Warn users about || in let chain expressions

3 files changed, 179 insertions, 96 deletions

diff --git a/compiler/rustc_ast_passes/src/ast_validation.rs b/compiler/rustc_ast_passes/src/ast_validation.rs
index 0cf73178d67..8f0b12cb4fe 100644
--- a/compiler/rustc_ast_passes/src/ast_validation.rs
+++ b/compiler/rustc_ast_passes/src/ast_validation.rs
@@ -64,8 +64,8 @@ struct AstValidator<'a> {
     /// certain positions.
     is_assoc_ty_bound_banned: bool,
 
-    /// Used to allow `let` expressions in certain syntactic locations.
-    is_let_allowed: bool,
+    /// See [ForbiddenLetReason]
+    forbidden_let_reason: Option<ForbiddenLetReason>,
 
     lint_buffer: &'a mut LintBuffer,
 }
@@ -103,20 +103,28 @@ impl<'a> AstValidator<'a> {
         self.is_tilde_const_allowed = old;
     }
 
-    fn with_let_allowed(&mut self, allowed: bool, f: impl FnOnce(&mut Self, bool)) {
-        let old = mem::replace(&mut self.is_let_allowed, allowed);
+    fn with_let_management(
+        &mut self,
+        forbidden_let_reason: Option<ForbiddenLetReason>,
+        f: impl FnOnce(&mut Self, Option<ForbiddenLetReason>),
+    ) {
+        let old = mem::replace(&mut self.forbidden_let_reason, forbidden_let_reason);
         f(self, old);
-        self.is_let_allowed = old;
+        self.forbidden_let_reason = old;
     }
 
     /// Emits an error banning the `let` expression provided in the given location.
-    fn ban_let_expr(&self, expr: &'a Expr) {
+    fn ban_let_expr(&self, expr: &'a Expr, forbidden_let_reason: ForbiddenLetReason) {
         let sess = &self.session;
         if sess.opts.unstable_features.is_nightly_build() {
-            sess.struct_span_err(expr.span, "`let` expressions are not supported here")
-                .note("only supported directly in conditions of `if`- and `while`-expressions")
-                .note("as well as when nested within `&&` and parentheses in those conditions")
-                .emit();
+            let err = "`let` expressions are not supported here";
+            let mut diag = sess.struct_span_err(expr.span, err);
+            diag.note("only supported directly in conditions of `if` and `while` expressions");
+            diag.note("as well as when nested within `&&` and parentheses in those conditions");
+            if let ForbiddenLetReason::ForbiddenWithOr(span) = forbidden_let_reason {
+                diag.span_note(span, "`||` operators are not allowed in let chain expressions");
+            }
+            diag.emit();
         } else {
             sess.struct_span_err(expr.span, "expected expression, found statement (`let`)")
                 .note("variable declaration using `let` is a statement")
@@ -988,39 +996,48 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
     }
 
