Respect spans when resizing grid cells (#6685)

**Problem:**

Resizing grid cells always forces explicit numerical placement pins,
chomping any `span`s that may have been defined on the cell.

**Fix:**

After determining the right numerical positions for the resized cell
bounds, do a normalization pass so that the new grid props are rewritten
to respect the new bounds but also to express them with `spans` if the
original pins were spans in the first place.

For example, assuming enlarging to the right by 1 cell:

| Initial | Result |
|--------|----------|
| `gridColumn: span 2` | `gridColumn: span 3` |
| `gridColumn 3 / span 2` | `gridColumn: 3 / span 3` |

**Manual Tests:**
I hereby swear that:

- [x] I opened a hydrogen project and it loaded
- [x] I could navigate to various routes in Play mode

Fixes #6683

editor/src/components/canvas/canvas-strategies/strategies/grid-resize-element-strategy.spec.browser2.tsx

@@ -671,6 +671,185 @@ export var storyboard = (
       gridRowEnd: 'auto',
     })
   })
+
+  describe('spans', () => {
+    it('respects column start spans', async () => {
+      const editor = await renderTestEditorWithCode(
+        makeProjectCodeWithCustomPlacement({ gridColumn: 'span 2', gridRow: '2' }),
+        'await-first-dom-report',
+      )
+
+      // enlarge to the right
+      {
+        await runCellResizeTest(
+          editor,
+          'column-end',
+          gridCellTargetId(EP.fromString('sb/grid'), 2, 3),
+          EP.fromString('sb/grid/cell'),
+        )
+
+        const { gridRowStart, gridRowEnd, gridColumnStart, gridColumnEnd } =
+          editor.renderedDOM.getByTestId('cell').style
+        expect({ gridRowStart, gridRowEnd, gridColumnStart, gridColumnEnd }).toEqual({
+          gridColumnEnd: 'auto',
+          gridColumnStart: 'span 3',
+          gridRowEnd: 'auto',
+          gridRowStart: '2',
+        })
+      }
+
+      // shrink from the left
+      {
+        await runCellResizeTest(
+          editor,
+          'column-start',
+          gridCellTargetId(EP.fromString('sb/grid'), 2, 2),
+          EP.fromString('sb/grid/cell'),
+        )
+
+        const { gridRowStart, gridRowEnd, gridColumnStart, gridColumnEnd } =
+          editor.renderedDOM.getByTestId('cell').style
+        expect({ gridRowStart, gridRowEnd, gridColumnStart, gridColumnEnd }).toEqual({
+          gridColumnEnd: '4',
+          gridColumnStart: 'span 2',
+          gridRowEnd: 'auto',
+          gridRowStart: '2',
+        })
+      }
+
+      // enlarge back from the left
+      {
+        await runCellResizeTest(
+          editor,
+          'column-start',
+          gridCellTargetId(EP.fromString('sb/grid'), 2, 1),
+          EP.fromString('sb/grid/cell'),
+        )
+
+        const { gridRowStart, gridRowEnd, gridColumnStart, gridColumnEnd } =
+          editor.renderedDOM.getByTestId('cell').style
+        expect({ gridRowStart, gridRowEnd, gridColumnStart, gridColumnEnd }).toEqual({
+          gridColumnEnd: 'auto',
+          gridColumnStart: 'span 3',
+          gridRowEnd: 'auto',
+          gridRowStart: '2',
+        })
+      }
+    })
+    it('respects column end spans', async () => {
+      const editor = await renderTestEditorWithCode(
+        makeProjectCodeWithCustomPlacement({ gridColumn: '2 / span 2', gridRow: '2' }),
+        'await-first-dom-report',
+      )
+
+      // enlarge to the right
+      {
+        await runCellResizeTest(
+          editor,
+          'column-end',
+          gridCellTargetId(EP.fromString('sb/grid'), 2, 4),
+          EP.fromString('sb/grid/cell'),
+        )
+
+        const { gridRowStart, gridRowEnd, gridColumnStart, gridColumnEnd } =
+          editor.renderedDOM.getByTestId('cell').style
+        expect({ gridRowStart, gridRowEnd, gridColumnStart, gridColumnEnd }).toEqual({
+          gridColumnEnd: 'span 3',
+          gridColumnStart: '2',
+          gridRowEnd: 'auto',
+          gridRowStart: '2',
+        })
+      }
+    })
+    it('respects row start spans', async () => {
+      const editor = await renderTestEditorWithCode(
+        makeProjectCodeWithCustomPlacement({ gridColumn: '2', gridRow: 'span 2' }),
+        'await-first-dom-report',
+      )
+
+      // enlarge to the bottom
+      {
+        await runCellResizeTest(
+          editor,
+          'row-end',
+          gridCellTargetId(EP.fromString('sb/grid'), 3, 2),
+          EP.fromString('sb/grid/cell'),
+        )
+
+        const { gridRowStart, gridRowEnd, gridColumnStart, gridColumnEnd } =
+          editor.renderedDOM.getByTestId('cell').style
+        expect({ gridRowStart, gridRowEnd, gridColumnStart, gridColumnEnd }).toEqual({
+          gridColumnEnd: 'auto',
+          gridColumnStart: '2',
+          gridRowEnd: 'auto',
+          gridRowStart: 'span 3',
+        })
+      }
+
+      // shrink from the top
+      {
+        await runCellResizeTest(
+          editor,
+          'row-start',
+          gridCellTargetId(EP.fromString('sb/grid'), 2, 2),
+          EP.fromString('sb/grid/cell'),
+        )
+
+        const { gridRowStart, gridRowEnd, gridColumnStart, gridColumnEnd } =
+          editor.renderedDOM.getByTestId('cell').style
+        expect({ gridRowStart, gridRowEnd, gridColumnStart, gridColumnEnd }).toEqual({
+          gridColumnEnd: 'auto',
+          gridColumnStart: '2',
+          gridRowEnd: '4',
+          gridRowStart: 'span 2',
+        })
+      }
+
+      // enlarge back from the top
+      {
+        await runCellResizeTest(
+          editor,
+          'row-start',
+          gridCellTargetId(EP.fromString('sb/grid'), 1, 2),
+          EP.fromString('sb/grid/cell'),
+        )
+
+        const { gridRowStart, gridRowEnd, gridColumnStart, gridColumnEnd } =
+          editor.renderedDOM.getByTestId('cell').style
+        expect({ gridRowStart, gridRowEnd, gridColumnStart, gridColumnEnd }).toEqual({
+          gridColumnEnd: 'auto',
+          gridColumnStart: '2',
+          gridRowEnd: 'auto',
+          gridRowStart: 'span 3',
+        })
+      }
+    })
+    it('respects row end spans', async () => {
+      const editor = await renderTestEditorWithCode(
+        makeProjectCodeWithCustomPlacement({ gridColumn: '2', gridRow: '2 / span 2' }),
+        'await-first-dom-report',
+      )
+
+      // enlarge to the bottom
+      {
+        await runCellResizeTest(
+          editor,
+          'row-end',
+          gridCellTargetId(EP.fromString('sb/grid'), 4, 2),
+          EP.fromString('sb/grid/cell'),
+        )
+
+        const { gridRowStart, gridRowEnd, gridColumnStart, gridColumnEnd } =
+          editor.renderedDOM.getByTestId('cell').style
+        expect({ gridRowStart, gridRowEnd, gridColumnStart, gridColumnEnd }).toEqual({
+          gridColumnEnd: 'auto',
+          gridColumnStart: '2',
+          gridRowEnd: 'span 3',
+          gridRowStart: '2',
+        })
+      }
+    })
+  })
 })
 
