Improve logic for when to show a decoration as a widget

FIX: Properly display diagnostics that just cover multiple newlines as widgets.

See https://discuss.codemirror.net/t/request-make-mark-decorations-visible-on-empty-lines/9532

Author: marijnh

src/lint.ts

@@ -103,6 +103,7 @@ class LintState {
 
     let sorted = diagnostics.slice().sort((a, b) => a.from - b.from || a.to - b.to)
     let deco = new RangeSetBuilder<Decoration>(), active: Diagnostic[] = [], pos = 0
+    let scan = state.doc.iter(), scanPos = 0
     for (let i = 0;;) {
       let next = i == sorted.length ? null : sorted[i]
       if (!next && !active.length) break
@@ -127,8 +128,23 @@ class LintState {
           break
         }
       }
+      let widget = false
+      if (active.some(d => d.from == from && d.to == to)) {
+        widget = from == to
+        if (!widget && to - from < 10) {
+          let behind = from - (scanPos + scan.value.length)
+          if (behind > 0) { scan.next(behind); scanPos = from }
+          for (let check = from;;) {
+            if (check >= to) { widget = true; break }
+            if (!scan.lineBreak && scanPos + scan.value.length > check) break
+            check = scanPos + scan.value.length
+            scanPos += scan.value.length
+            scan.next()
+          }
+        }
+      }
       let sev = maxSeverity(active)
-      if (active.some(d => d.from == d.to || (d.from == d.to - 1 && state.doc.lineAt(d.from).to == d.from))) {
+      if (widget) {
         deco.add(from, from, Decoration.widget({
           widget: new DiagnosticWidget(sev),
           diagnostics: active.slice()

test/test-lint.ts

@@ -18,8 +18,8 @@ function diagnostics(s: EditorState) {
   return found
 }
 
-function state(ds: readonly Diagnostic[]) {
-  let s = EditorState.create({doc: "0123456789"})
+function state(ds: readonly Diagnostic[], doc = "0123456789") {
+  let s = EditorState.create({doc})
   return s.update(setDiagnostics(s, ds)).state
 }
 
@@ -58,4 +58,14 @@ describe("lint", () => {
     })
     istJSON(result, [[0, 3, "error"], [3, 4, "error"], [4, 5, "error"], [5, 8, "warning"]])
   })
+
+  it("creates widgets for empty and newline-only ranges", () => {
+    let ds = [w(0, 0, "a"), e(1, 2, "b"), e(3, 5, "c"), w(6, 6, "d")]
+    let deco = state(ds, "a\nb\n\ncd").facet(EditorView.decorations)[0] as DecorationSet
+    let result: [number, number, boolean][] = []
+    deco.between(0, 10, (from, to, val) => {
+      result.push([from, to, !!val.widget])
+    })
+    istJSON(result, [[0, 0, true], [1, 1, true], [3, 3, true], [6, 6, true]])
+  })
 })