diff --git a/Cargo.lock b/Cargo.lock
index d325171eec..bbe15c5493 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -2814,6 +2814,7 @@ dependencies = [
  "regex",
  "ruff_annotate_snippets",
  "ruff_cache",
+ "ruff_db",
  "ruff_diagnostics",
  "ruff_macros",
  "ruff_notebook",
diff --git a/crates/ruff/src/cache.rs b/crates/ruff/src/cache.rs
index e30c461a12..127f6292b2 100644
--- a/crates/ruff/src/cache.rs
+++ b/crates/ruff/src/cache.rs
@@ -439,7 +439,7 @@ impl LintCacheData {
             .map(|msg| {
                 // Make sure that all message use the same source file.
                 assert_eq!(
-                    &msg.file,
+                    msg.file,
                     messages.first().unwrap().source_file(),
                     "message uses a different source file"
                 );
diff --git a/crates/ruff/src/diagnostics.rs b/crates/ruff/src/diagnostics.rs
index fc462de30f..4610eca5c4 100644
--- a/crates/ruff/src/diagnostics.rs
+++ b/crates/ruff/src/diagnostics.rs
@@ -15,7 +15,7 @@ use rustc_hash::FxHashMap;
 use ruff_diagnostics::Diagnostic;
 use ruff_linter::codes::Rule;
 use ruff_linter::linter::{lint_fix, lint_only, FixTable, FixerResult, LinterResult, ParseSource};
-use ruff_linter::message::{Message, SyntaxErrorMessage};
+use ruff_linter::message::Message;
 use ruff_linter::package::PackageRoot;
 use ruff_linter::pyproject_toml::lint_pyproject_toml;
 use ruff_linter::settings::types::UnsafeFixes;
@@ -102,11 +102,7 @@ impl Diagnostics {
                 let name = path.map_or_else(|| "-".into(), Path::to_string_lossy);
                 let dummy = SourceFileBuilder::new(name, "").finish();
                 Self::new(
-                    vec![Message::SyntaxError(SyntaxErrorMessage {
-                        message: err.to_string(),
-                        range: TextRange::default(),
-                        file: dummy,
-                    })],
+                    vec![Message::syntax_error(err, TextRange::default(), dummy)],
                     FxHashMap::default(),
                 )
             }
diff --git a/crates/ruff_benchmark/benches/ty.rs b/crates/ruff_benchmark/benches/ty.rs
index 028a3e8563..83c58e5e82 100644
--- a/crates/ruff_benchmark/benches/ty.rs
+++ b/crates/ruff_benchmark/benches/ty.rs
@@ -197,7 +197,7 @@ fn assert_diagnostics(db: &dyn Db, diagnostics: &[Diagnostic], expected: &[KeyDi
                 diagnostic.id(),
                 diagnostic
                     .primary_span()
-                    .map(|span| span.file())
+                    .map(|span| span.expect_ty_file())
                     .map(|file| file.path(db).as_str()),
                 diagnostic
                     .primary_span()
diff --git a/crates/ruff_db/src/diagnostic/mod.rs b/crates/ruff_db/src/diagnostic/mod.rs
index b3b82486b3..2f61c8a15d 100644
--- a/crates/ruff_db/src/diagnostic/mod.rs
+++ b/crates/ruff_db/src/diagnostic/mod.rs
@@ -1,15 +1,15 @@
 use std::{fmt::Formatter, sync::Arc};
 
+use render::{FileResolver, Input};
+use ruff_source_file::{SourceCode, SourceFile};
 use thiserror::Error;
 
 use ruff_annotate_snippets::Level as AnnotateLevel;
 use ruff_text_size::{Ranged, TextRange};
 
 pub use self::render::DisplayDiagnostic;
-use crate::files::File;
-use crate::Db;
+use crate::{files::File, Db};
 
-use self::render::FileResolver;
 mod render;
 mod stylesheet;
 
@@ -115,10 +115,9 @@ impl Diagnostic {
     /// callers should prefer using this with `write!` instead of `writeln!`.
     pub fn display<'a>(
         &'a self,
-        db: &'a dyn Db,
+        resolver: &'a dyn FileResolver,
         config: &'a DisplayDiagnosticConfig,
     ) -> DisplayDiagnostic<'a> {
-        let resolver = FileResolver::new(db);
         DisplayDiagnostic::new(resolver, config, self)
     }
 
@@ -233,6 +232,16 @@ impl Diagnostic {
         self.primary_annotation().map(|ann| ann.tags.as_slice())
     }
 
+    /// Returns the "primary" span of this diagnostic, panicking if it does not exist.
+    ///
+    /// This should typically only be used when working with diagnostics in Ruff, where diagnostics
+    /// are currently required to have a primary span.
+    ///
+    /// See [`Diagnostic::primary_span`] for more details.
+    pub fn expect_primary_span(&self) -> Span {
+        self.primary_span().expect("Expected a primary span")
+    }
+
     /// Returns a key that can be used to sort two diagnostics into the canonical order
     /// in which they should appear when rendered.
     pub fn rendering_sort_key<'a>(&'a self, db: &'a dyn Db) -> impl Ord + 'a {
@@ -267,11 +276,7 @@ impl Ord for RenderingSortKey<'_> {
             self.diagnostic.primary_span(),
             other.diagnostic.primary_span(),
         ) {
-            let order = span1
-                .file()
-                .path(self.db)
-                .as_str()
-                .cmp(span2.file().path(self.db).as_str());
+            let order = span1.file().path(&self.db).cmp(span2.file().path(&self.db));
             if order.is_ne() {
                 return order;
             }
@@ -643,6 +648,10 @@ impl DiagnosticId {
             DiagnosticId::UnknownRule => "unknown-rule",
         })
     }
+
+    pub fn is_invalid_syntax(&self) -> bool {
+        matches!(self, Self::InvalidSyntax)
+    }
 }
 
 #[derive(Copy, Clone, Debug, Eq, PartialEq, Error)]
@@ -668,6 +677,62 @@ impl std::fmt::Display for DiagnosticId {
     }
 }
 
