:12
+  --> $DIR/feature-gate.rs:20:12
    |
 LL |         () if let 0 = 1 && true => {}
    |            ^^^^^^^^^^^^^^^^^^^^
@@ -164,7 +164,7 @@ LL |         () if let 0 = 1 && true => {}
    = help: you can write `if matches!(<expr>, <pattern>)` instead of `if let <pattern> = <expr>`
 
 error[E0658]: `if let` guards are experimental
-  --> $DIR/feature-gate.rs:40:12
+  --> $DIR/feature-gate.rs:34:12
    |
 LL |         () if let 0 = 1 && let 1 = 2 && (let 2 = 3 && let 3 = 4 && let 4 = 5) => {}
    |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -174,7 +174,7 @@ LL |         () if let 0 = 1 && let 1 = 2 && (let 2 = 3 && let 3 = 4 && let 4 =
    = help: you can write `if matches!(<expr>, <pattern>)` instead of `if let <pattern> = <expr>`
 
 error[E0658]: `if let` guards are experimental
-  --> $DIR/feature-gate.rs:52:12
+  --> $DIR/feature-gate.rs:43:12
    |
 LL |         () if let Range { start: _, end: _ } = (true..true) && false => {}
    |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -184,7 +184,7 @@ LL |         () if let Range { start: _, end: _ } = (true..true) && false => {}
    = help: you can write `if matches!(<expr>, <pattern>)` instead of `if let <pattern> = <expr>`
 
 error[E0658]: `if let` guards are experimental
-  --> $DIR/feature-gate.rs:75:12
+  --> $DIR/feature-gate.rs:66:12
    |
 LL |         () if let 0 = 1 => {}
    |            ^^^^^^^^^^^^
@@ -194,25 +194,7 @@ LL |         () if let 0 = 1 => {}
    = help: you can write `if matches!(<expr>, <pattern>)` instead of `if let <pattern> = <expr>`
 
 error[E0658]: `let` expressions in this position are unstable
-  --> $DIR/feature-gate.rs:10:16
-   |
-LL |         () if (let 0 = 1) => {}
-   |                ^^^^^^^^^
-   |
-   = note: see issue #53667 <https://github.com/rust-lang/rust/issues/53667> for more information
-   = help: add `#![feature(let_chains)]` to the crate attributes to enable
-
-error[E0658]: `let` expressions in this position are unstable
-  --> $DIR/feature-gate.rs:14:18
-   |
-LL |         () if (((let 0 = 1))) => {}
-   |                  ^^^^^^^^^
-   |
-   = note: see issue #53667 <https://github.com/rust-lang/rust/issues/53667> for more information
-   = help: add `#![feature(let_chains)]` to the crate attributes to enable
-
-error[E0658]: `let` expressions in this position are unstable
-  --> $DIR/feature-gate.rs:18:23
+  --> $DIR/feature-gate.rs:16:23
    |
 LL |         () if true && let 0 = 1 => {}
    |                       ^^^^^^^^^
@@ -221,7 +203,7 @@ LL |         () if true && let 0 = 1 => {}
    = help: add `#![feature(let_chains)]` to the crate attributes to enable
 
 error[E0658]: `let` expressions in this position are unstable
-  --> $DIR/feature-gate.rs:22:15
+  --> $DIR/feature-gate.rs:20:15
    |
 LL |         () if let 0 = 1 && true => {}
    |               ^^^^^^^^^
@@ -230,43 +212,7 @@ LL |         () if let 0 = 1 && true => {}
    = help: add `#![feature(let_chains)]` to the crate attributes to enable
 
 error[E0658]: `let` expressions in this position are unstable
-  --> $DIR/feature-gate.rs:26:16
-   |
-LL |         () if (let 0 = 1) && true => {}
-   |                ^^^^^^^^^
-   |
-   = note: see issue #53667 <https://github.com/rust-lang/rust/issues/53667> for more information
-   = help: add `#![feature(let_chains)]` to the crate attributes to enable
-
-error[E0658]: `let` expressions in this position are unstable
-  --> $DIR/feature-gate.rs:30:24
-   |
-LL |         () if true && (let 0 = 1) => {}
-   |                        ^^^^^^^^^
-   |
-   = note: see issue #53667 <https://github.com/rust-lang/rust/issues/53667> for more information
-   = help: add `#![feature(let_chains)]` to the crate attributes to enable
-
-error[E0658]: `let` expressions in this position are unstable
-  --> $DIR/feature-gate.rs:34:16
-   |
-LL |         () if (let 0 = 1) && (let 0 = 1) => {}
-   |                ^^^^^^^^^
-   |
-   = note: see issue #53667 <https://github.com/rust-lang/rust/issues/53667> for more information
-   = help: add `#![feature(let_chains)]` to the crate attributes to enable
-
-error[E0658]: `let` expressions in this position are unstable
-  --> $DIR/feature-gate.rs:34:31
-   |
-LL |         () if (let 0 = 1) && (let 0 = 1) => {}
-   |                               ^^^^^^^^^
-   |
-   = note: see issue #53667 <https://github.com/rust-lang/rust/issues/53667> for more information
-   = help: add `#![feature(let_chains)]` to the crate attributes to enable
-
-error[E0658]: `let` expressions in this position are unstable
-  --> $DIR/feature-gate.rs:40:15
+  --> $DIR/feature-gate.rs:34:15
    |
 LL |         () if let 0 = 1 && let 1 = 2 && (let 2 = 3 && let 3 = 4 && let 4 = 5) => {}
    |               ^^^^^^^^^
@@ -275,7 +221,7 @@ LL |         () if let 0 = 1 && let 1 = 2 && (let 2 = 3 && let 3 = 4 && let 4 =
    = help: add `#![feature(let_chains)]` to the crate attributes to enable
 
 error[E0658]: `let` expressions in this position are unstable
-  --> $DIR/feature-gate.rs:40:28
+  --> $DIR/feature-gate.rs:34:28
    |
 LL |         () if let 0 = 1 && let 1 = 2 && (let 2 = 3 && let 3 = 4 && let 4 = 5) => {}
    |                            ^^^^^^^^^
@@ -284,34 +230,7 @@ LL |         () if let 0 = 1 && let 1 = 2 && (let 2 = 3 && let 3 = 4 && let 4 =
    = help: add `#![feature(let_chains)]` to the crate attributes to enable
 
 error[E0658]: `let` expressions in this position are unstable
-  --> $DIR/feature-gate.rs:40:42
-   |
-LL |         () if let 0 = 1 && let 1 = 2 && (let 2 = 3 && let 3 = 4 && let 4 = 5) => {}
-   |                                          ^^^^^^^^^
-   |
