Error thrown when inserting overlapping isolate markers

src/line/saw_special_spans.js

@@ -1,5 +1,5 @@
 // Optimize some code when these features are not used.
-export let sawReadOnlySpans = false, sawCollapsedSpans = false
+export let sawReadOnlySpans = false, sawCollapsedSpans = false, sawIsolateSpans = false
 
 export function seeReadOnlySpans() {
   sawReadOnlySpans = true
@@ -8,3 +8,7 @@ export function seeReadOnlySpans() {
 export function seeCollapsedSpans() {
   sawCollapsedSpans = true
 }
+
+export function seeIsolateSpans() {
+  sawIsolateSpans = true
+}

src/line/spans.js

@@ -1,7 +1,7 @@
 import { indexOf, lst } from "../util/misc.js"
 
 import { cmp } from "./pos.js"
-import { sawCollapsedSpans } from "./saw_special_spans.js"
+import { sawCollapsedSpans, sawIsolateSpans } from "./saw_special_spans.js"
 import { getLine, isLine, lineNo } from "./utils_line.js"
 
 // TEXTMARKER SPANS
@@ -247,6 +247,21 @@ export function conflictingCollapsedRange(doc, lineNo, from, to, marker) {
   }
 }
 
+// Test whether two isolate ranges overlap, which is not allowed
+export function conflictingIsolateRange(doc, lineNo$$2, from, to, marker) {
+  let line = getLine(doc, lineNo$$2)
+  let sis = sawIsolateSpans && line.markedSpans
+  if (sis) { for (let i = 0; i < sis.length; ++i) {
+    let si = sis[i]
+    if (!si.marker.isolate) { continue }
+    let found = si.marker.find(0)
+    let fromCmp = cmp(found.from, from) || extraLeft(si.marker) - extraLeft(marker)
+    if (fromCmp <= 0 && (si.marker.inclusiveRight && marker.inclusiveLeft ? cmp(found.to, from) >= 0 : cmp(found.to, from) > 0) ||
+        fromCmp >= 0 && (si.marker.inclusiveRight && marker.inclusiveLeft ? cmp(found.from, to) <= 0 : cmp(found.from, to) < 0))
+        { return true }
+  } }
+}
+
 // A visual line is a line as drawn on the screen. Folding, for
 // example, can cause multiple logical lines to appear on the same
 // visual line. This finds the start of the visual line that the

src/model/mark_text.js

@@ -4,8 +4,8 @@ import { endOperation, operation, runInOp, startOperation } from "../display/ope
 import { clipPos, cmp, Pos } from "../line/pos.js"
 import { lineNo, updateLineHeight } from "../line/utils_line.js"
 import { clearLineMeasurementCacheFor, findViewForLine, textHeight } from "../measurement/position_measurement.js"
-import { seeReadOnlySpans, seeCollapsedSpans } from "../line/saw_special_spans.js"
-import { addMarkedSpan, conflictingCollapsedRange, getMarkedSpanFor, lineIsHidden, lineLength, MarkedSpan, removeMarkedSpan, visualLine } from "../line/spans.js"
+import { seeReadOnlySpans, seeCollapsedSpans, seeIsolateSpans } from "../line/saw_special_spans.js"
+import { addMarkedSpan, conflictingCollapsedRange, conflictingIsolateRange, getMarkedSpanFor, lineIsHidden, lineLength, MarkedSpan, removeMarkedSpan, visualLine } from "../line/spans.js"
 import { copyObj, indexOf, lst } from "../util/misc.js"
 import { signalLater } from "../util/operation_group.js"
 import { widgetHeight } from "../measurement/widgets.js"
@@ -177,6 +177,12 @@ export function markText(doc, from, to, options, type) {
       throw new Error("Inserting collapsed marker partially overlapping an existing one")
     seeCollapsedSpans()
   }
+  if (marker.isolate) {
+    if (conflictingIsolateRange(doc, from.line, from, to, marker) ||
+        from.line != to.line && conflictingIsolateRange(doc, to.line, from, to, marker))
+        { throw new Error("Inserting isolate marker partially overlapping an existing one") }
+    seeIsolateSpans()
+  }
 
   if (marker.addToHistory)
     addChangeToHistory(doc, {from: from, to: to, origin: "markText"}, doc.sel, NaN)