Merging upstream version 1.73.0+dfsg1.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

22 files changed, 223 insertions, 163 deletions

diff --git a/compiler/rustc_builtin_macros/src/asm.rs b/compiler/rustc_builtin_macros/src/asm.rs
index 6187e4f51..9e66eaf73 100644
--- a/compiler/rustc_builtin_macros/src/asm.rs
+++ b/compiler/rustc_builtin_macros/src/asm.rs
@@ -157,8 +157,7 @@ pub fn parse_asm_args<'a>(
         } else if p.eat_keyword(sym::sym) {
             let expr = p.parse_expr()?;
             let ast::ExprKind::Path(qself, path) = &expr.kind else {
-                let err = diag
-                    .create_err(errors::AsmSymNoPath { span: expr.span });
+                let err = diag.create_err(errors::AsmSymNoPath { span: expr.span });
                 return Err(err);
             };
             let sym = ast::InlineAsmSym {
@@ -402,7 +401,7 @@ fn parse_clobber_abi<'a>(p: &mut Parser<'a>, args: &mut AsmArgs) -> PResult<'a,
         // should have errored above during parsing
         [] => unreachable!(),
         [(abi, _span)] => args.clobber_abis.push((*abi, full_span)),
-        [abis @ ..] => {
+        abis => {
             for (abi, span) in abis {
                 args.clobber_abis.push((*abi, *span));
             }
@@ -576,7 +575,7 @@ fn expand_preparsed_asm(ecx: &mut ExtCtxt<'_>, args: AsmArgs) -> Option<ast::Inl
                                 || named_pos.contains_key(&idx)
                                 || args.reg_args.contains(idx)
                             {
-                                let msg = format!("invalid reference to argument at index {}", idx);
+                                let msg = format!("invalid reference to argument at index {idx}");
                                 let mut err = ecx.struct_span_err(span, msg);
                                 err.span_label(span, "from here");
 
@@ -589,9 +588,9 @@ fn expand_preparsed_asm(ecx: &mut ExtCtxt<'_>, args: AsmArgs) -> Option<ast::Inl
                                     ""
                                 };
                                 let msg = match positional_args {
-                                    0 => format!("no {}arguments were given", positional),
-                                    1 => format!("there is 1 {}argument", positional),
-                                    x => format!("there are {} {}arguments", x, positional),
+                                    0 => format!("no {positional}arguments were given"),
+                                    1 => format!("there is 1 {positional}argument"),
+                                    x => format!("there are {x} {positional}arguments"),
                                 };
                                 err.note(msg);
 
@@ -625,7 +624,7 @@ fn expand_preparsed_asm(ecx: &mut ExtCtxt<'_>, args: AsmArgs) -> Option<ast::Inl
                             match args.named_args.get(&Symbol::intern(name)) {
                                 Some(&idx) => Some(idx),
                                 None => {
-                                    let msg = format!("there is no argument named `{}`", name);
+                                    let msg = format!("there is no argument named `{name}`");
                                     let span = arg.position_span;
                                     ecx.struct_span_err(
                                         template_span
@@ -698,8 +697,7 @@ fn expand_preparsed_asm(ecx: &mut ExtCtxt<'_>, args: AsmArgs) -> Option<ast::Inl
             err.span_label(sp, msg);
             err.help(format!(
                 "if this argument is intentionally unused, \
-                 consider using it in an asm comment: `\"/*{} */\"`",
-                help_str
+                 consider using it in an asm comment: `\"/*{help_str} */\"`"
             ));
             err.emit();
         }
@@ -713,8 +711,7 @@ fn expand_preparsed_asm(ecx: &mut ExtCtxt<'_>, args: AsmArgs) -> Option<ast::Inl
             }
             err.help(format!(
                 "if these arguments are intentionally unused, \
-                 consider using them in an asm comment: `\"/*{} */\"`",
-                help_str
+                 consider using them in an asm comment: `\"/*{help_str} */\"`"
             ));
             err.emit();
         }
diff --git a/compiler/rustc_builtin_macros/src/assert.rs b/compiler/rustc_builtin_macros/src/assert.rs
index ab4ea9c8c..9302db104 100644
--- a/compiler/rustc_builtin_macros/src/assert.rs
+++ b/compiler/rustc_builtin_macros/src/assert.rs
@@ -4,8 +4,9 @@ use crate::edition_panic::use_panic_2021;
 use crate::errors;
 use rustc_ast::ptr::P;
 use rustc_ast::token;
+use rustc_ast::token::Delimiter;
 use rustc_ast::tokenstream::{DelimSpan, TokenStream};
-use rustc_ast::{DelimArgs, Expr, ExprKind, MacCall, MacDelimiter, Path, PathSegment, UnOp};
+use rustc_ast::{DelimArgs, Expr, ExprKind, MacCall, Path, PathSegment, UnOp};
 use rustc_ast_pretty::pprust;
 use rustc_errors::PResult;
 use rustc_expand::base::{DummyResult, ExtCtxt, MacEager, MacResult};
@@ -58,7 +59,7 @@ pub fn expand_assert<'cx>(
                 path: panic_path(),
                 args: P(DelimArgs {
                     dspan: DelimSpan::from_single(call_site_span),
-                    delim: MacDelimiter::Parenthesis,
+                    delim: Delimiter::Parenthesis,
                     tokens,
                 }),
             })),
@@ -68,7 +69,7 @@ pub fn expand_assert<'cx>(
     // If `generic_assert` is enabled, generates rich captured outputs
     //
     // FIXME(c410-f3r) See https://github.com/rust-lang/rust/issues/96949
-    else if let Some(features) = cx.ecfg.features && features.generic_assert {
+    else if cx.ecfg.features.generic_assert {
         context::Context::new(cx, call_site_span).build(cond_expr, panic_path())
     }
     // If `generic_assert` is not enabled, only outputs a literal "assertion failed: ..."
diff --git a/compiler/rustc_builtin_macros/src/assert/context.rs b/compiler/rustc_builtin_macros/src/assert/context.rs
index 902c1e40c..bda473120 100644
--- a/compiler/rustc_builtin_macros/src/assert/context.rs
+++ b/compiler/rustc_builtin_macros/src/assert/context.rs
@@ -1,9 +1,10 @@
 use rustc_ast::{
     ptr::P,
     token,
+    token::Delimiter,
     tokenstream::{DelimSpan, TokenStream, TokenTree},
-    BinOpKind, BorrowKind, DelimArgs, Expr, ExprKind, ItemKind, MacCall, MacDelimiter, MethodCall,
-    Mutability, Path, PathSegment, Stmt, StructRest, UnOp, UseTree, UseTreeKind, DUMMY_NODE_ID,
+    BinOpKind, BorrowKind, DelimArgs, Expr, ExprKind, ItemKind, MacCall, MethodCall, Mutability,
+    Path, PathSegment, Stmt, StructRest, UnOp, UseTree, UseTreeKind, DUMMY_NODE_ID,
 };
 use rustc_ast_pretty::pprust;
 use rustc_data_structures::fx::FxHashSet;
@@ -179,7 +180,7 @@ impl<'cx, 'a> Context<'cx, 'a> {
                 path: panic_path,
                 args: P(DelimArgs {
                     dspan: DelimSpan::from_single(self.span),
-                    delim: MacDelimiter::Parenthesis,
+                    delim: Delimiter::Parenthesis,
                     tokens: initial.into_iter().chain(captures).collect::<TokenStream>(),
                 }),
             })),
@@ -236,7 +237,7 @@ impl<'cx, 'a> Context<'cx, 'a> {
             ExprKind::If(local_expr, _, _) => {
                 self.manage_cond_expr(local_expr);
             }
-            ExprKind::Index(prefix, suffix) => {
+            ExprKind::Index(prefix, suffix, _) => {
                 self.manage_cond_expr(prefix);
                 self.manage_cond_expr(suffix);
             }
diff --git a/compiler/rustc_builtin_macros/src/cfg.rs b/compiler/rustc_builtin_macros/src/cfg.rs
index 1397cee7a..31cac5184 100644
--- a/compiler/rustc_builtin_macros/src/cfg.rs
+++ b/compiler/rustc_builtin_macros/src/cfg.rs
@@ -24,7 +24,7 @@ pub fn expand_cfg(
                 &cfg,
                 &cx.sess.parse_sess,
                 cx.current_expansion.lint_node_id,
-                cx.ecfg.features,
+                Some(cx.ecfg.features),
             );
             MacEager::expr(cx.expr_bool(sp, matches_cfg))
         }
diff --git a/compiler/rustc_builtin_macros/src/cfg_eval.rs b/compiler/rustc_builtin_macros/src/cfg_eval.rs
index 49401e9ca..f826c6e77 100644
--- a/compiler/rustc_builtin_macros/src/cfg_eval.rs
+++ b/compiler/rustc_builtin_macros/src/cfg_eval.rs
@@ -31,10 +31,11 @@ pub(crate) fn expand(
 
