From 701dd632ec6ca5304353d7ced0cec61d336c47d8 Mon Sep 17 00:00:00 2001
From: Deadbeef <ent3rm4n@gmail.com>
Date: Wed, 23 Apr 2025 19:52:36 +0800
Subject: [PATCH] gate `let_chains` in all places before the 2024 edition

Since `let_chains` relies on the 2024 edition drop order to be
consistent, it makes sense for us to gate it in all places, even when
there are unstable features such as with `if_let_guard`s in matches.
This removes the need for us to pass in an enum to `CondChecker` as we
can just always pass in the edition instead.
---
 compiler/rustc_parse/src/parser/expr.rs       |  43 +++-----
 .../rfc-2294-if-let-guard/feature-gate.rs     |   5 +
 .../rfc-2294-if-let-guard/feature-gate.stderr | 100 +++++++++++++-----
 .../rfc-2497-if-let-chains/issue-93150.rs     |   3 +-
 .../rfc-2497-if-let-chains/issue-93150.stderr |  12 ++-
 5 files changed, 108 insertions(+), 55 deletions(-)

diff --git a/compiler/rustc_parse/src/parser/expr.rs b/compiler/rustc_parse/src/parser/expr.rs
index 370eb3f402d93..5e6e9404189c7 100644
--- a/compiler/rustc_parse/src/parser/expr.rs
+++ b/compiler/rustc_parse/src/parser/expr.rs
@@ -2605,8 +2605,7 @@ impl<'a> Parser<'a> {
         let lo = self.prev_token.span;
         // Scoping code checks the top level edition of the `if`; let's match it here.
         // The `CondChecker` also checks the edition of the `let` itself, just to make sure.
-        let let_chains_policy = LetChainsPolicy::EditionDependent { current_edition: lo.edition() };
-        let cond = self.parse_expr_cond(let_chains_policy)?;
+        let cond = self.parse_expr_cond(lo.edition())?;
         self.parse_if_after_cond(lo, cond)
     }
 
@@ -2716,16 +2715,16 @@ impl<'a> Parser<'a> {
 
     /// Parses the condition of a `if` or `while` expression.
     ///
-    /// The specified `edition` in `let_chains_policy` should be that of the whole `if` construct,
-    /// i.e. the same span we use to later decide whether the drop behaviour should be that of
-    /// edition `..=2021` or that of `2024..`.
+    /// The specified `edition` should be that of the whole `if` construct, i.e. the same span
+    /// we use to later decide whether the drop behaviour should be that of edition `..=2021`
+    /// or that of `2024..`.
     // Public because it is used in rustfmt forks such as https://github.com/tucant/rustfmt/blob/30c83df9e1db10007bdd16dafce8a86b404329b2/src/parse/macros/html.rs#L57 for custom if expressions.
-    pub fn parse_expr_cond(&mut self, let_chains_policy: LetChainsPolicy) -> PResult<'a, P<Expr>> {
+    pub fn parse_expr_cond(&mut self, edition: Edition) -> PResult<'a, P<Expr>> {
         let attrs = self.parse_outer_attributes()?;
         let (mut cond, _) =
             self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL | Restrictions::ALLOW_LET, attrs)?;
 
-        CondChecker::new(self, let_chains_policy).visit_expr(&mut cond);
+        CondChecker::new(self, edition).visit_expr(&mut cond);
 
         Ok(cond)
     }
@@ -3020,8 +3019,7 @@ impl<'a> Parser<'a> {
 
     /// Parses a `while` or `while let` expression (`while` token already eaten).
     fn parse_expr_while(&mut self, opt_label: Option<Label>, lo: Span) -> PResult<'a, P<Expr>> {
-        let policy = LetChainsPolicy::EditionDependent { current_edition: lo.edition() };
-        let cond = self.parse_expr_cond(policy).map_err(|mut err| {
+        let cond = self.parse_expr_cond(lo.edition()).map_err(|mut err| {
             err.span_label(lo, "while parsing the condition of this `while` expression");
             err
         })?;
@@ -3426,7 +3424,8 @@ impl<'a> Parser<'a> {
         let if_span = self.prev_token.span;
         let mut cond = self.parse_match_guard_condition()?;
 
