fix(rustfmt): resolve generated file formatting issue

Author: calebcartwright

src/tools/rustfmt/Configurations.md

@@ -929,9 +929,9 @@ fn add_one(x: i32) -> i32 {
 ## `format_generated_files`
 
 Format generated files. A file is considered generated
-if any of the first five lines contains `@generated` marker.
+if any of the first five lines contain a `@generated` comment marker.
 
-- **Default value**: `false`
+- **Default value**: `true`
 - **Possible values**: `true`, `false`
 - **Stable**: No
 

src/tools/rustfmt/src/config/mod.rs

@@ -138,7 +138,7 @@ create_config! {
     inline_attribute_width: usize, 0, false,
         "Write an item and its attribute on the same line \
         if their combined width is below a threshold";
-    format_generated_files: bool, false, false, "Format generated files";
+    format_generated_files: bool, true, false, "Format generated files";
 
     // Options that can change the source code beyond whitespace/blocks (somewhat linty things)
     merge_derives: bool, true, true, "Merge multiple `#[derive(...)]` into a single one";
@@ -608,7 +608,7 @@ blank_lines_lower_bound = 0
 edition = "2015"
 version = "One"
 inline_attribute_width = 0
-format_generated_files = false
+format_generated_files = true
 merge_derives = true
 use_try_shorthand = false
 use_field_init_shorthand = false

src/tools/rustfmt/src/formatting.rs

@@ -109,7 +109,7 @@ fn format_project<T: FormatHandler>(
         let src = source_file.src.as_ref().expect("SourceFile without src");
 
         let should_ignore = (!input_is_stdin && context.ignore_file(&path))
-            || (!config.format_generated_files() && is_generated_file(src));
+            || (!input_is_stdin && !config.format_generated_files() && is_generated_file(src));
 
         if (config.skip_children() && path != main_file) || should_ignore {
             continue;

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

@@ -490,6 +490,24 @@ fn stdin_disable_all_formatting_test() {
     assert_eq!(input, String::from_utf8(output.stdout).unwrap());
 }
 
+#[test]
+fn stdin_generated_files_issue_5172() {
+    init_log();
+    let input = Input::Text("//@generated\nfn   main() {}".to_owned());
+    let mut config = Config::default();
+    config.set().emit_mode(EmitMode::Stdout);
+    config.set().format_generated_files(false);
+    config.set().newline_style(NewlineStyle::Unix);
+    let mut buf: Vec<u8> = vec![];
+    {
+        let mut session = Session::new(config, Some(&mut buf));
+        session.format(input).unwrap();
+        assert!(session.has_no_errors());
+    }
+    // N.B. this should be changed once `format_generated_files` is supported with stdin
+    assert_eq!(buf, "stdin:\n\n//@generated\nfn main() {}\n".as_bytes());
+}
+
 #[test]
 fn format_lines_errors_are_reported() {
     init_log();