6 files changed, 19 insertions, 11 deletions
diff --git a/src/tools/rustfmt/src/chains.rs b/src/tools/rustfmt/src/chains.rs
index 39b8d687809..cbe523c6c3c 100644
--- a/src/tools/rustfmt/src/chains.rs
+++ b/src/tools/rustfmt/src/chains.rs
@@ -74,6 +74,8 @@ use crate::utils::{
     rewrite_ident, trimmed_last_line_width, wrap_str,
 };
 
+use thin_vec::ThinVec;
+
 /// Provides the original input contents from the span
 /// of a chain element with trailing spaces trimmed.
 fn format_overflow_style(span: Span, context: &RewriteContext<'_>) -> Option<String> {
@@ -168,7 +170,7 @@ enum ChainItemKind {
     MethodCall(
         ast::PathSegment,
         Vec<ast::GenericArg>,
-        Vec<ptr::P<ast::Expr>>,
+        ThinVec<ptr::P<ast::Expr>>,
     ),
     StructField(symbol::Ident),
     TupleField(symbol::Ident, bool),
diff --git a/src/tools/rustfmt/src/closures.rs b/src/tools/rustfmt/src/closures.rs
index 8fd0fcf8f5c..340113866c4 100644
--- a/src/tools/rustfmt/src/closures.rs
+++ b/src/tools/rustfmt/src/closures.rs
@@ -1,5 +1,6 @@
 use rustc_ast::{ast, ptr};
 use rustc_span::Span;
+use thin_vec::thin_vec;
 
 use crate::attr::get_attrs_from_stmt;
 use crate::config::lists::*;
@@ -150,7 +151,7 @@ fn rewrite_closure_with_block(
     }
 
     let block = ast::Block {
-        stmts: vec![ast::Stmt {
+        stmts: thin_vec![ast::Stmt {
             id: ast::NodeId::root(),
             kind: ast::StmtKind::Expr(ptr::P(body.clone())),
             span: body.span,
diff --git a/src/tools/rustfmt/src/lib.rs b/src/tools/rustfmt/src/lib.rs
index 0c27bcacfb8..b27405efdb7 100644
--- a/src/tools/rustfmt/src/lib.rs
+++ b/src/tools/rustfmt/src/lib.rs
@@ -23,6 +23,7 @@ extern crate rustc_expand;
 extern crate rustc_parse;
 extern crate rustc_session;
 extern crate rustc_span;
+extern crate thin_vec;
 
 // Necessary to pull in object code as the rest of the rustc crates are shipped only as rmeta
 // files.
diff --git a/src/tools/rustfmt/src/modules.rs b/src/tools/rustfmt/src/modules.rs
index 7a0d1736c59..af9a154a6ae 100644
--- a/src/tools/rustfmt/src/modules.rs
+++ b/src/tools/rustfmt/src/modules.rs
@@ -6,6 +6,7 @@ use rustc_ast::ast;
 use rustc_ast::visit::Visitor;
 use rustc_span::symbol::{self, sym, Symbol};
 use rustc_span::Span;
+use thin_vec::ThinVec;
 use thiserror::Error;
 
