feat: display a message when importer cannot find lat/lng columns

fix #1699

umap/static/umap/js/umap.layer.js

@@ -463,8 +463,8 @@ U.Layer.Heat = L.HeatLayer.extend({
         this._latlngs[i].alt !== undefined
           ? this._latlngs[i].alt
           : this._latlngs[i][2] !== undefined
-            ? +this._latlngs[i][2]
+          ? +this._latlngs[i][2]
-            : 1
+          : 1
 
       grid[y] = grid[y] || []
       cell = grid[y][x]
@@ -947,6 +947,17 @@ U.DataLayer = L.Evented.extend({
           includeLatLon: false,
         },
         (err, result) => {
+          // csv2geojson fallback to null geometries when it cannot determine
+          // lat or lon columns. This is valid geojson, but unwanted from a user
+          // point of view.
+          if (result && result.features.length) {
+            if (result.features[0].geometry === null) {
+              err = {
+                type: 'Error',
+                message: L._('Cannot determine latitude and longitude columns.'),
+              }
+            }
+          }
           if (err) {
             let message
             if (err.type === 'Error') {

umap/tests/integration/test_import.py

@@ -411,3 +411,19 @@ def test_import_multipolyline(live_server, page, tilelayer):
     # A layer has been created
     expect(layers).to_have_count(1)
     expect(paths).to_have_count(1)
+
+
+def test_import_csv_without_valid_latlon_headers(tilelayer, live_server, page):
+    page.goto(f"{live_server.url}/map/new/")
+    page.get_by_title("See layers").click()
+    layers = page.locator(".umap-browser .datalayer")
+    markers = page.locator(".leaflet-marker-icon")
+    page.get_by_title("Import data").click()
+    textarea = page.locator(".umap-upload textarea")
+    textarea.fill("a,b,c\n12.23,48.34,mypoint\n12.23,48.34,mypoint2")
+    page.locator('select[name="format"]').select_option("csv")
+    page.get_by_role("button", name="Import", exact=True).click()
+    # FIXME do not create a layer
+    expect(layers).to_have_count(1)
+    expect(markers).to_have_count(0)
+    expect(page.locator(".umap-alert")).to_be_visible()