+/// A unified file representation for both ruff and ty.
+///
+/// Such a representation is needed for rendering [`Diagnostic`]s that can optionally contain
+/// [`Annotation`]s with [`Span`]s that need to refer to the text of a file. However, ty and ruff
+/// use very different file types: a `Copy`-able salsa-interned [`File`], and a heavier-weight
+/// [`SourceFile`], respectively.
+///
+/// This enum presents a unified interface to these two types for the sake of creating [`Span`]s and
+/// emitting diagnostics from both ty and ruff.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum UnifiedFile {
+    Ty(File),
+    Ruff(SourceFile),
+}
+
+impl UnifiedFile {
+    pub fn path<'a>(&'a self, resolver: &'a dyn FileResolver) -> &'a str {
+        match self {
+            UnifiedFile::Ty(file) => resolver.path(*file),
+            UnifiedFile::Ruff(file) => file.name(),
+        }
+    }
+
+    fn diagnostic_source(&self, resolver: &dyn FileResolver) -> DiagnosticSource {
+        match self {
+            UnifiedFile::Ty(file) => DiagnosticSource::Ty(resolver.input(*file)),
+            UnifiedFile::Ruff(file) => DiagnosticSource::Ruff(file.clone()),
+        }
+    }
+}
+
+/// A unified wrapper for types that can be converted to a [`SourceCode`].
+///
+/// As with [`UnifiedFile`], ruff and ty use slightly different representations for source code.
+/// [`DiagnosticSource`] wraps both of these and provides the single
+/// [`DiagnosticSource::as_source_code`] method to produce a [`SourceCode`] with the appropriate
+/// lifetimes.
+///
+/// See [`UnifiedFile::diagnostic_source`] for a way to obtain a [`DiagnosticSource`] from a file
+/// and [`FileResolver`].
+#[derive(Clone, Debug)]
+enum DiagnosticSource {
+    Ty(Input),
+    Ruff(SourceFile),
+}
+
+impl DiagnosticSource {
+    /// Returns this input as a `SourceCode` for convenient querying.
+    fn as_source_code(&self) -> SourceCode {
+        match self {
+            DiagnosticSource::Ty(input) => SourceCode::new(input.text.as_str(), &input.line_index),
+            DiagnosticSource::Ruff(source) => SourceCode::new(source.source_text(), source.index()),
+        }
+    }
+}
+
 /// A span represents the source of a diagnostic.
 ///
 /// It consists of a `File` and an optional range into that file. When the
@@ -675,14 +740,14 @@ impl std::fmt::Display for DiagnosticId {
 /// the entire file. For example, when the file should be executable but isn't.
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct Span {
-    file: File,
+    file: UnifiedFile,
     range: Option<TextRange>,
 }
 
 impl Span {
-    /// Returns the `File` attached to this `Span`.
-    pub fn file(&self) -> File {
-        self.file
+    /// Returns the `UnifiedFile` attached to this `Span`.
+    pub fn file(&self) -> &UnifiedFile {
+        &self.file
     }
 
     /// Returns the range, if available, attached to this `Span`.
@@ -703,10 +768,38 @@ impl Span {
     pub fn with_optional_range(self, range: Option<TextRange>) -> Span {
         Span { range, ..self }
     }
+
+    /// Returns the [`File`] attached to this [`Span`].
+    ///
+    /// Panics if the file is a [`UnifiedFile::Ruff`] instead of a [`UnifiedFile::Ty`].
+    pub fn expect_ty_file(&self) -> File {
+        match self.file {
+            UnifiedFile::Ty(file) => file,
+            UnifiedFile::Ruff(_) => panic!("Expected a ty `File`, found a ruff `SourceFile`"),
+        }
+    }
+
+    /// Returns the [`SourceFile`] attached to this [`Span`].
+    ///
+    /// Panics if the file is a [`UnifiedFile::Ty`] instead of a [`UnifiedFile::Ruff`].
+    pub fn expect_ruff_file(&self) -> &SourceFile {
+        match &self.file {
+            UnifiedFile::Ty(_) => panic!("Expected a ruff `SourceFile`, found a ty `File`"),
+            UnifiedFile::Ruff(file) => file,
+        }
+    }
 }
 
 impl From<File> for Span {
     fn from(file: File) -> Span {
+        let file = UnifiedFile::Ty(file);
+        Span { file, range: None }
+    }
+}
+
+impl From<SourceFile> for Span {
+    fn from(file: SourceFile) -> Self {
+        let file = UnifiedFile::Ruff(file);
         Span { file, range: None }
     }
 }
diff --git a/crates/ruff_db/src/diagnostic/render.rs b/crates/ruff_db/src/diagnostic/render.rs
index 1676347f33..c02565c684 100644
--- a/crates/ruff_db/src/diagnostic/render.rs
+++ b/crates/ruff_db/src/diagnostic/render.rs
@@ -16,7 +16,8 @@ use crate::{
 };
 
 use super::{
-    Annotation, Diagnostic, DiagnosticFormat, DisplayDiagnosticConfig, Severity, SubDiagnostic,
+    Annotation, Diagnostic, DiagnosticFormat, DiagnosticSource, DisplayDiagnosticConfig, Severity,
+    SubDiagnostic,
 };
 
 /// A type that implements `std::fmt::Display` for diagnostic rendering.
@@ -30,17 +31,16 @@ use super::{
 ///   values. When using Salsa, this most commonly corresponds to the lifetime
 ///   of a Salsa `Db`.
 /// * The lifetime of the diagnostic being rendered.
-#[derive(Debug)]
 pub struct DisplayDiagnostic<'a> {
     config: &'a DisplayDiagnosticConfig,
-    resolver: FileResolver<'a>,
+    resolver: &'a dyn FileResolver,
     annotate_renderer: AnnotateRenderer,
     diag: &'a Diagnostic,
 }
 
 impl<'a> DisplayDiagnostic<'a> {
     pub(crate) fn new(
-        resolver: FileResolver<'a>,
+        resolver: &'a dyn FileResolver,
         config: &'a DisplayDiagnosticConfig,
         diag: &'a Diagnostic,
     ) -> DisplayDiagnostic<'a> {
@@ -86,11 +86,13 @@ impl std::fmt::Display for DisplayDiagnostic<'_> {
                 write!(
                     f,
                     " {path}",
-                    path = fmt_styled(self.resolver.path(span.file()), stylesheet.emphasis)
+                    path = fmt_styled(span.file().path(self.resolver), stylesheet.emphasis)
                 )?;
                 if let Some(range) = span.range() {
-                    let input = self.resolver.input(span.file());
-                    let start = input.as_source_code().line_column(range.start());
+                    let diagnostic_source = span.file().diagnostic_source(self.resolver);
+                    let start = diagnostic_source
+                        .as_source_code()
+                        .line_column(range.start());
 
                     write!(
                         f,
@@ -115,7 +117,7 @@ impl std::fmt::Display for DisplayDiagnostic<'_> {
             .emphasis(stylesheet.emphasis)
             .none(stylesheet.none);
 