 pub(crate) fn cfg_eval(
     sess: &Session,
-    features: Option<&Features>,
+    features: &Features,
     annotatable: Annotatable,
     lint_node_id: NodeId,
 ) -> Annotatable {
+    let features = Some(features);
     CfgEval { cfg: &mut StripUnconfigured { sess, features, config_tokens: true, lint_node_id } }
         .configure_annotatable(annotatable)
         // Since the item itself has already been configured by the `InvocationCollector`,
diff --git a/compiler/rustc_builtin_macros/src/deriving/clone.rs b/compiler/rustc_builtin_macros/src/deriving/clone.rs
index 9ba98d0a5..b468abe32 100644
--- a/compiler/rustc_builtin_macros/src/deriving/clone.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/clone.rs
@@ -144,7 +144,7 @@ fn cs_clone_simple(
             }
             _ => cx.span_bug(
                 trait_span,
-                format!("unexpected substructure in simple `derive({})`", name),
+                format!("unexpected substructure in simple `derive({name})`"),
             ),
         }
     }
@@ -178,10 +178,10 @@ fn cs_clone(
             vdata = &variant.data;
         }
         EnumTag(..) | AllFieldlessEnum(..) => {
-            cx.span_bug(trait_span, format!("enum tags in `derive({})`", name,))
+            cx.span_bug(trait_span, format!("enum tags in `derive({name})`",))
         }
         StaticEnum(..) | StaticStruct(..) => {
-            cx.span_bug(trait_span, format!("associated function in `derive({})`", name))
+            cx.span_bug(trait_span, format!("associated function in `derive({name})`"))
         }
     }
 