-   = note: see issue #53667 <https://github.com/rust-lang/rust/issues/53667> for more information
-   = help: add `#![feature(let_chains)]` to the crate attributes to enable
-
-error[E0658]: `let` expressions in this position are unstable
-  --> $DIR/feature-gate.rs:40:55
-   |
-LL |         () if let 0 = 1 && let 1 = 2 && (let 2 = 3 && let 3 = 4 && let 4 = 5) => {}
-   |                                                       ^^^^^^^^^
-   |
-   = note: see issue #53667 <https://github.com/rust-lang/rust/issues/53667> for more information
-   = help: add `#![feature(let_chains)]` to the crate attributes to enable
-
-error[E0658]: `let` expressions in this position are unstable
-  --> $DIR/feature-gate.rs:40:68
-   |
-LL |         () if let 0 = 1 && let 1 = 2 && (let 2 = 3 && let 3 = 4 && let 4 = 5) => {}
-   |                                                                    ^^^^^^^^^
-   |
-   = note: see issue #53667 <https://github.com/rust-lang/rust/issues/53667> for more information
-   = help: add `#![feature(let_chains)]` to the crate attributes to enable
-
-error[E0658]: `let` expressions in this position are unstable
-  --> $DIR/feature-gate.rs:52:15
+  --> $DIR/feature-gate.rs:43:15
    |
 LL |         () if let Range { start: _, end: _ } = (true..true) && false => {}
    |               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -319,6 +238,6 @@ LL |         () if let Range { start: _, end: _ } = (true..true) && false => {}
    = note: see issue #53667 <https://github.com/rust-lang/rust/issues/53667> for more information
    = help: add `#![feature(let_chains)]` to the crate attributes to enable
 
-error: aborting due to 32 previous errors
+error: aborting due to 23 previous errors
 
 For more information about this error, try `rustc --explain E0658`.
diff --git a/tests/ui/rfcs/rfc-2497-if-let-chains/disallowed-positions-without-feature-gate.rs b/tests/ui/rfcs/rfc-2497-if-let-chains/disallowed-positions-without-feature-gate.rs
new file mode 100644
index 00000000000..096036bb133
--- /dev/null
+++ b/tests/ui/rfcs/rfc-2497-if-let-chains/disallowed-positions-without-feature-gate.rs
@@ -0,0 +1,340 @@
+// Check that we don't suggest enabling a feature for code that's
+// not accepted even with that feature.
+
+#![allow(irrefutable_let_patterns)]
+
+use std::ops::Range;
+
+fn main() {}
+
+fn _if() {
+    if (let 0 = 1) {}
+    //~^ ERROR expected expression, found `let` statement
+
+    if (((let 0 = 1))) {}
+    //~^ ERROR expected expression, found `let` statement
+
+    if (let 0 = 1) && true {}
+    //~^ ERROR expected expression, found `let` statement
+
+    if true && (let 0 = 1) {}
+    //~^ ERROR expected expression, found `let` statement
+
+    if (let 0 = 1) && (let 0 = 1) {}
+    //~^ ERROR expected expression, found `let` statement
+    //~| ERROR expected expression, found `let` statement
+
+    if (let 2 = 3 && let 3 = 4 && let 4 = 5) {}
+    //~^ ERROR expected expression, found `let` statement
+    //~| ERROR expected expression, found `let` statement
+    //~| ERROR expected expression, found `let` statement
+}
+
+fn _while() {
+    while (let 0 = 1) {}
+    //~^ ERROR expected expression, found `let` statement
+
+    while (((let 0 = 1))) {}
+    //~^ ERROR expected expression, found `let` statement
+
+    while (let 0 = 1) && true {}
+    //~^ ERROR expected expression, found `let` statement
+
+    while true && (let 0 = 1) {}
+    //~^ ERROR expected expression, found `let` statement
+
+    while (let 0 = 1) && (let 0 = 1) {}
+    //~^ ERROR expected expression, found `let` statement
+    //~| ERROR expected expression, found `let` statement
+
+    while (let 2 = 3 && let 3 = 4 && let 4 = 5) {}
+    //~^ ERROR expected expression, found `let` statement
+    //~| ERROR expected expression, found `let` statement
+    //~| ERROR expected expression, found `let` statement
+}
+
+fn _macros() {
+    macro_rules! use_expr {
+        ($e:expr) => {
+            if $e {}
+            while $e {}
+        }
+    }
+    use_expr!((let 0 = 1 && 0 == 0));
+    //~^ ERROR expected expression, found `let` statement
+    use_expr!((let 0 = 1));
+    //~^ ERROR expected expression, found `let` statement
+}
+
+fn nested_within_if_expr() {
+    if &let 0 = 0 {}
+    //~^ ERROR expected expression, found `let` statement
+
+    if !let 0 = 0 {}
+    //~^ ERROR expected expression, found `let` statement
+    if *let 0 = 0 {}
+    //~^ ERROR expected expression, found `let` statement
+    if -let 0 = 0 {}
+    //~^ ERROR expected expression, found `let` statement
+
+    fn _check_try_binds_tighter() -> Result<(), ()> {
+        if let 0 = 0? {}
+        //~^ ERROR the `?` operator can only be applied to values that implement `Try`
+        Ok(())
+    }
+    if (let 0 = 0)? {}
+    //~^ ERROR expected expression, found `let` statement
+
+    if true || let 0 = 0 {}
+    //~^ ERROR expected expression, found `let` statement
+    if (true || let 0 = 0) {}
+    //~^ ERROR expected expression, found `let` statement
+    if true && (true || let 0 = 0) {}
+    //~^ ERROR expected expression, found `let` statement
+    if true || (true && let 0 = 0) {}
+    //~^ ERROR expected expression, found `let` statement
+
+    let mut x = true;
+    if x = let 0 = 0 {}
+    //~^ ERROR expected expression, found `let` statement
+
+    if true..(let 0 = 0) {}
+    //~^ ERROR expected expression, found `let` statement
+    //~| ERROR mismatched types
+    if ..(let 0 = 0) {}
+    //~^ ERROR expected expression, found `let` statement
+    if (let 0 = 0).. {}
+    //~^ ERROR expected expression, found `let` statement
+
+    // Binds as `(let ... = true)..true &&/|| false`.