     fn visit_expr(&mut self, expr: &'a Expr) {
-        self.with_let_allowed(false, |this, let_allowed| match &expr.kind {
-            ExprKind::If(cond, then, opt_else) => {
-                this.visit_block(then);
-                walk_list!(this, visit_expr, opt_else);
-                this.with_let_allowed(true, |this, _| this.visit_expr(cond));
-                return;
-            }
-            ExprKind::Let(..) if !let_allowed => this.ban_let_expr(expr),
-            ExprKind::Match(expr, arms) => {
-                this.visit_expr(expr);
-                for arm in arms {
-                    this.visit_expr(&arm.body);
-                    this.visit_pat(&arm.pat);
-                    walk_list!(this, visit_attribute, &arm.attrs);
-                    if let Some(ref guard) = arm.guard {
-                        if let ExprKind::Let(_, ref expr, _) = guard.kind {
-                            this.with_let_allowed(true, |this, _| this.visit_expr(expr));
+        self.with_let_management(Some(ForbiddenLetReason::GenericForbidden), |this, forbidden_let_reason| {
+            match &expr.kind {
+                ExprKind::Binary(Spanned { node: BinOpKind::Or, span }, lhs, rhs) => {
+                    let forbidden_let_reason = Some(ForbiddenLetReason::ForbiddenWithOr(*span));
+                    this.with_let_management(forbidden_let_reason, |this, _| this.visit_expr(lhs));
+                    this.with_let_management(forbidden_let_reason, |this, _| this.visit_expr(rhs));
+                }
+                ExprKind::If(cond, then, opt_else) => {
+                    this.visit_block(then);
+                    walk_list!(this, visit_expr, opt_else);
+                    this.with_let_management(None, |this, _| this.visit_expr(cond));
+                    return;
+                }
+                ExprKind::Let(..) if let Some(elem) = forbidden_let_reason => {
+                    this.ban_let_expr(expr, elem);
+                },
+                ExprKind::Match(scrutinee, arms) => {
+                    this.visit_expr(scrutinee);
+                    for arm in arms {
+                        this.visit_expr(&arm.body);
+                        this.visit_pat(&arm.pat);
+                        walk_list!(this, visit_attribute, &arm.attrs);
+                        if let Some(guard) = &arm.guard && let ExprKind::Let(_, guard_expr, _) = &guard.kind {
+                            this.with_let_management(None, |this, _| {
+                                this.visit_expr(guard_expr)
+                            });
                             return;
                         }
                     }
                 }
+                ExprKind::Paren(_) | ExprKind::Binary(Spanned { node: BinOpKind::And, .. }, ..) => {
+                    this.with_let_management(forbidden_let_reason, |this, _| visit::walk_expr(this, expr));
+                    return;
+                }
+                ExprKind::While(cond, then, opt_label) => {
+                    walk_list!(this, visit_label, opt_label);
+                    this.visit_block(then);
+                    this.with_let_management(None, |this, _| this.visit_expr(cond));
+                    return;
+                }
+                _ => visit::walk_expr(this, expr),
             }
-            ExprKind::Paren(_) | ExprKind::Binary(Spanned { node: BinOpKind::And, .. }, ..) => {
-                this.with_let_allowed(let_allowed, |this, _| visit::walk_expr(this, expr));
-                return;
-            }
-            ExprKind::While(cond, then, opt_label) => {
-                walk_list!(this, visit_label, opt_label);
-                this.visit_block(then);
-                this.with_let_allowed(true, |this, _| this.visit_expr(cond));
-                return;
-            }
-            _ => visit::walk_expr(this, expr),
         });
     }
 
@@ -1772,10 +1789,19 @@ pub fn check_crate(session: &Session, krate: &Crate, lints: &mut LintBuffer) ->
         is_tilde_const_allowed: false,
         is_impl_trait_banned: false,
         is_assoc_ty_bound_banned: false,
-        is_let_allowed: false,
+        forbidden_let_reason: Some(ForbiddenLetReason::GenericForbidden),
         lint_buffer: lints,
     };
     visit::walk_crate(&mut validator, krate);
 
     validator.has_proc_macro_decls
 }
+
+/// Used to forbid `let` expressions in certain syntactic locations.
+#[derive(Clone, Copy)]
+enum ForbiddenLetReason {
+    /// A let chain with the `||` operator
+    ForbiddenWithOr(Span),
+    /// `let` is not valid and the source environment is not important
+    GenericForbidden,
+}
diff --git a/compiler/rustc_ast_passes/src/lib.rs b/compiler/rustc_ast_passes/src/lib.rs
index 876dd7f757c..9d52c32885d 100644
--- a/compiler/rustc_ast_passes/src/lib.rs
+++ b/compiler/rustc_ast_passes/src/lib.rs
@@ -4,11 +4,13 @@
 //!
 //! The crate also contains other misc AST visitors, e.g. `node_count` and `show_span`.
 
