[ty] Add GitLab output format (#20155)

## Summary

This wires up the GitLab output format moved into `ruff_db` in
https://github.com/astral-sh/ruff/pull/20117 to the ty CLI.

While I was here, I made one unrelated change to the CLI docs. Clap was
rendering the escapes around the `\[default\]` brackets for the `full`
output, so I just switched those to parentheses:

```
--output-format <OUTPUT_FORMAT>
    The format to use for printing diagnostic messages

    Possible values:
    - full:    Print diagnostics verbosely, with context and helpful hints \[default\]
    - concise: Print diagnostics concisely, one per line
    - gitlab:  Print diagnostics in the JSON format expected by GitLab Code Quality reports
```

## Test Plan

New CLI test, and a manual test with `--config 'terminal.output-format =
"gitlab"'` to make sure this works as a configuration option too. I also
tried piping the output through jq to make sure it's at least valid JSON

crates/ruff_db/src/diagnostic/mod.rs

@@ -1444,7 +1444,7 @@ pub enum DiagnosticFormat {
     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
+    /// [Code Quality]: https://docs.gitlab.com/ci/testing/code_quality/#code-quality-report-format
     #[cfg(feature = "serde")]
     Gitlab,
 }

crates/ty/docs/cli.md

@@ -60,8 +60,9 @@ over all configuration files.</p>
 </dd><dt id="ty-check--output-format"><a href="#ty-check--output-format"><code>--output-format</code></a> <i>output-format</i></dt><dd><p>The format to use for printing diagnostic messages</p>
 <p>Possible values:</p>
 <ul>
-<li><code>full</code>:  Print diagnostics verbosely, with context and helpful hints [default]</li>
+<li><code>full</code>:  Print diagnostics verbosely, with context and helpful hints (default)</li>
 <li><code>concise</code>:  Print diagnostics concisely, one per line</li>
+<li><code>gitlab</code>:  Print diagnostics in the JSON format expected by GitLab Code Quality reports</li>
 </ul></dd><dt id="ty-check--project"><a href="#ty-check--project"><code>--project</code></a> <i>project</i></dt><dd><p>Run the command within the given project directory.</p>
 <p>All <code>pyproject.toml</code> files will be discovered by walking up the directory tree from the given project directory, as will the project's virtual environment (<code>.venv</code>) unless the <code>venv-path</code> option is set.</p>
 <p>Other command-line arguments (such as relative paths) will be resolved relative to the current working directory.</p>

crates/ty/src/args.rs

@@ -306,7 +306,7 @@ impl clap::Args for RulesArg {
 /// The diagnostic output format.
 #[derive(Copy, Clone, Hash, Debug, PartialEq, Eq, PartialOrd, Ord, Default, clap::ValueEnum)]
 pub enum OutputFormat {
-    /// Print diagnostics verbosely, with context and helpful hints \[default\].
+    /// Print diagnostics verbosely, with context and helpful hints (default).
     ///
     /// Diagnostic messages may include additional context and
     /// annotations on the input to help understand the message.
@@ -321,6 +321,9 @@ pub enum OutputFormat {
     /// dropped.
     #[value(name = "concise")]
     Concise,
+    /// Print diagnostics in the JSON format expected by GitLab Code Quality reports.
+    #[value(name = "gitlab")]
+    Gitlab,
 }
 
 impl From<OutputFormat> for ty_project::metadata::options::OutputFormat {
@@ -328,6 +331,7 @@ impl From<OutputFormat> for ty_project::metadata::options::OutputFormat {
         match format {
             OutputFormat::Full => Self::Full,
             OutputFormat::Concise => Self::Concise,
+            OutputFormat::Gitlab => Self::Gitlab,
         }
     }
 }

crates/ty/src/lib.rs

@@ -21,7 +21,7 @@ use clap::{CommandFactory, Parser};
 use colored::Colorize;
 use crossbeam::channel as crossbeam_channel;
 use rayon::ThreadPoolBuilder;
-use ruff_db::diagnostic::{Diagnostic, DisplayDiagnosticConfig, Severity};
+use ruff_db::diagnostic::{Diagnostic, DisplayDiagnosticConfig, DisplayDiagnostics, Severity};
 use ruff_db::files::File;
 use ruff_db::max_parallelism;
 use ruff_db::system::{OsSystem, SystemPath, SystemPathBuf};
@@ -319,37 +319,48 @@ impl MainLoop {
                             return Ok(ExitStatus::Success);
                         }
 
+                        let is_human_readable = terminal_settings.output_format.is_human_readable();
+
                         if result.is_empty() {
+                            if is_human_readable {
                                 writeln!(
                                     self.printer.stream_for_success_summary(),
                                     "{}",
                                     "All checks passed!".green().bold()
                                 )?;
+                            }
 
                             if self.watcher.is_none() {
                                 return Ok(ExitStatus::Success);
                             }
                         } else {
-                            let mut max_severity = Severity::Info;
                             let diagnostics_count = result.len();
 