-        CondChecker::new(self, LetChainsPolicy::AlwaysAllowed).visit_expr(&mut cond);
+        // TODO explain
+        CondChecker::new(self, if_span.edition()).visit_expr(&mut cond);
 
         if has_let_expr(&cond) {
             let span = if_span.to(cond.span);
@@ -3455,7 +3454,7 @@ impl<'a> Parser<'a> {
                     unreachable!()
                 };
                 self.psess.gated_spans.ungate_last(sym::guard_patterns, cond.span);
-                CondChecker::new(self, LetChainsPolicy::AlwaysAllowed).visit_expr(&mut cond);
+                CondChecker::new(self, span.edition()).visit_expr(&mut cond);
                 let right = self.prev_token.span;
                 self.dcx().emit_err(errors::ParenthesesInMatchPat {
                     span: vec![left, right],
@@ -4026,13 +4025,6 @@ pub(crate) enum ForbiddenLetReason {
     NotSupportedParentheses(#[primary_span] Span),
 }
 
-/// Whether let chains are allowed on all editions, or it's edition dependent (allowed only on
-/// 2024 and later). In case of edition dependence, specify the currently present edition.
-pub enum LetChainsPolicy {
-    AlwaysAllowed,
-    EditionDependent { current_edition: Edition },
-}
-
 /// Visitor to check for invalid use of `ExprKind::Let` that can't
 /// easily be caught in parsing. For example:
 ///
@@ -4044,7 +4036,7 @@ pub enum LetChainsPolicy {
 /// ```
 struct CondChecker<'a> {
     parser: &'a Parser<'a>,
-    let_chains_policy: LetChainsPolicy,
+    current_edition: Edition,
     depth: u32,
     forbid_let_reason: Option<ForbiddenLetReason>,
     missing_let: Option<errors::MaybeMissingLet>,
@@ -4052,13 +4044,13 @@ struct CondChecker<'a> {
 }
 
 impl<'a> CondChecker<'a> {
-    fn new(parser: &'a Parser<'a>, let_chains_policy: LetChainsPolicy) -> Self {
+    fn new(parser: &'a Parser<'a>, current_edition: Edition) -> Self {
         CondChecker {
             parser,
             forbid_let_reason: None,
             missing_let: None,
             comparison: None,
-            let_chains_policy,
+            current_edition,
             depth: 0,
         }
     }
@@ -4083,13 +4075,8 @@ impl MutVisitor for CondChecker<'_> {
                     ));
                 } else if self.depth > 1 {
                     // Top level `let` is always allowed; only gate chains
-                    match self.let_chains_policy {
-                        LetChainsPolicy::AlwaysAllowed => (),
-                        LetChainsPolicy::EditionDependent { current_edition } => {
-                            if !current_edition.at_least_rust_2024() || !span.at_least_rust_2024() {
-                                self.parser.psess.gated_spans.gate(sym::let_chains, span);
-                            }
-                        }
+                    if !self.current_edition.at_least_rust_2024() || !span.at_least_rust_2024() {
+                        self.parser.psess.gated_spans.gate(sym::let_chains, span);
                     }
                 }
             }
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 b1e305834cb2e..983fe87451f24 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
@@ -15,9 +15,11 @@ fn _if_let_guard() {
 
         () if true && let 0 = 1 => {}
         //~^ ERROR `if let` guards are experimental
+        //~| ERROR `let` expressions in this position are unstable
 
         () if let 0 = 1 && true => {}
         //~^ ERROR `if let` guards are experimental
+        //~| ERROR `let` expressions in this position are unstable
 
         () if (let 0 = 1) && true => {}
         //~^ ERROR expected expression, found `let` statement
@@ -31,6 +33,8 @@ fn _if_let_guard() {
 
         () 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 expected expression, found `let` statement
         //~| ERROR expected expression, found `let` statement
         //~| ERROR expected expression, found `let` statement
@@ -38,6 +42,7 @@ fn _if_let_guard() {
 
         () if let Range { start: _, end: _ } = (true..true) && false => {}
         //~^ ERROR `if let` guards are experimental
+        //~| ERROR `let` expressions in this position are unstable
 