-#![feature(iter_is_partitioned)]
+#![allow(rustc::potential_query_instability)]
 #![feature(box_patterns)]
+#![feature(if_let_guard)]
+#![feature(iter_is_partitioned)]
+#![feature(let_chains)]
 #![feature(let_else)]
 #![recursion_limit = "256"]
-#![allow(rustc::potential_query_instability)]
 
 pub mod ast_validation;
 pub mod feature_gate;
diff --git a/src/test/ui/rfc-2497-if-let-chains/disallowed-positions.stderr b/src/test/ui/rfc-2497-if-let-chains/disallowed-positions.stderr
index 897de54a7bf..dd090a3a548 100644
--- a/src/test/ui/rfc-2497-if-let-chains/disallowed-positions.stderr
+++ b/src/test/ui/rfc-2497-if-let-chains/disallowed-positions.stderr
@@ -15,7 +15,7 @@ error: `let` expressions are not supported here
 LL |     if &let 0 = 0 {}
    |         ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
+   = note: only supported directly in conditions of `if` and `while` expressions
    = note: as well as when nested within `&&` and parentheses in those conditions
 
 error: `let` expressions are not supported here
@@ -24,7 +24,7 @@ error: `let` expressions are not supported here
 LL |     if !let 0 = 0 {}
    |         ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
+   = note: only supported directly in conditions of `if` and `while` expressions
    = note: as well as when nested within `&&` and parentheses in those conditions
 
 error: `let` expressions are not supported here
@@ -33,7 +33,7 @@ error: `let` expressions are not supported here
 LL |     if *let 0 = 0 {}
    |         ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
+   = note: only supported directly in conditions of `if` and `while` expressions
    = note: as well as when nested within `&&` and parentheses in those conditions
 
 error: `let` expressions are not supported here
@@ -42,7 +42,7 @@ error: `let` expressions are not supported here
 LL |     if -let 0 = 0 {}
    |         ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
+   = note: only supported directly in conditions of `if` and `while` expressions
    = note: as well as when nested within `&&` and parentheses in those conditions
 
 error: `let` expressions are not supported here
@@ -51,7 +51,7 @@ error: `let` expressions are not supported here
 LL |     if (let 0 = 0)? {}
    |         ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
+   = note: only supported directly in conditions of `if` and `while` expressions
    = note: as well as when nested within `&&` and parentheses in those conditions
 
 error: `let` expressions are not supported here
@@ -60,8 +60,13 @@ error: `let` expressions are not supported here
 LL |     if true || let 0 = 0 {}
    |                ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
+   = note: only supported directly in conditions of `if` and `while` expressions
    = note: as well as when nested within `&&` and parentheses in those conditions
+note: `||` operators are not allowed in let chain expressions
+  --> $DIR/disallowed-positions.rs:47:13
+   |
+LL |     if true || let 0 = 0 {}
+   |             ^^
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:48:17
@@ -69,8 +74,13 @@ error: `let` expressions are not supported here
 LL |     if (true || let 0 = 0) {}
    |                 ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
+   = note: only supported directly in conditions of `if` and `while` expressions
    = note: as well as when nested within `&&` and parentheses in those conditions
+note: `||` operators are not allowed in let chain expressions
+  --> $DIR/disallowed-positions.rs:48:14
+   |
+LL |     if (true || let 0 = 0) {}
+   |              ^^
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:49:25
@@ -78,8 +88,13 @@ error: `let` expressions are not supported here
 LL |     if true && (true || let 0 = 0) {}
    |                         ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
+   = note: only supported directly in conditions of `if` and `while` expressions
    = note: as well as when nested within `&&` and parentheses in those conditions
+note: `||` operators are not allowed in let chain expressions
+  --> $DIR/disallowed-positions.rs:49:22
+   |
+LL |     if true && (true || let 0 = 0) {}
+   |                      ^^
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:50:25
@@ -87,8 +102,13 @@ error: `let` expressions are not supported here
 LL |     if true || (true && let 0 = 0) {}
    |                         ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
+   = note: only supported directly in conditions of `if` and `while` expressions
    = note: as well as when nested within `&&` and parentheses in those conditions
+note: `||` operators are not allowed in let chain expressions
+  --> $DIR/disallowed-positions.rs:50:13
+   |
+LL |     if true || (true && let 0 = 0) {}
+   |             ^^
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:53:12
@@ -96,7 +116,7 @@ error: `let` expressions are not supported here
 LL |     if x = let 0 = 0 {}
    |            ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
+   = note: only supported directly in conditions of `if` and `while` expressions
    = note: as well as when nested within `&&` and parentheses in those conditions
 