@@ -193,7 +193,7 @@ fn cs_clone(
                     let Some(ident) = field.name else {
                         cx.span_bug(
                             trait_span,
-                            format!("unnamed field in normal struct in `derive({})`", name,),
+                            format!("unnamed field in normal struct in `derive({name})`",),
                         );
                     };
                     let call = subcall(cx, field);
diff --git a/compiler/rustc_builtin_macros/src/deriving/cmp/ord.rs b/compiler/rustc_builtin_macros/src/deriving/cmp/ord.rs
index 4401cf8a9..ea81cee78 100644
--- a/compiler/rustc_builtin_macros/src/deriving/cmp/ord.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/cmp/ord.rs
@@ -61,8 +61,8 @@ pub fn cs_cmp(cx: &mut ExtCtxt<'_>, span: Span, substr: &Substructure<'_>) -> Bl
         |cx, fold| match fold {
             CsFold::Single(field) => {
                 let [other_expr] = &field.other_selflike_exprs[..] else {
-                        cx.span_bug(field.span, "not exactly 2 arguments in `derive(Ord)`");
-                    };
+                    cx.span_bug(field.span, "not exactly 2 arguments in `derive(Ord)`");
+                };
                 let args = thin_vec![field.self_expr.clone(), other_expr.clone()];
                 cx.expr_call_global(field.span, cmp_path.clone(), args)
             }
diff --git a/compiler/rustc_builtin_macros/src/deriving/cmp/partial_ord.rs b/compiler/rustc_builtin_macros/src/deriving/cmp/partial_ord.rs
index 54b6cb7d7..a5b3a504e 100644
--- a/compiler/rustc_builtin_macros/src/deriving/cmp/partial_ord.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/cmp/partial_ord.rs
@@ -94,8 +94,8 @@ fn cs_partial_cmp(
         |cx, fold| match fold {
             CsFold::Single(field) => {
                 let [other_expr] = &field.other_selflike_exprs[..] else {
-                        cx.span_bug(field.span, "not exactly 2 arguments in `derive(Ord)`");
-                    };
+                    cx.span_bug(field.span, "not exactly 2 arguments in `derive(Ord)`");
+                };
                 let args = thin_vec![field.self_expr.clone(), other_expr.clone()];
                 cx.expr_call_global(field.span, partial_cmp_path.clone(), args)
             }
diff --git a/compiler/rustc_builtin_macros/src/deriving/decodable.rs b/compiler/rustc_builtin_macros/src/deriving/decodable.rs
index 3921533c8..bcf11cb4c 100644
--- a/compiler/rustc_builtin_macros/src/deriving/decodable.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/decodable.rs
@@ -204,7 +204,7 @@ where
                 let fields = fields
                     .iter()
                     .enumerate()
-                    .map(|(i, &span)| getarg(cx, span, Symbol::intern(&format!("_field{}", i)), i))
+                    .map(|(i, &span)| getarg(cx, span, Symbol::intern(&format!("_field{i}")), i))
                     .collect();
 
                 cx.expr_call(trait_span, path_expr, fields)
diff --git a/compiler/rustc_builtin_macros/src/deriving/encodable.rs b/compiler/rustc_builtin_macros/src/deriving/encodable.rs
index a3b11309d..2dc20c324 100644
--- a/compiler/rustc_builtin_macros/src/deriving/encodable.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/encodable.rs
@@ -173,7 +173,7 @@ fn encodable_substructure(
             for (i, &FieldInfo { name, ref self_expr, span, .. }) in fields.iter().enumerate() {
                 let name = match name {
                     Some(id) => id.name,
-                    None => Symbol::intern(&format!("_field{}", i)),
+                    None => Symbol::intern(&format!("_field{i}")),
                 };
                 let self_ref = cx.expr_addr_of(span, self_expr.clone());
                 let enc =
diff --git a/compiler/rustc_builtin_macros/src/deriving/generic/mod.rs b/compiler/rustc_builtin_macros/src/deriving/generic/mod.rs
index 4ba09335c..6597ee3cf 100644
--- a/compiler/rustc_builtin_macros/src/deriving/generic/mod.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/generic/mod.rs
@@ -1134,9 +1134,14 @@ impl<'a> MethodDef<'a> {
         trait_: &TraitDef<'b>,
         enum_def: &'b EnumDef,
         type_ident: Ident,
-        selflike_args: ThinVec<P<Expr>>,
+        mut selflike_args: ThinVec<P<Expr>>,
         nonselflike_args: &[P<Expr>],
     ) -> BlockOrExpr {
+        assert!(
+            !selflike_args.is_empty(),
+            "static methods must use `expand_static_enum_method_body`",
+        );
+
         let span = trait_.span;
         let variants = &enum_def.variants;
 
@@ -1144,10 +1149,15 @@ impl<'a> MethodDef<'a> {
         let unify_fieldless_variants =
             self.fieldless_variants_strategy == FieldlessVariantsStrategy::Unify;
 
-        // There is no sensible code to be generated for *any* deriving on a
-        // zero-variant enum. So we just generate a failing expression.
+        // For zero-variant enum, this function body is unreachable. Generate
+        // `match *self {}`. This produces machine code identical to `unsafe {
+        // core::intrinsics::unreachable() }` while being safe and stable.
         if variants.is_empty() {
-            return BlockOrExpr(ThinVec::new(), Some(deriving::call_unreachable(cx, span)));
+            selflike_args.truncate(1);
+            let match_arg = cx.expr_deref(span, selflike_args.pop().unwrap());
+            let match_arms = ThinVec::new();
+            let expr = cx.expr_match(span, match_arg, match_arms);
+            return BlockOrExpr(ThinVec::new(), Some(expr));
         }
 
         let prefixes = iter::once("__self".to_string())
@@ -1156,7 +1166,7 @@ impl<'a> MethodDef<'a> {
                     .iter()
                     .enumerate()
                     .skip(1)
-                    .map(|(arg_count, _selflike_arg)| format!("__arg{}", arg_count)),
+                    .map(|(arg_count, _selflike_arg)| format!("__arg{arg_count}")),
             )
             .collect::<Vec<String>>();
 
@@ -1171,7 +1181,7 @@ impl<'a> MethodDef<'a> {
         let get_tag_pieces = |cx: &ExtCtxt<'_>| {
             let tag_idents: Vec<_> = prefixes
                 .iter()
-                .map(|name| Ident::from_str_and_span(&format!("{}_tag", name), span))
+                .map(|name| Ident::from_str_and_span(&format!("{name}_tag"), span))
                 .collect();
 
             let mut tag_exprs: Vec<_> = tag_idents
@@ -1511,7 +1521,7 @@ impl<'a> TraitDef<'a> {
     }
 
     fn mk_pattern_ident(&self, prefix: &str, i: usize) -> Ident {
-        Ident::from_str_and_span(&format!("{}_{}", prefix, i), self.span)
+        Ident::from_str_and_span(&format!("{prefix}_{i}"), self.span)
     }
 