-        let resolved = Resolved::new(&self.resolver, self.diag);
+        let resolved = Resolved::new(self.resolver, self.diag);
         let renderable = resolved.to_renderable(self.config.context);
         for diag in renderable.diagnostics.iter() {
             writeln!(f, "{}", renderer.render(diag.to_annotate()))?;
@@ -144,7 +146,7 @@ struct Resolved<'a> {
 
 impl<'a> Resolved<'a> {
     /// Creates a new resolved set of diagnostics.
-    fn new(resolver: &FileResolver<'a>, diag: &'a Diagnostic) -> Resolved<'a> {
+    fn new(resolver: &'a dyn FileResolver, diag: &'a Diagnostic) -> Resolved<'a> {
         let mut diagnostics = vec![];
         diagnostics.push(ResolvedDiagnostic::from_diagnostic(resolver, diag));
         for sub in &diag.inner.subs {
@@ -182,7 +184,7 @@ struct ResolvedDiagnostic<'a> {
 impl<'a> ResolvedDiagnostic<'a> {
     /// Resolve a single diagnostic.
     fn from_diagnostic(
-        resolver: &FileResolver<'a>,
+        resolver: &'a dyn FileResolver,
         diag: &'a Diagnostic,
     ) -> ResolvedDiagnostic<'a> {
         let annotations: Vec<_> = diag
@@ -190,9 +192,9 @@ impl<'a> ResolvedDiagnostic<'a> {
             .annotations
             .iter()
             .filter_map(|ann| {
-                let path = resolver.path(ann.span.file);
-                let input = resolver.input(ann.span.file);
-                ResolvedAnnotation::new(path, &input, ann)
+                let path = ann.span.file.path(resolver);
+                let diagnostic_source = ann.span.file.diagnostic_source(resolver);
+                ResolvedAnnotation::new(path, &diagnostic_source, ann)
             })
             .collect();
         let message = if diag.inner.message.as_str().is_empty() {
@@ -216,7 +218,7 @@ impl<'a> ResolvedDiagnostic<'a> {
 
     /// Resolve a single sub-diagnostic.
     fn from_sub_diagnostic(
-        resolver: &FileResolver<'a>,
+        resolver: &'a dyn FileResolver,
         diag: &'a SubDiagnostic,
     ) -> ResolvedDiagnostic<'a> {
         let annotations: Vec<_> = diag
@@ -224,9 +226,9 @@ impl<'a> ResolvedDiagnostic<'a> {
             .annotations
             .iter()
             .filter_map(|ann| {
-                let path = resolver.path(ann.span.file);
-                let input = resolver.input(ann.span.file);
-                ResolvedAnnotation::new(path, &input, ann)
+                let path = ann.span.file.path(resolver);
+                let diagnostic_source = ann.span.file.diagnostic_source(resolver);
+                ResolvedAnnotation::new(path, &diagnostic_source, ann)
             })
             .collect();
         ResolvedDiagnostic {
@@ -259,10 +261,18 @@ impl<'a> ResolvedDiagnostic<'a> {
                     continue;
                 };
 
-                let prev_context_ends =
-                    context_after(&prev.input.as_source_code(), context, prev.line_end).get();
-                let this_context_begins =
-                    context_before(&ann.input.as_source_code(), context, ann.line_start).get();
+                let prev_context_ends = context_after(
+                    &prev.diagnostic_source.as_source_code(),
+                    context,
+                    prev.line_end,
+                )
+                .get();
+                let this_context_begins = context_before(
+                    &ann.diagnostic_source.as_source_code(),
+                    context,
+                    ann.line_start,
+                )
+                .get();
                 // The boundary case here is when `prev_context_ends`
                 // is exactly one less than `this_context_begins`. In
                 // that case, the context windows are adajcent and we
@@ -304,7 +314,7 @@ impl<'a> ResolvedDiagnostic<'a> {
 #[derive(Debug)]
 struct ResolvedAnnotation<'a> {
     path: &'a str,
-    input: Input,
+    diagnostic_source: DiagnosticSource,
     range: TextRange,
     line_start: OneIndexed,
     line_end: OneIndexed,
@@ -318,8 +328,12 @@ impl<'a> ResolvedAnnotation<'a> {
     /// `path` is the path of the file that this annotation points to.
     ///
     /// `input` is the contents of the file that this annotation points to.
-    fn new(path: &'a str, input: &Input, ann: &'a Annotation) -> Option<ResolvedAnnotation<'a>> {
-        let source = input.as_source_code();
+    fn new(
+        path: &'a str,
+        diagnostic_source: &DiagnosticSource,
+        ann: &'a Annotation,
+    ) -> Option<ResolvedAnnotation<'a>> {
+        let source = diagnostic_source.as_source_code();
         let (range, line_start, line_end) = match (ann.span.range(), ann.message.is_some()) {
             // An annotation with no range AND no message is probably(?)
             // meaningless, but we should try to render it anyway.
@@ -345,7 +359,7 @@ impl<'a> ResolvedAnnotation<'a> {
         };
         Some(ResolvedAnnotation {
             path,
-            input: input.clone(),
+            diagnostic_source: diagnostic_source.clone(),
             range,
             line_start,
             line_end,
@@ -510,8 +524,8 @@ impl<'r> RenderableSnippet<'r> {
             !anns.is_empty(),
             "creating a renderable snippet requires a non-zero number of annotations",
         );
-        let input = &anns[0].input;
-        let source = input.as_source_code();
+        let diagnostic_source = &anns[0].diagnostic_source;
+        let source = diagnostic_source.as_source_code();
         let has_primary = anns.iter().any(|ann| ann.is_primary);
 
         let line_start = context_before(
@@ -527,7 +541,7 @@ impl<'r> RenderableSnippet<'r> {
 
         let snippet_start = source.line_start(line_start);
         let snippet_end = source.line_end(line_end);
-        let snippet = input
+        let snippet = diagnostic_source
             .as_source_code()
             .slice(TextRange::new(snippet_start, snippet_end));
 
@@ -613,7 +627,7 @@ impl<'r> RenderableAnnotation<'r> {
     }
 }
 
-/// A type that facilitates the retrieval of source code from a `Span`.
+/// A trait that facilitates the retrieval of source code from a `Span`.
 ///
 /// At present, this is tightly coupled with a Salsa database. In the future,
 /// it is intended for this resolver to become an abstraction providing a
@@ -628,36 +642,24 @@ impl<'r> RenderableAnnotation<'r> {
 /// callers will need to pass in a different "resolver" for turning `Span`s
 /// into actual file paths/contents. The infrastructure for this isn't fully in
 /// place, but this type serves to demarcate the intended abstraction boundary.
-pub(crate) struct FileResolver<'a> {
-    db: &'a dyn Db,
-}
-
-impl<'a> FileResolver<'a> {
-    /// Creates a new resolver from a Salsa database.
-    pub(crate) fn new(db: &'a dyn Db) -> FileResolver<'a> {
-        FileResolver { db }
-    }
-
+pub trait FileResolver {
     /// Returns the path associated with the file given.
-    fn path(&self, file: File) -> &'a str {
-        relativize_path(
-            self.db.system().current_directory(),
-            file.path(self.db).as_str(),
-        )
-    }
+    fn path(&self, file: File) -> &str;
 
     /// Returns the input contents associated with the file given.
-    fn input(&self, file: File) -> Input {
-        Input {
-            text: source_text(self.db, file),
-            line_index: line_index(self.db, file),
-        }
-    }
+    fn input(&self, file: File) -> Input;
 }
 