         _ => {}
     }
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 19d1f4b0a573b..0997f0c81a019 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
@@ -25,98 +25,98 @@ LL |         () if (((let 0 = 1))) => {}
    |                  ^^^^^^^^^
 
 error: expected expression, found `let` statement
-  --> $DIR/feature-gate.rs:22:16
+  --> $DIR/feature-gate.rs:24:16
    |
 LL |         () if (let 0 = 1) && true => {}
    |                ^^^^^^^^^
    |
    = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
-  --> $DIR/feature-gate.rs:22:16
+  --> $DIR/feature-gate.rs:24:16
    |
 LL |         () if (let 0 = 1) && true => {}
    |                ^^^^^^^^^
 
 error: expected expression, found `let` statement
-  --> $DIR/feature-gate.rs:25:24
+  --> $DIR/feature-gate.rs:27:24
    |
 LL |         () if true && (let 0 = 1) => {}
    |                        ^^^^^^^^^
    |
    = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
-  --> $DIR/feature-gate.rs:25:24
+  --> $DIR/feature-gate.rs:27:24
    |
 LL |         () if true && (let 0 = 1) => {}
    |                        ^^^^^^^^^
 
 error: expected expression, found `let` statement
-  --> $DIR/feature-gate.rs:28:16
+  --> $DIR/feature-gate.rs:30:16
    |
 LL |         () if (let 0 = 1) && (let 0 = 1) => {}
    |                ^^^^^^^^^
    |
    = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
-  --> $DIR/feature-gate.rs:28:16
+  --> $DIR/feature-gate.rs:30:16
    |
 LL |         () if (let 0 = 1) && (let 0 = 1) => {}
    |                ^^^^^^^^^
 
 error: expected expression, found `let` statement
-  --> $DIR/feature-gate.rs:28:31
+  --> $DIR/feature-gate.rs:30:31
    |
 LL |         () if (let 0 = 1) && (let 0 = 1) => {}
    |                               ^^^^^^^^^
    |
    = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
-  --> $DIR/feature-gate.rs:28:31
+  --> $DIR/feature-gate.rs:30:31
    |
 LL |         () if (let 0 = 1) && (let 0 = 1) => {}
    |                               ^^^^^^^^^
 
 error: expected expression, found `let` statement
-  --> $DIR/feature-gate.rs:32:42
+  --> $DIR/feature-gate.rs:34:42
    |
 LL |         () if let 0 = 1 && let 1 = 2 && (let 2 = 3 && let 3 = 4 && let 4 = 5) => {}
    |                                          ^^^^^^^^^
    |
    = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
-  --> $DIR/feature-gate.rs:32:42
+  --> $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:32:55
+  --> $DIR/feature-gate.rs:34:55
    |
 LL |         () if let 0 = 1 && let 1 = 2 && (let 2 = 3 && let 3 = 4 && let 4 = 5) => {}
    |                                                       ^^^^^^^^^
    |
    = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
-  --> $DIR/feature-gate.rs:32:42
+  --> $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:32:68
+  --> $DIR/feature-gate.rs:34:68
    |
 LL |         () if let 0 = 1 && let 1 = 2 && (let 2 = 3 && let 3 = 4 && let 4 = 5) => {}
    |                                                                    ^^^^^^^^^
    |
    = note: only supported directly in conditions of `if` and `while` expressions
 note: `let`s wrapped in parentheses are not supported in a context with let chains
-  --> $DIR/feature-gate.rs:32:42
+  --> $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:55:16
+  --> $DIR/feature-gate.rs:60:16
    |
 LL |     use_expr!((let 0 = 1 && 0 == 0));
    |                ^^^
@@ -124,7 +124,7 @@ LL |     use_expr!((let 0 = 1 && 0 == 0));
    = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
-  --> $DIR/feature-gate.rs:55:16
+  --> $DIR/feature-gate.rs:60:16
    |
 LL |     use_expr!((let 0 = 1 && 0 == 0));
    |                ^^^
@@ -133,7 +133,7 @@ LL |     use_expr!((let 0 = 1 && 0 == 0));
    = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: expected expression, found `let` statement
-  --> $DIR/feature-gate.rs:58:16
+  --> $DIR/feature-gate.rs:63:16
    |
 LL |     use_expr!((let 0 = 1));
    |                ^^^
@@ -141,7 +141,7 @@ LL |     use_expr!((let 0 = 1));
    = note: only supported directly in conditions of `if` and `while` expressions
 