     fn create_struct_pattern_fields(
@@ -1592,8 +1602,7 @@ impl<'a> TraitDef<'a> {
                                 sp,
                                 ast::CRATE_NODE_ID,
                                 format!(
-                                    "{} slice in a packed struct that derives a built-in trait",
-                                    ty
+                                    "{ty} slice in a packed struct that derives a built-in trait"
                                 ),
                                 rustc_lint_defs::BuiltinLintDiagnostics::ByteSliceInPackedStructWithDerive
                             );
diff --git a/compiler/rustc_builtin_macros/src/edition_panic.rs b/compiler/rustc_builtin_macros/src/edition_panic.rs
index ef0db23ff..1e1dadab4 100644
--- a/compiler/rustc_builtin_macros/src/edition_panic.rs
+++ b/compiler/rustc_builtin_macros/src/edition_panic.rs
@@ -1,4 +1,5 @@
 use rustc_ast::ptr::P;
+use rustc_ast::token::Delimiter;
 use rustc_ast::tokenstream::{DelimSpan, TokenStream};
 use rustc_ast::*;
 use rustc_expand::base::*;
@@ -60,7 +61,7 @@ fn expand<'cx>(
                 },
                 args: P(DelimArgs {
                     dspan: DelimSpan::from_single(sp),
-                    delim: MacDelimiter::Parenthesis,
+                    delim: Delimiter::Parenthesis,
                     tokens: tts,
                 }),
             })),
diff --git a/compiler/rustc_builtin_macros/src/env.rs b/compiler/rustc_builtin_macros/src/env.rs
index 8f64e3328..92da0c069 100644
--- a/compiler/rustc_builtin_macros/src/env.rs
+++ b/compiler/rustc_builtin_macros/src/env.rs
@@ -4,7 +4,7 @@
 //
 
 use rustc_ast::tokenstream::TokenStream;
-use rustc_ast::{self as ast, GenericArg};
+use rustc_ast::{self as ast, AstDeref, GenericArg};
 use rustc_expand::base::{self, *};
 use rustc_span::symbol::{kw, sym, Ident, Symbol};
 use rustc_span::Span;
@@ -76,22 +76,36 @@ pub fn expand_env<'cx>(
         },
     };
 
-    let sp = cx.with_def_site_ctxt(sp);
+    let span = cx.with_def_site_ctxt(sp);
     let value = env::var(var.as_str()).ok().as_deref().map(Symbol::intern);
     cx.sess.parse_sess.env_depinfo.borrow_mut().insert((var, value));
     let e = match value {
         None => {
-            // Use the string literal in the code in the diagnostic to avoid confusing diagnostics,
-            // e.g. when the literal contains escape sequences.
-            let ast::ExprKind::Lit(ast::token::Lit { kind: ast::token::LitKind::Str, symbol: original_var, ..}) = &var_expr.kind else {
+            let ast::ExprKind::Lit(ast::token::Lit {
+                kind: ast::token::LitKind::Str | ast::token::LitKind::StrRaw(..),
+                symbol,
+                ..
+            }) = &var_expr.kind
+            else {
                 unreachable!("`expr_to_string` ensures this is a string lit")
             };
-            cx.emit_err(errors::EnvNotDefined {
-                span: sp,
-                msg: custom_msg,
-                var: *original_var,
-                help: custom_msg.is_none().then(|| help_for_missing_env_var(var.as_str())),
-            });
+
+            if let Some(msg_from_user) = custom_msg {
+                cx.emit_err(errors::EnvNotDefinedWithUserMessage { span, msg_from_user });
+            } else if is_cargo_env_var(var.as_str()) {
+                cx.emit_err(errors::EnvNotDefined::CargoEnvVar {
+                    span,
+                    var: *symbol,
+                    var_expr: var_expr.ast_deref(),
+                });
+            } else {
+                cx.emit_err(errors::EnvNotDefined::CustomEnvVar {
+                    span,
+                    var: *symbol,
+                    var_expr: var_expr.ast_deref(),
+                });
+            }
+
             return DummyResult::any(sp);
         }
         Some(value) => cx.expr_str(sp, value),
@@ -99,13 +113,9 @@ pub fn expand_env<'cx>(
     MacEager::expr(e)
 }
 
-fn help_for_missing_env_var(var: &str) -> errors::EnvNotDefinedHelp {
-    if var.starts_with("CARGO_")
+/// Returns `true` if an environment variable from `env!` is one used by Cargo.
+fn is_cargo_env_var(var: &str) -> bool {
+    var.starts_with("CARGO_")
         || var.starts_with("DEP_")
         || matches!(var, "OUT_DIR" | "OPT_LEVEL" | "PROFILE" | "HOST" | "TARGET")
-    {
-        errors::EnvNotDefinedHelp::CargoVar
-    } else {
-        errors::EnvNotDefinedHelp::Other
-    }
 }
diff --git a/compiler/rustc_builtin_macros/src/errors.rs b/compiler/rustc_builtin_macros/src/errors.rs
index 7b2a375a8..fbf0395bb 100644
--- a/compiler/rustc_builtin_macros/src/errors.rs
+++ b/compiler/rustc_builtin_macros/src/errors.rs
@@ -440,43 +440,43 @@ pub(crate) struct EnvTakesArgs {
     pub(crate) span: Span,
 }
 
-//#[derive(Diagnostic)]
-//#[diag(builtin_macros_env_not_defined)]
-pub(crate) struct EnvNotDefined {
+pub(crate) struct EnvNotDefinedWithUserMessage {
     pub(crate) span: Span,
-    pub(crate) msg: Option<Symbol>,
-    pub(crate) var: Symbol,
-    pub(crate) help: Option<EnvNotDefinedHelp>,
+    pub(crate) msg_from_user: Symbol,
 }
 
-// Hand-written implementation to support custom user messages
-impl<'a, G: EmissionGuarantee> IntoDiagnostic<'a, G> for EnvNotDefined {
+// Hand-written implementation to support custom user messages.
+impl<'a, G: EmissionGuarantee> IntoDiagnostic<'a, G> for EnvNotDefinedWithUserMessage {
     #[track_caller]
     fn into_diagnostic(self, handler: &'a Handler) -> DiagnosticBuilder<'a, G> {
-        let mut diag = if let Some(msg) = self.msg {
-            #[expect(
-                rustc::untranslatable_diagnostic,
-                reason = "cannot translate user-provided messages"
-            )]
-            handler.struct_diagnostic(msg.to_string())
-        } else {
-            handler.struct_diagnostic(crate::fluent_generated::builtin_macros_env_not_defined)
-        };
-        diag.set_arg("var", self.var);
+        #[expect(
+            rustc::untranslatable_diagnostic,
+            reason = "cannot translate user-provided messages"
+        )]
+        let mut diag = handler.struct_diagnostic(self.msg_from_user.to_string());
         diag.set_span(self.span);
-        if let Some(help) = self.help {
-            diag.subdiagnostic(help);
-        }
         diag
     }
 }
 