-impl std::fmt::Debug for FileResolver<'_> {
-    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
-        write!(f, "<salsa based file resolver>")
+impl FileResolver for &dyn Db {
+    fn path(&self, file: File) -> &str {
+        relativize_path(self.system().current_directory(), file.path(*self).as_str())
+    }
+
+    fn input(&self, file: File) -> Input {
+        Input {
+            text: source_text(*self, file),
+            line_index: line_index(*self, file),
+        }
     }
 }
 
@@ -667,16 +669,9 @@ impl std::fmt::Debug for FileResolver<'_> {
 /// This contains the actual content of that input as well as a
 /// line index for efficiently querying its contents.
 #[derive(Clone, Debug)]
-struct Input {
-    text: SourceText,
-    line_index: LineIndex,
-}
-
-impl Input {
-    /// Returns this input as a `SourceCode` for convenient querying.
-    fn as_source_code(&self) -> SourceCode<'_, '_> {
-        SourceCode::new(self.text.as_str(), &self.line_index)
-    }
+pub struct Input {
+    pub(crate) text: SourceText,
+    pub(crate) line_index: LineIndex,
 }
 
 /// Returns the line number accounting for the given `len`
@@ -730,6 +725,7 @@ mod tests {
     use crate::files::system_path_to_file;
     use crate::system::{DbWithWritableSystem, SystemPath};
     use crate::tests::TestDb;
+    use crate::Upcast;
 
     use super::*;
 
@@ -2174,8 +2170,9 @@ watermelon
         fn span(&self, path: &str, line_offset_start: &str, line_offset_end: &str) -> Span {
             let span = self.path(path);
 
-            let text = source_text(&self.db, span.file());
-            let line_index = line_index(&self.db, span.file());
+            let file = span.expect_ty_file();
+            let text = source_text(&self.db, file);
+            let line_index = line_index(&self.db, file);
             let source = SourceCode::new(text.as_str(), &line_index);
 
             let (line_start, offset_start) = parse_line_offset(line_offset_start);
@@ -2237,7 +2234,7 @@ watermelon
         ///
         /// (This will set the "printed" flag on `Diagnostic`.)
         fn render(&self, diag: &Diagnostic) -> String {
-            diag.display(&self.db, &self.config).to_string()
+            diag.display(&self.db.upcast(), &self.config).to_string()
         }
     }
 
diff --git a/crates/ruff_db/src/lib.rs b/crates/ruff_db/src/lib.rs
index cdb3071553..c970a99d12 100644
--- a/crates/ruff_db/src/lib.rs
+++ b/crates/ruff_db/src/lib.rs
@@ -67,7 +67,7 @@ mod tests {
     use crate::system::TestSystem;
     use crate::system::{DbWithTestSystem, System};
     use crate::vendored::VendoredFileSystem;
-    use crate::Db;
+    use crate::{Db, Upcast};
 
     type Events = Arc<Mutex<Vec<salsa::Event>>>;
 
@@ -140,6 +140,15 @@ mod tests {
         }
     }
 
+    impl Upcast<dyn Db> for TestDb {
+        fn upcast(&self) -> &(dyn Db + 'static) {
+            self
+        }
+        fn upcast_mut(&mut self) -> &mut (dyn Db + 'static) {
+            self
+        }
+    }
+
     impl DbWithTestSystem for TestDb {
         fn test_system(&self) -> &TestSystem {
             &self.system
diff --git a/crates/ruff_linter/Cargo.toml b/crates/ruff_linter/Cargo.toml
index 2e48fbde19..0c204714a4 100644
--- a/crates/ruff_linter/Cargo.toml
+++ b/crates/ruff_linter/Cargo.toml
@@ -15,6 +15,7 @@ license = { workspace = true }
 [dependencies]
 ruff_annotate_snippets = { workspace = true }
 ruff_cache = { workspace = true }
+ruff_db = { workspace = true }
 ruff_diagnostics = { workspace = true, features = ["serde"] }
 ruff_notebook = { workspace = true }
 ruff_macros = { workspace = true }
diff --git a/crates/ruff_linter/src/message/azure.rs b/crates/ruff_linter/src/message/azure.rs
index 727a427f9b..bb20d710f4 100644
--- a/crates/ruff_linter/src/message/azure.rs
+++ b/crates/ruff_linter/src/message/azure.rs
@@ -17,7 +17,7 @@ impl Emitter for AzureEmitter {
         context: &EmitterContext,
     ) -> anyhow::Result<()> {
         for message in messages {
-            let location = if context.is_notebook(message.filename()) {
+            let location = if context.is_notebook(&message.filename()) {
                 // We can't give a reasonable location for the structured formats,
                 // so we show one that's clearly a fallback
                 LineColumn::default()
diff --git a/crates/ruff_linter/src/message/diff.rs b/crates/ruff_linter/src/message/diff.rs
index 0e56578e17..c0358d0b08 100644
--- a/crates/ruff_linter/src/message/diff.rs
+++ b/crates/ruff_linter/src/message/diff.rs
@@ -22,7 +22,7 @@ use crate::text_helpers::ShowNonprinting;
 /// * Compute the diff from the [`Edit`] because diff calculation is expensive.
 pub(super) struct Diff<'a> {
     fix: &'a Fix,
-    source_code: &'a SourceFile,
+    source_code: SourceFile,
 }
 
 impl<'a> Diff<'a> {
diff --git a/crates/ruff_linter/src/message/github.rs b/crates/ruff_linter/src/message/github.rs
index a038b17704..acff9e4c68 100644
--- a/crates/ruff_linter/src/message/github.rs
+++ b/crates/ruff_linter/src/message/github.rs
@@ -19,7 +19,7 @@ impl Emitter for GithubEmitter {
     ) -> anyhow::Result<()> {
         for message in messages {
             let source_location = message.compute_start_location();
-            let location = if context.is_notebook(message.filename()) {
+            let location = if context.is_notebook(&message.filename()) {
                 // We can't give a reasonable location for the structured formats,
                 // so we show one that's clearly a fallback
                 LineColumn::default()
@@ -43,7 +43,7 @@ impl Emitter for GithubEmitter {
             write!(
                 writer,
                 "{path}:{row}:{column}:",
-                path = relativize_path(message.filename()),
+                path = relativize_path(&*message.filename()),
                 row = location.line,
                 column = location.column,
             )?;
diff --git a/crates/ruff_linter/src/message/gitlab.rs b/crates/ruff_linter/src/message/gitlab.rs
index 6d03a7c803..0ea0af43cf 100644
--- a/crates/ruff_linter/src/message/gitlab.rs
+++ b/crates/ruff_linter/src/message/gitlab.rs
@@ -62,7 +62,7 @@ impl Serialize for SerializedMessages<'_> {
             let start_location = message.compute_start_location();
             let end_location = message.compute_end_location();
 