 error: expected expression, found `let` statement
-  --> $DIR/feature-gate.rs:58:16
+  --> $DIR/feature-gate.rs:63:16
    |
 LL |     use_expr!((let 0 = 1));
    |                ^^^
@@ -150,7 +150,7 @@ LL |     use_expr!((let 0 = 1));
    = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error: no rules expected keyword `let`
-  --> $DIR/feature-gate.rs:67:15
+  --> $DIR/feature-gate.rs:72:15
    |
 LL |     macro_rules! use_expr {
    |     --------------------- when calling this macro
@@ -159,7 +159,7 @@ LL |     use_expr!(let 0 = 1);
    |               ^^^ no rules expected this token in macro call
    |
 note: while trying to match meta-variable `$e:expr`
-  --> $DIR/feature-gate.rs:48:10
+  --> $DIR/feature-gate.rs:53:10
    |
 LL |         ($e:expr) => {
    |          ^^^^^^^
@@ -187,7 +187,7 @@ 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:19:12
+  --> $DIR/feature-gate.rs:20:12
    |
 LL |         () if let 0 = 1 && true => {}
    |            ^^^^^^^^^^^^^^^^^^^^
@@ -198,7 +198,7 @@ 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:32:12
+  --> $DIR/feature-gate.rs:34:12
    |
 LL |         () if let 0 = 1 && let 1 = 2 && (let 2 = 3 && let 3 = 4 && let 4 = 5) => {}
    |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -209,7 +209,7 @@ 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:39:12
+  --> $DIR/feature-gate.rs:43:12
    |
 LL |         () if let Range { start: _, end: _ } = (true..true) && false => {}
    |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -220,7 +220,7 @@ 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:63:12
+  --> $DIR/feature-gate.rs:68:12
    |
 LL |         () if let 0 = 1 => {}
    |            ^^^^^^^^^^^^
@@ -230,6 +230,56 @@ LL |         () if let 0 = 1 => {}
    = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
    = help: you can write `if matches!(<expr>, <pattern>)` instead of `if let <pattern> = <expr>`
 
-error: aborting due to 20 previous errors
+error[E0658]: `let` expressions in this position are unstable
+  --> $DIR/feature-gate.rs:16:23
+   |
+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
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: `let` expressions in this position are unstable
+  --> $DIR/feature-gate.rs:20:15
+   |
+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
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: `let` expressions in this position are unstable
+  --> $DIR/feature-gate.rs:34:15
+   |
+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
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: `let` expressions in this position are unstable
+  --> $DIR/feature-gate.rs:34:28
+   |
+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
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: `let` expressions in this position are unstable
+  --> $DIR/feature-gate.rs:43:15
+   |
+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
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error: aborting due to 25 previous errors
 
 For more information about this error, try `rustc --explain E0658`.
diff --git a/tests/ui/rfcs/rfc-2497-if-let-chains/issue-93150.rs b/tests/ui/rfcs/rfc-2497-if-let-chains/issue-93150.rs
index f6de37867d855..ccd4950c805d8 100644
--- a/tests/ui/rfcs/rfc-2497-if-let-chains/issue-93150.rs
+++ b/tests/ui/rfcs/rfc-2497-if-let-chains/issue-93150.rs
@@ -1,7 +1,8 @@
 fn main() {
     match true {
         _ if let true = true && true => {}
-        //~^ ERROR `if let` guards are
+        //~^ ERROR `if let` guards are experimental
+        //~| ERROR `let` expressions in this position are unstable
         _ => {}
     }
 }
diff --git a/tests/ui/rfcs/rfc-2497-if-let-chains/issue-93150.stderr b/tests/ui/rfcs/rfc-2497-if-let-chains/issue-93150.stderr
index 17fa37d2df322..637ae4915ed14 100644
--- a/tests/ui/rfcs/rfc-2497-if-let-chains/issue-93150.stderr
+++ b/tests/ui/rfcs/rfc-2497-if-let-chains/issue-93150.stderr
@@ -9,6 +9,16 @@ LL |         _ if let true = true && true => {}
    = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
    = help: you can write `if matches!(<expr>, <pattern>)` instead of `if let <pattern> = <expr>`
 
-error: aborting due to 1 previous error
+error[E0658]: `let` expressions in this position are unstable
+  --> $DIR/issue-93150.rs:3:14
+   |
+LL |         _ if let true = true && 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
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error: aborting due to 2 previous errors
 
 For more information about this error, try `rustc --explain E0658`.