-#[derive(Subdiagnostic)]
-pub(crate) enum EnvNotDefinedHelp {
+#[derive(Diagnostic)]
+pub(crate) enum EnvNotDefined<'a> {
+    #[diag(builtin_macros_env_not_defined)]
     #[help(builtin_macros_cargo)]
-    CargoVar,
-    #[help(builtin_macros_other)]
-    Other,
+    CargoEnvVar {
+        #[primary_span]
+        span: Span,
+        var: Symbol,
+        var_expr: &'a rustc_ast::Expr,
+    },
+    #[diag(builtin_macros_env_not_defined)]
+    #[help(builtin_macros_custom)]
+    CustomEnvVar {
+        #[primary_span]
+        span: Span,
+        var: Symbol,
+        var_expr: &'a rustc_ast::Expr,
+    },
 }
 
 #[derive(Diagnostic)]
diff --git a/compiler/rustc_builtin_macros/src/format.rs b/compiler/rustc_builtin_macros/src/format.rs
index 4c878785b..ede95dbf8 100644
--- a/compiler/rustc_builtin_macros/src/format.rs
+++ b/compiler/rustc_builtin_macros/src/format.rs
@@ -1,6 +1,6 @@
 use rustc_ast::ptr::P;
-use rustc_ast::token;
 use rustc_ast::tokenstream::TokenStream;
+use rustc_ast::{token, StmtKind};
 use rustc_ast::{
     Expr, ExprKind, FormatAlignment, FormatArgPosition, FormatArgPositionKind, FormatArgs,
     FormatArgsPiece, FormatArgument, FormatArgumentKind, FormatArguments, FormatCount,
@@ -163,7 +163,7 @@ fn make_format_args(
 
     let MacroInput { fmtstr: efmt, mut args, is_direct_literal } = input;
 
-    let (fmt_str, fmt_style, fmt_span) = match expr_to_spanned_string(ecx, efmt, msg) {
+    let (fmt_str, fmt_style, fmt_span) = match expr_to_spanned_string(ecx, efmt.clone(), msg) {
         Ok(mut fmt) if append_newline => {
             fmt.0 = Symbol::intern(&format!("{}\n", fmt.0));
             fmt
@@ -171,17 +171,33 @@ fn make_format_args(
         Ok(fmt) => fmt,
         Err(err) => {
             if let Some((mut err, suggested)) = err {
-                let sugg_fmt = match args.explicit_args().len() {
-                    0 => "{}".to_string(),
-                    _ => format!("{}{{}}", "{} ".repeat(args.explicit_args().len())),
-                };
                 if !suggested {
-                    err.span_suggestion(
-                        unexpanded_fmt_span.shrink_to_lo(),
-                        "you might be missing a string literal to format with",
-                        format!("\"{}\", ", sugg_fmt),
-                        Applicability::MaybeIncorrect,
-                    );
+                    if let ExprKind::Block(block, None) = &efmt.kind
+                        && block.stmts.len() == 1
+                        && let StmtKind::Expr(expr) = &block.stmts[0].kind
+                        && let ExprKind::Path(None, path) = &expr.kind
+                            && path.is_potential_trivial_const_arg()
+                    {
+                        err.multipart_suggestion(
+                            "quote your inlined format argument to use as string literal",
+                            vec![
+                                (unexpanded_fmt_span.shrink_to_hi(), "\"".to_string()),
+                                (unexpanded_fmt_span.shrink_to_lo(), "\"".to_string()),
+                            ],
+                             Applicability::MaybeIncorrect,
+                        );
+                    } else {
+                        let sugg_fmt = match args.explicit_args().len() {
+                            0 => "{}".to_string(),
+                            _ => format!("{}{{}}", "{} ".repeat(args.explicit_args().len())),
+                        };
+                        err.span_suggestion(
+                            unexpanded_fmt_span.shrink_to_lo(),
+                            "you might be missing a string literal to format with",
+                            format!("\"{sugg_fmt}\", "),
+                            Applicability::MaybeIncorrect,
+                        );
+                    }
                 }
                 err.emit();
             }
@@ -668,7 +684,7 @@ fn report_invalid_references(
     let num_args_desc = match args.explicit_args().len() {
         0 => "no arguments were given".to_string(),
         1 => "there is 1 argument".to_string(),
-        n => format!("there are {} arguments", n),
+        n => format!("there are {n} arguments"),
     };
 
