Outline formatting code from the panic! macro

compiler/rustc_ast/src/ast.rs

@@ -2439,6 +2439,12 @@ pub enum Const {
     No,
 }
 
+impl Const {
+    pub fn is_const(self) -> bool {
+        matches!(self, Const::Yes { .. })
+    }
+}
+
 /// Item defaultness.
 /// For details see the [RFC #2532](/~https://github.com/rust-lang/rfcs/pull/2532).
 #[derive(Copy, Clone, PartialEq, Encodable, Decodable, Debug, HashStable_Generic)]

compiler/rustc_ast/src/format.rs

@@ -1,5 +1,7 @@
 use crate::ptr::P;
+use crate::Const;
 use crate::Expr;
+use crate::NodeId;
 use rustc_data_structures::fx::FxHashMap;
 use rustc_span::symbol::{Ident, Symbol};
 use rustc_span::Span;
@@ -44,6 +46,20 @@ pub struct FormatArgs {
     pub span: Span,
     pub template: Vec<FormatArgsPiece>,
     pub arguments: FormatArguments,
+    pub panic: FormatPanicKind,
+}
+
+#[derive(Clone, Encodable, Decodable, Debug)]
+pub enum FormatPanicKind {
+    /// Regular `format_args!`.
+    Format,
+
+    /// Format and panic. Used by `panic_args!`.
+    Panic {
+        /// The id of the generated cold path function.
+        id: NodeId,
+        constness: Const,
+    },
 }
 
 /// A piece of a format template string.

compiler/rustc_ast/src/mut_visit.rs

@@ -109,6 +109,10 @@ pub trait MutVisitor: Sized {
         noop_visit_item_kind(i, self);
     }
 
+    fn visit_assoc_item_kind(&mut self, i: &mut AssocItemKind) {
+        noop_visit_assoc_item_kind(i, self);
+    }
+
     fn flat_map_trait_item(&mut self, i: P<AssocItem>) -> SmallVec<[P<AssocItem>; 1]> {
         noop_flat_map_assoc_item(i, self)
     }
@@ -1120,6 +1124,13 @@ pub fn noop_flat_map_assoc_item<T: MutVisitor>(
     visitor.visit_ident(ident);
     visitor.visit_vis(vis);
     visit_attrs(attrs, visitor);
+    visitor.visit_assoc_item_kind(kind);
+    visitor.visit_span(span);
+    visit_lazy_tts(tokens, visitor);
+    smallvec![item]
+}
+
+pub fn noop_visit_assoc_item_kind<T: MutVisitor>(kind: &mut AssocItemKind, visitor: &mut T) {
     match kind {
         AssocItemKind::Const(item) => {
             visit_const_item(item, visitor);
@@ -1147,9 +1158,6 @@ pub fn noop_flat_map_assoc_item<T: MutVisitor>(
         }
         AssocItemKind::MacCall(mac) => visitor.visit_mac_call(mac),
     }
-    visitor.visit_span(span);
-    visit_lazy_tts(tokens, visitor);
-    smallvec![item]
 }
 
 fn visit_const_item<T: MutVisitor>(
@@ -1313,6 +1321,13 @@ pub fn noop_visit_inline_asm_sym<T: MutVisitor>(
 }
 
 pub fn noop_visit_format_args<T: MutVisitor>(fmt: &mut FormatArgs, vis: &mut T) {
+    match &mut fmt.panic {
+        FormatPanicKind::Format => (),
+        FormatPanicKind::Panic { id, constness } => {
+            vis.visit_id(id);
+            visit_constness(constness, vis);
+        }
+    }
     for arg in fmt.arguments.all_args_mut() {
         if let FormatArgumentKind::Named(name) = &mut arg.kind {
             vis.visit_ident(name);

compiler/rustc_ast_lowering/src/expr.rs

@@ -1790,7 +1790,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
         self.arena.alloc(self.expr_call_mut(span, e, args))
     }
 
-    fn expr_call_lang_item_fn_mut(
+    pub(super) fn expr_call_lang_item_fn_mut(
         &mut self,
         span: Span,
         lang_item: hir::LangItem,
@@ -1811,7 +1811,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
         self.arena.alloc(self.expr_call_lang_item_fn_mut(span, lang_item, args, hir_id))
     }
 
-    fn expr_lang_item_path(
+    pub(super) fn expr_lang_item_path(
         &mut self,
         span: Span,
         lang_item: hir::LangItem,