From 266c14d5d28358a1e9e3b83edda855e1adeb740f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Nicol=C3=A1s=20Hatcher?= <nicolas@theuniverse.today>
Date: Sat, 19 Jul 2025 07:51:05 +0200
Subject: [PATCH] FIX: Apply copilot suggestions

---
 base/src/user_model/common.rs                 |  6 +++--
 .../WorksheetCanvas/worksheetCanvas.ts        | 23 +++++--------------
 2 files changed, 10 insertions(+), 19 deletions(-)

diff --git a/base/src/user_model/common.rs b/base/src/user_model/common.rs
index 156a60a..dcb4269 100644
--- a/base/src/user_model/common.rs
+++ b/base/src/user_model/common.rs
@@ -1603,7 +1603,7 @@ impl UserModel {
     }
 
     /// Returns the largest column in the row less than a column whose cell has a non empty value.
-    /// If the row is empty, it returns `None`.
+    /// If there are none it returns `None`.
     /// This is useful when rendering a part of a worksheet to know which cells spill over
     pub fn get_last_non_empty_in_row_before_column(
         &self,
@@ -1633,7 +1633,9 @@ impl UserModel {
         }
     }
 
-    /// Returns the largest column in the row greater than a column whose cell has a non empty value.
+    /// Returns the smallest column in the row larger than "column" whose cell has a non empty value.
+    /// If there are none it returns `None`.
+    /// This is useful when rendering a part of a worksheet to know which cells spill over
     pub fn get_first_non_empty_in_row_after_column(
         &self,
         sheet: u32,
diff --git a/webapp/IronCalc/src/components/WorksheetCanvas/worksheetCanvas.ts b/webapp/IronCalc/src/components/WorksheetCanvas/worksheetCanvas.ts
index 798449e..e7e8275 100644
--- a/webapp/IronCalc/src/components/WorksheetCanvas/worksheetCanvas.ts
+++ b/webapp/IronCalc/src/components/WorksheetCanvas/worksheetCanvas.ts
@@ -55,8 +55,6 @@ export const defaultCellFontFamily = fonts.regular;
 export const headerFontFamily = fonts.regular;
 export const frozenSeparatorWidth = 3;
 
-type Tuple = [number, number];
-
 interface TextProperties {
   row: number;
   column: number;
@@ -136,14 +134,9 @@ export default class WorksheetCanvas {
     this.onRowHeightChanges = options.onRowHeightChanges;
     this.resetHeaders();
     this.cellOutlineHandle = attachOutlineHandle(this);
-    // +1 means the cell is filled with a spill from a cell in the left
-    // -1 means the cell is filled with a spill from a cell in the right
-    this.spills = new Map<string, number>();
-    this.cells = [];
-  }
 
-  removeSpills(): void {
-    this.spills.clear();
+    // a cell marked as "spill" means its left border should be skipped
+    this.spills = new Map<string, number>();
     this.cells = [];
   }
 
@@ -685,12 +678,14 @@ export default class WorksheetCanvas {
         leftColumnX > minX &&
         this.model.getFormattedCellValue(selectedSheet, row, spillColumn) ===
           "" &&
-        spillColumn > 0 &&
+        spillColumn >= 1 &&
         ((column <= frozenColumnsCount && spillColumn <= frozenColumnsCount) ||
           column > frozenColumnsCount)
       ) {
         leftColumnX -= this.getColumnWidth(selectedSheet, spillColumn);
-        // marks (row, spillColumn) as spilling so we don't draw a border to the left
+        // This is tricky but correct. The reason is we only draw the left borders of the cells
+        // (because the left border of a cell MUST be the right border of the one to the left).
+        // So if we want to remove the right border of this cell we need to skip the left border of the next.
         this.spills.set(`${row}-${spillColumn + 1}`, 1);
         spillColumn -= 1;
       }
@@ -1735,12 +1730,6 @@ export default class WorksheetCanvas {
   }
 
   renderSheet(): void {
-    console.time("renderSheet");
-    this._renderSheet();
-    console.timeEnd("renderSheet");
-  }
-
-  _renderSheet(): void {
     const context = this.ctx;
     const { canvas } = this;
     const selectedSheet = this.model.getSelectedSheet();