Add R backend-controlled format options to data explorer

crates/amalthea/src/comm/data_explorer_comm.rs

@@ -92,9 +92,12 @@ pub struct BackendState {
 	/// requests. This parameter may change.
 	pub connected: Option<bool>,
 
-	/// Optional experimental parameter to provide an explanation when
-	/// connected=false. This parameter may change.
-	pub error_message: Option<String>
+    /// Optional experimental parameter to provide an explanation when
+    /// connected=false. This parameter may change.
+    pub error_message: Option<String>,
+
+    /// Optional formatting options for frontend display
+    pub format_options: Option<FormatOptions>,
 }
 
 /// Schema for a column in a table

crates/ark/src/data_explorer/r_data_explorer.rs

@@ -72,6 +72,7 @@ use crossbeam::channel::Sender;
 use crossbeam::select;
 use harp::exec::RFunction;
 use harp::exec::RFunctionExt;
+use harp::get_option;
 use harp::object::RObject;
 use harp::r_symbol;
 use harp::table_kind;
@@ -1159,6 +1160,7 @@ impl RDataExplorer {
                     }]),
                 },
             },
+            format_options: Some(Self::current_format_options()),
         };
         Ok(DataExplorerBackendReply::GetStateReply(state))
     }
@@ -1299,6 +1301,36 @@ impl RDataExplorer {
         // Call the conversion function with resolved sort keys
         convert_to_code::convert_to_code(params, object_name, &resolved_sort_keys)
     }
+
+    /// Returns the current format options as a `FormatOptions` object.
+    ///
+    /// These options are derived from the R options "scipen" and "digits". The
+    /// thresholds for scientific notation are calculated based on these
+    /// options. The `max_value_length` is set to 1000, and `thousands_sep`
+    /// is set to `None`.
+    fn current_format_options() -> FormatOptions {
+        // In R 4.2, Rf_GetOption1 (used by get_option) doesn't work correctly for scipen
+        // due to special handling added in later versions. We need to use the R interpreter's
+        // getOption() function instead. See: https://github.com/wch/r-source/commit/7f20c19
+        // Note: 'digits' works fine with Rf_GetOption1, so we don't need to change it.
+        let scipen: i64 = harp::parse_eval_global("as.integer(getOption('scipen', 0))")
+            .and_then(|obj| obj.try_into())
+            .unwrap_or(0); // R default
+        let digits: i64 = get_option("digits").try_into().unwrap_or(7); // R default
+
+        // Calculate thresholds for scientific notation
+        let max_integral_digits = (scipen + 5).max(1); // only depends on scipen
+        let large_num_digits = (digits - 5).max(0); // default to 2 d.p.
+        let small_num_digits = (scipen + 6).max(1); // only depends on scipen
+
+        FormatOptions {
+            large_num_digits,
+            small_num_digits,
+            max_integral_digits,
+            max_value_length: 1000,
+            thousands_sep: None,
+        }
+    }
 }
 
 /// Open an R object in the data viewer.

crates/ark/tests/data_explorer.rs

@@ -3108,3 +3108,63 @@ fn test_single_row_data_frame_column_profiles() {
         });
     }
 }
+
+#[test]
+fn test_format_options_state_change() {
+    let _lock = r_test_lock();
+
+    // Save the current R options so we can restore them later
+    let (original_scipen, original_digits) = r_task(|| {
+        let scipen_obj = harp::parse_eval_global("getOption('scipen')").expect("Failed to get scipen option");
+        let digits_obj = harp::parse_eval_global("getOption('digits')").expect("Failed to get digits option");
+        let scipen: i64 = scipen_obj.try_into().unwrap_or(0);
+        let digits: i64 = digits_obj.try_into().unwrap_or(7);
+        (scipen, digits)
+    });
+
+    // Set known R options for testing
+    r_task(|| {
+        harp::parse_eval_global("options(scipen = 0, digits = 7)").unwrap();
+    });
+
+    // Open a data explorer with mtcars
+    let setup = TestSetup::new("mtcars");
+    let socket = setup.socket();
+
+    // Get the initial state and verify format_options
+    TestAssertions::assert_state(&socket, |state| {
+        let format_options = state.format_options.as_ref().expect("format_options should be present");
+
+        // With scipen=0, digits=7:
+        // max_integral_digits = (0 + 5).max(1) = 5
+        // large_num_digits = (7 - 5).max(0) = 2
+        // small_num_digits = (0 + 6).max(1) = 6
+        assert_eq!(format_options.max_integral_digits, 5);
+        assert_eq!(format_options.large_num_digits, 2);
+        assert_eq!(format_options.small_num_digits, 6);
+    });
+
+    // Change R options to different values
+    r_task(|| {
+        harp::parse_eval_global("options(scipen = 10, digits = 10)").unwrap();
+    });
+
+    // Get the state again and verify format_options changed
+    TestAssertions::assert_state(&socket, |state| {
+        let format_options = state.format_options.as_ref().expect("format_options should be present");
+
+        // With scipen=10, digits=10:
+        // max_integral_digits = (10 + 5).max(1) = 15
+        // large_num_digits = (10 - 5).max(0) = 5
+        // small_num_digits = (10 + 6).max(1) = 16
+        assert_eq!(format_options.max_integral_digits, 15);
+        assert_eq!(format_options.large_num_digits, 5);
+        assert_eq!(format_options.small_num_digits, 16);
+    });
+
+    // Restore original R options
+    r_task(|| {
+        let restore_cmd = format!("options(scipen = {}, digits = {})", original_scipen, original_digits);
+        harp::parse_eval_global(&restore_cmd).expect("Failed to restore original R options");
+    });
+}