-            let lines = if self.context.is_notebook(message.filename()) {
+            let lines = if self.context.is_notebook(&message.filename()) {
                 // We can't give a reasonable location for the structured formats,
                 // so we show one that's clearly a fallback
                 json!({
@@ -77,8 +77,8 @@ impl Serialize for SerializedMessages<'_> {
             };
 
             let path = self.project_dir.as_ref().map_or_else(
-                || relativize_path(message.filename()),
-                |project_dir| relativize_path_to(message.filename(), project_dir),
+                || relativize_path(&*message.filename()),
+                |project_dir| relativize_path_to(&*message.filename(), project_dir),
             );
 
             let mut message_fingerprint = fingerprint(message, &path, 0);
diff --git a/crates/ruff_linter/src/message/grouped.rs b/crates/ruff_linter/src/message/grouped.rs
index b60830c961..c21198f89c 100644
--- a/crates/ruff_linter/src/message/grouped.rs
+++ b/crates/ruff_linter/src/message/grouped.rs
@@ -65,7 +65,7 @@ impl Emitter for GroupedEmitter {
             let column_length = calculate_print_width(max_column_length);
 
             // Print the filename.
-            writeln!(writer, "{}:", relativize_path(filename).underline())?;
+            writeln!(writer, "{}:", relativize_path(&*filename).underline())?;
 
             // Print each message.
             for message in messages {
@@ -73,7 +73,7 @@ impl Emitter for GroupedEmitter {
                     writer,
                     "{}",
                     DisplayGroupedMessage {
-                        notebook_index: context.notebook_index(message.filename()),
+                        notebook_index: context.notebook_index(&message.filename()),
                         message,
                         show_fix_status: self.show_fix_status,
                         unsafe_fixes: self.unsafe_fixes,
diff --git a/crates/ruff_linter/src/message/json.rs b/crates/ruff_linter/src/message/json.rs
index b8d91c7db3..21b1d6d6ad 100644
--- a/crates/ruff_linter/src/message/json.rs
+++ b/crates/ruff_linter/src/message/json.rs
@@ -49,8 +49,9 @@ impl Serialize for ExpandedMessages<'_> {
 }
 
 pub(crate) fn message_to_json_value(message: &Message, context: &EmitterContext) -> Value {
-    let source_code = message.source_file().to_source_code();
-    let notebook_index = context.notebook_index(message.filename());
+    let source_file = message.source_file();
+    let source_code = source_file.to_source_code();
+    let notebook_index = context.notebook_index(&message.filename());
 
     let fix = message.fix().map(|fix| {
         json!({
diff --git a/crates/ruff_linter/src/message/junit.rs b/crates/ruff_linter/src/message/junit.rs
index 38edfdfca8..44f1fbe7c1 100644
--- a/crates/ruff_linter/src/message/junit.rs
+++ b/crates/ruff_linter/src/message/junit.rs
@@ -32,7 +32,7 @@ impl Emitter for JunitEmitter {
             report.add_test_suite(test_suite);
         } else {
             for (filename, messages) in group_messages_by_filename(messages) {
-                let mut test_suite = TestSuite::new(filename);
+                let mut test_suite = TestSuite::new(&filename);
                 test_suite
                     .extra
                     .insert(XmlString::new("package"), XmlString::new("org.ruff"));
@@ -44,7 +44,7 @@ impl Emitter for JunitEmitter {
                     } = message;
                     let mut status = TestCaseStatus::non_success(NonSuccessKind::Failure);
                     status.set_message(message.body());
-                    let location = if context.is_notebook(message.filename()) {
+                    let location = if context.is_notebook(&message.filename()) {
                         // We can't give a reasonable location for the structured formats,
                         // so we show one that's clearly a fallback
                         LineColumn::default()
@@ -66,7 +66,7 @@ impl Emitter for JunitEmitter {
                         },
                         status,
                     );
-                    let file_path = Path::new(filename);
+                    let file_path = Path::new(&*filename);
                     let file_stem = file_path.file_stem().unwrap().to_str().unwrap();
                     let classname = file_path.parent().unwrap().join(file_stem);
                     case.set_classname(classname.to_str().unwrap());
diff --git a/crates/ruff_linter/src/message/mod.rs b/crates/ruff_linter/src/message/mod.rs
index a3146ed93d..9ca16bc2be 100644
--- a/crates/ruff_linter/src/message/mod.rs
+++ b/crates/ruff_linter/src/message/mod.rs
@@ -1,8 +1,10 @@
+use std::borrow::Cow;
 use std::cmp::Ordering;
 use std::collections::BTreeMap;
 use std::io::Write;
 use std::ops::Deref;
 
+use ruff_db::diagnostic::{self as db, Annotation, DiagnosticId, Severity, Span};
 use ruff_python_parser::semantic_errors::SemanticSyntaxError;
 use rustc_hash::FxHashMap;
 
@@ -45,7 +47,7 @@ mod text;
 #[derive(Clone, Debug, PartialEq, Eq)]
 pub enum Message {
     Diagnostic(DiagnosticMessage),
-    SyntaxError(SyntaxErrorMessage),
+    SyntaxError(db::Diagnostic),
 }
 
 /// A diagnostic message corresponding to a rule violation.
@@ -59,14 +61,6 @@ pub struct DiagnosticMessage {
     pub noqa_offset: TextSize,
 }
 
-/// A syntax error message raised by the parser.
-#[derive(Clone, Debug, PartialEq, Eq)]
-pub struct SyntaxErrorMessage {
-    pub message: String,
-    pub range: TextRange,
-    pub file: SourceFile,
-}
-
 #[derive(Clone, Copy, Debug, PartialEq, Eq, PartialOrd, Ord)]
 pub enum MessageKind {
     Diagnostic(Rule),
@@ -83,6 +77,17 @@ impl MessageKind {
 }
 
 impl Message {
+    pub fn syntax_error(
+        message: impl std::fmt::Display,
+        range: TextRange,
+        file: SourceFile,
+    ) -> Message {
+        let mut diag = db::Diagnostic::new(DiagnosticId::InvalidSyntax, Severity::Error, "");
+        let span = Span::from(file).with_range(range);
+        diag.annotate(Annotation::primary(span).message(message));
+        Self::SyntaxError(diag)
+    }
+
     /// Create a [`Message`] from the given [`Diagnostic`] corresponding to a rule violation.
     pub fn from_diagnostic(
         diagnostic: Diagnostic,
@@ -114,14 +119,14 @@ impl Message {
             .next()
             .map_or(TextSize::new(0), TextLen::text_len);
 
-        Message::SyntaxError(SyntaxErrorMessage {
-            message: format!(
+        Message::syntax_error(
+            format_args!(
                 "SyntaxError: {}",
                 DisplayParseErrorType::new(&parse_error.error)
             ),
-            range: TextRange::at(parse_error.location.start(), len),
+            TextRange::at(parse_error.location.start(), len),
             file,
-        })
+        )
     }
 
