FIX: Don't let table-build automatically fill empty headers with default values (#27894)

* FIX: Don't let table-build automatically fill empty headers with default values

The old table builder would fill empty headers with default values A~Z when editing.
This commit makes table-builder respect the old empty headers

related meta topic: https://meta.discourse.org/t/editing-a-table-with-empty-headers-fills-them-in-with-the-default-text-column-a-column-b/268472

app/assets/javascripts/discourse/app/components/modal/spreadsheet-editor.gjs

@@ -90,7 +90,10 @@ export default class SpreadsheetEditor extends Component {
 
   @action
   insertTable() {
-    const updatedHeaders = this.spreadsheet.getHeaders().split(","); // keys
+    const updatedHeaders = this.spreadsheet
+      .getHeaders()
+      .split(",")
+      .map((c) => c.trim()); // keys
     const updatedData = this.spreadsheet.getData(); // values
     const markdownTable = this.buildTableMarkdown(updatedHeaders, updatedData);
 
@@ -205,7 +208,7 @@ export default class SpreadsheetEditor extends Component {
         // headings
         headings = this.extractTableContent(row).map((heading) => {
           return {
-            title: heading,
+            title: heading || " ",
             width: Math.max(
               heading.length * rowWidthFactor,
               this.defaultColWidth
@@ -221,7 +224,9 @@ export default class SpreadsheetEditor extends Component {
       }
     });
 
-    headings.forEach((h, i) => (h.align = this.alignments?.[i] ?? "left"));
+    headings.forEach((h, i) => {
+      h.align = this.alignments?.[i] ?? "left";
+    });
 
     return this.buildSpreadsheet(rows, headings);
   }

spec/system/table_builder_spec.rb

@@ -5,6 +5,7 @@ describe "Table Builder", type: :system do
   let(:composer) { PageObjects::Components::Composer.new }
   let(:insert_table_modal) { PageObjects::Modals::InsertTable.new }
   fab!(:topic) { Fabricate(:topic, user: user) }
+  fab!(:topic2) { Fabricate(:topic, user: user) }
   fab!(:post1) { create_post(user: user, topic: topic, raw: <<~RAW) }
         |Make   | Model   | Year|
         |--- | --- | ---|
@@ -12,6 +13,12 @@ describe "Table Builder", type: :system do
         |Nissan | Skyline | 1999|
         |Honda  | S2000  | 2001|
         RAW
+  fab!(:post2) { create_post(user: user, topic: topic2, raw: <<~RAW) }
+        | |  | |
+        |--- | --- | ---|
+        |Some | content | here|
+        |1 | 2 | 3|
+        RAW
 
   let(:topic_page) { PageObjects::Pages::Topic.new }
 
@@ -108,6 +115,25 @@ describe "Table Builder", type: :system do
       end
     end
 
+    it "should respect the original empty header" do
+      topic_page.visit_topic(topic2)
+      topic_page.find(".btn-edit-table", visible: :all).click
+      expect(page).to have_selector(".insert-table-modal")
+      insert_table_modal.type_in_cell(0, 0, " updated")
+      insert_table_modal.click_insert_table
+
+      updated_post = <<~RAW
+      | |  | |
+      |--- | --- | ---|
+      |Some updated | content | here|
+      |1 | 2 | 3|
+      RAW
+
+      try_until_success do
+        expect(normalize_value(post2.reload.raw)).to eq(normalize_value(updated_post))
+      end
+    end
+
     context "when adding an edit reason" do
       it "should add the edit reason to the edit history" do
         edit_reason = "Updated Nissan model"