     let mut e;
@@ -780,7 +796,7 @@ fn report_invalid_references(
                         if num_placeholders == 1 {
                             "is 1 argument".to_string()
                         } else {
-                            format!("are {} arguments", num_placeholders)
+                            format!("are {num_placeholders} arguments")
                         },
                     ),
                 );
@@ -811,7 +827,7 @@ fn report_invalid_references(
         };
         e = ecx.struct_span_err(
             span,
-            format!("invalid reference to positional {} ({})", arg_list, num_args_desc),
+            format!("invalid reference to positional {arg_list} ({num_args_desc})"),
         );
         e.note("positional arguments are zero-based");
     }
diff --git a/compiler/rustc_builtin_macros/src/format_foreign.rs b/compiler/rustc_builtin_macros/src/format_foreign.rs
index bd5356575..2fc8a0763 100644
--- a/compiler/rustc_builtin_macros/src/format_foreign.rs
+++ b/compiler/rustc_builtin_macros/src/format_foreign.rs
@@ -86,10 +86,7 @@ pub(crate) mod printf {
                         '-' => c_left = true,
                         '+' => c_plus = true,
                         _ => {
-                            return Err(Some(format!(
-                                "the flag `{}` is unknown or unsupported",
-                                c
-                            )));
+                            return Err(Some(format!("the flag `{c}` is unknown or unsupported")));
                         }
                     }
                 }
@@ -268,21 +265,21 @@ pub(crate) mod printf {
     impl Num {
         fn from_str(s: &str, arg: Option<&str>) -> Self {
             if let Some(arg) = arg {
-                Num::Arg(arg.parse().unwrap_or_else(|_| panic!("invalid format arg `{:?}`", arg)))
+                Num::Arg(arg.parse().unwrap_or_else(|_| panic!("invalid format arg `{arg:?}`")))
             } else if s == "*" {
                 Num::Next
             } else {
-                Num::Num(s.parse().unwrap_or_else(|_| panic!("invalid format num `{:?}`", s)))
+                Num::Num(s.parse().unwrap_or_else(|_| panic!("invalid format num `{s:?}`")))
             }
         }
 
         fn translate(&self, s: &mut String) -> std::fmt::Result {
             use std::fmt::Write;
             match *self {
-                Num::Num(n) => write!(s, "{}", n),
+                Num::Num(n) => write!(s, "{n}"),
                 Num::Arg(n) => {
                     let n = n.checked_sub(1).ok_or(std::fmt::Error)?;
-                    write!(s, "{}$", n)
+                    write!(s, "{n}$")
                 }
                 Num::Next => write!(s, "*"),
             }
@@ -626,8 +623,8 @@ pub mod shell {
     impl Substitution<'_> {
         pub fn as_str(&self) -> String {
             match self {
-                Substitution::Ordinal(n, _) => format!("${}", n),
-                Substitution::Name(n, _) => format!("${}", n),
+                Substitution::Ordinal(n, _) => format!("${n}"),
+                Substitution::Name(n, _) => format!("${n}"),
                 Substitution::Escape(_) => "$$".into(),
             }
         }
diff --git a/compiler/rustc_builtin_macros/src/global_allocator.rs b/compiler/rustc_builtin_macros/src/global_allocator.rs
index 577247193..1bec00add 100644
--- a/compiler/rustc_builtin_macros/src/global_allocator.rs
+++ b/compiler/rustc_builtin_macros/src/global_allocator.rs
@@ -2,7 +2,7 @@ use crate::util::check_builtin_macro_attribute;
 
 use crate::errors;
 use rustc_ast::expand::allocator::{
-    global_fn_name, AllocatorMethod, AllocatorTy, ALLOCATOR_METHODS,
+    global_fn_name, AllocatorMethod, AllocatorMethodInput, AllocatorTy, ALLOCATOR_METHODS,
 };
 use rustc_ast::ptr::P;
 use rustc_ast::{self as ast, AttrVec, Expr, FnHeader, FnSig, Generics, Param, StmtKind};
@@ -70,19 +70,13 @@ struct AllocFnFactory<'a, 'b> {
 impl AllocFnFactory<'_, '_> {
     fn allocator_fn(&self, method: &AllocatorMethod) -> Stmt {
         let mut abi_args = ThinVec::new();
-        let mut i = 0;
-        let mut mk = || {
-            let name = Ident::from_str_and_span(&format!("arg{}", i), self.span);
-            i += 1;
-            name
-        };
-        let args = method.inputs.iter().map(|ty| self.arg_ty(ty, &mut abi_args, &mut mk)).collect();
+        let args = method.inputs.iter().map(|input| self.arg_ty(input, &mut abi_args)).collect();
         let result = self.call_allocator(method.name, args);
-        let (output_ty, output_expr) = self.ret_ty(&method.output, result);
+        let output_ty = self.ret_ty(&method.output);
         let decl = self.cx.fn_decl(abi_args, ast::FnRetTy::Ty(output_ty));
         let header = FnHeader { unsafety: Unsafe::Yes(self.span), ..FnHeader::default() };
         let sig = FnSig { decl, header, span: self.span };
-        let body = Some(self.cx.block_expr(output_expr));
+        let body = Some(self.cx.block_expr(result));
         let kind = ItemKind::Fn(Box::new(Fn {
             defaultness: ast::Defaultness::Final,
             sig,
@@ -113,18 +107,19 @@ impl AllocFnFactory<'_, '_> {
         thin_vec![self.cx.attr_word(sym::rustc_std_internal_symbol, self.span)]
     }
 
-    fn arg_ty(
-        &self,
-        ty: &AllocatorTy,
-        args: &mut ThinVec<Param>,
-        ident: &mut dyn FnMut() -> Ident,
-    ) -> P<Expr> {
-        match *ty {
+    fn arg_ty(&self, input: &AllocatorMethodInput, args: &mut ThinVec<Param>) -> P<Expr> {
+        match input.ty {
             AllocatorTy::Layout => {
+                // If an allocator method is ever introduced having multiple
+                // Layout arguments, these argument names need to be
+                // disambiguated somehow. Currently the generated code would
+                // fail to compile with "identifier is bound more than once in
+                // this parameter list".
+                let size = Ident::from_str_and_span("size", self.span);
+                let align = Ident::from_str_and_span("align", self.span);
+
                 let usize = self.cx.path_ident(self.span, Ident::new(sym::usize, self.span));
                 let ty_usize = self.cx.ty_path(usize);
-                let size = ident();
-                let align = ident();
                 args.push(self.cx.param(self.span, size, ty_usize.clone()));
                 args.push(self.cx.param(self.span, align, ty_usize));
 
@@ -138,14 +133,13 @@ impl AllocFnFactory<'_, '_> {
             }
 
             AllocatorTy::Ptr => {
-                let ident = ident();
+                let ident = Ident::from_str_and_span(input.name, self.span);
                 args.push(self.cx.param(self.span, ident, self.ptr_u8()));
-                let arg = self.cx.expr_ident(self.span, ident);
-                self.cx.expr_cast(self.span, arg, self.ptr_u8())
+                self.cx.expr_ident(self.span, ident)
             }
 