 error: `let` expressions are not supported here
@@ -105,7 +125,7 @@ error: `let` expressions are not supported here
 LL |     if true..(let 0 = 0) {}
    |               ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
+   = note: only supported directly in conditions of `if` and `while` expressions
    = note: as well as when nested within `&&` and parentheses in those conditions
 
 error: `let` expressions are not supported here
@@ -114,7 +134,7 @@ error: `let` expressions are not supported here
 LL |     if ..(let 0 = 0) {}
    |           ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
+   = note: only supported directly in conditions of `if` and `while` expressions
    = note: as well as when nested within `&&` and parentheses in those conditions
 
 error: `let` expressions are not supported here
@@ -123,7 +143,7 @@ error: `let` expressions are not supported here
 LL |     if (let 0 = 0).. {}
    |         ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
+   = note: only supported directly in conditions of `if` and `while` expressions
    = note: as well as when nested within `&&` and parentheses in those conditions
 
 error: `let` expressions are not supported here
@@ -132,7 +152,7 @@ error: `let` expressions are not supported here
 LL |     if let Range { start: _, end: _ } = true..true && false {}
    |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
+   = note: only supported directly in conditions of `if` and `while` expressions
    = note: as well as when nested within `&&` and parentheses in those conditions
 
 error: `let` expressions are not supported here
@@ -141,7 +161,7 @@ error: `let` expressions are not supported here
 LL |     if let Range { start: _, end: _ } = true..true || false {}
    |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
+   = note: only supported directly in conditions of `if` and `while` expressions
    = note: as well as when nested within `&&` and parentheses in those conditions
 
 error: `let` expressions are not supported here
@@ -150,7 +170,7 @@ error: `let` expressions are not supported here
 LL |     if let Range { start: F, end } = F..|| true {}
    |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
+   = note: only supported directly in conditions of `if` and `while` expressions
    = note: as well as when nested within `&&` and parentheses in those conditions
 
 error: `let` expressions are not supported here
@@ -159,7 +179,7 @@ error: `let` expressions are not supported here
 LL |     if let Range { start: true, end } = t..&&false {}
    |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
+   = note: only supported directly in conditions of `if` and `while` expressions
    = note: as well as when nested within `&&` and parentheses in those conditions
 
 error: `let` expressions are not supported here
@@ -168,7 +188,7 @@ error: `let` expressions are not supported here
 LL |     if let true = let true = true {}
    |                   ^^^^^^^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
+   = note: only supported directly in conditions of `if` and `while` expressions
    = note: as well as when nested within `&&` and parentheses in those conditions
 
 error: `let` expressions are not supported here
@@ -177,7 +197,7 @@ error: `let` expressions are not supported here
 LL |     while &let 0 = 0 {}
    |            ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
+   = note: only supported directly in conditions of `if` and `while` expressions
    = note: as well as when nested within `&&` and parentheses in those conditions
 
 error: `let` expressions are not supported here
@@ -186,7 +206,7 @@ error: `let` expressions are not supported here
 LL |     while !let 0 = 0 {}
    |            ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
+   = note: only supported directly in conditions of `if` and `while` expressions
    = note: as well as when nested within `&&` and parentheses in those conditions
 
 error: `let` expressions are not supported here
@@ -195,7 +215,7 @@ error: `let` expressions are not supported here
 LL |     while *let 0 = 0 {}
    |            ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
+   = note: only supported directly in conditions of `if` and `while` expressions
    = note: as well as when nested within `&&` and parentheses in those conditions
 
