Move GitLab output rendering to ruff_db (#20117)

## Summary

This PR is a first step toward adding a GitLab output format to ty. It
converts the `GitlabEmitter` from `ruff_linter` to a `GitlabRenderer` in
`ruff_db` and updates its implementation to handle non-Ruff files and
diagnostics without primary spans. I tried to break up the changes here
so that they're easy to review commit-by-commit, or at least in groups
of commits:
- [preparatory changes in-place in `ruff_linter` and a `ruff_db`
skeleton](https://github.com/astral-sh/ruff/pull/20117/files/0761b73a615537fe75fc54ba8f7d5f52c28b2a2a)
- [moving the code over with no implementation changes mixed
in](https://github.com/astral-sh/ruff/pull/20117/files/0761b73a615537fe75fc54ba8f7d5f52c28b2a2a..8f909ea0bb0892107824b311f3982eb3cb1833ed)
- [tidying up the code now in
`ruff_db`](https://github.com/astral-sh/ruff/pull/20117/files/9f047c4f9f1c826b963f0fa82ca2411d01d6ec83..e5e217fcd611ab24f516b2af4fa21e25eadc5645)

This wasn't strictly necessary, but I also added some `Serialize`
structs instead of calling `json!` to make it a little clearer that we
weren't modifying the schema (e4c4bee).

I plan to follow this up with a separate PR exposing this output format
in the ty CLI, which should be quite straightforward.

## Test Plan

Existing tests, especially the two that show up in the diff as renamed
nearly without changes

Author: ntBre

Cargo.lock

@@ -15,8 +15,7 @@ use ruff_db::diagnostic::{
 use ruff_linter::fs::relativize_path;
 use ruff_linter::logging::LogLevel;
 use ruff_linter::message::{
-    Emitter, EmitterContext, GithubEmitter, GitlabEmitter, GroupedEmitter, SarifEmitter,
-    TextEmitter,
+    Emitter, EmitterContext, GithubEmitter, GroupedEmitter, SarifEmitter, TextEmitter,
 };
 use ruff_linter::notify_user;
 use ruff_linter::settings::flags::{self};
@@ -296,7 +295,11 @@ impl Printer {
                 GithubEmitter.emit(writer, &diagnostics.inner, &context)?;
             }
             OutputFormat::Gitlab => {
-                GitlabEmitter::default().emit(writer, &diagnostics.inner, &context)?;
+                let config = DisplayDiagnosticConfig::default()
+                    .format(DiagnosticFormat::Gitlab)
+                    .preview(preview);
+                let value = DisplayDiagnostics::new(&context, &config, &diagnostics.inner);
+                write!(writer, "{value}")?;
             }
             OutputFormat::Pylint => {
                 let config = DisplayDiagnosticConfig::default()

crates/ruff/src/printer.rs

@@ -20,59 +20,59 @@ exit_code: 1
   {
     "check_name": "F401",
     "description": "F401: `os` imported but unused",
+    "severity": "major",
     "fingerprint": "4dbad37161e65c72",
     "location": {
       "path": "input.py",
       "positions": {
         "begin": {
-          "column": 8,
-          "line": 1
+          "line": 1,
+          "column": 8
         },
         "end": {
-          "column": 10,
-          "line": 1
+          "line": 1,
+          "column": 10
         }
       }
-    },
-    "severity": "major"
+    }
   },
   {
     "check_name": "F821",
     "description": "F821: Undefined name `y`",
+    "severity": "major",
     "fingerprint": "7af59862a085230",
     "location": {
       "path": "input.py",
       "positions": {
         "begin": {
-          "column": 5,
-          "line": 2
+          "line": 2,
+          "column": 5
         },
         "end": {
-          "column": 6,
-          "line": 2
+          "line": 2,
+          "column": 6
         }
       }
-    },
-    "severity": "major"
+    }
   },
   {
     "check_name": "invalid-syntax",
     "description": "invalid-syntax: Cannot use `match` statement on Python 3.9 (syntax was added in Python 3.10)",
+    "severity": "major",
     "fingerprint": "e558cec859bb66e8",
     "location": {
       "path": "input.py",
       "positions": {
         "begin": {
-          "column": 1,
-          "line": 3
+          "line": 3,
+          "column": 1
         },
         "end": {
-          "column": 6,
-          "line": 3
+          "line": 3,
+          "column": 6
         }
       }
-    },
-    "severity": "major"
+    }
   }
 ]
 ----- stderr -----

crates/ruff/tests/snapshots/lint__output_format_gitlab.snap

@@ -34,6 +34,7 @@ glob = { workspace = true }
 ignore = { workspace = true, optional = true }
 matchit = { workspace = true }
 path-slash = { workspace = true }
+pathdiff = { workspace = true }
 quick-junit = { workspace = true, optional = true }
 rustc-hash = { workspace = true }
 salsa = { workspace = true }
@@ -53,7 +54,7 @@ web-time = { version = "1.1.0" }
 etcetera = { workspace = true, optional = true }
 
