fix(rustfmt): load nested out-of-line mods correctly

src/tools/rustfmt/src/modules.rs

@@ -318,7 +318,7 @@ impl<'ast, 'sess, 'c> ModResolver<'ast, 'sess> {
             self.directory = directory;
         }
         match (sub_mod.ast_mod_kind, sub_mod.items) {
-            (Some(Cow::Borrowed(ast::ModKind::Loaded(items, ast::Inline::No, _))), _) => {
+            (Some(Cow::Borrowed(ast::ModKind::Loaded(items, _, _))), _) => {
                 self.visit_mod_from_ast(&items)
             }
             (Some(Cow::Owned(..)), Cow::Owned(items)) => self.visit_mod_outside_ast(items),

src/tools/rustfmt/src/test/mod.rs

@@ -16,6 +16,7 @@ use crate::source_file;
 use crate::{is_nightly_channel, FormatReport, FormatReportFormatterBuilder, Input, Session};
 
 mod configuration_snippet;
+mod mod_resolver;
 mod parser;
 
 const DIFF_CONTEXT_SIZE: usize = 3;

src/tools/rustfmt/src/test/mod_resolver.rs

@@ -0,0 +1,25 @@
+use std::io;
+use std::path::PathBuf;
+
+use super::read_config;
+
+use crate::{FileName, Input, Session};
+
+#[test]
+fn nested_out_of_line_mods_loaded() {
+    // See also https://github.com/rust-lang/rustfmt/issues/4874
+    let filename = "tests/mod-resolver/issue-4874/main.rs";
+    let input_file = PathBuf::from(filename);
+    let config = read_config(&input_file);
+    let mut session = Session::<io::Stdout>::new(config, None);
+    let report = session
+        .format(Input::File(filename.into()))
+        .expect("Should not have had any execution errors");
+    let errors_by_file = &report.internal.borrow().0;
+    assert!(errors_by_file.contains_key(&FileName::Real(PathBuf::from(
+        "tests/mod-resolver/issue-4874/bar/baz.rs",
+    ))));
+    assert!(errors_by_file.contains_key(&FileName::Real(PathBuf::from(
+        "tests/mod-resolver/issue-4874/foo/qux.rs",
+    ))));
+}

src/tools/rustfmt/tests/mod-resolver/issue-4874/bar/baz.rs

@@ -0,0 +1,5 @@
+fn 
+     fail_fmt_check
+   (
+
+   ) {}

src/tools/rustfmt/tests/mod-resolver/issue-4874/foo.rs

@@ -0,0 +1 @@
+mod qux;

src/tools/rustfmt/tests/mod-resolver/issue-4874/foo/qux.rs

@@ -0,0 +1,5 @@
+ fn 
+ badly_formatted
+    (
+
+    ) {}

src/tools/rustfmt/tests/mod-resolver/issue-4874/main.rs

@@ -0,0 +1,8 @@
+fn main() {
+    println!("Hello, world!");
+}
+
+mod foo;
+mod bar {
+    mod baz;
+}