Improve posAtCoords in non-uniform height lines

FIX: Fix an issue where `EditorView.posAtCoords` could incorrectly return a position
near a higher element on the line, in mixed-font-size lines.

Author: marijnh

src/cursor.ts

@@ -327,6 +327,18 @@ class InlineCoordsScan {
       this.y = (side.top + side.bottom) / 2
       return this.scan(positions, getRects)
     }
+    // Handle the case where closest matched a higher element on the
+    // same line as an element below/above the coords
+    if (closestDx) {
+      if (above && above.bottom > closestRect.top) {
+        this.y = above.bottom - 1
+        return this.scan(positions, getRects)
+      }
+      if (below && below.top < closestRect.bottom) {
+        this.y = below.top + 1
+        return this.scan(positions, getRects)
+      }
+    }
     let ltr = (bidi ? this.dirAt(positions[closestI], 1) : this.baseDir) == Direction.LTR
     return {
       i: closestI,

test/webtest-coords.ts

@@ -243,6 +243,12 @@ describe("EditorView coords", () => {
     let c4 = cm.coordsAtPos(4)!
     ist(cm.posAtCoords({x: c4.left + 5, y: c4.bottom + 7}), 9)
   })
+
+  it("can handle coordinates above small text in a non-uniform line", () => {
+    let cm = tempView("abcdefgh", [deco(Decoration.mark({attributes: {style: "font-size: 200%"}}).range(6, 7))])
+    let c4 = cm.coordsAtPos(4)!
+    ist(cm.posAtCoords({x: c4.left, y: c4.top - 4}), 4)
+  })
 })
 
 describe("coordsForChar", () => {