ruff_db: add "secondary" messages to Diagnostic trait

This is a small little hack to make the `Diagnostic` trait
capable of supporting attaching multiple spans.

This design should be considered transient. This was just the
quickest way that I could see to pass multiple spans through from
the type checker to the diagnostic renderer.

crates/red_knot_python_semantic/src/suppression.rs

@@ -325,6 +325,7 @@ impl<'a> CheckSuppressionsContext<'a> {
             range,
             severity,
             file: self.file,
+            secondary_messages: vec![],
         });
     }
 }

crates/red_knot_python_semantic/src/types/context.rs

@@ -2,7 +2,7 @@ use std::fmt;
 
 use drop_bomb::DebugDropBomb;
 use ruff_db::{
-    diagnostic::{DiagnosticId, Severity},
+    diagnostic::{DiagnosticId, SecondaryDiagnosticMessage, Severity},
     files::File,
 };
 use ruff_python_ast::AnyNodeRef;
@@ -73,6 +73,17 @@ impl<'db> InferContext<'db> {
         lint: &'static LintMetadata,
         node: AnyNodeRef,
         message: fmt::Arguments,
+    ) {
+        self.report_lint_with_secondary_messages(lint, node, message, vec![]);
+    }
+
+    /// Reports a lint located at `node`.
+    pub(super) fn report_lint_with_secondary_messages(
+        &self,
+        lint: &'static LintMetadata,
+        node: AnyNodeRef,
+        message: fmt::Arguments,
+        secondary_messages: Vec<SecondaryDiagnosticMessage>,
     ) {
         if !self.db.is_file_open(self.file) {
             return;
@@ -94,7 +105,13 @@ impl<'db> InferContext<'db> {
             return;
         }
 
-        self.report_diagnostic(node, DiagnosticId::Lint(lint.name()), severity, message);
+        self.report_diagnostic(
+            node,
+            DiagnosticId::Lint(lint.name()),
+            severity,
+            message,
+            secondary_messages,
+        );
     }
 
     /// Adds a new diagnostic.
@@ -106,6 +123,7 @@ impl<'db> InferContext<'db> {
         id: DiagnosticId,
         severity: Severity,
         message: fmt::Arguments,
+        secondary_messages: Vec<SecondaryDiagnosticMessage>,
     ) {
         if !self.db.is_file_open(self.file) {
             return;
@@ -123,6 +141,7 @@ impl<'db> InferContext<'db> {
             message: message.to_string(),
             range: node.range(),
             severity,
+            secondary_messages,
         });
     }
 

crates/red_knot_python_semantic/src/types/diagnostic.rs

@@ -8,7 +8,7 @@ use crate::types::string_annotation::{
 };
 use crate::types::{ClassLiteralType, KnownInstanceType, Type};
 use crate::{declare_lint, Db};
-use ruff_db::diagnostic::{Diagnostic, DiagnosticId, Severity, Span};
+use ruff_db::diagnostic::{Diagnostic, DiagnosticId, SecondaryDiagnosticMessage, Severity, Span};
 use ruff_db::files::File;
 use ruff_python_ast::{self as ast, AnyNodeRef};
 use ruff_text_size::TextRange;
@@ -777,6 +777,7 @@ pub struct TypeCheckDiagnostic {
     pub(crate) range: TextRange,
     pub(crate) severity: Severity,
     pub(crate) file: File,
+    pub(crate) secondary_messages: Vec<SecondaryDiagnosticMessage>,
 }
 
 impl TypeCheckDiagnostic {
@@ -806,6 +807,10 @@ impl Diagnostic for TypeCheckDiagnostic {
         Some(Span::from(self.file).with_range(self.range))
     }
 
