Use structs for JSON serialization (#19270)

## Summary

See https://github.com/astral-sh/ruff/pull/19133#discussion_r2198413586
for recent discussion. This PR moves to using structs for the types in
our JSON output format instead of the `json!` macro.

I didn't rename any of the `message` references because that should be
handled when rebasing #19133 onto this.

My plan for handling the `preview` behavior with the new diagnostics is
to use a wrapper enum. Something like:

```rust
#[derive(Serialize)]
#[serde(untagged)]
pub(crate) enum JsonDiagnostic<'a> {
    Old(OldJsonDiagnostic<'a>),
}

#[derive(Serialize)]
pub(crate) struct OldJsonDiagnostic<'a> {
    // ...
}
```

Initially I thought I could use a `&dyn Serialize` for the affected
fields, but I see that `Serialize` isn't dyn-compatible in testing this
now.

## Test Plan

Existing tests. One quirk of the new types is that their fields are in
alphabetical order. I guess `json!` sorts the fields alphabetically? The
tests were failing before I sorted the struct fields.

## Other formats

It looks like the `rdjson`, `sarif`, and `gitlab` formats also use
`json!`, so if we decide to merge this, I can do something similar for
those before moving them to the new diagnostic format.

crates/ruff_db/src/diagnostic/mod.rs

@@ -432,8 +432,9 @@ impl Diagnostic {
     /// Returns the [`SourceFile`] which the message belongs to.
     ///
     /// Panics if the diagnostic has no primary span, or if its file is not a `SourceFile`.
-    pub fn expect_ruff_source_file(&self) -> SourceFile {
-        self.expect_primary_span().expect_ruff_file().clone()
+    pub fn expect_ruff_source_file(&self) -> &SourceFile {
+        self.ruff_source_file()
+            .expect("Expected a ruff source file")
     }
 
     /// Returns the [`TextRange`] for the diagnostic.

crates/ruff_linter/src/message/diff.rs

@@ -21,7 +21,7 @@ use crate::{Applicability, Fix};
 /// * Compute the diff from the [`Edit`] because diff calculation is expensive.
 pub(super) struct Diff<'a> {
     fix: &'a Fix,
-    source_code: SourceFile,
+    source_code: &'a SourceFile,
 }
 
 impl<'a> Diff<'a> {

crates/ruff_linter/src/message/json.rs

@@ -1,10 +1,10 @@
 use std::io::Write;
 
+use ruff_diagnostics::Applicability;
 use serde::ser::SerializeSeq;
 use serde::{Serialize, Serializer};
-use serde_json::{Value, json};
 
-use ruff_db::diagnostic::Diagnostic;
+use ruff_db::diagnostic::{Diagnostic, SecondaryCode};
 use ruff_notebook::NotebookIndex;
 use ruff_source_file::{LineColumn, OneIndexed, SourceCode};
 use ruff_text_size::Ranged;
@@ -55,20 +55,15 @@ impl Serialize for ExpandedMessages<'_> {
     }
 }
 
-pub(crate) fn message_to_json_value(message: &Diagnostic, context: &EmitterContext) -> Value {
+pub(crate) fn message_to_json_value<'a>(
+    message: &'a Diagnostic,
+    context: &'a EmitterContext<'a>,
+) -> JsonDiagnostic<'a> {
     let source_file = message.expect_ruff_source_file();
     let source_code = source_file.to_source_code();
     let filename = message.expect_ruff_filename();
     let notebook_index = context.notebook_index(&filename);
 
-    let fix = message.fix().map(|fix| {
-        json!({
-            "applicability": fix.applicability(),
-            "message": message.suggestion(),
-            "edits": &ExpandedEdits { edits: fix.edits(), source_code: &source_code, notebook_index },
-        })
-    });
-
     let mut start_location = source_code.line_column(message.expect_range().start());
     let mut end_location = source_code.line_column(message.expect_range().end());
     let mut noqa_location = message
@@ -88,29 +83,32 @@ pub(crate) fn message_to_json_value(message: &Diagnostic, context: &EmitterConte
             noqa_location.map(|location| notebook_index.translate_line_column(&location));
     }
 
-    json!({
-        "code": message.secondary_code(),
-        "url": message.to_url(),
-        "message": message.body(),
-        "fix": fix,
-        "cell": notebook_cell_index,
-        "location": location_to_json(start_location),
-        "end_location": location_to_json(end_location),
-        "filename": filename,
-        "noqa_row": noqa_location.map(|location| location.line)
-    })
-}
+    let fix = message.fix().map(|fix| JsonFix {
+        applicability: fix.applicability(),
+        message: message.suggestion(),
+        edits: ExpandedEdits {
+            edits: fix.edits(),
+            source_code,
+            notebook_index,
+        },
+    });
 
-fn location_to_json(location: LineColumn) -> serde_json::Value {
-    json!({
-        "row": location.line,
-        "column": location.column
-    })
+    JsonDiagnostic {
+        code: message.secondary_code(),
+        url: message.to_url(),
+        message: message.body(),
+        fix,
+        cell: notebook_cell_index,
+        location: start_location.into(),
+        end_location: end_location.into(),
+        filename,
+        noqa_row: noqa_location.map(|location| location.line),
+    }
 }
 
 struct ExpandedEdits<'a> {
     edits: &'a [Edit],
-    source_code: &'a SourceCode<'a, 'a>,
+    source_code: SourceCode<'a, 'a>,
     notebook_index: Option<&'a NotebookIndex>,
 }
 
@@ -169,11 +167,11 @@ impl Serialize for ExpandedEdits<'_> {
                 location = notebook_index.translate_line_column(&location);
             }
 
-            let value = json!({
-                "content": edit.content().unwrap_or_default(),
-                "location": location_to_json(location),
-                "end_location": location_to_json(end_location)
-            });
+            let value = JsonEdit {
+                content: edit.content().unwrap_or_default(),
+                location: location.into(),
+                end_location: end_location.into(),
+            };
 
             s.serialize_element(&value)?;
         }
@@ -182,6 +180,48 @@ impl Serialize for ExpandedEdits<'_> {
     }
 }
 
+#[derive(Serialize)]
+pub(crate) struct JsonDiagnostic<'a> {
+    cell: Option<OneIndexed>,
+    code: Option<&'a SecondaryCode>,
+    end_location: JsonLocation,
+    filename: String,
+    fix: Option<JsonFix<'a>>,
+    location: JsonLocation,
+    message: &'a str,
+    noqa_row: Option<OneIndexed>,
+    url: Option<String>,
+}
+
+#[derive(Serialize)]
+struct JsonFix<'a> {
+    applicability: Applicability,
+    edits: ExpandedEdits<'a>,
+    message: Option<&'a str>,
+}
+
+#[derive(Serialize)]
+struct JsonLocation {
+    column: OneIndexed,
+    row: OneIndexed,
+}
+
+impl From<LineColumn> for JsonLocation {
+    fn from(location: LineColumn) -> Self {
+        JsonLocation {
+            row: location.line,
+            column: location.column,
+        }
+    }
+}
+
+#[derive(Serialize)]
+struct JsonEdit<'a> {
+    content: &'a str,
+    end_location: JsonLocation,
+    location: JsonLocation,
+}
+
 #[cfg(test)]
 mod tests {
     use insta::assert_snapshot;