     /// Create a [`Message`] from the given [`UnsupportedSyntaxError`].
@@ -129,11 +134,11 @@ impl Message {
         unsupported_syntax_error: &UnsupportedSyntaxError,
         file: SourceFile,
     ) -> Message {
-        Message::SyntaxError(SyntaxErrorMessage {
-            message: format!("SyntaxError: {unsupported_syntax_error}"),
-            range: unsupported_syntax_error.range,
+        Message::syntax_error(
+            format_args!("SyntaxError: {unsupported_syntax_error}"),
+            unsupported_syntax_error.range,
             file,
-        })
+        )
     }
 
     /// Create a [`Message`] from the given [`SemanticSyntaxError`].
@@ -141,11 +146,11 @@ impl Message {
         semantic_syntax_error: &SemanticSyntaxError,
         file: SourceFile,
     ) -> Message {
-        Message::SyntaxError(SyntaxErrorMessage {
-            message: format!("SyntaxError: {semantic_syntax_error}"),
-            range: semantic_syntax_error.range,
+        Message::syntax_error(
+            format_args!("SyntaxError: {semantic_syntax_error}"),
+            semantic_syntax_error.range,
             file,
-        })
+        )
     }
 
     pub const fn as_diagnostic_message(&self) -> Option<&DiagnosticMessage> {
@@ -168,8 +173,11 @@ impl Message {
     }
 
     /// Returns `true` if `self` is a syntax error message.
-    pub const fn is_syntax_error(&self) -> bool {
-        matches!(self, Message::SyntaxError(_))
+    pub fn is_syntax_error(&self) -> bool {
+        match self {
+            Message::Diagnostic(_) => false,
+            Message::SyntaxError(diag) => diag.id().is_invalid_syntax(),
+        }
     }
 
     /// Returns a message kind.
@@ -192,7 +200,11 @@ impl Message {
     pub fn body(&self) -> &str {
         match self {
             Message::Diagnostic(m) => &m.kind.body,
-            Message::SyntaxError(m) => &m.message,
+            Message::SyntaxError(m) => m
+                .primary_annotation()
+                .expect("Expected a primary annotation for a ruff diagnostic")
+                .get_message()
+                .expect("Expected a message for a ruff diagnostic"),
         }
     }
 
@@ -234,27 +246,47 @@ impl Message {
     }
 
     /// Returns the filename for the message.
-    pub fn filename(&self) -> &str {
-        self.source_file().name()
+    pub fn filename(&self) -> Cow<'_, str> {
+        match self {
+            Message::Diagnostic(m) => Cow::Borrowed(m.file.name()),
+            Message::SyntaxError(diag) => Cow::Owned(
+                diag.expect_primary_span()
+                    .expect_ruff_file()
+                    .name()
+                    .to_string(),
+            ),
+        }
     }
 
     /// Computes the start source location for the message.
     pub fn compute_start_location(&self) -> LineColumn {
-        self.source_file()
-            .to_source_code()
-            .line_column(self.start())
+        match self {
+            Message::Diagnostic(m) => m.file.to_source_code().line_column(m.range.start()),
+            Message::SyntaxError(diag) => diag
+                .expect_primary_span()
+                .expect_ruff_file()
+                .to_source_code()
+                .line_column(self.start()),
+        }
     }
 
     /// Computes the end source location for the message.
     pub fn compute_end_location(&self) -> LineColumn {
-        self.source_file().to_source_code().line_column(self.end())
+        match self {
+            Message::Diagnostic(m) => m.file.to_source_code().line_column(m.range.end()),
+            Message::SyntaxError(diag) => diag
+                .expect_primary_span()
+                .expect_ruff_file()
+                .to_source_code()
+                .line_column(self.end()),
+        }
     }
 
     /// Returns the [`SourceFile`] which the message belongs to.
-    pub fn source_file(&self) -> &SourceFile {
+    pub fn source_file(&self) -> SourceFile {
         match self {
-            Message::Diagnostic(m) => &m.file,
-            Message::SyntaxError(m) => &m.file,
+            Message::Diagnostic(m) => m.file.clone(),
+            Message::SyntaxError(m) => m.expect_primary_span().expect_ruff_file().clone(),
         }
     }
 }
@@ -275,7 +307,10 @@ impl Ranged for Message {
     fn range(&self) -> TextRange {
         match self {
             Message::Diagnostic(m) => m.range,
-            Message::SyntaxError(m) => m.range,
+            Message::SyntaxError(m) => m
+                .expect_primary_span()
+                .range()
+                .expect("Expected range for ruff span"),
         }
     }
 }
@@ -293,11 +328,11 @@ impl Deref for MessageWithLocation<'_> {
     }
 }
 
-fn group_messages_by_filename(messages: &[Message]) -> BTreeMap<&str, Vec<MessageWithLocation>> {
+fn group_messages_by_filename(messages: &[Message]) -> BTreeMap<String, Vec<MessageWithLocation>> {
     let mut grouped_messages = BTreeMap::default();
     for message in messages {
         grouped_messages
-            .entry(message.filename())
+            .entry(message.filename().to_string())
             .or_insert_with(Vec::new)
             .push(MessageWithLocation {
                 message,
diff --git a/crates/ruff_linter/src/message/pylint.rs b/crates/ruff_linter/src/message/pylint.rs
index 91d79326a7..24c79c0bf2 100644
--- a/crates/ruff_linter/src/message/pylint.rs
+++ b/crates/ruff_linter/src/message/pylint.rs
@@ -18,7 +18,7 @@ impl Emitter for PylintEmitter {
         context: &EmitterContext,
     ) -> anyhow::Result<()> {
         for message in messages {
-            let row = if context.is_notebook(message.filename()) {
+            let row = if context.is_notebook(&message.filename()) {
                 // We can't give a reasonable location for the structured formats,
                 // so we show one that's clearly a fallback
                 OneIndexed::from_zero_indexed(0)
@@ -39,7 +39,7 @@ impl Emitter for PylintEmitter {
             writeln!(
                 writer,
                 "{path}:{row}: {body}",
-                path = relativize_path(message.filename()),
+                path = relativize_path(&*message.filename()),
             )?;
         }
 
diff --git a/crates/ruff_linter/src/message/rdjson.rs b/crates/ruff_linter/src/message/rdjson.rs
index 26c3e1d091..6a323cc56e 100644
--- a/crates/ruff_linter/src/message/rdjson.rs
+++ b/crates/ruff_linter/src/message/rdjson.rs
@@ -57,7 +57,8 @@ impl Serialize for ExpandedMessages<'_> {
 }
 
 fn message_to_rdjson_value(message: &Message) -> Value {
-    let source_code = message.source_file().to_source_code();
+    let source_file = message.source_file();
+    let source_code = source_file.to_source_code();
 