+    if let Range { start: _, end: _ } = true..true && false {}
+    //~^ ERROR expected expression, found `let` statement
+    //~| ERROR mismatched types
+    if let Range { start: _, end: _ } = true..true || false {}
+    //~^ ERROR expected expression, found `let` statement
+    //~| ERROR mismatched types
+
+    // Binds as `(let Range { start: F, end } = F)..(|| true)`.
+    const F: fn() -> bool = || true;
+    if let Range { start: F, end } = F..|| true {}
+    //~^ ERROR expected expression, found `let` statement
+    //~| ERROR mismatched types
+
+    // Binds as `(let Range { start: true, end } = t)..(&&false)`.
+    let t = &&true;
+    if let Range { start: true, end } = t..&&false {}
+    //~^ ERROR expected expression, found `let` statement
+    //~| ERROR mismatched types
+
+    if let true = let true = true {}
+    //~^ ERROR expected expression, found `let` statement
+}
+
+fn nested_within_while_expr() {
+    while &let 0 = 0 {}
+    //~^ ERROR expected expression, found `let` statement
+
+    while !let 0 = 0 {}
+    //~^ ERROR expected expression, found `let` statement
+    while *let 0 = 0 {}
+    //~^ ERROR expected expression, found `let` statement
+    while -let 0 = 0 {}
+    //~^ ERROR expected expression, found `let` statement
+
+    fn _check_try_binds_tighter() -> Result<(), ()> {
+        while let 0 = 0? {}
+        //~^ ERROR the `?` operator can only be applied to values that implement `Try`
+        Ok(())
+    }
+    while (let 0 = 0)? {}
+    //~^ ERROR expected expression, found `let` statement
+
+    while true || let 0 = 0 {}
+    //~^ ERROR expected expression, found `let` statement
+    while (true || let 0 = 0) {}
+    //~^ ERROR expected expression, found `let` statement
+    while true && (true || let 0 = 0) {}
+    //~^ ERROR expected expression, found `let` statement
+    while true || (true && let 0 = 0) {}
+    //~^ ERROR expected expression, found `let` statement
+
+    let mut x = true;
+    while x = let 0 = 0 {}
+    //~^ ERROR expected expression, found `let` statement
+
+    while true..(let 0 = 0) {}
+    //~^ ERROR expected expression, found `let` statement
+    //~| ERROR mismatched types
+    while ..(let 0 = 0) {}
+    //~^ ERROR expected expression, found `let` statement
+    while (let 0 = 0).. {}
+    //~^ ERROR expected expression, found `let` statement
+
+    // Binds as `(let ... = true)..true &&/|| false`.
+    while let Range { start: _, end: _ } = true..true && false {}
+    //~^ ERROR expected expression, found `let` statement
+    //~| ERROR mismatched types
+    while let Range { start: _, end: _ } = true..true || false {}
+    //~^ ERROR expected expression, found `let` statement
+    //~| ERROR mismatched types
+
+    // Binds as `(let Range { start: F, end } = F)..(|| true)`.
+    const F: fn() -> bool = || true;
+    while let Range { start: F, end } = F..|| true {}
+    //~^ ERROR expected expression, found `let` statement
+    //~| ERROR mismatched types
+
+    // Binds as `(let Range { start: true, end } = t)..(&&false)`.