             AllocatorTy::Usize => {
-                let ident = ident();
+                let ident = Ident::from_str_and_span(input.name, self.span);
                 args.push(self.cx.param(self.span, ident, self.usize()));
                 self.cx.expr_ident(self.span, ident)
             }
@@ -156,18 +150,11 @@ impl AllocFnFactory<'_, '_> {
         }
     }
 
-    fn ret_ty(&self, ty: &AllocatorTy, expr: P<Expr>) -> (P<Ty>, P<Expr>) {
+    fn ret_ty(&self, ty: &AllocatorTy) -> P<Ty> {
         match *ty {
-            AllocatorTy::ResultPtr => {
-                // We're creating:
-                //
-                //      #expr as *mut u8
-
-                let expr = self.cx.expr_cast(self.span, expr, self.ptr_u8());
-                (self.ptr_u8(), expr)
-            }
+            AllocatorTy::ResultPtr => self.ptr_u8(),
 
-            AllocatorTy::Unit => (self.cx.ty(self.span, TyKind::Tup(ThinVec::new())), expr),
+            AllocatorTy::Unit => self.cx.ty(self.span, TyKind::Tup(ThinVec::new())),
 
             AllocatorTy::Layout | AllocatorTy::Usize | AllocatorTy::Ptr => {
                 panic!("can't convert `AllocatorTy` to an output")
diff --git a/compiler/rustc_builtin_macros/src/proc_macro_harness.rs b/compiler/rustc_builtin_macros/src/proc_macro_harness.rs
index b35a2e2a2..dae1bc5bf 100644
--- a/compiler/rustc_builtin_macros/src/proc_macro_harness.rs
+++ b/compiler/rustc_builtin_macros/src/proc_macro_harness.rs
@@ -5,6 +5,7 @@ use rustc_ast::{self as ast, attr, NodeId};
 use rustc_ast_pretty::pprust;
 use rustc_expand::base::{parse_macro_name_and_helper_attrs, ExtCtxt, ResolverExpand};
 use rustc_expand::expand::{AstFragment, ExpansionConfig};
+use rustc_feature::Features;
 use rustc_session::Session;
 use rustc_span::hygiene::AstPass;
 use rustc_span::source_map::SourceMap;
@@ -46,13 +47,14 @@ struct CollectProcMacros<'a> {
 pub fn inject(
     krate: &mut ast::Crate,
     sess: &Session,
+    features: &Features,
     resolver: &mut dyn ResolverExpand,
     is_proc_macro_crate: bool,
     has_proc_macro_decls: bool,
     is_test_crate: bool,
     handler: &rustc_errors::Handler,
 ) {
-    let ecfg = ExpansionConfig::default("proc_macro".to_string());
+    let ecfg = ExpansionConfig::default("proc_macro".to_string(), features);
     let mut cx = ExtCtxt::new(sess, ecfg, resolver, None);
 
     let mut collect = CollectProcMacros {
@@ -89,7 +91,9 @@ impl<'a> CollectProcMacros<'a> {
     }
 
     fn collect_custom_derive(&mut self, item: &'a ast::Item, attr: &'a ast::Attribute) {
-        let Some((trait_name, proc_attrs)) = parse_macro_name_and_helper_attrs(self.handler, attr, "derive") else {
+        let Some((trait_name, proc_attrs)) =
+            parse_macro_name_and_helper_attrs(self.handler, attr, "derive")
+        else {
             return;
         };
 
@@ -177,8 +181,7 @@ impl<'a> Visitor<'a> for CollectProcMacros<'a> {
                         == prev_item.path.segments[0].ident.name
                     {
                         format!(
-                            "only one `#[{}]` attribute is allowed on any given function",
-                            path_str,
+                            "only one `#[{path_str}]` attribute is allowed on any given function",
                         )
                     } else {
                         format!(
diff --git a/compiler/rustc_builtin_macros/src/source_util.rs b/compiler/rustc_builtin_macros/src/source_util.rs
index e613b904d..433da7423 100644
--- a/compiler/rustc_builtin_macros/src/source_util.rs
+++ b/compiler/rustc_builtin_macros/src/source_util.rs
@@ -149,7 +149,7 @@ pub fn expand_include<'cx>(
                     Ok(None) => {
                         if self.p.token != token::Eof {
                             let token = pprust::token_to_string(&self.p.token);
-                            let msg = format!("expected item, found `{}`", token);
+                            let msg = format!("expected item, found `{token}`");
                             self.p.struct_span_err(self.p.token.span, msg).emit();
                         }
 
diff --git a/compiler/rustc_builtin_macros/src/standard_library_imports.rs b/compiler/rustc_builtin_macros/src/standard_library_imports.rs
index 6493c6f13..3ee3112f0 100644
--- a/compiler/rustc_builtin_macros/src/standard_library_imports.rs
+++ b/compiler/rustc_builtin_macros/src/standard_library_imports.rs
@@ -1,6 +1,7 @@
 use rustc_ast::{self as ast, attr};
 use rustc_expand::base::{ExtCtxt, ResolverExpand};
 use rustc_expand::expand::ExpansionConfig;
+use rustc_feature::Features;
 use rustc_session::Session;
 use rustc_span::edition::Edition::*;
 use rustc_span::hygiene::AstPass;
@@ -13,6 +14,7 @@ pub fn inject(
     pre_configured_attrs: &[ast::Attribute],
     resolver: &mut dyn ResolverExpand,
     sess: &Session,
+    features: &Features,
 ) -> usize {
     let orig_num_items = krate.items.len();
     let edition = sess.parse_sess.edition;
@@ -39,25 +41,34 @@ pub fn inject(
     let span = DUMMY_SP.with_def_site_ctxt(expn_id.to_expn_id());
     let call_site = DUMMY_SP.with_call_site_ctxt(expn_id.to_expn_id());
 