 error: `let` expressions are not supported here
@@ -204,7 +224,7 @@ error: `let` expressions are not supported here
 LL |     while -let 0 = 0 {}
    |            ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
+   = note: only supported directly in conditions of `if` and `while` expressions
    = note: as well as when nested within `&&` and parentheses in those conditions
 
 error: `let` expressions are not supported here
@@ -213,7 +233,7 @@ error: `let` expressions are not supported here
 LL |     while (let 0 = 0)? {}
    |            ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
+   = note: only supported directly in conditions of `if` and `while` expressions
    = note: as well as when nested within `&&` and parentheses in those conditions
 
 error: `let` expressions are not supported here
@@ -222,8 +242,13 @@ error: `let` expressions are not supported here
 LL |     while true || let 0 = 0 {}
    |                   ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
+   = note: only supported directly in conditions of `if` and `while` expressions
    = note: as well as when nested within `&&` and parentheses in those conditions
+note: `||` operators are not allowed in let chain expressions
+  --> $DIR/disallowed-positions.rs:111:16
+   |
+LL |     while true || let 0 = 0 {}
+   |                ^^
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:112:20
@@ -231,8 +256,13 @@ error: `let` expressions are not supported here
 LL |     while (true || let 0 = 0) {}
    |                    ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
+   = note: only supported directly in conditions of `if` and `while` expressions
    = note: as well as when nested within `&&` and parentheses in those conditions
+note: `||` operators are not allowed in let chain expressions
+  --> $DIR/disallowed-positions.rs:112:17
+   |
+LL |     while (true || let 0 = 0) {}
+   |                 ^^
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:113:28
@@ -240,8 +270,13 @@ error: `let` expressions are not supported here
 LL |     while true && (true || let 0 = 0) {}
    |                            ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
+   = note: only supported directly in conditions of `if` and `while` expressions
    = note: as well as when nested within `&&` and parentheses in those conditions
+note: `||` operators are not allowed in let chain expressions
+  --> $DIR/disallowed-positions.rs:113:25
+   |
+LL |     while true && (true || let 0 = 0) {}
+   |                         ^^
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:114:28
@@ -249,8 +284,13 @@ error: `let` expressions are not supported here
 LL |     while true || (true && let 0 = 0) {}
    |                            ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
+   = note: only supported directly in conditions of `if` and `while` expressions
    = note: as well as when nested within `&&` and parentheses in those conditions
+note: `||` operators are not allowed in let chain expressions
+  --> $DIR/disallowed-positions.rs:114:16
+   |
+LL |     while true || (true && let 0 = 0) {}
+   |                ^^
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:117:15
@@ -258,7 +298,7 @@ error: `let` expressions are not supported here
 LL |     while x = let 0 = 0 {}
    |               ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
+   = note: only supported directly in conditions of `if` and `while` expressions
    = note: as well as when nested within `&&` and parentheses in those conditions
 
 error: `let` expressions are not supported here
@@ -267,7 +307,7 @@ error: `let` expressions are not supported here
 LL |     while true..(let 0 = 0) {}
    |                  ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
+   = note: only supported directly in conditions of `if` and `while` expressions
    = note: as well as when nested within `&&` and parentheses in those conditions
 
 error: `let` expressions are not supported here
@@ -276,7 +316,7 @@ error: `let` expressions are not supported here
 LL |     while ..(let 0 = 0) {}
    |              ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
+   = note: only supported directly in conditions of `if` and `while` expressions
    = note: as well as when nested within `&&` and parentheses in those conditions
 
 error: `let` expressions are not supported here
@@ -285,7 +325,7 @@ error: `let` expressions are not supported here
 LL |     while (let 0 = 0).. {}
    |            ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
+   = note: only supported directly in conditions of `if` and `while` expressions
    = note: as well as when nested within `&&` and parentheses in those conditions
 
