Allow positional aesthetic names to be used in LABEL

src/plot/main.rs

@@ -169,6 +169,7 @@ impl Plot {
     /// - Layer aesthetics
     /// - Layer remappings
     /// - Scale aesthetics
+    /// - Label keys
     pub fn transform_aesthetics_to_internal(&mut self) {
         let ctx = self.get_aesthetic_context();
 
@@ -187,6 +188,19 @@ impl Plot {
                 scale.aesthetic = internal.to_string();
             }
         }
+
+        // Transform label keys
+        if let Some(labels) = &mut self.labels {
+            let mut transformed = HashMap::new();
+            for (key, value) in labels.labels.drain() {
+                let internal_key = ctx
+                    .map_user_to_internal(&key)
+                    .map(|s| s.to_string())
+                    .unwrap_or(key);
+                transformed.insert(internal_key, value);
+            }
+            labels.labels = transformed;
+        }
     }
 
     /// Check if the spec has any layers
@@ -716,4 +730,120 @@ mod tests {
             "Non-color aesthetic should keep its name"
         );
     }
+
+    // ========================================
+    // Label Transformation Tests
+    // ========================================
+
+    #[test]
+    fn test_label_transform_with_default_project() {
+        // LABEL x/y with default cartesian should transform to pos1/pos2
+        use crate::plot::projection::{Coord, Projection};
+
+        let mut spec = Plot::new();
+        spec.project = Some(Projection {
+            coord: Coord::cartesian(),
+            aesthetics: vec!["x".to_string(), "y".to_string()],
+            properties: HashMap::new(),
+        });
+        spec.labels = Some(Labels {
+            labels: HashMap::from([
+                ("x".to_string(), "X Axis".to_string()),
+                ("y".to_string(), "Y Axis".to_string()),
+            ]),
+        });
+
+        spec.initialize_aesthetic_context();
+        spec.transform_aesthetics_to_internal();
+
+        let labels = spec.labels.as_ref().unwrap();
+        assert_eq!(labels.labels.get("pos1"), Some(&"X Axis".to_string()));
+        assert_eq!(labels.labels.get("pos2"), Some(&"Y Axis".to_string()));
+        assert!(labels.labels.get("x").is_none());
+        assert!(labels.labels.get("y").is_none());
+    }
+
+    #[test]
+    fn test_label_transform_with_flipped_project() {
+        // LABEL x/y with PROJECT y, x TO cartesian should swap the mappings
+        use crate::plot::projection::{Coord, Projection};
+
+        let mut spec = Plot::new();
+        // PROJECT y, x TO cartesian means y maps to pos1, x maps to pos2
+        spec.project = Some(Projection {
+            coord: Coord::cartesian(),
+            aesthetics: vec!["y".to_string(), "x".to_string()],
+            properties: HashMap::new(),
+        });
+        spec.labels = Some(Labels {
+            labels: HashMap::from([
+                ("x".to_string(), "Category".to_string()),
+                ("y".to_string(), "Value".to_string()),
+            ]),
+        });
+
+        spec.initialize_aesthetic_context();
+        spec.transform_aesthetics_to_internal();
+
+        let labels = spec.labels.as_ref().unwrap();
+        // x maps to pos2 (second positional), y maps to pos1 (first positional)
+        assert_eq!(labels.labels.get("pos1"), Some(&"Value".to_string()));
+        assert_eq!(labels.labels.get("pos2"), Some(&"Category".to_string()));
+    }
+
+    #[test]
+    fn test_label_transform_with_polar_project() {
+        // LABEL theta/radius with polar should transform to pos1/pos2
+        use crate::plot::projection::{Coord, Projection};
+
+        let mut spec = Plot::new();
+        spec.project = Some(Projection {
+            coord: Coord::polar(),
+            aesthetics: vec!["theta".to_string(), "radius".to_string()],
+            properties: HashMap::new(),
+        });
+        spec.labels = Some(Labels {
+            labels: HashMap::from([
+                ("theta".to_string(), "Angle".to_string()),
+                ("radius".to_string(), "Distance".to_string()),
+            ]),
+        });
+
+        spec.initialize_aesthetic_context();
+        spec.transform_aesthetics_to_internal();
+
+        let labels = spec.labels.as_ref().unwrap();
+        assert_eq!(labels.labels.get("pos1"), Some(&"Angle".to_string()));
+        assert_eq!(labels.labels.get("pos2"), Some(&"Distance".to_string()));
+    }
+
+    #[test]
+    fn test_label_transform_preserves_non_positional() {
+        // LABEL title/color should be preserved unchanged
+        use crate::plot::projection::{Coord, Projection};
+
+        let mut spec = Plot::new();
+        spec.project = Some(Projection {
+            coord: Coord::cartesian(),
+            aesthetics: vec!["x".to_string(), "y".to_string()],
+            properties: HashMap::new(),
+        });
+        spec.labels = Some(Labels {
+            labels: HashMap::from([
+                ("title".to_string(), "My Chart".to_string()),
+                ("color".to_string(), "Category".to_string()),
+                ("x".to_string(), "X Axis".to_string()),
+            ]),
+        });
+
+        spec.initialize_aesthetic_context();
+        spec.transform_aesthetics_to_internal();
+
+        let labels = spec.labels.as_ref().unwrap();
+        // Non-positional labels should remain unchanged
+        assert_eq!(labels.labels.get("title"), Some(&"My Chart".to_string()));
+        assert_eq!(labels.labels.get("color"), Some(&"Category".to_string()));
+        // Positional label should be transformed
+        assert_eq!(labels.labels.get("pos1"), Some(&"X Axis".to_string()));
+    }
 }