     let start_location = source_code.line_column(message.start());
     let end_location = source_code.line_column(message.end());
diff --git a/crates/ruff_linter/src/message/sarif.rs b/crates/ruff_linter/src/message/sarif.rs
index 12dfd3a1a5..d6ad7e0115 100644
--- a/crates/ruff_linter/src/message/sarif.rs
+++ b/crates/ruff_linter/src/message/sarif.rs
@@ -121,7 +121,7 @@ impl SarifResult {
     fn from_message(message: &Message) -> Result<Self> {
         let start_location = message.compute_start_location();
         let end_location = message.compute_end_location();
-        let path = normalize_path(message.filename());
+        let path = normalize_path(&*message.filename());
         Ok(Self {
             rule: message.rule(),
             level: "error".to_string(),
@@ -141,7 +141,7 @@ impl SarifResult {
     fn from_message(message: &Message) -> Result<Self> {
         let start_location = message.compute_start_location();
         let end_location = message.compute_end_location();
-        let path = normalize_path(message.filename());
+        let path = normalize_path(&*message.filename());
         Ok(Self {
             rule: message.rule(),
             level: "error".to_string(),
diff --git a/crates/ruff_linter/src/message/text.rs b/crates/ruff_linter/src/message/text.rs
index f1ede8c621..53896b651c 100644
--- a/crates/ruff_linter/src/message/text.rs
+++ b/crates/ruff_linter/src/message/text.rs
@@ -73,12 +73,12 @@ impl Emitter for TextEmitter {
             write!(
                 writer,
                 "{path}{sep}",
-                path = relativize_path(message.filename()).bold(),
+                path = relativize_path(&*message.filename()).bold(),
                 sep = ":".cyan(),
             )?;
 
             let start_location = message.compute_start_location();
-            let notebook_index = context.notebook_index(message.filename());
+            let notebook_index = context.notebook_index(&message.filename());
 
             // Check if we're working on a jupyter notebook and translate positions with cell accordingly
             let diagnostic_location = if let Some(notebook_index) = notebook_index {
@@ -191,7 +191,8 @@ impl Display for MessageCodeFrame<'_> {
             Vec::new()
         };
 
-        let source_code = self.message.source_file().to_source_code();
+        let source_file = self.message.source_file();
+        let source_code = source_file.to_source_code();
 
         let content_start_index = source_code.line_index(self.message.start());
         let mut start_index = content_start_index.saturating_sub(2);
diff --git a/crates/ruff_server/src/lint.rs b/crates/ruff_server/src/lint.rs
index 5281c49040..670b43cb75 100644
--- a/crates/ruff_server/src/lint.rs
+++ b/crates/ruff_server/src/lint.rs
@@ -14,7 +14,7 @@ use ruff_linter::{
     directives::{extract_directives, Flags},
     generate_noqa_edits,
     linter::check_path,
-    message::{DiagnosticMessage, Message, SyntaxErrorMessage},
+    message::{DiagnosticMessage, Message},
     package::PackageRoot,
     packaging::detect_package_root,
     registry::AsRule,
@@ -173,10 +173,10 @@ pub(crate) fn check(
                     locator.to_index(),
                     encoding,
                 )),
-                Message::SyntaxError(syntax_error_message) => {
+                Message::SyntaxError(_) => {
                     if show_syntax_errors {
                         Some(syntax_error_to_lsp_diagnostic(
-                            syntax_error_message,
+                            &message,
                             &source_kind,
                             locator.to_index(),
                             encoding,
@@ -322,7 +322,7 @@ fn to_lsp_diagnostic(
 }
 
 fn syntax_error_to_lsp_diagnostic(
-    syntax_error: SyntaxErrorMessage,
+    syntax_error: &Message,
     source_kind: &SourceKind,
     index: &LineIndex,
     encoding: PositionEncoding,
@@ -331,7 +331,7 @@ fn syntax_error_to_lsp_diagnostic(
     let cell: usize;
 
     if let Some(notebook_index) = source_kind.as_ipy_notebook().map(Notebook::index) {
-        NotebookRange { cell, range } = syntax_error.range.to_notebook_range(
+        NotebookRange { cell, range } = syntax_error.range().to_notebook_range(
             source_kind.source_code(),
             index,
             notebook_index,
@@ -340,7 +340,7 @@ fn syntax_error_to_lsp_diagnostic(
     } else {
         cell = usize::default();
         range = syntax_error
-            .range
+            .range()
             .to_range(source_kind.source_code(), index, encoding);
     }
 
@@ -353,7 +353,7 @@ fn syntax_error_to_lsp_diagnostic(
             code: None,
             code_description: None,
             source: Some(DIAGNOSTIC_NAME.into()),
-            message: syntax_error.message,
+            message: syntax_error.body().to_string(),
             related_information: None,
             data: None,
         },
diff --git a/crates/ruff_source_file/src/lib.rs b/crates/ruff_source_file/src/lib.rs
index 51bd8852a1..bdf3d45573 100644
--- a/crates/ruff_source_file/src/lib.rs
+++ b/crates/ruff_source_file/src/lib.rs
@@ -195,7 +195,7 @@ impl SourceFile {
         }
     }
 
-    fn index(&self) -> &LineIndex {
+    pub fn index(&self) -> &LineIndex {
         self.inner
             .line_index
             .get_or_init(|| LineIndex::from_source_text(self.source_text()))
diff --git a/crates/ruff_wasm/src/lib.rs b/crates/ruff_wasm/src/lib.rs
index e93f2aa187..dc9c20323b 100644
--- a/crates/ruff_wasm/src/lib.rs
+++ b/crates/ruff_wasm/src/lib.rs
@@ -1,7 +1,7 @@
 use std::path::Path;
 
 use js_sys::Error;
-use ruff_linter::message::{DiagnosticMessage, Message, SyntaxErrorMessage};
+use ruff_linter::message::{DiagnosticMessage, Message};
 use ruff_linter::settings::types::PythonVersion;
 use serde::{Deserialize, Serialize};
 use wasm_bindgen::prelude::*;
@@ -230,15 +230,13 @@ impl Workspace {
                             .collect(),
                     }),
                 },
-                Message::SyntaxError(SyntaxErrorMessage { message, range, .. }) => {
-                    ExpandedMessage {
-                        code: None,
-                        message,
-                        start_location: source_code.line_column(range.start()).into(),
-                        end_location: source_code.line_column(range.end()).into(),
-                        fix: None,
-                    }
-                }
+                Message::SyntaxError(_) => ExpandedMessage {
+                    code: None,
+                    message: message.body().to_string(),
+                    start_location: source_code.line_column(message.range().start()).into(),
+                    end_location: source_code.line_column(message.range().end()).into(),
+                    fix: None,
+                },
             })
             .collect();
 
diff --git a/crates/ty/src/main.rs b/crates/ty/src/main.rs
index 96ed01c97a..2f5e31358b 100644
--- a/crates/ty/src/main.rs
+++ b/crates/ty/src/main.rs
@@ -14,6 +14,7 @@ use rayon::ThreadPoolBuilder;
 use ruff_db::diagnostic::{Diagnostic, DisplayDiagnosticConfig, Severity};
 use ruff_db::max_parallelism;
 use ruff_db::system::{OsSystem, SystemPath, SystemPathBuf};
+use ruff_db::Upcast;
 use salsa::plumbing::ZalsaDatabase;
 use ty_project::metadata::options::Options;
 use ty_project::watch::ProjectWatcher;
@@ -298,7 +299,11 @@ impl MainLoop {
                             let diagnostics_count = result.len();
 