 error: `let` expressions are not supported here
@@ -294,7 +334,7 @@ error: `let` expressions are not supported here
 LL |     while let Range { start: _, end: _ } = true..true && false {}
    |           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
+   = note: only supported directly in conditions of `if` and `while` expressions
    = note: as well as when nested within `&&` and parentheses in those conditions
 
 error: `let` expressions are not supported here
@@ -303,7 +343,7 @@ error: `let` expressions are not supported here
 LL |     while let Range { start: _, end: _ } = true..true || false {}
    |           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
+   = note: only supported directly in conditions of `if` and `while` expressions
    = note: as well as when nested within `&&` and parentheses in those conditions
 
 error: `let` expressions are not supported here
@@ -312,7 +352,7 @@ error: `let` expressions are not supported here
 LL |     while let Range { start: F, end } = F..|| true {}
    |           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
+   = note: only supported directly in conditions of `if` and `while` expressions
    = note: as well as when nested within `&&` and parentheses in those conditions
 
 error: `let` expressions are not supported here
@@ -321,7 +361,7 @@ error: `let` expressions are not supported here
 LL |     while let Range { start: true, end } = t..&&false {}
    |           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
+   = note: only supported directly in conditions of `if` and `while` expressions
    = note: as well as when nested within `&&` and parentheses in those conditions
 
 error: `let` expressions are not supported here
@@ -330,7 +370,7 @@ error: `let` expressions are not supported here
 LL |     while let true = let true = true {}
    |                      ^^^^^^^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
+   = note: only supported directly in conditions of `if` and `while` expressions
    = note: as well as when nested within `&&` and parentheses in those conditions
 
 error: `let` expressions are not supported here
@@ -339,7 +379,7 @@ error: `let` expressions are not supported here
 LL |     &let 0 = 0;
    |      ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
+   = note: only supported directly in conditions of `if` and `while` expressions
    = note: as well as when nested within `&&` and parentheses in those conditions
 
 error: `let` expressions are not supported here
@@ -348,7 +388,7 @@ error: `let` expressions are not supported here
 LL |     !let 0 = 0;
    |      ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
+   = note: only supported directly in conditions of `if` and `while` expressions
    = note: as well as when nested within `&&` and parentheses in those conditions
 
 error: `let` expressions are not supported here
@@ -357,7 +397,7 @@ error: `let` expressions are not supported here
 LL |     *let 0 = 0;
    |      ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
+   = note: only supported directly in conditions of `if` and `while` expressions
    = note: as well as when nested within `&&` and parentheses in those conditions
 
 error: `let` expressions are not supported here
@@ -366,7 +406,7 @@ error: `let` expressions are not supported here
 LL |     -let 0 = 0;
    |      ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
+   = note: only supported directly in conditions of `if` and `while` expressions
    = note: as well as when nested within `&&` and parentheses in those conditions
 
 error: `let` expressions are not supported here
@@ -375,7 +415,7 @@ error: `let` expressions are not supported here
 LL |     (let 0 = 0)?;
    |      ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
+   = note: only supported directly in conditions of `if` and `while` expressions
    = note: as well as when nested within `&&` and parentheses in those conditions
 
