1 files changed, 150 insertions, 0 deletions
diff --git a/src/tools/rustfmt/src/emitter/checkstyle.rs b/src/tools/rustfmt/src/emitter/checkstyle.rs
new file mode 100644
index 000000000..545b25997
--- /dev/null
+++ b/src/tools/rustfmt/src/emitter/checkstyle.rs
@@ -0,0 +1,150 @@
+use self::xml::XmlEscaped;
+use super::*;
+use crate::rustfmt_diff::{make_diff, DiffLine, Mismatch};
+use std::io::{self, Write};
+
+mod xml;
+
+#[derive(Debug, Default)]
+pub(crate) struct CheckstyleEmitter;
+
+impl Emitter for CheckstyleEmitter {
+    fn emit_header(&self, output: &mut dyn Write) -> Result<(), io::Error> {
+        writeln!(output, r#"<?xml version="1.0" encoding="utf-8"?>"#)?;
+        write!(output, r#"<checkstyle version="4.3">"#)?;
+        Ok(())
+    }
+
+    fn emit_footer(&self, output: &mut dyn Write) -> Result<(), io::Error> {
+        writeln!(output, "</checkstyle>")
+    }
+
+    fn emit_formatted_file(
+        &mut self,
+        output: &mut dyn Write,
+        FormattedFile {
+            filename,
+            original_text,
+            formatted_text,
+        }: FormattedFile<'_>,
+    ) -> Result<EmitterResult, io::Error> {
+        const CONTEXT_SIZE: usize = 0;
+        let diff = make_diff(original_text, formatted_text, CONTEXT_SIZE);
+        output_checkstyle_file(output, filename, diff)?;
+        Ok(EmitterResult::default())
+    }
+}
+
+pub(crate) fn output_checkstyle_file<T>(
+    mut writer: T,
+    filename: &FileName,
+    diff: Vec<Mismatch>,
+) -> Result<(), io::Error>
+where
+    T: Write,
+{
+    write!(writer, r#"<file name="{}">"#, filename)?;
+    for mismatch in diff {
+        let begin_line = mismatch.line_number;
+        let mut current_line;
+        let mut line_counter = 0;
+        for line in mismatch.lines {
+            // Do nothing with `DiffLine::Context` and `DiffLine::Resulting`.
+            if let DiffLine::Expected(message) = line {
+                current_line = begin_line + line_counter;
+                line_counter += 1;
+                write!(
+                    writer,
+                    r#"<error line="{}" severity="warning" message="Should be `{}`" />"#,
+                    current_line,
+                    XmlEscaped(&message)
+                )?;
+            }
+        }
+    }
+    write!(writer, "</file>")?;
+    Ok(())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::path::PathBuf;
+
+    #[test]
+    fn emits_empty_record_on_file_with_no_mismatches() {
+        let file_name = "src/well_formatted.rs";
+        let mut writer = Vec::new();
+        let _ = output_checkstyle_file(
+            &mut writer,
+            &FileName::Real(PathBuf::from(file_name)),
+            vec![],
+        );
+        assert_eq!(
+            &writer[..],
+            format!(r#"<file name="{}"></file>"#, file_name).as_bytes()
+        );
+    }
+
+    // https://github.com/rust-lang/rustfmt/issues/1636
+    #[test]
+    fn emits_single_xml_tree_containing_all_files() {
+        let bin_file = "src/bin.rs";
+        let bin_original = vec!["fn main() {", "println!(\"Hello, world!\");", "}"];
+        let bin_formatted = vec!["fn main() {", "    println!(\"Hello, world!\");", "}"];
+        let lib_file = "src/lib.rs";
+        let lib_original = vec!["fn greet() {", "println!(\"Greetings!\");", "}"];
+        let lib_formatted = vec!["fn greet() {", "    println!(\"Greetings!\");", "}"];
+        let mut writer = Vec::new();
+        let mut emitter = CheckstyleEmitter::default();
+        let _ = emitter.emit_header(&mut writer);
+        let _ = emitter
+            .emit_formatted_file(
+                &mut writer,
+                FormattedFile {
+                    filename: &FileName::Real(PathBuf::from(bin_file)),
+                    original_text: &bin_original.join("\n"),
+                    formatted_text: &bin_formatted.join("\n"),
+                },
+            )
+            .unwrap();
+        let _ = emitter
+            .emit_formatted_file(
+                &mut writer,
+                FormattedFile {
+                    filename: &FileName::Real(PathBuf::from(lib_file)),
+                    original_text: &lib_original.join("\n"),
+                    formatted_text: &lib_formatted.join("\n"),
+                },
+            )
+            .unwrap();
+        let _ = emitter.emit_footer(&mut writer);
+        let exp_bin_xml = vec![
+            format!(r#"<file name="{}">"#, bin_file),
+            format!(
+                r#"<error line="2" severity="warning" message="Should be `{}`" />"#,
+                XmlEscaped(r#"    println!("Hello, world!");"#),
+            ),
+            String::from("</file>"),
+        ];
+        let exp_lib_xml = vec![
+            format!(r#"<file name="{}">"#, lib_file),
+            format!(
+                r#"<error line="2" severity="warning" message="Should be `{}`" />"#,
+                XmlEscaped(r#"    println!("Greetings!");"#),
+            ),
+            String::from("</file>"),
+        ];
+        assert_eq!(
+            String::from_utf8(writer).unwrap(),
+            vec![
+                r#"<?xml version="1.0" encoding="utf-8"?>"#,
+                "\n",
+                r#"<checkstyle version="4.3">"#,
+                &format!("{}{}", exp_bin_xml.join(""), exp_lib_xml.join("")),
+                "</checkstyle>\n",
+            ]
+            .join(""),
+        );
+    }
+}