Fix a stack overflow with long else if chains

Author: Zoxc

compiler/rustc_ast/src/mut_visit.rs

@@ -13,6 +13,7 @@ use crate::tokenstream::*;
 use crate::{ast::*, StaticItem};
 
 use rustc_data_structures::flat_map_in_place::FlatMapInPlace;
+use rustc_data_structures::stack::ensure_sufficient_stack;
 use rustc_data_structures::sync::Lrc;
 use rustc_span::source_map::Spanned;
 use rustc_span::symbol::Ident;
@@ -1369,7 +1370,7 @@ pub fn noop_visit_expr<T: MutVisitor>(
         ExprKind::If(cond, tr, fl) => {
             vis.visit_expr(cond);
             vis.visit_block(tr);
-            visit_opt(fl, |fl| vis.visit_expr(fl));
+            visit_opt(fl, |fl| ensure_sufficient_stack(|| vis.visit_expr(fl)));
         }
         ExprKind::While(cond, body, label) => {
             vis.visit_expr(cond);

compiler/rustc_parse/src/parser/expr.rs

@@ -22,6 +22,7 @@ use rustc_ast::{AnonConst, BinOp, BinOpKind, FnDecl, FnRetTy, MacCall, Param, Ty
 use rustc_ast::{Arm, Async, BlockCheckMode, Expr, ExprKind, Label, Movability, RangeLimits};
 use rustc_ast::{ClosureBinder, MetaItemLit, StmtKind};
 use rustc_ast_pretty::pprust;
+use rustc_data_structures::stack::ensure_sufficient_stack;
 use rustc_errors::{
     AddToDiagnostic, Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed, IntoDiagnostic,
     PResult, StashKey,
@@ -2489,7 +2490,7 @@ impl<'a> Parser<'a> {
         let else_span = self.prev_token.span; // `else`
         let attrs = self.parse_outer_attributes()?; // For recovery.
         let expr = if self.eat_keyword(kw::If) {
-            self.parse_expr_if()?
+            ensure_sufficient_stack(|| self.parse_expr_if())?
         } else if self.check(&TokenKind::OpenDelim(Delimiter::Brace)) {
             self.parse_simple_block()?
         } else {