 use crate::attr::MetaVisitor;
@@ -25,7 +26,7 @@ type FileModMap<'ast> = BTreeMap<FileName, Module<'ast>>;
 #[derive(Debug, Clone)]
 pub(crate) struct Module<'a> {
     ast_mod_kind: Option<Cow<'a, ast::ModKind>>,
-    pub(crate) items: Cow<'a, Vec<rustc_ast::ptr::P<ast::Item>>>,
+    pub(crate) items: Cow<'a, ThinVec<rustc_ast::ptr::P<ast::Item>>>,
     inner_attr: ast::AttrVec,
     pub(crate) span: Span,
 }
@@ -34,7 +35,7 @@ impl<'a> Module<'a> {
     pub(crate) fn new(
         mod_span: Span,
         ast_mod_kind: Option<Cow<'a, ast::ModKind>>,
-        mod_items: Cow<'a, Vec<rustc_ast::ptr::P<ast::Item>>>,
+        mod_items: Cow<'a, ThinVec<rustc_ast::ptr::P<ast::Item>>>,
         mod_attrs: Cow<'a, ast::AttrVec>,
     ) -> Self {
         let inner_attr = mod_attrs
@@ -157,7 +158,7 @@ impl<'ast, 'sess, 'c> ModResolver<'ast, 'sess> {
                     Module::new(
                         module_item.item.span,
                         Some(Cow::Owned(sub_mod_kind.clone())),
-                        Cow::Owned(vec![]),
+                        Cow::Owned(ThinVec::new()),
                         Cow::Owned(ast::AttrVec::new()),
                     ),
                 )?;
@@ -169,7 +170,7 @@ impl<'ast, 'sess, 'c> ModResolver<'ast, 'sess> {
     /// Visit modules defined inside macro calls.
     fn visit_mod_outside_ast(
         &mut self,
-        items: Vec<rustc_ast::ptr::P<ast::Item>>,
+        items: ThinVec<rustc_ast::ptr::P<ast::Item>>,
     ) -> Result<(), ModuleResolutionError> {
         for item in items {
             if is_cfg_if(&item) {
@@ -184,7 +185,7 @@ impl<'ast, 'sess, 'c> ModResolver<'ast, 'sess> {
                     Module::new(
                         span,
                         Some(Cow::Owned(sub_mod_kind.clone())),
-                        Cow::Owned(vec![]),
+                        Cow::Owned(ThinVec::new()),
                         Cow::Owned(ast::AttrVec::new()),
                     ),
                 )?;
@@ -210,7 +211,7 @@ impl<'ast, 'sess, 'c> ModResolver<'ast, 'sess> {
                     Module::new(
                         span,
                         Some(Cow::Borrowed(sub_mod_kind)),
-                        Cow::Owned(vec![]),
+                        Cow::Owned(ThinVec::new()),
                         Cow::Borrowed(&item.attrs),
                     ),
                 )?;
diff --git a/src/tools/rustfmt/src/parse/parser.rs b/src/tools/rustfmt/src/parse/parser.rs
index e0bd065518b..7ab042506bd 100644
--- a/src/tools/rustfmt/src/parse/parser.rs
+++ b/src/tools/rustfmt/src/parse/parser.rs
@@ -6,6 +6,7 @@ use rustc_ast::{ast, ptr};
 use rustc_errors::Diagnostic;
 use rustc_parse::{new_parser_from_file, parser::Parser as RawParser};
 use rustc_span::{sym, Span};
+use thin_vec::ThinVec;
 
 use crate::attr::first_attr_value_str_by_name;
 use crate::parse::session::ParseSess;
@@ -109,7 +110,7 @@ impl<'a> Parser<'a> {
         sess: &'a ParseSess,
         path: &Path,
         span: Span,
-    ) -> Result<(ast::AttrVec, Vec<ptr::P<ast::Item>>, Span), ParserError> {
+    ) -> Result<(ast::AttrVec, ThinVec<ptr::P<ast::Item>>, Span), ParserError> {
         let result = catch_unwind(AssertUnwindSafe(|| {
             let mut parser = new_parser_from_file(sess.inner(), path, Some(span));
             match parser.parse_mod(&TokenKind::Eof) {
diff --git a/src/tools/rustfmt/src/parse/session.rs b/src/tools/rustfmt/src/parse/session.rs
index 9014026b0aa..a64963db6a7 100644
--- a/src/tools/rustfmt/src/parse/session.rs
+++ b/src/tools/rustfmt/src/parse/session.rs
@@ -123,8 +123,10 @@ fn default_handler(
     let emitter = if hide_parse_errors {
         silent_emitter()
     } else {
-        let fallback_bundle =
-            rustc_errors::fallback_fluent_bundle(rustc_errors::DEFAULT_LOCALE_RESOURCES, false);
+        let fallback_bundle = rustc_errors::fallback_fluent_bundle(
+            rustc_driver::DEFAULT_LOCALE_RESOURCES.to_vec(),
+            false,
+        );
         Box::new(EmitterWriter::stderr(
             color_cfg,
             Some(source_map.clone()),