+    let t = &&true;
+    while let Range { start: true, end } = t..&&false {}
+    //~^ ERROR expected expression, found `let` statement
+    //~| ERROR mismatched types
+
+    while let true = let true = true {}
+    //~^ ERROR expected expression, found `let` statement
+}
+
+fn not_error_because_clarified_intent() {
+    if let Range { start: _, end: _ } = (true..true || false) { }
+
+    if let Range { start: _, end: _ } = (true..true && false) { }
+
+    while let Range { start: _, end: _ } = (true..true || false) { }
+
+    while let Range { start: _, end: _ } = (true..true && false) { }
+}
+
+fn outside_if_and_while_expr() {
+    &let 0 = 0;
+    //~^ ERROR expected expression, found `let` statement
+
+    !let 0 = 0;
+    //~^ ERROR expected expression, found `let` statement
+    *let 0 = 0;
+    //~^ ERROR expected expression, found `let` statement
+    -let 0 = 0;
+    //~^ ERROR expected expression, found `let` statement
+    let _ = let _ = 3;
+    //~^ ERROR expected expression, found `let` statement
+
+    fn _check_try_binds_tighter() -> Result<(), ()> {
+        let 0 = 0?;
+        //~^ ERROR the `?` operator can only be applied to values that implement `Try`
+        Ok(())
+    }
+    (let 0 = 0)?;
+    //~^ ERROR expected expression, found `let` statement
+
+    true || let 0 = 0;
+    //~^ ERROR expected expression, found `let` statement
+    (true || let 0 = 0);
+    //~^ ERROR expected expression, found `let` statement
+    true && (true || let 0 = 0);
+    //~^ ERROR expected expression, found `let` statement
+
+    let mut x = true;
+    x = let 0 = 0;
+    //~^ ERROR expected expression, found `let` statement
+
+    true..(let 0 = 0);
+    //~^ ERROR expected expression, found `let` statement
+    ..(let 0 = 0);
+    //~^ ERROR expected expression, found `let` statement
+    (let 0 = 0)..;
+    //~^ ERROR expected expression, found `let` statement
+
+    (let Range { start: _, end: _ } = true..true || false);
+    //~^ ERROR mismatched types
+    //~| ERROR expected expression, found `let` statement
+
+    (let true = let true = true);
+    //~^ ERROR expected expression, found `let` statement
+    //~| ERROR expected expression, found `let` statement
+
+    {
+        #[cfg(FALSE)]
+        let x = true && let y = 1;
+        //~^ ERROR expected expression, found `let` statement
+    }
+
+    #[cfg(FALSE)]
+    {
+        [1, 2, 3][let _ = ()]
+        //~^ ERROR expected expression, found `let` statement
+    }
+
+    // Check function tail position.
+    &let 0 = 0
+    //~^ ERROR expected expression, found `let` statement
+}
+
+// Let's make sure that `let` inside const generic arguments are considered.
+fn inside_const_generic_arguments() {
+    struct A<const B: bool>;
+    impl<const B: bool> A<{B}> { const O: u32 = 5; }
+
+    if let A::<{
+        true && let 1 = 1
+        //~^ ERROR expected expression, found `let` statement
+    }>::O = 5 {}
+
+    while let A::<{
+        true && let 1 = 1
+        //~^ ERROR expected expression, found `let` statement
+    }>::O = 5 {}
+
+    if A::<{
+        true && let 1 = 1
+        //~^ ERROR expected expression, found `let` statement
+    }>::O == 5 {}
+
+    // In the cases above we have `ExprKind::Block` to help us out.
+    // Below however, we would not have a block and so an implementation might go
+    // from visiting expressions to types without banning `let` expressions down the tree.
+    // This tests ensures that we are not caught by surprise should the parser
+    // admit non-IDENT expressions in const generic arguments.
+
+    if A::<
+        true && let 1 = 1
+        //~^ ERROR expressions must be enclosed in braces
+        //~| ERROR expected expression, found `let` statement
+    >::O == 5 {}
+}
+
+fn with_parenthesis() {
+    let opt = Some(Some(1i32));
+
+    if (let Some(a) = opt && true) {
+    //~^ ERROR expected expression, found `let` statement
+    }
+
+    if (let Some(a) = opt) && true {
+    //~^ ERROR expected expression, found `let` statement
+    }
+    if (let Some(a) = opt) && (let Some(b) = a) {
+    //~^ ERROR expected expression, found `let` statement
+    //~| ERROR expected expression, found `let` statement
+    }
+
+    if (let Some(a) = opt && (let Some(b) = a)) && b == 1 {
+    //~^ ERROR expected expression, found `let` statement
+    //~| ERROR expected expression, found `let` statement
+    }
+    if (let Some(a) = opt && (let Some(b) = a)) && true {
+    //~^ ERROR expected expression, found `let` statement
+    //~| ERROR expected expression, found `let` statement
+    }
+    if (let Some(a) = opt && (true)) && true {
+    //~^ ERROR expected expression, found `let` statement
+    }
+
+    #[cfg(FALSE)]
+    let x = (true && let y = 1);
+    //~^ ERROR expected expression, found `let` statement
+
+    #[cfg(FALSE)]
+    {
+        ([1, 2, 3][let _ = ()])
+        //~^ ERROR expected expression, found `let` statement
+    }
+}
diff --git a/tests/ui/rfcs/rfc-2497-if-let-chains/disallowed-positions-without-feature-gate.stderr b/tests/ui/rfcs/rfc-2497-if-let-chains/disallowed-positions-without-feature-gate.stderr
new file mode 100644
index 00000000000..218ca254d0f
--- /dev/null
+++ b/tests/ui/rfcs/rfc-2497-if-let-chains/disallowed-positions-without-feature-gate.stderr
@@ -0,0 +1,870 @@
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:11:9
+   |
+LL |     if (let 0 = 1) {}
+   |         ^^^^^^^^^
+   |
+note: `let`s wrapped in parentheses are not supported in a context with let chains
+  --> $DIR/disallowed-positions-without-feature-gate.rs:11:9
+   |
+LL |     if (let 0 = 1) {}
+   |         ^^^^^^^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:14:11
+   |
+LL |     if (((let 0 = 1))) {}
+   |           ^^^^^^^^^
+   |
+note: `let`s wrapped in parentheses are not supported in a context with let chains
+  --> $DIR/disallowed-positions-without-feature-gate.rs:14:11
+   |
+LL |     if (((let 0 = 1))) {}