                             for diagnostic in result {
-                                write!(stdout, "{}", diagnostic.display(db, &display_config))?;
+                                write!(
+                                    stdout,
+                                    "{}",
+                                    diagnostic.display(&db.upcast(), &display_config)
+                                )?;
 
                                 max_severity = max_severity.max(diagnostic.severity());
                             }
diff --git a/crates/ty_ide/src/hover.rs b/crates/ty_ide/src/hover.rs
index df00a0ccb8..7ddd4212c4 100644
--- a/crates/ty_ide/src/hover.rs
+++ b/crates/ty_ide/src/hover.rs
@@ -136,6 +136,7 @@ mod tests {
         Annotation, Diagnostic, DiagnosticFormat, DiagnosticId, DisplayDiagnosticConfig, LintName,
         Severity, Span,
     };
+    use ruff_db::Upcast;
     use ruff_text_size::{Ranged, TextRange};
 
     #[test]
@@ -773,7 +774,7 @@ mod tests {
                 .message("Cursor offset"),
             );
 
-            write!(buf, "{}", diagnostic.display(&self.db, &config)).unwrap();
+            write!(buf, "{}", diagnostic.display(&self.db.upcast(), &config)).unwrap();
 
             buf
         }
diff --git a/crates/ty_ide/src/lib.rs b/crates/ty_ide/src/lib.rs
index fa06058e5e..5e49f1da5d 100644
--- a/crates/ty_ide/src/lib.rs
+++ b/crates/ty_ide/src/lib.rs
@@ -204,6 +204,7 @@ mod tests {
     use ruff_db::diagnostic::{Diagnostic, DiagnosticFormat, DisplayDiagnosticConfig};
     use ruff_db::files::{system_path_to_file, File};
     use ruff_db::system::{DbWithWritableSystem, SystemPath, SystemPathBuf};
+    use ruff_db::Upcast;
     use ruff_python_ast::PythonVersion;
     use ruff_text_size::TextSize;
     use ty_python_semantic::{
@@ -285,7 +286,7 @@ mod tests {
                 .format(DiagnosticFormat::Full);
             for diagnostic in diagnostics {
                 let diag = diagnostic.into_diagnostic();
-                write!(buf, "{}", diag.display(&self.db, &config)).unwrap();
+                write!(buf, "{}", diag.display(&self.db.upcast(), &config)).unwrap();
             }
 
             buf
diff --git a/crates/ty_project/src/db.rs b/crates/ty_project/src/db.rs
index 05cb69f066..b656f9d337 100644
--- a/crates/ty_project/src/db.rs
+++ b/crates/ty_project/src/db.rs
@@ -126,6 +126,16 @@ impl Upcast<dyn IdeDb> for ProjectDatabase {
     }
 }
 
+impl Upcast<dyn Db> for ProjectDatabase {
+    fn upcast(&self) -> &(dyn Db + 'static) {
+        self
+    }
+
+    fn upcast_mut(&mut self) -> &mut (dyn Db + 'static) {
+        self
+    }
+}
+
 #[salsa::db]
 impl IdeDb for ProjectDatabase {}
 
diff --git a/crates/ty_python_semantic/src/types/context.rs b/crates/ty_python_semantic/src/types/context.rs
index 6e0b52acee..454f8ce7d7 100644
--- a/crates/ty_python_semantic/src/types/context.rs
+++ b/crates/ty_python_semantic/src/types/context.rs
@@ -521,7 +521,7 @@ impl Drop for DiagnosticGuard<'_, '_> {
         };
 
         let expected_file = self.ctx.file();
-        let got_file = ann.get_span().file();
+        let got_file = ann.get_span().expect_ty_file();
         assert_eq!(
             expected_file,
             got_file,
diff --git a/crates/ty_server/src/server/api/requests/diagnostic.rs b/crates/ty_server/src/server/api/requests/diagnostic.rs
index 201d5db91b..ea4648efb1 100644
--- a/crates/ty_server/src/server/api/requests/diagnostic.rs
+++ b/crates/ty_server/src/server/api/requests/diagnostic.rs
@@ -76,8 +76,9 @@ fn to_lsp_diagnostic(
     encoding: crate::PositionEncoding,
 ) -> Diagnostic {
     let range = if let Some(span) = diagnostic.primary_span() {
-        let index = line_index(db.upcast(), span.file());
-        let source = source_text(db.upcast(), span.file());
+        let file = span.expect_ty_file();
+        let index = line_index(db.upcast(), file);
+        let source = source_text(db.upcast(), file);
 
         span.range()
             .map(|range| range.to_lsp_range(&source, &index, encoding))
diff --git a/crates/ty_test/src/lib.rs b/crates/ty_test/src/lib.rs
index e0838249f2..43e6b14108 100644
--- a/crates/ty_test/src/lib.rs
+++ b/crates/ty_test/src/lib.rs
@@ -13,6 +13,7 @@ use ruff_db::panic::catch_unwind;
 use ruff_db::parsed::parsed_module;
 use ruff_db::system::{DbWithWritableSystem as _, SystemPath, SystemPathBuf};
 use ruff_db::testing::{setup_logging, setup_logging_with_filter};
+use ruff_db::Upcast;
 use ruff_source_file::{LineIndex, OneIndexed};
 use std::backtrace::BacktraceStatus;
 use std::fmt::Write;
@@ -464,7 +465,7 @@ fn create_diagnostic_snapshot(
             writeln!(snapshot).unwrap();
         }
         writeln!(snapshot, "```").unwrap();
-        write!(snapshot, "{}", diag.display(db, &display_config)).unwrap();
+        write!(snapshot, "{}", diag.display(&db.upcast(), &display_config)).unwrap();
         writeln!(snapshot, "```").unwrap();
     }
     snapshot
diff --git a/crates/ty_wasm/src/lib.rs b/crates/ty_wasm/src/lib.rs
index 53969603ac..9ed86299e8 100644
--- a/crates/ty_wasm/src/lib.rs
+++ b/crates/ty_wasm/src/lib.rs
@@ -373,7 +373,7 @@ impl Diagnostic {
         self.inner.primary_span().and_then(|span| {
             Some(Range::from_file_range(
                 &workspace.db,
-                FileRange::new(span.file(), span.range()?),
+                FileRange::new(span.expect_ty_file(), span.range()?),
                 workspace.position_encoding,
             ))
         })
@@ -383,7 +383,7 @@ impl Diagnostic {
     pub fn display(&self, workspace: &Workspace) -> JsString {
         let config = DisplayDiagnosticConfig::default().color(false);
         self.inner
-            .display(workspace.db.upcast(), &config)
+            .display(&workspace.db.upcast(), &config)
             .to_string()
             .into()
     }