 const ProjectCode = `import * as React from 'react'
@@ -948,3 +1127,42 @@ export var storyboard = (
 function unsafeCast<T>(a: unknown): T {
   return a as T
 }
+
+function makeProjectCodeWithCustomPlacement(params: {
+  gridColumn: string
+  gridRow: string
+}): string {
+  return `import * as React from 'react'
+import { Storyboard } from 'utopia-api'
+
+export var storyboard = (
+  <Storyboard data-uid='sb'>
+    <div
+      style={{
+        backgroundColor: '#aaaaaa33',
+        position: 'absolute',
+        width: 600,
+        height: 400,
+        display: 'grid',
+        gap: 10,
+        gridTemplateColumns: '1fr 1fr 1fr 1fr',
+        gridTemplateRows: '1fr 1fr 1fr 1fr',
+      }}
+      data-uid='grid'
+    >
+      <div
+        style={{
+          backgroundColor: '#aaaaaa33',
+          alignSelf: 'stretch',
+          justifySelf: 'stretch',
+          gridColumn: '${params.gridColumn}',
+          gridRow: '${params.gridRow}',
+        }}
+        data-uid='cell'
+		data-testid='cell'
+      />
+    </div>
+  </Storyboard>
+)
+`
+}

editor/src/components/canvas/canvas-strategies/strategies/grid-resize-element-strategy.ts