+   |           ^^^^^^^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:17:9
+   |
+LL |     if (let 0 = 1) && true {}
+   |         ^^^^^^^^^
+   |
+note: `let`s wrapped in parentheses are not supported in a context with let chains
+  --> $DIR/disallowed-positions-without-feature-gate.rs:17:9
+   |
+LL |     if (let 0 = 1) && true {}
+   |         ^^^^^^^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:20:17
+   |
+LL |     if true && (let 0 = 1) {}
+   |                 ^^^^^^^^^
+   |
+note: `let`s wrapped in parentheses are not supported in a context with let chains
+  --> $DIR/disallowed-positions-without-feature-gate.rs:20:17
+   |
+LL |     if true && (let 0 = 1) {}
+   |                 ^^^^^^^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:23:9
+   |
+LL |     if (let 0 = 1) && (let 0 = 1) {}
+   |         ^^^^^^^^^
+   |
+note: `let`s wrapped in parentheses are not supported in a context with let chains
+  --> $DIR/disallowed-positions-without-feature-gate.rs:23:9
+   |
+LL |     if (let 0 = 1) && (let 0 = 1) {}
+   |         ^^^^^^^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:23:24
+   |
+LL |     if (let 0 = 1) && (let 0 = 1) {}
+   |                        ^^^^^^^^^
+   |
+note: `let`s wrapped in parentheses are not supported in a context with let chains
+  --> $DIR/disallowed-positions-without-feature-gate.rs:23:24
+   |
+LL |     if (let 0 = 1) && (let 0 = 1) {}
+   |                        ^^^^^^^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:27:9
+   |
+LL |     if (let 2 = 3 && let 3 = 4 && let 4 = 5) {}
+   |         ^^^^^^^^^
+   |
+note: `let`s wrapped in parentheses are not supported in a context with let chains
+  --> $DIR/disallowed-positions-without-feature-gate.rs:27:9
+   |
+LL |     if (let 2 = 3 && let 3 = 4 && let 4 = 5) {}
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:27:22
+   |
+LL |     if (let 2 = 3 && let 3 = 4 && let 4 = 5) {}
+   |                      ^^^^^^^^^
+   |
+note: `let`s wrapped in parentheses are not supported in a context with let chains
+  --> $DIR/disallowed-positions-without-feature-gate.rs:27:9
+   |
+LL |     if (let 2 = 3 && let 3 = 4 && let 4 = 5) {}
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:27:35
+   |
+LL |     if (let 2 = 3 && let 3 = 4 && let 4 = 5) {}
+   |                                   ^^^^^^^^^
+   |
+note: `let`s wrapped in parentheses are not supported in a context with let chains
+  --> $DIR/disallowed-positions-without-feature-gate.rs:27:9
+   |
+LL |     if (let 2 = 3 && let 3 = 4 && let 4 = 5) {}
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:34:12
+   |
+LL |     while (let 0 = 1) {}
+   |            ^^^^^^^^^
+   |
+note: `let`s wrapped in parentheses are not supported in a context with let chains
+  --> $DIR/disallowed-positions-without-feature-gate.rs:34:12
+   |
+LL |     while (let 0 = 1) {}
+   |            ^^^^^^^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:37:14
+   |
+LL |     while (((let 0 = 1))) {}
+   |              ^^^^^^^^^
+   |
+note: `let`s wrapped in parentheses are not supported in a context with let chains
+  --> $DIR/disallowed-positions-without-feature-gate.rs:37:14
+   |
+LL |     while (((let 0 = 1))) {}
+   |              ^^^^^^^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:40:12
+   |
+LL |     while (let 0 = 1) && true {}
+   |            ^^^^^^^^^
+   |
+note: `let`s wrapped in parentheses are not supported in a context with let chains
+  --> $DIR/disallowed-positions-without-feature-gate.rs:40:12
+   |
+LL |     while (let 0 = 1) && true {}
+   |            ^^^^^^^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:43:20
+   |
+LL |     while true && (let 0 = 1) {}
+   |                    ^^^^^^^^^
+   |
+note: `let`s wrapped in parentheses are not supported in a context with let chains
+  --> $DIR/disallowed-positions-without-feature-gate.rs:43:20
+   |
+LL |     while true && (let 0 = 1) {}
+   |                    ^^^^^^^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:46:12
+   |
+LL |     while (let 0 = 1) && (let 0 = 1) {}
+   |            ^^^^^^^^^
+   |
+note: `let`s wrapped in parentheses are not supported in a context with let chains
+  --> $DIR/disallowed-positions-without-feature-gate.rs:46:12
+   |
+LL |     while (let 0 = 1) && (let 0 = 1) {}
+   |            ^^^^^^^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:46:27
+   |
+LL |     while (let 0 = 1) && (let 0 = 1) {}
+   |                           ^^^^^^^^^
+   |
+note: `let`s wrapped in parentheses are not supported in a context with let chains
+  --> $DIR/disallowed-positions-without-feature-gate.rs:46:27
+   |
+LL |     while (let 0 = 1) && (let 0 = 1) {}
+   |                           ^^^^^^^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:50:12
+   |
+LL |     while (let 2 = 3 && let 3 = 4 && let 4 = 5) {}
+   |            ^^^^^^^^^
+   |
+note: `let`s wrapped in parentheses are not supported in a context with let chains
+  --> $DIR/disallowed-positions-without-feature-gate.rs:50:12
+   |
+LL |     while (let 2 = 3 && let 3 = 4 && let 4 = 5) {}
+   |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:50:25
+   |
+LL |     while (let 2 = 3 && let 3 = 4 && let 4 = 5) {}
+   |                         ^^^^^^^^^
+   |
+note: `let`s wrapped in parentheses are not supported in a context with let chains
+  --> $DIR/disallowed-positions-without-feature-gate.rs:50:12
+   |
+LL |     while (let 2 = 3 && let 3 = 4 && let 4 = 5) {}
+   |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:50:38
+   |
+LL |     while (let 2 = 3 && let 3 = 4 && let 4 = 5) {}
+   |                                      ^^^^^^^^^
+   |
+note: `let`s wrapped in parentheses are not supported in a context with let chains
+  --> $DIR/disallowed-positions-without-feature-gate.rs:50:12
+   |
+LL |     while (let 2 = 3 && let 3 = 4 && let 4 = 5) {}
+   |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:70:9
