Added pylint formatter (#1995)

Fixes: #1953

@charliermarsh thank you for the tips in the issue.

I'm not very familiar with Rust, so please excuse if my string formatting syntax is messy.

In terms of testing, I compared output of `flake8 --format=pylint ` and `cargo run --format=pylint` on the same code and the output syntax seems to check out.

README.md

@@ -381,7 +381,7 @@ Options:
       --per-file-ignores <PER_FILE_IGNORES>
           List of mappings from file pattern to code to exclude
       --format <FORMAT>
-          Output serialization format for violations [env: RUFF_FORMAT=] [possible values: text, json, junit, grouped, github, gitlab]
+          Output serialization format for violations [env: RUFF_FORMAT=] [possible values: text, json, junit, grouped, github, gitlab, pylint]
       --stdin-filename <STDIN_FILENAME>
           The name of the file when passing it through stdin
       --cache-dir <CACHE_DIR>
@@ -2120,9 +2120,9 @@ force-exclude = true
 
 The style in which violation messages should be formatted: `"text"`
 (default), `"grouped"` (group messages by file), `"json"`
-(machine-readable), `"junit"` (machine-readable XML), `"github"`
-(GitHub Actions annotations) or `"gitlab"`
-(GitLab CI code quality report).
+(machine-readable), `"junit"` (machine-readable XML), `"github"` (GitHub
+Actions annotations), `"gitlab"` (GitLab CI code quality report), or
+`"pylint"` (Pylint text format).
 
 **Default value**: `"text"`
 

ruff.schema.json

@@ -227,7 +227,7 @@
       ]
     },
     "format": {
-      "description": "The style in which violation messages should be formatted: `\"text\"` (default), `\"grouped\"` (group messages by file), `\"json\"` (machine-readable), `\"junit\"` (machine-readable XML), `\"github\"` (GitHub Actions annotations) or `\"gitlab\"` (GitLab CI code quality report).",
+      "description": "The style in which violation messages should be formatted: `\"text\"` (default), `\"grouped\"` (group messages by file), `\"json\"` (machine-readable), `\"junit\"` (machine-readable XML), `\"github\"` (GitHub Actions annotations), `\"gitlab\"` (GitLab CI code quality report), or `\"pylint\"` (Pylint text format).",
       "anyOf": [
         {
           "$ref": "#/definitions/SerializationFormat"
@@ -1804,7 +1804,8 @@
         "junit",
         "grouped",
         "github",
-        "gitlab"
+        "gitlab",
+        "pylint"
       ]
     },
     "Strictness": {

ruff_cli/src/commands.rs

@@ -319,6 +319,9 @@ pub fn explain(rule: &Rule, format: SerializationFormat) -> Result<()> {
         SerializationFormat::Gitlab => {
             bail!("`--explain` does not support GitLab format")
         }
+        SerializationFormat::Pylint => {
+            bail!("`--explain` does not support pylint format")
+        }
     };
     Ok(())
 }

ruff_cli/src/printer.rs

@@ -285,7 +285,7 @@ impl<'a> Printer<'a> {
                 }
             }
             SerializationFormat::Gitlab => {
-                // Generate JSON with errors in GitLab CI format
+                // Generate JSON with violations in GitLab CI format
                 // https://docs.gitlab.com/ee/ci/testing/code_quality.html#implementing-a-custom-tool
                 writeln!(stdout,
                     "{}",
@@ -312,6 +312,20 @@ impl<'a> Printer<'a> {
                     )?
                 )?;
             }
+            SerializationFormat::Pylint => {
+                // Generate violations in Pylint format.
+                // See: https://flake8.pycqa.org/en/latest/internal/formatters.html#pylint-formatter
+                for message in &diagnostics.messages {
+                    let label = format!(
+                        "{}:{}: [{}] {}",
+                        relativize_path(Path::new(&message.filename)),
+                        message.location.row(),
+                        message.kind.rule().code(),
+                        message.kind.body(),
+                    );
+                    writeln!(stdout, "{label}")?;
+                }
+            }
         }
 
         stdout.flush()?;

src/settings/options.rs

@@ -208,9 +208,9 @@ pub struct Options {
     )]
     /// The style in which violation messages should be formatted: `"text"`
     /// (default), `"grouped"` (group messages by file), `"json"`
-    /// (machine-readable), `"junit"` (machine-readable XML), `"github"`
-    /// (GitHub Actions annotations) or `"gitlab"`
-    /// (GitLab CI code quality report).
+    /// (machine-readable), `"junit"` (machine-readable XML), `"github"` (GitHub
+    /// Actions annotations), `"gitlab"` (GitLab CI code quality report), or
+    /// `"pylint"` (Pylint text format).
     pub format: Option<SerializationFormat>,
     #[option(
         default = r#"false"#,

src/settings/types.rs

@@ -156,6 +156,7 @@ pub enum SerializationFormat {
     Grouped,
     Github,
     Gitlab,
+    Pylint,
 }
 
 impl Default for SerializationFormat {