Let empty files be empty files (#6839)

* Empty files don't need trailing newlines
* Move reorder_modules 2027 tests into reorder_modules_2027
* Rename test: empty_file_style_edition_2024 to newline_file
* invert check. fix newline_file.
* Move empty_file test from tests/{source,target,config}/ to next to append_newline
* Make tests/source/recorder_modules_2027/*/mod.rs empty files

Author: notpeter

src/formatting.rs

@@ -230,7 +230,7 @@ impl<'a, T: FormatHandler + 'a> FormatContext<'a, T> {
 
         // For some reason, the source_map does not include terminating
         // newlines so we must add one on for each file. This is sad.
-        source_file::append_newline(&mut visitor.buffer);
+        source_file::append_newline(&mut visitor.buffer, self.config.style_edition());
 
         format_lines(
             &mut visitor.buffer,

src/source_file.rs

@@ -3,10 +3,10 @@ use std::io::{self, Write};
 use std::path::Path;
 use std::sync::Arc;
 
-use crate::NewlineStyle;
 use crate::config::FileName;
 use crate::emitter::{self, Emitter};
 use crate::parse::session::ParseSess;
+use crate::{NewlineStyle, StyleEdition};
 
 #[cfg(test)]
 use crate::config::Config;
@@ -16,10 +16,27 @@ use crate::create_emitter;
 use crate::formatting::FileRecord;
 
 // Append a newline to the end of each file.
-pub(crate) fn append_newline(s: &mut String) {
+pub(crate) fn append_newline(s: &mut String, style_edition: StyleEdition) {
+    if style_edition >= StyleEdition::Edition2027 && s.is_empty() {
+        return;
+    }
     s.push('\n');
 }
 
+#[test]
+fn append_newline_adds_newlines_before_2027() {
+    let mut text = String::new();
+    append_newline(&mut text, StyleEdition::Edition2024);
+    assert_eq!(text, "\n");
+}
+
+#[test]
+fn append_newline_leaves_empty_files_empty_in_2027() {
+    let mut text = String::new();
+    append_newline(&mut text, StyleEdition::Edition2027);
+    assert!(text.is_empty());
+}
+
 #[cfg(test)]
 pub(crate) fn write_all_files<T>(
     source_file: &[FileRecord],

src/test/mod.rs

@@ -49,6 +49,7 @@ const FILE_SKIP_LIST: &[&str] = &[
     "cfg_mod/bar.rs",
     "cfg_mod/foo.rs",
     "cfg_mod/wasm32.rs",
+    "reorder_modules_2027",
     "skip/foo.rs",
 ];
 

tests/config/newline_file.toml

@@ -0,0 +1 @@
+style_edition = "2024"

tests/source/newline_file.rs

@@ -0,0 +1 @@
+