+   |
+LL |     if &let 0 = 0 {}
+   |         ^^^^^^^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:73:9
+   |
+LL |     if !let 0 = 0 {}
+   |         ^^^^^^^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:75:9
+   |
+LL |     if *let 0 = 0 {}
+   |         ^^^^^^^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:77:9
+   |
+LL |     if -let 0 = 0 {}
+   |         ^^^^^^^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:85:9
+   |
+LL |     if (let 0 = 0)? {}
+   |         ^^^^^^^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:88:16
+   |
+LL |     if true || let 0 = 0 {}
+   |                ^^^^^^^^^
+   |
+note: `||` operators are not supported in let chain expressions
+  --> $DIR/disallowed-positions-without-feature-gate.rs:88:13
+   |
+LL |     if true || let 0 = 0 {}
+   |             ^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:90:17
+   |
+LL |     if (true || let 0 = 0) {}
+   |                 ^^^^^^^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:92:25
+   |
+LL |     if true && (true || let 0 = 0) {}
+   |                         ^^^^^^^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:94:25
+   |
+LL |     if true || (true && let 0 = 0) {}
+   |                         ^^^^^^^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:98:12
+   |
+LL |     if x = let 0 = 0 {}
+   |            ^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:101:15
+   |
+LL |     if true..(let 0 = 0) {}
+   |               ^^^^^^^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:104:11
+   |
+LL |     if ..(let 0 = 0) {}
+   |           ^^^^^^^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:106:9
+   |
+LL |     if (let 0 = 0).. {}
+   |         ^^^^^^^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:110:8
+   |
+LL |     if let Range { start: _, end: _ } = true..true && false {}
+   |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:113:8
+   |
+LL |     if let Range { start: _, end: _ } = true..true || false {}
+   |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:119:8
+   |
+LL |     if let Range { start: F, end } = F..|| true {}
+   |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:125:8
+   |
+LL |     if let Range { start: true, end } = t..&&false {}
+   |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:129:19
+   |
+LL |     if let true = let true = true {}
+   |                   ^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:134:12
+   |
+LL |     while &let 0 = 0 {}
+   |            ^^^^^^^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:137:12
+   |
+LL |     while !let 0 = 0 {}
+   |            ^^^^^^^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:139:12
+   |
+LL |     while *let 0 = 0 {}
+   |            ^^^^^^^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:141:12
+   |
+LL |     while -let 0 = 0 {}
+   |            ^^^^^^^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:149:12
+   |
+LL |     while (let 0 = 0)? {}
+   |            ^^^^^^^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:152:19
+   |
+LL |     while true || let 0 = 0 {}
+   |                   ^^^^^^^^^
+   |
+note: `||` operators are not supported in let chain expressions
+  --> $DIR/disallowed-positions-without-feature-gate.rs:152:16
+   |
+LL |     while true || let 0 = 0 {}
+   |                ^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:154:20
+   |
+LL |     while (true || let 0 = 0) {}
+   |                    ^^^^^^^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:156:28
+   |
+LL |     while true && (true || let 0 = 0) {}
+   |                            ^^^^^^^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:158:28
+   |
+LL |     while true || (true && let 0 = 0) {}
+   |                            ^^^^^^^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:162:15
+   |
+LL |     while x = let 0 = 0 {}
+   |               ^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:165:18
+   |
+LL |     while true..(let 0 = 0) {}
+   |                  ^^^^^^^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:168:14
+   |
+LL |     while ..(let 0 = 0) {}
+   |              ^^^^^^^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:170:12
+   |
+LL |     while (let 0 = 0).. {}
+   |            ^^^^^^^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:174:11
+   |
+LL |     while let Range { start: _, end: _ } = true..true && false {}
+   |           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:177:11
+   |
+LL |     while let Range { start: _, end: _ } = true..true || false {}
+   |           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:183:11
+   |
+LL |     while let Range { start: F, end } = F..|| true {}
+   |           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:189:11
+   |
+LL |     while let Range { start: true, end } = t..&&false {}
+   |           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:193:22
+   |
+LL |     while let true = let true = true {}
+   |                      ^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:208:6
+   |
+LL |     &let 0 = 0;
+   |      ^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:211:6
+   |
+LL |     !let 0 = 0;
+   |      ^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:213:6
+   |
+LL |     *let 0 = 0;
+   |      ^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:215:6
+   |
+LL |     -let 0 = 0;
+   |      ^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:217:13
+   |
+LL |     let _ = let _ = 3;
+   |             ^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:225:6
+   |
+LL |     (let 0 = 0)?;
+   |      ^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:228:13
+   |
+LL |     true || let 0 = 0;
+   |             ^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:230:14
+   |
+LL |     (true || let 0 = 0);