 [dev-dependencies]
-insta = { workspace = true }
+insta = { workspace = true, features = ["filters"] }
 tempfile = { workspace = true }
 
 [features]

crates/ruff_db/Cargo.toml

@@ -1435,6 +1435,11 @@ pub enum DiagnosticFormat {
     /// Print diagnostics in the format expected by JUnit.
     #[cfg(feature = "junit")]
     Junit,
+    /// Print diagnostics in the JSON format used by GitLab [Code Quality] reports.
+    ///
+    /// [Code Quality]: https://docs.gitlab.com/ee/ci/testing/code_quality.html#implement-a-custom-tool
+    #[cfg(feature = "serde")]
+    Gitlab,
 }
 
 /// A representation of the kinds of messages inside a diagnostic.

crates/ruff_db/src/diagnostic/mod.rs

@@ -31,6 +31,8 @@ mod azure;
 mod concise;
 mod full;
 #[cfg(feature = "serde")]
+mod gitlab;
+#[cfg(feature = "serde")]
 mod json;
 #[cfg(feature = "serde")]
 mod json_lines;
@@ -136,6 +138,10 @@ impl std::fmt::Display for DisplayDiagnostics<'_> {
             DiagnosticFormat::Junit => {
                 junit::JunitRenderer::new(self.resolver).render(f, self.diagnostics)?;
             }
+            #[cfg(feature = "serde")]
+            DiagnosticFormat::Gitlab => {
+                gitlab::GitlabRenderer::new(self.resolver).render(f, self.diagnostics)?;
+            }
         }
 
         Ok(())