 error: `let` expressions are not supported here
@@ -384,8 +424,13 @@ error: `let` expressions are not supported here
 LL |     true || let 0 = 0;
    |             ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
+   = note: only supported directly in conditions of `if` and `while` expressions
    = note: as well as when nested within `&&` and parentheses in those conditions
+note: `||` operators are not allowed in let chain expressions
+  --> $DIR/disallowed-positions.rs:184:10
+   |
+LL |     true || let 0 = 0;
+   |          ^^
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:185:14
@@ -393,8 +438,13 @@ error: `let` expressions are not supported here
 LL |     (true || let 0 = 0);
    |              ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
+   = note: only supported directly in conditions of `if` and `while` expressions
    = note: as well as when nested within `&&` and parentheses in those conditions
+note: `||` operators are not allowed in let chain expressions
+  --> $DIR/disallowed-positions.rs:185:11
+   |
+LL |     (true || let 0 = 0);
+   |           ^^
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:186:22
@@ -402,8 +452,13 @@ error: `let` expressions are not supported here
 LL |     true && (true || let 0 = 0);
    |                      ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
+   = note: only supported directly in conditions of `if` and `while` expressions
    = note: as well as when nested within `&&` and parentheses in those conditions
+note: `||` operators are not allowed in let chain expressions
+  --> $DIR/disallowed-positions.rs:186:19
+   |
+LL |     true && (true || let 0 = 0);
+   |                   ^^
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:189:9
@@ -411,7 +466,7 @@ error: `let` expressions are not supported here
 LL |     x = let 0 = 0;
    |         ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
+   = note: only supported directly in conditions of `if` and `while` expressions
    = note: as well as when nested within `&&` and parentheses in those conditions
 
 error: `let` expressions are not supported here
@@ -420,7 +475,7 @@ error: `let` expressions are not supported here
 LL |     true..(let 0 = 0);
    |            ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
+   = note: only supported directly in conditions of `if` and `while` expressions
    = note: as well as when nested within `&&` and parentheses in those conditions
 
 error: `let` expressions are not supported here
@@ -429,7 +484,7 @@ error: `let` expressions are not supported here
 LL |     ..(let 0 = 0);
    |        ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
+   = note: only supported directly in conditions of `if` and `while` expressions
    = note: as well as when nested within `&&` and parentheses in those conditions
 
 error: `let` expressions are not supported here
@@ -438,7 +493,7 @@ error: `let` expressions are not supported here
 LL |     (let 0 = 0)..;
    |      ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
+   = note: only supported directly in conditions of `if` and `while` expressions
    = note: as well as when nested within `&&` and parentheses in those conditions
 
 error: `let` expressions are not supported here
@@ -447,7 +502,7 @@ error: `let` expressions are not supported here
 LL |     (let Range { start: _, end: _ } = true..true || false);
    |      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
+   = note: only supported directly in conditions of `if` and `while` expressions
    = note: as well as when nested within `&&` and parentheses in those conditions
 
 error: `let` expressions are not supported here
@@ -456,7 +511,7 @@ error: `let` expressions are not supported here
 LL |     (let true = let true = true);
    |      ^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
+   = note: only supported directly in conditions of `if` and `while` expressions
    = note: as well as when nested within `&&` and parentheses in those conditions
 
 error: `let` expressions are not supported here
@@ -465,7 +520,7 @@ error: `let` expressions are not supported here
 LL |     &let 0 = 0
    |      ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
+   = note: only supported directly in conditions of `if` and `while` expressions
    = note: as well as when nested within `&&` and parentheses in those conditions
 
 error: `let` expressions are not supported here
@@ -474,7 +529,7 @@ error: `let` expressions are not supported here
 LL |         true && let 1 = 1
    |                 ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
+   = note: only supported directly in conditions of `if` and `while` expressions
    = note: as well as when nested within `&&` and parentheses in those conditions
 
 error: `let` expressions are not supported here
@@ -483,7 +538,7 @@ error: `let` expressions are not supported here
 LL |         true && let 1 = 1
    |                 ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
+   = note: only supported directly in conditions of `if` and `while` expressions
    = note: as well as when nested within `&&` and parentheses in those conditions
 
 error: `let` expressions are not supported here
@@ -492,7 +547,7 @@ error: `let` expressions are not supported here
 LL |         true && let 1 = 1
    |                 ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
+   = note: only supported directly in conditions of `if` and `while` expressions
    = note: as well as when nested within `&&` and parentheses in those conditions
 
 error: `let` expressions are not supported here
@@ -501,7 +556,7 @@ error: `let` expressions are not supported here
 LL |         true && let 1 = 1
    |                 ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
+   = note: only supported directly in conditions of `if` and `while` expressions
    = note: as well as when nested within `&&` and parentheses in those conditions
 
 error[E0308]: mismatched types