+   |              ^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:232:22
+   |
+LL |     true && (true || let 0 = 0);
+   |                      ^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:236:9
+   |
+LL |     x = let 0 = 0;
+   |         ^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:239:12
+   |
+LL |     true..(let 0 = 0);
+   |            ^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:241:8
+   |
+LL |     ..(let 0 = 0);
+   |        ^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:243:6
+   |
+LL |     (let 0 = 0)..;
+   |      ^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:246:6
+   |
+LL |     (let Range { start: _, end: _ } = true..true || false);
+   |      ^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:250:6
+   |
+LL |     (let true = let true = true);
+   |      ^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:250:17
+   |
+LL |     (let true = let true = true);
+   |                 ^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:256:25
+   |
+LL |         let x = true && let y = 1;
+   |                         ^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:262:19
+   |
+LL |         [1, 2, 3][let _ = ()]
+   |                   ^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:267:6
+   |
+LL |     &let 0 = 0
+   |      ^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:277:17
+   |
+LL |         true && let 1 = 1
+   |                 ^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:282:17
+   |
+LL |         true && let 1 = 1
+   |                 ^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:287:17
+   |
+LL |         true && let 1 = 1
+   |                 ^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:298:17
+   |
+LL |         true && let 1 = 1
+   |                 ^^^
+
+error: expressions must be enclosed in braces to be used as const generic arguments
+  --> $DIR/disallowed-positions-without-feature-gate.rs:298:9
+   |
+LL |         true && let 1 = 1
+   |         ^^^^^^^^^^^^^^^^^
+   |
+help: enclose the `const` expression in braces
+   |
+LL |         { true && let 1 = 1 }
+   |         +                   +
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:307:9
+   |
+LL |     if (let Some(a) = opt && true) {
+   |         ^^^^^^^^^^^^^^^^^
+   |
+note: `let`s wrapped in parentheses are not supported in a context with let chains
+  --> $DIR/disallowed-positions-without-feature-gate.rs:307:9
+   |
+LL |     if (let Some(a) = opt && true) {
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:311:9
+   |
+LL |     if (let Some(a) = opt) && true {
+   |         ^^^^^^^^^^^^^^^^^
+   |
+note: `let`s wrapped in parentheses are not supported in a context with let chains
+  --> $DIR/disallowed-positions-without-feature-gate.rs:311:9
+   |
+LL |     if (let Some(a) = opt) && true {
+   |         ^^^^^^^^^^^^^^^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:314:9
+   |
+LL |     if (let Some(a) = opt) && (let Some(b) = a) {
+   |         ^^^^^^^^^^^^^^^^^
+   |
+note: `let`s wrapped in parentheses are not supported in a context with let chains
+  --> $DIR/disallowed-positions-without-feature-gate.rs:314:9
+   |
+LL |     if (let Some(a) = opt) && (let Some(b) = a) {
+   |         ^^^^^^^^^^^^^^^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:314:32
+   |
+LL |     if (let Some(a) = opt) && (let Some(b) = a) {
+   |                                ^^^^^^^^^^^^^^^
+   |
+note: `let`s wrapped in parentheses are not supported in a context with let chains
+  --> $DIR/disallowed-positions-without-feature-gate.rs:314:32
+   |
+LL |     if (let Some(a) = opt) && (let Some(b) = a) {
+   |                                ^^^^^^^^^^^^^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:319:9
+   |
+LL |     if (let Some(a) = opt && (let Some(b) = a)) && b == 1 {
+   |         ^^^^^^^^^^^^^^^^^
+   |
+note: `let`s wrapped in parentheses are not supported in a context with let chains
+  --> $DIR/disallowed-positions-without-feature-gate.rs:319:9
+   |
+LL |     if (let Some(a) = opt && (let Some(b) = a)) && b == 1 {
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:319:31
+   |
+LL |     if (let Some(a) = opt && (let Some(b) = a)) && b == 1 {
+   |                               ^^^^^^^^^^^^^^^
+   |
+note: `let`s wrapped in parentheses are not supported in a context with let chains
+  --> $DIR/disallowed-positions-without-feature-gate.rs:319:31
+   |
+LL |     if (let Some(a) = opt && (let Some(b) = a)) && b == 1 {
+   |                               ^^^^^^^^^^^^^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:323:9
+   |
+LL |     if (let Some(a) = opt && (let Some(b) = a)) && true {
+   |         ^^^^^^^^^^^^^^^^^
+   |
+note: `let`s wrapped in parentheses are not supported in a context with let chains
+  --> $DIR/disallowed-positions-without-feature-gate.rs:323:9
+   |
+LL |     if (let Some(a) = opt && (let Some(b) = a)) && true {
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:323:31
+   |
+LL |     if (let Some(a) = opt && (let Some(b) = a)) && true {
+   |                               ^^^^^^^^^^^^^^^
+   |
+note: `let`s wrapped in parentheses are not supported in a context with let chains
+  --> $DIR/disallowed-positions-without-feature-gate.rs:323:31
+   |
+LL |     if (let Some(a) = opt && (let Some(b) = a)) && true {
+   |                               ^^^^^^^^^^^^^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:327:9
+   |
+LL |     if (let Some(a) = opt && (true)) && true {
+   |         ^^^^^^^^^^^^^^^^^
+   |
+note: `let`s wrapped in parentheses are not supported in a context with let chains
+  --> $DIR/disallowed-positions-without-feature-gate.rs:327:9
+   |
+LL |     if (let Some(a) = opt && (true)) && true {
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:332:22
+   |
+LL |     let x = (true && let y = 1);
+   |                      ^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:337:20
