Auto merge of #143214 - camsteffen:remove-let-chains-feature, r=est31

Remove let_chains unstable feature

Per #53667 (comment) (but then I also noticed #140722)

This replaces the feature gate with a parser error that says let chains require 2024.

A lot of tests were using the unstable feature. I either added edition:2024 to the test or split out the parts that require 2024.

Author: bors

compiler/rustc_ast_passes/src/feature_gate.rs

@@ -469,7 +469,6 @@ pub fn check_crate(krate: &ast::Crate, sess: &Session, features: &Features) {
         "`if let` guards are experimental",
         "you can write `if matches!(<expr>, <pattern>)` instead of `if let <pattern> = <expr>`"
     );
-    gate_all!(let_chains, "`let` expressions in this position are unstable");
     gate_all!(
         async_trait_bounds,
         "`async` trait bounds are unstable",

compiler/rustc_feature/src/accepted.rs

@@ -265,6 +265,8 @@ declare_features! (
     (accepted, keylocker_x86, "1.89.0", Some(134813)),
     /// Allows `'a: { break 'a; }`.
     (accepted, label_break_value, "1.65.0", Some(48594)),
+    /// Allows `if/while p && let q = r && ...` chains.
+    (accepted, let_chains, "1.88.0", Some(53667)),
     /// Allows `let...else` statements.
     (accepted, let_else, "1.65.0", Some(87335)),
     /// Allows using `reason` in lint attributes and the `#[expect(lint)]` lint check.

compiler/rustc_feature/src/unstable.rs

@@ -550,8 +550,6 @@ declare_features! (
     (unstable, large_assignments, "1.52.0", Some(83518)),
     /// Allow to have type alias types for inter-crate use.
     (incomplete, lazy_type_alias, "1.72.0", Some(112792)),
-    /// Allows `if/while p && let q = r && ...` chains.
-    (unstable, let_chains, "1.37.0", Some(53667)),
     /// Allows using `#[link(kind = "link-arg", name = "...")]`
     /// to pass custom arguments to the linker.
     (unstable, link_arg_attribute, "1.76.0", Some(99427)),

compiler/rustc_parse/messages.ftl

@@ -512,6 +512,8 @@ parse_leading_underscore_unicode_escape_label = invalid start of unicode escape
 parse_left_arrow_operator = unexpected token: `<-`
     .suggestion = if you meant to write a comparison against a negative value, add a space in between `<` and `-`
 
+parse_let_chain_pre_2024 = let chains are only allowed in Rust 2024 or later
+
 parse_lifetime_after_mut = lifetime must precede `mut`
     .suggestion = place the lifetime before `mut`
 

compiler/rustc_parse/src/errors.rs

@@ -1778,6 +1778,13 @@ pub(crate) struct AsyncBoundModifierIn2015 {
     pub help: HelpUseLatestEdition,
 }
 
+#[derive(Diagnostic)]
+#[diag(parse_let_chain_pre_2024)]
+pub(crate) struct LetChainPre2024 {
+    #[primary_span]
+    pub span: Span,
+}
+
 #[derive(Diagnostic)]
 #[diag(parse_self_argument_pointer)]
 pub(crate) struct SelfArgumentPointer {

compiler/rustc_parse/src/parser/expr.rs

@@ -4117,7 +4117,7 @@ impl MutVisitor for CondChecker<'_> {
                         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);
+                                self.parser.dcx().emit_err(errors::LetChainPre2024 { span });
                             }
                         }
                     }

src/tools/rustfmt/tests/source/let_chains.rs

@@ -1,3 +1,5 @@
+// rustfmt-edition: 2024
+
 fn main() {
     if let x = x && x {}
 

src/tools/rustfmt/tests/target/let_chains.rs

@@ -1,3 +1,5 @@
+// rustfmt-edition: 2024
+
 fn main() {
     if let x = x
         && x

tests/coverage/branch/if-let.coverage

@@ -1,5 +1,5 @@
-   LL|       |#![feature(coverage_attribute, let_chains)]
-   LL|       |//@ edition: 2021
+   LL|       |#![feature(coverage_attribute)]
+   LL|       |//@ edition: 2024
    LL|       |//@ compile-flags: -Zcoverage-options=branch
    LL|       |//@ llvm-cov-flags: --show-branches=count
    LL|       |

tests/coverage/branch/if-let.rs

@@ -1,5 +1,5 @@
-#![feature(coverage_attribute, let_chains)]
-//@ edition: 2021
+#![feature(coverage_attribute)]
+//@ edition: 2024
 //@ compile-flags: -Zcoverage-options=branch
 //@ llvm-cov-flags: --show-branches=count