+    fn secondary_messages(&self) -> &[SecondaryDiagnosticMessage] {
+        &self.secondary_messages
+    }
+
     fn severity(&self) -> Severity {
         self.severity
     }

crates/red_knot_python_semantic/src/types/infer.rs

@@ -3272,6 +3272,7 @@ impl<'db> TypeInferenceBuilder<'db> {
                                         "Revealed type is `{}`",
                                         revealed_type.display(self.db())
                                     ),
+                                    vec![],
                                 );
                             }
                         }

crates/ruff_db/src/diagnostic.rs

@@ -173,6 +173,12 @@ pub trait Diagnostic: Send + Sync + std::fmt::Debug {
     /// or it applies to the entire file (e.g. the file should be executable but isn't).
     fn span(&self) -> Option<Span>;
 
+    /// Returns an optional sequence of "secondary" messages (with spans) to
+    /// include in the rendering of this diagnostic.
+    fn secondary_messages(&self) -> &[SecondaryDiagnosticMessage] {
+        &[]
+    }
+
     fn severity(&self) -> Severity;
 
     fn display<'db, 'diag, 'config>(
@@ -191,6 +197,22 @@ pub trait Diagnostic: Send + Sync + std::fmt::Debug {
     }
 }
 
+/// A single secondary message assigned to a `Diagnostic`.
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub struct SecondaryDiagnosticMessage {
+    span: Span,
+    message: String,
+}
+
+impl SecondaryDiagnosticMessage {
+    pub fn new(span: Span, message: impl Into<String>) -> SecondaryDiagnosticMessage {
+        SecondaryDiagnosticMessage {
+            span,
+            message: message.into(),
+        }
+    }
+}
+
 /// A span represents the source of a diagnostic.
 ///
 /// It consists of a `File` and an optional range into that file. When the
@@ -219,10 +241,12 @@ impl Span {
 
     /// Returns a new `Span` with the given `range` attached to it.
     pub fn with_range(self, range: TextRange) -> Span {
-        Span {
-            range: Some(range),
-            ..self
-        }
+        self.with_optional_range(Some(range))
+    }
+
+    /// Returns a new `Span` with the given optional `range` attached to it.
+    pub fn with_optional_range(self, range: Option<TextRange>) -> Span {
+        Span { range, ..self }
     }
 }
 
@@ -311,6 +335,14 @@ impl std::fmt::Display for DisplayDiagnostic<'_, '_, '_> {
             &span,
             &self.diagnostic.message(),
         ));
+        for secondary_msg in self.diagnostic.secondary_messages() {
+            message.add_snippet(Snippet::new(
+                self.db,
+                Severity::Info,
+                &secondary_msg.span,
+                &secondary_msg.message,
+            ));
+        }
         render(f, message.to_annotate())
     }
 }
@@ -445,6 +477,10 @@ where
         (**self).span()
     }
 
+    fn secondary_messages(&self) -> &[SecondaryDiagnosticMessage] {
+        (**self).secondary_messages()
+    }
+
     fn severity(&self) -> Severity {
         (**self).severity()
     }
@@ -466,6 +502,10 @@ where
         (**self).span()
     }
 
+    fn secondary_messages(&self) -> &[SecondaryDiagnosticMessage] {
+        (**self).secondary_messages()
+    }
+
     fn severity(&self) -> Severity {
         (**self).severity()
     }
@@ -484,6 +524,10 @@ impl Diagnostic for Box<dyn Diagnostic> {
         (**self).span()
     }
 
+    fn secondary_messages(&self) -> &[SecondaryDiagnosticMessage] {
+        (**self).secondary_messages()
+    }
+
     fn severity(&self) -> Severity {
         (**self).severity()
     }
@@ -502,6 +546,10 @@ impl Diagnostic for &'_ dyn Diagnostic {
         (**self).span()
     }
 
+    fn secondary_messages(&self) -> &[SecondaryDiagnosticMessage] {
+        (**self).secondary_messages()
+    }
+
     fn severity(&self) -> Severity {
         (**self).severity()
     }
@@ -520,6 +568,10 @@ impl Diagnostic for std::sync::Arc<dyn Diagnostic> {
         (**self).span()
     }
 
+    fn secondary_messages(&self) -> &[SecondaryDiagnosticMessage] {
+        (**self).secondary_messages()
+    }
+
     fn severity(&self) -> Severity {
         (**self).severity()
     }