@@ -1,11 +1,18 @@
 import { MetadataUtils } from '../../../../core/model/element-metadata-utils'
 import * as EP from '../../../../core/shared/element-path'
+import type {
+  GridElementProperties,
+  GridPositionOrSpan,
+  GridPositionValue,
+} from '../../../../core/shared/element-template'
+import { gridSpanNumeric, isGridSpan } from '../../../../core/shared/element-template'
 import {
   type CanvasRectangle,
   isInfinityRectangle,
   rectangleIntersection,
 } from '../../../../core/shared/math-utils'
 import { gridContainerIdentifier, gridItemIdentifier } from '../../../editor/store/editor-state'
+import { cssKeyword } from '../../../inspector/common/css-utils'
 import { isFillOrStretchModeAppliedOnAnySide } from '../../../inspector/inspector-common'
 import {
   controlsForGridPlaceholders,
@@ -21,7 +28,7 @@ import {
   strategyApplicationResult,
 } from '../canvas-strategy-types'
 import type { InteractionSession } from '../interaction-state'
-import { findOriginalGrid, getCommandsForGridItemPlacement } from './grid-helpers'
+import { getCommandsForGridItemPlacement } from './grid-helpers'
 import { resizeBoundingBoxFromSide } from './resize-helpers'
 
 export const gridResizeElementStrategy: CanvasStrategyFactory = (
@@ -104,15 +111,60 @@ export const gridResizeElementStrategy: CanvasStrategyFactory = (
         null,
       )
 
-      const gridProps = getNewGridPropsFromResizeBox(resizeBoundingBox, allCellBounds)
+      const gridPropsNumeric = getNewGridPropsFromResizeBox(resizeBoundingBox, allCellBounds)
 
-      if (gridProps == null) {
+      if (gridPropsNumeric == null) {
         return emptyStrategyApplicationResult
       }
 
       const gridTemplate =
         selectedElementMetadata.specialSizeMeasurements.parentContainerGridProperties
 
+      const elementGridPropertiesFromProps =
+        selectedElementMetadata.specialSizeMeasurements.elementGridPropertiesFromProps
+
+      const columnCount =
+        gridPropsNumeric.gridColumnEnd.numericalPosition -
+        gridPropsNumeric.gridColumnStart.numericalPosition
+      const rowCount =
+        gridPropsNumeric.gridRowEnd.numericalPosition -
+        gridPropsNumeric.gridRowStart.numericalPosition
+
+      const gridProps: GridElementProperties = {
+        gridColumnStart: normalizePositionAfterResize(
+          elementGridPropertiesFromProps.gridColumnStart,
+          gridPropsNumeric.gridColumnStart,
+          columnCount,
+          'start',
+          elementGridPropertiesFromProps.gridColumnEnd,
+          gridPropsNumeric.gridColumnEnd,
+        ),
+        gridColumnEnd: normalizePositionAfterResize(
+          elementGridPropertiesFromProps.gridColumnEnd,
+          gridPropsNumeric.gridColumnEnd,
+          columnCount,
+          'end',
+          elementGridPropertiesFromProps.gridColumnStart,
+          gridPropsNumeric.gridColumnStart,
+        ),
+        gridRowStart: normalizePositionAfterResize(
+          elementGridPropertiesFromProps.gridRowStart,
+          gridPropsNumeric.gridRowStart,
+          rowCount,
+          'start',
+          elementGridPropertiesFromProps.gridRowEnd,
+          gridPropsNumeric.gridRowEnd,
+        ),
+        gridRowEnd: normalizePositionAfterResize(
+          elementGridPropertiesFromProps.gridRowEnd,
+          gridPropsNumeric.gridRowEnd,
+          rowCount,
+          'end',
+          elementGridPropertiesFromProps.gridRowStart,
+          gridPropsNumeric.gridRowStart,
+        ),
+      }
+
       return strategyApplicationResult(
         getCommandsForGridItemPlacement(selectedElement, gridTemplate, gridProps),
         [EP.parentPath(selectedElement)],
@@ -158,3 +210,30 @@ function getNewGridPropsFromResizeBox(
     gridColumnEnd: { numericalPosition: newColumnEnd },
   }
 }
+
+// After a resize happens and we know the numerical grid positioning of the new bounds,
+// return a normalized version of the new position so that it respects any spans that
+// may have been there before the resize, and/or default it to 'auto' when it would become redundant.
+function normalizePositionAfterResize(
+  position: GridPositionOrSpan | null,
+  resizedPosition: GridPositionValue,
+  size: number, // the number of cols/rows the cell occupies
+  bound: 'start' | 'end',
+  counterpart: GridPositionOrSpan | null,
+  counterpartResizedPosition: GridPositionValue,
+): GridPositionOrSpan | null {
+  if (isGridSpan(position)) {
+    if (size === 1) {
+      return cssKeyword('auto')
+    }
+    return gridSpanNumeric(size)
+  }
+  if (
+    isGridSpan(counterpart) &&
+    counterpartResizedPosition.numericalPosition === 1 &&
+    bound === 'end'
+  ) {
+    return cssKeyword('auto')
+  }
+  return resizedPosition
+}