add JsonLines support

crates/ruff_db/src/diagnostic/mod.rs

@@ -1237,7 +1237,14 @@ pub enum DiagnosticFormat {
     /// [Azure Pipelines]: https://learn.microsoft.com/en-us/azure/devops/pipelines/scripts/logging-commands?view=azure-devops&tabs=bash#logissue-log-an-error-or-warning
     Azure,
     /// Print diagnostics in JSON format.
+    ///
+    /// Unlike `json-lines`, this prints all of the diagnostics as a JSON array.
     Json,
+    /// Print diagnostics in JSON format, one per line.
+    ///
+    /// This will print each diagnostic as a separate JSON object on its own line. See the `json`
+    /// format for an array of all diagnostics.
+    JsonLines,
 }
 
 impl DiagnosticFormat {

crates/ruff_db/src/diagnostic/render.rs

@@ -63,52 +63,6 @@ impl<'a> DisplayDiagnostic<'a> {
     }
 }
 
-/// A type that implements `std::fmt::Display` for rendering a collection of diagnostics.
-///
-/// It intended for collections of diagnostics that need to be serialized together, as is the case
-/// for JSON, for example.
-///
-/// See [`DisplayDiagnostic`] for rendering individual `Diagnostic`s and details about the lifetime
-/// constraints.
-pub struct DisplayDiagnostics<'a> {
-    config: &'a DisplayDiagnosticConfig,
-    resolver: &'a dyn FileResolver,
-    diagnostics: &'a [Diagnostic],
-}
-
-impl<'a> DisplayDiagnostics<'a> {
-    pub fn new(
-        resolver: &'a dyn FileResolver,
-        config: &'a DisplayDiagnosticConfig,
-        diagnostics: &'a [Diagnostic],
-    ) -> DisplayDiagnostics<'a> {
-        DisplayDiagnostics {
-            config,
-            resolver,
-            diagnostics,
-        }
-    }
-}
-
-impl std::fmt::Display for DisplayDiagnostics<'_> {
-    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
-        match self.config.format {
-            DiagnosticFormat::Concise | DiagnosticFormat::Azure | DiagnosticFormat::Full => {
-                for diag in self.diagnostics {
-                    write!(f, "{}", diag.display(self.resolver, self.config))?;
-                }
-            }
-            DiagnosticFormat::Json => write!(
-                f,
-                "{:#}",
-                diagnostics_to_json_value(self.diagnostics, self.resolver)
-            )?,
-        }
-
-        Ok(())
-    }
-}
-
 impl std::fmt::Display for DisplayDiagnostic<'_> {
     fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
         let stylesheet = if self.config.color {
@@ -187,11 +141,15 @@ impl std::fmt::Display for DisplayDiagnostic<'_> {
                     body = self.diag.body(),
                 )?;
             }
-            DiagnosticFormat::Json => {
+            DiagnosticFormat::JsonLines => {
                 if let Some(value) = message_to_json_value(self.diag, self.resolver) {
                     writeln!(f, "{value}")?;
                 }
             }
+            DiagnosticFormat::Json => {
+                let value = diagnostics_to_json_value(std::iter::once(self.diag), self.resolver);
+                writeln!(f, "{value}")?;
+            }
             DiagnosticFormat::Full => {
                 let mut renderer = self.annotate_renderer.clone();
                 renderer = renderer
@@ -217,6 +175,55 @@ impl std::fmt::Display for DisplayDiagnostic<'_> {
     }
 }
 
+/// A type that implements `std::fmt::Display` for rendering a collection of diagnostics.
+///
+/// It intended for collections of diagnostics that need to be serialized together, as is the case
+/// for JSON, for example.
+///
+/// See [`DisplayDiagnostic`] for rendering individual `Diagnostic`s and details about the lifetime
+/// constraints.
+pub struct DisplayDiagnostics<'a> {
+    config: &'a DisplayDiagnosticConfig,
+    resolver: &'a dyn FileResolver,
+    diagnostics: &'a [Diagnostic],
+}
+
+impl<'a> DisplayDiagnostics<'a> {
+    pub fn new(
+        resolver: &'a dyn FileResolver,
+        config: &'a DisplayDiagnosticConfig,
+        diagnostics: &'a [Diagnostic],
+    ) -> DisplayDiagnostics<'a> {
+        DisplayDiagnostics {
+            config,
+            resolver,
+            diagnostics,
+        }
+    }
+}
+
+impl std::fmt::Display for DisplayDiagnostics<'_> {
+    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+        match self.config.format {
+            DiagnosticFormat::Concise
+            | DiagnosticFormat::Azure
+            | DiagnosticFormat::Full
+            | DiagnosticFormat::JsonLines => {
+                for diag in self.diagnostics {
+                    write!(f, "{}", diag.display(self.resolver, self.config))?;
+                }
+            }
+            DiagnosticFormat::Json => write!(
+                f,
+                "{:#}",
+                diagnostics_to_json_value(self.diagnostics, self.resolver)
+            )?,
+        }
+
+        Ok(())
+    }
+}
+
 /// A sequence of resolved diagnostics.
 ///
 /// Resolving a diagnostic refers to the process of restructuring its internal

crates/ruff_linter/src/message/json_lines.rs

@@ -14,7 +14,7 @@ impl Emitter for JsonLinesEmitter {
         diagnostics: &[Diagnostic],
         context: &EmitterContext,
     ) -> anyhow::Result<()> {
-        let config = DisplayDiagnosticConfig::default().format(DiagnosticFormat::Json);
+        let config = DisplayDiagnosticConfig::default().format(DiagnosticFormat::JsonLines);
         for diagnostic in diagnostics {
             write!(writer, "{}", diagnostic.display(context, &config))?;
         }

ty.schema.json

@@ -83,11 +83,18 @@
           ]
         },
         {
-          "description": "Print diagnostics in JSON format.",
+          "description": "Print diagnostics in JSON format.\n\nUnlike `json-lines`, this prints all of the diagnostics as a JSON array.",
           "type": "string",
           "enum": [
             "json"
           ]
+        },
+        {
+          "description": "Print diagnostics in JSON format, one per line.\n\nThis will print each diagnostic as a separate JSON object on its own line. See the `json` format for an array of all diagnostics.",
+          "type": "string",
+          "enum": [
+            "json-lines"
+          ]
         }
       ]
     },