src/reader/mod.rs

@@ -1044,4 +1044,76 @@ mod tests {
             "Identity position should not have xOffset encoding"
         );
     }
+
+    #[test]
+    fn test_label_with_flipped_project() {
+        // End-to-end test: LABEL x/y with PROJECT y, x TO cartesian
+        // Labels should be correctly applied to the flipped axes
+        let reader = DuckDBReader::from_connection_string("duckdb://memory").unwrap();
+        let query = r#"
+            SELECT * FROM (VALUES (1, 10), (2, 20)) AS t(x, y)
+            VISUALISE
+            DRAW bar MAPPING x AS y, y AS x
+            PROJECT y, x TO cartesian
+            LABEL x => 'Value', y => 'Category'
+        "#;
+
+        let spec = reader.execute(query).unwrap();
+        let writer = VegaLiteWriter::new();
+        let result = writer.render(&spec).unwrap();
+
+        let json: serde_json::Value = serde_json::from_str(&result).unwrap();
+        let layer = json["layer"].as_array().unwrap().first().unwrap();
+        let encoding = &layer["encoding"];
+
+        // With PROJECT y, x TO cartesian:
+        // - y is pos1 (first positional), renders to VL x-axis in cartesian
+        // - x is pos2 (second positional), renders to VL y-axis in cartesian
+        // So LABEL y => 'Category' should appear on VL x-axis, LABEL x => 'Value' on VL y-axis
+        let x_title = encoding["x"]["title"].as_str();
+        let y_title = encoding["y"]["title"].as_str();
+
+        assert_eq!(
+            x_title,
+            Some("Category"),
+            "x-axis should have 'Category' title (from LABEL y). Got encoding: {}",
+            serde_json::to_string_pretty(encoding).unwrap()
+        );
+        assert_eq!(
+            y_title,
+            Some("Value"),
+            "y-axis should have 'Value' title (from LABEL x). Got encoding: {}",
+            serde_json::to_string_pretty(encoding).unwrap()
+        );
+    }
+
+    #[test]
+    fn test_label_with_polar_project() {
+        // End-to-end test: LABEL theta/radius with PROJECT TO polar
+        let reader = DuckDBReader::from_connection_string("duckdb://memory").unwrap();
+        let query = r#"
+            SELECT * FROM (VALUES ('A', 10), ('B', 20)) AS t(category, value)
+            VISUALISE value AS theta, category AS fill
+            DRAW bar
+            PROJECT TO polar
+            LABEL theta => 'Angle', radius => 'Distance'
+        "#;
+
+        let spec = reader.execute(query).unwrap();
+        let writer = VegaLiteWriter::new();
+        let result = writer.render(&spec).unwrap();
+
+        let json: serde_json::Value = serde_json::from_str(&result).unwrap();
+        let layer = json["layer"].as_array().unwrap().first().unwrap();
+        let encoding = &layer["encoding"];
+
+        // Verify theta encoding has the label
+        let theta_title = encoding["theta"]["title"].as_str();
+        assert_eq!(
+            theta_title,
+            Some("Angle"),
+            "theta encoding should have 'Angle' title. Got encoding: {}",
+            serde_json::to_string_pretty(encoding).unwrap()
+        );
+    }
 }