                             let mut stdout = self.printer.stream_for_details().lock();
-                            for diagnostic in result {
+                            let max_severity = result
+                                .iter()
+                                .map(Diagnostic::severity)
+                                .max()
+                                .unwrap_or(Severity::Info);
+
                             // Only render diagnostics if they're going to be displayed, since doing
                             // so is expensive.
                             if stdout.is_enabled() {
-                                    write!(stdout, "{}", diagnostic.display(db, &display_config))?;
+                                write!(
-                                }
+                                    stdout,
-
+                                    "{}",
-                                max_severity = max_severity.max(diagnostic.severity());
+                                    DisplayDiagnostics::new(db, &display_config, &result)
+                                )?;
                             }
 
+                            if is_human_readable {
                                 writeln!(
                                     self.printer.stream_for_failure_summary(),
                                     "Found {} diagnostic{}",
                                     diagnostics_count,
                                     if diagnostics_count > 1 { "s" } else { "" }
                                 )?;
+                            }
 
                             if max_severity.is_fatal() {
                                 tracing::warn!(

crates/ty/tests/cli/main.rs

@@ -618,6 +618,71 @@ fn concise_diagnostics() -> anyhow::Result<()> {
     Ok(())
 }
 
+#[test]
+fn gitlab_diagnostics() -> anyhow::Result<()> {
+    let case = CliTest::with_file(
+        "test.py",
+        r#"
+        print(x)     # [unresolved-reference]
+        print(4[1])  # [non-subscriptable]
+        "#,
+    )?;
+
+    let mut settings = insta::Settings::clone_current();
+    settings.add_filter(r#"("fingerprint": ")[a-z0-9]+(",)"#, "$1[FINGERPRINT]$2");
+    let _s = settings.bind_to_scope();
+
+    assert_cmd_snapshot!(case.command().arg("--output-format=gitlab").arg("--warn").arg("unresolved-reference"), @r#"
+    success: false
+    exit_code: 1
+    ----- stdout -----
+    [
+      {
+        "check_name": "unresolved-reference",
+        "description": "unresolved-reference: Name `x` used when not defined",
+        "severity": "minor",
+        "fingerprint": "[FINGERPRINT]",
+        "location": {
+          "path": "test.py",
+          "positions": {
+            "begin": {
+              "line": 2,
+              "column": 7
+            },
+            "end": {
+              "line": 2,
+              "column": 8
+            }
+          }
+        }
+      },
+      {
+        "check_name": "non-subscriptable",
+        "description": "non-subscriptable: Cannot subscript object of type `Literal[4]` with no `__getitem__` method",
+        "severity": "major",
+        "fingerprint": "[FINGERPRINT]",
+        "location": {
+          "path": "test.py",
+          "positions": {
+            "begin": {
+              "line": 3,
+              "column": 7
+            },
+            "end": {
+              "line": 3,
+              "column": 8
+            }
+          }
+        }
+      }
+    ]
+    ----- stderr -----
+    WARN ty is pre-release software and not ready for production use. Expect to encounter bugs, missing features, and fatal errors.
+    "#);
+
+    Ok(())
+}
+
 /// This tests the diagnostic format for revealed type.
 ///
 /// This test was introduced because changes were made to

crates/ty_project/src/metadata/options.rs

@@ -1055,6 +1055,21 @@ pub enum OutputFormat {
     ///
     /// This may use color when printing to a `tty`.
     Concise,
+    /// Print diagnostics in the JSON format expected by GitLab [Code Quality] reports.
+    ///
+    /// [Code Quality]: https://docs.gitlab.com/ci/testing/code_quality/#code-quality-report-format
+    Gitlab,
+}
+
+impl OutputFormat {
+    /// Returns `true` if this format is intended for users to read directly, in contrast to
+    /// machine-readable or structured formats.
+    ///
+    /// This can be used to check whether information beyond the diagnostics, such as a header or
+    /// `Found N diagnostics` footer, should be included.
+    pub const fn is_human_readable(&self) -> bool {
+        matches!(self, OutputFormat::Full | OutputFormat::Concise)
+    }
 }
 
 impl From<OutputFormat> for DiagnosticFormat {
@@ -1062,6 +1077,7 @@ impl From<OutputFormat> for DiagnosticFormat {
         match value {
             OutputFormat::Full => Self::Full,
             OutputFormat::Concise => Self::Concise,
+            OutputFormat::Gitlab => Self::Gitlab,
         }
     }
 }

ty.schema.json

@@ -164,6 +164,13 @@
           "enum": [
             "concise"
           ]
+        },
+        {
+          "description": "Print diagnostics in the JSON format expected by GitLab [Code Quality] reports.\n\n[Code Quality]: https://docs.gitlab.com/ci/testing/code_quality/#code-quality-report-format",
+          "type": "string",
+          "enum": [
+            "gitlab"
+          ]
         }
       ]
     },