Experiment: New fmt::Arguments implementation

compiler/rustc_ast_lowering/messages.ftl

@@ -169,6 +169,9 @@ ast_lowering_template_modifier = template modifier
 
 ast_lowering_this_not_async = this is not `async`
 
+ast_lowering_too_many_format_arguments =
+    too many arguments used in format string
+
 ast_lowering_underscore_expr_lhs_assign =
     in expressions, `_` can only be used on the left-hand side of an assignment
     .label = `_` not allowed here

compiler/rustc_ast_lowering/src/errors.rs

@@ -475,3 +475,10 @@ pub(crate) struct UnionWithDefault {
     #[primary_span]
     pub span: Span,
 }
+
+#[derive(Diagnostic)]
+#[diag(ast_lowering_too_many_format_arguments)]
+pub(crate) struct TooManyFormatArguments {
+    #[primary_span]
+    pub span: Span,
+}

compiler/rustc_ast_lowering/src/expr.rs

@@ -924,7 +924,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                     arena_vec![self; new_unchecked, get_context],
                 ),
             };
-            self.arena.alloc(self.expr_unsafe(call))
+            self.arena.alloc(self.expr_unsafe(span, call))
         };
 
         // `::std::task::Poll::Ready(result) => break result`
@@ -1826,7 +1826,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                         arena_vec![self; iter],
                     ));
                     // `unsafe { ... }`
-                    let iter = self.arena.alloc(self.expr_unsafe(iter));
+                    let iter = self.arena.alloc(self.expr_unsafe(head_span, iter));
                     let kind = self.make_lowered_await(head_span, iter, FutureKind::AsyncIterator);
                     self.arena.alloc(hir::Expr { hir_id: self.next_id(), kind, span: head_span })
                 }
@@ -1881,7 +1881,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                     arena_vec![self; iter],
                 ));
                 // `unsafe { ... }`
-                let iter = self.arena.alloc(self.expr_unsafe(iter));
+                let iter = self.arena.alloc(self.expr_unsafe(head_span, iter));
                 let inner_match_expr = self.arena.alloc(self.expr_match(
                     for_span,
                     iter,
@@ -2105,18 +2105,10 @@ impl<'hir> LoweringContext<'_, 'hir> {
         self.expr(sp, hir::ExprKind::Lit(lit))
     }
 
-    pub(super) fn expr_usize(&mut self, sp: Span, value: usize) -> hir::Expr<'hir> {
+    pub(super) fn expr_usize(&mut self, sp: Span, value: u64) -> hir::Expr<'hir> {
         self.expr_uint(sp, ast::UintTy::Usize, value as u128)
     }
 
-    pub(super) fn expr_u32(&mut self, sp: Span, value: u32) -> hir::Expr<'hir> {
-        self.expr_uint(sp, ast::UintTy::U32, value as u128)
-    }
-
-    pub(super) fn expr_u16(&mut self, sp: Span, value: u16) -> hir::Expr<'hir> {
-        self.expr_uint(sp, ast::UintTy::U16, value as u128)
-    }
-
     pub(super) fn expr_str(&mut self, sp: Span, value: Symbol) -> hir::Expr<'hir> {
         let lit = hir::Lit {
             span: self.lower_span(sp),
@@ -2256,9 +2248,12 @@ impl<'hir> LoweringContext<'_, 'hir> {
         self.expr(span, expr_path)
     }
 
-    fn expr_unsafe(&mut self, expr: &'hir hir::Expr<'hir>) -> hir::Expr<'hir> {
+    pub(super) fn expr_unsafe(
+        &mut self,
+        span: Span,
+        expr: &'hir hir::Expr<'hir>,
+    ) -> hir::Expr<'hir> {
         let hir_id = self.next_id();
-        let span = expr.span;
         self.expr(
             span,
             hir::ExprKind::Block(