-    let ecfg = ExpansionConfig::default("std_lib_injection".to_string());
+    let ecfg = ExpansionConfig::default("std_lib_injection".to_string(), features);
     let cx = ExtCtxt::new(sess, ecfg, resolver, None);
 
     // .rev() to preserve ordering above in combination with insert(0, ...)
     for &name in names.iter().rev() {
-        let ident = if edition >= Edition2018 {
-            Ident::new(name, span)
+        let ident_span = if edition >= Edition2018 { span } else { call_site };
+        let item = if name == sym::compiler_builtins {
+            // compiler_builtins is a private implementation detail. We only
+            // need to insert it into the crate graph for linking and should not
+            // expose any of its public API.
+            //
+            // FIXME(#113634) We should inject this during post-processing like
+            // we do for the panic runtime, profiler runtime, etc.
+            cx.item(
+                span,
+                Ident::new(kw::Underscore, ident_span),
+                thin_vec![],
+                ast::ItemKind::ExternCrate(Some(name)),
+            )
         } else {
-            Ident::new(name, call_site)
-        };
-        krate.items.insert(
-            0,
             cx.item(
                 span,
-                ident,
+                Ident::new(name, ident_span),
                 thin_vec![cx.attr_word(sym::macro_use, span)],
                 ast::ItemKind::ExternCrate(None),
-            ),
-        );
+            )
+        };
+        krate.items.insert(0, item);
     }
 
     // The crates have been injected, the assumption is that the first one is
diff --git a/compiler/rustc_builtin_macros/src/test.rs b/compiler/rustc_builtin_macros/src/test.rs
index 6bc4f6fc1..1580a6f6d 100644
--- a/compiler/rustc_builtin_macros/src/test.rs
+++ b/compiler/rustc_builtin_macros/src/test.rs
@@ -255,6 +255,7 @@ pub fn expand_test_or_bench(
             ast::ItemKind::Const(
                 ast::ConstItem {
                     defaultness: ast::Defaultness::Final,
+                    generics: ast::Generics::default(),
                     ty: cx.ty(sp, ast::TyKind::Path(None, test_path("TestDescAndFn"))),
                     // test::TestDescAndFn {
                     expr: Some(
diff --git a/compiler/rustc_builtin_macros/src/test_harness.rs b/compiler/rustc_builtin_macros/src/test_harness.rs
index 81b618548..d8846a9f0 100644
--- a/compiler/rustc_builtin_macros/src/test_harness.rs
+++ b/compiler/rustc_builtin_macros/src/test_harness.rs
@@ -4,10 +4,12 @@ use rustc_ast as ast;
 use rustc_ast::entry::EntryPointType;
 use rustc_ast::mut_visit::{ExpectOne, *};
 use rustc_ast::ptr::P;
+use rustc_ast::visit::{walk_item, Visitor};
 use rustc_ast::{attr, ModKind};
 use rustc_expand::base::{ExtCtxt, ResolverExpand};
 use rustc_expand::expand::{AstFragment, ExpansionConfig};
 use rustc_feature::Features;
+use rustc_session::lint::builtin::UNNAMEABLE_TEST_ITEMS;
 use rustc_session::Session;
 use rustc_span::hygiene::{AstPass, SyntaxContext, Transparency};
 use rustc_span::symbol::{sym, Ident, Symbol};
@@ -39,7 +41,12 @@ struct TestCtxt<'a> {
 
 /// Traverse the crate, collecting all the test functions, eliding any
 /// existing main functions, and synthesizing a main test harness
-pub fn inject(krate: &mut ast::Crate, sess: &Session, resolver: &mut dyn ResolverExpand) {
+pub fn inject(
+    krate: &mut ast::Crate,
+    sess: &Session,
+    features: &Features,
+    resolver: &mut dyn ResolverExpand,
+) {
     let span_diagnostic = sess.diagnostic();
     let panic_strategy = sess.panic_strategy();
     let platform_panic_strategy = sess.target.panic_strategy;
@@ -74,7 +81,7 @@ pub fn inject(krate: &mut ast::Crate, sess: &Session, resolver: &mut dyn Resolve
             resolver,
             reexport_test_harness_main,
             krate,
-            &sess.features_untracked(),
+            features,
             panic_strategy,
             test_runner,
         )
@@ -137,11 +144,31 @@ impl<'a> MutVisitor for TestHarnessGenerator<'a> {
             let prev_tests = mem::take(&mut self.tests);
             noop_visit_item_kind(&mut item.kind, self);
             self.add_test_cases(item.id, span, prev_tests);
+        } else {
+            // But in those cases, we emit a lint to warn the user of these missing tests.
+            walk_item(&mut InnerItemLinter { sess: self.cx.ext_cx.sess }, &item);
         }
         smallvec![P(item)]
     }
 }
 
+struct InnerItemLinter<'a> {
+    sess: &'a Session,
+}
+
+impl<'a> Visitor<'a> for InnerItemLinter<'_> {
+    fn visit_item(&mut self, i: &'a ast::Item) {
+        if let Some(attr) = attr::find_by_name(&i.attrs, sym::rustc_test_marker) {
+            self.sess.parse_sess.buffer_lint(
+                UNNAMEABLE_TEST_ITEMS,
+                attr.span,
+                i.id,
+                crate::fluent_generated::builtin_macros_unnameable_test_items,
+            );
+        }
+    }
+}
+
 // Beware, this is duplicated in librustc_passes/entry.rs (with
 // `rustc_hir::Item`), so make sure to keep them in sync.
 fn entry_point_type(item: &ast::Item, depth: usize) -> EntryPointType {
@@ -221,9 +248,7 @@ fn generate_test_harness(
     panic_strategy: PanicStrategy,
     test_runner: Option<ast::Path>,
 ) {
-    let mut econfig = ExpansionConfig::default("test".to_string());
-    econfig.features = Some(features);
-
+    let econfig = ExpansionConfig::default("test".to_string(), features);
     let ext_cx = ExtCtxt::new(sess, econfig, resolver, None);
 
     let expn_id = ext_cx.resolver.expansion_for_ast_pass(