+   |
+LL |         ([1, 2, 3][let _ = ()])
+   |                    ^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:63:16
+   |
+LL |     use_expr!((let 0 = 1 && 0 == 0));
+   |                ^^^
+
+error: expected expression, found `let` statement
+  --> $DIR/disallowed-positions-without-feature-gate.rs:65:16
+   |
+LL |     use_expr!((let 0 = 1));
+   |                ^^^
+
+error[E0308]: mismatched types
+  --> $DIR/disallowed-positions-without-feature-gate.rs:101:8
+   |
+LL |     if true..(let 0 = 0) {}
+   |        ^^^^^^^^^^^^^^^^^ expected `bool`, found `Range<bool>`
+   |
+   = note: expected type `bool`
+            found struct `std::ops::Range<bool>`
+
+error[E0308]: mismatched types
+  --> $DIR/disallowed-positions-without-feature-gate.rs:110:12
+   |
+LL |     if let Range { start: _, end: _ } = true..true && false {}
+   |            ^^^^^^^^^^^^^^^^^^^^^^^^^^   ---- this expression has type `bool`
+   |            |
+   |            expected `bool`, found `Range<_>`
+   |
+   = note: expected type `bool`
+            found struct `std::ops::Range<_>`
+
+error[E0308]: mismatched types
+  --> $DIR/disallowed-positions-without-feature-gate.rs:113:12
+   |
+LL |     if let Range { start: _, end: _ } = true..true || false {}
+   |            ^^^^^^^^^^^^^^^^^^^^^^^^^^   ---- this expression has type `bool`
+   |            |
+   |            expected `bool`, found `Range<_>`
+   |
+   = note: expected type `bool`
+            found struct `std::ops::Range<_>`
+
+error[E0308]: mismatched types
+  --> $DIR/disallowed-positions-without-feature-gate.rs:119:12
+   |
+LL |     if let Range { start: F, end } = F..|| true {}
+   |            ^^^^^^^^^^^^^^^^^^^^^^^   - this expression has type `fn() -> bool`
+   |            |
+   |            expected fn pointer, found `Range<_>`
+   |
+   = note: expected fn pointer `fn() -> bool`
+                  found struct `std::ops::Range<_>`
+
+error[E0308]: mismatched types
+  --> $DIR/disallowed-positions-without-feature-gate.rs:125:12
+   |
+LL |     if let Range { start: true, end } = t..&&false {}
+   |            ^^^^^^^^^^^^^^^^^^^^^^^^^^   - this expression has type `&&bool`
+   |            |
+   |            expected `bool`, found `Range<_>`
+   |
+   = note: expected type `bool`
+            found struct `std::ops::Range<_>`
+
+error[E0277]: the `?` operator can only be applied to values that implement `Try`
+  --> $DIR/disallowed-positions-without-feature-gate.rs:81:20
+   |
+LL |         if let 0 = 0? {}
+   |                    ^^ the `?` operator cannot be applied to type `{integer}`
+   |
+   = help: the trait `Try` is not implemented for `{integer}`
+
+error[E0308]: mismatched types
+  --> $DIR/disallowed-positions-without-feature-gate.rs:165:11
+   |
+LL |     while true..(let 0 = 0) {}
+   |           ^^^^^^^^^^^^^^^^^ expected `bool`, found `Range<bool>`
+   |
+   = note: expected type `bool`
+            found struct `std::ops::Range<bool>`
+
+error[E0308]: mismatched types
+  --> $DIR/disallowed-positions-without-feature-gate.rs:174:15
+   |
+LL |     while let Range { start: _, end: _ } = true..true && false {}
+   |               ^^^^^^^^^^^^^^^^^^^^^^^^^^   ---- this expression has type `bool`
+   |               |
+   |               expected `bool`, found `Range<_>`
+   |
+   = note: expected type `bool`
+            found struct `std::ops::Range<_>`
+
+error[E0308]: mismatched types
+  --> $DIR/disallowed-positions-without-feature-gate.rs:177:15
+   |
+LL |     while let Range { start: _, end: _ } = true..true || false {}
+   |               ^^^^^^^^^^^^^^^^^^^^^^^^^^   ---- this expression has type `bool`
+   |               |
+   |               expected `bool`, found `Range<_>`
+   |
+   = note: expected type `bool`
+            found struct `std::ops::Range<_>`
+
+error[E0308]: mismatched types
+  --> $DIR/disallowed-positions-without-feature-gate.rs:183:15
+   |
+LL |     while let Range { start: F, end } = F..|| true {}
+   |               ^^^^^^^^^^^^^^^^^^^^^^^   - this expression has type `fn() -> bool`
+   |               |
+   |               expected fn pointer, found `Range<_>`
+   |
+   = note: expected fn pointer `fn() -> bool`
+                  found struct `std::ops::Range<_>`
+
+error[E0308]: mismatched types
+  --> $DIR/disallowed-positions-without-feature-gate.rs:189:15
+   |
+LL |     while let Range { start: true, end } = t..&&false {}
+   |               ^^^^^^^^^^^^^^^^^^^^^^^^^^   - this expression has type `&&bool`
+   |               |
+   |               expected `bool`, found `Range<_>`
+   |
+   = note: expected type `bool`
+            found struct `std::ops::Range<_>`
+
+error[E0277]: the `?` operator can only be applied to values that implement `Try`
+  --> $DIR/disallowed-positions-without-feature-gate.rs:145:23
+   |
+LL |         while let 0 = 0? {}
+   |                       ^^ the `?` operator cannot be applied to type `{integer}`
+   |
+   = help: the trait `Try` is not implemented for `{integer}`
+
+error[E0308]: mismatched types
+  --> $DIR/disallowed-positions-without-feature-gate.rs:246:10
+   |
+LL |     (let Range { start: _, end: _ } = true..true || false);
+   |          ^^^^^^^^^^^^^^^^^^^^^^^^^^   ---- this expression has type `bool`
+   |          |
+   |          expected `bool`, found `Range<_>`
+   |
+   = note: expected type `bool`
+            found struct `std::ops::Range<_>`
+
+error[E0277]: the `?` operator can only be applied to values that implement `Try`
+  --> $DIR/disallowed-positions-without-feature-gate.rs:221:17
+   |
+LL |         let 0 = 0?;
+   |                 ^^ the `?` operator cannot be applied to type `{integer}`
+   |
+   = help: the trait `Try` is not implemented for `{integer}`
+
+error: aborting due to 105 previous errors
+
+Some errors have detailed explanations: E0277, E0308.
+For more information about an error, try `rustc --explain E0277`.