Add GitHub output format (#975)

README.md

@@ -1465,7 +1465,7 @@ line-length = 120
 #### [`format`](#format)
 
 The style in which violation messages should be formatted: `"text"` (default), `"grouped"`
-(group messages by file), `"json"` (machine-readable), or `"junit"` (machine-readable XML).
+(group messages by file), `"json"` (machine-readable), `"junit"` (machine-readable XML), or `"github"` (GitHub Actions annotations).
 
 **Default value**: `"text"`
 

src/commands.rs

@@ -64,6 +64,9 @@ pub fn explain(code: &CheckCode, format: SerializationFormat) -> Result<()> {
         SerializationFormat::Junit => {
             bail!("`--explain` does not support junit format")
         }
+        SerializationFormat::Github => {
+            bail!("`--explain` does not support GitHub format")
+        }
     };
     Ok(())
 }

src/printer.rs

@@ -192,6 +192,25 @@ impl<'a> Printer<'a> {
 
                 self.post_text(num_fixable);
             }
+            SerializationFormat::Github => {
+                self.pre_text(diagnostics);
+
+                // Generate error workflow command in GitHub Actions format
+                // https://docs.github.com/en/actions/reference/workflow-commands-for-github-actions#setting-an-error-message
+                diagnostics.messages.iter().for_each(|message| {
+                    println!(
+                        "::notice title=Ruff,file={},line={},col={},endLine={},endColumn={}::({}) \
+                         {}",
+                        relativize_path(Path::new(&message.filename)),
+                        message.location.row(),
+                        message.location.column(),
+                        message.end_location.row(),
+                        message.end_location.column(),
+                        message.kind.code(),
+                        message.kind.body(),
+                    );
+                });
+            }
         }
 
         Ok(())

src/settings/configuration.rs

@@ -123,7 +123,7 @@ impl Configuration {
             fix: options.fix.unwrap_or_default(),
             fixable: options.fixable.unwrap_or_else(|| CATEGORIES.to_vec()),
             unfixable: options.unfixable.unwrap_or_default(),
-            format: options.format.unwrap_or(SerializationFormat::Text),
+            format: options.format.unwrap_or_default(),
             ignore: options.ignore.unwrap_or_default(),
             line_length: options.line_length.unwrap_or(88),
             per_file_ignores: options

src/settings/types.rs

@@ -1,4 +1,5 @@
 use std::collections::BTreeSet;
+use std::env;
 use std::hash::Hash;
 use std::path::{Path, PathBuf};
 use std::str::FromStr;
@@ -150,4 +151,16 @@ pub enum SerializationFormat {
     Json,
     Junit,
     Grouped,
+    Github,
+}
+
+impl Default for SerializationFormat {
+    fn default() -> Self {
+        if let Ok(github_actions) = env::var("GITHUB_ACTIONS") {
+            if github_actions == "true" {
+                return Self::Github;
+            }
+        }
+        Self::Text
+    }
 }