crates/ruff_db/src/diagnostic/render.rs

@@ -0,0 +1,205 @@
+use std::{
+    collections::HashSet,
+    hash::{DefaultHasher, Hash, Hasher},
+    path::Path,
+};
+
+use ruff_source_file::LineColumn;
+use serde::{Serialize, Serializer, ser::SerializeSeq};
+
+use crate::diagnostic::{Diagnostic, Severity};
+
+use super::FileResolver;
+
+pub(super) struct GitlabRenderer<'a> {
+    resolver: &'a dyn FileResolver,
+}
+
+impl<'a> GitlabRenderer<'a> {
+    pub(super) fn new(resolver: &'a dyn FileResolver) -> Self {
+        Self { resolver }
+    }
+}
+
+impl GitlabRenderer<'_> {
+    pub(super) fn render(
+        &self,
+        f: &mut std::fmt::Formatter,
+        diagnostics: &[Diagnostic],
+    ) -> std::fmt::Result {
+        write!(
+            f,
+            "{}",
+            serde_json::to_string_pretty(&SerializedMessages {
+                diagnostics,
+                resolver: self.resolver,
+                #[expect(
+                    clippy::disallowed_methods,
+                    reason = "We don't have access to a `System` here, \
+                              and this is only intended for use by GitLab CI, \
+                              which runs on a real `System`."
+                )]
+                project_dir: std::env::var("CI_PROJECT_DIR").ok().as_deref(),
+            })
+            .unwrap()
+        )
+    }
+}
+
+struct SerializedMessages<'a> {
+    diagnostics: &'a [Diagnostic],
+    resolver: &'a dyn FileResolver,
+    project_dir: Option<&'a str>,
+}
+
+impl Serialize for SerializedMessages<'_> {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        let mut s = serializer.serialize_seq(Some(self.diagnostics.len()))?;
+        let mut fingerprints = HashSet::<u64>::with_capacity(self.diagnostics.len());
+
+        for diagnostic in self.diagnostics {
+            let location = diagnostic
+                .primary_span()
+                .map(|span| {
+                    let file = span.file();
+                    let positions = if self.resolver.is_notebook(file) {
+                        // We can't give a reasonable location for the structured formats,
+                        // so we show one that's clearly a fallback
+                        Default::default()
+                    } else {
+                        let diagnostic_source = file.diagnostic_source(self.resolver);
+                        let source_code = diagnostic_source.as_source_code();
+                        span.range()
+                            .map(|range| Positions {
+                                begin: source_code.line_column(range.start()),
+                                end: source_code.line_column(range.end()),
+                            })
+                            .unwrap_or_default()
+                    };
+
+                    let path = self.project_dir.as_ref().map_or_else(
+                        || file.relative_path(self.resolver).display().to_string(),
+                        |project_dir| relativize_path_to(file.path(self.resolver), project_dir),
+                    );
+
+                    Location { path, positions }
+                })
+                .unwrap_or_default();
+
+            let mut message_fingerprint = fingerprint(diagnostic, &location.path, 0);
+
+            // Make sure that we do not get a fingerprint that is already in use
+            // by adding in the previously generated one.
+            while fingerprints.contains(&message_fingerprint) {
+                message_fingerprint = fingerprint(diagnostic, &location.path, message_fingerprint);
+            }
+            fingerprints.insert(message_fingerprint);
+
+            let description = diagnostic.body();
+            let check_name = diagnostic.secondary_code_or_id();
+            let severity = match diagnostic.severity() {
+                Severity::Info => "info",
+                Severity::Warning => "minor",
+                Severity::Error => "major",
+                // Another option here is `blocker`
+                Severity::Fatal => "critical",
+            };
+
+            let value = Message {
+                check_name,
+                // GitLab doesn't display the separate `check_name` field in a Code Quality report,
+                // so prepend it to the description too.
+                description: format!("{check_name}: {description}"),
+                severity,
+                fingerprint: format!("{:x}", message_fingerprint),
+                location,
+            };
+
+            s.serialize_element(&value)?;
+        }
+
+        s.end()
+    }
+}
+
+#[derive(Serialize)]
+struct Message<'a> {
+    check_name: &'a str,
+    description: String,
+    severity: &'static str,
+    fingerprint: String,
+    location: Location,
+}
+
+/// The place in the source code where the issue was discovered.
+///
+/// According to the CodeClimate report format [specification] linked from the GitLab [docs], this
+/// field is required, so we fall back on a default `path` and position if the diagnostic doesn't
+/// have a primary span.
+///
+/// [specification]: https://github.com/codeclimate/platform/blob/master/spec/analyzers/SPEC.md#data-types
+/// [docs]: https://docs.gitlab.com/ci/testing/code_quality/#code-quality-report-format
+#[derive(Default, Serialize)]
+struct Location {
+    path: String,
+    positions: Positions,
+}
+
+#[derive(Default, Serialize)]
+struct Positions {
+    begin: LineColumn,
+    end: LineColumn,
+}
+
+/// Generate a unique fingerprint to identify a violation.
+fn fingerprint(diagnostic: &Diagnostic, project_path: &str, salt: u64) -> u64 {
+    let mut hasher = DefaultHasher::new();
+
+    salt.hash(&mut hasher);
+    diagnostic.name().hash(&mut hasher);
+    project_path.hash(&mut hasher);
+
+    hasher.finish()
+}
+
+/// Convert an absolute path to be relative to the specified project root.
+fn relativize_path_to<P: AsRef<Path>, R: AsRef<Path>>(path: P, project_root: R) -> String {
+    format!(
+        "{}",
+        pathdiff::diff_paths(&path, project_root)
+            .expect("Could not diff paths")
+            .display()
+    )
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::diagnostic::{
+        DiagnosticFormat,
+        render::tests::{create_diagnostics, create_syntax_error_diagnostics},
+    };
+
+    const FINGERPRINT_FILTERS: [(&str, &str); 1] = [(
+        r#""fingerprint": "[a-z0-9]+","#,
+        r#""fingerprint": "<redacted>","#,
+    )];
+
+    #[test]
+    fn output() {
+        let (env, diagnostics) = create_diagnostics(DiagnosticFormat::Gitlab);
+        insta::with_settings!({filters => FINGERPRINT_FILTERS}, {
+            insta::assert_snapshot!(env.render_diagnostics(&diagnostics));
+        });
+    }
+
+    #[test]
+    fn syntax_errors() {
+        let (env, diagnostics) = create_syntax_error_diagnostics(DiagnosticFormat::Gitlab);
+        insta::with_settings!({filters => FINGERPRINT_FILTERS}, {
+            insta::assert_snapshot!(env.render_diagnostics(&diagnostics));
+        });
+    }
+}