1 files changed, 41 insertions, 0 deletions
diff --git a/src/diagnostics/duplicate_attribute_names.rs b/src/diagnostics/duplicate_attribute_names.rs
new file mode 100644
index 0000000..542d8ec
--- /dev/null
+++ b/src/diagnostics/duplicate_attribute_names.rs
@@ -0,0 +1,41 @@
+use std::collections::HashMap;
+
+use miette::Diagnostic;
+use thiserror::Error;
+
+use crate::{
+	diagnostics::AstDiagnostic,
+	parse::{Attribute, Element},
+	tokenize::Span,
+};
+
+#[derive(Error, Debug, Diagnostic)]
+#[error("Multiple attributes have the same name")]
+#[diagnostic(code(DuplicateAttributeNames), severity(Error))]
+pub struct DuplicateAttributeNames {
+	#[label(collection)]
+	duplicates: Vec<Span>,
+}
+
+impl AstDiagnostic for DuplicateAttributeNames {
+	fn handle_element(element: &Element<'_>) -> Option<Self> {
+		let mut seen_attributes = HashMap::<&str, Attribute<'_>>::new();
+		for attribute in element.attributes {
+			let Some(name) = attribute.name_lowercase() else {
+				continue;
+			};
+			if let Some(duplicate) = seen_attributes.get(name) {
+				return Some(Self {
+					duplicates: vec![
+						duplicate.name_token().expect("a named attribute").span,
+						attribute.name_token().expect("a named attribute").span,
+					],
+				});
+			}
+
+			seen_attributes.insert(name, *attribute);
+		}
+
+		None
+	}
+}