Remove quadratic complexity of adding lots of marks to a single line

(As long as this is done in an operation.)

Closes #6682

src/display/operations.js

@@ -36,7 +36,8 @@ export function startOperation(cm) {
     scrollLeft: null, scrollTop: null, // Intermediate scroll position, not pushed to DOM yet
     scrollToPos: null,       // Used to scroll to a specific position
     focus: false,
-    id: ++nextOpId           // Unique ID
+    id: ++nextOpId,          // Unique ID
+    markArrays: null         // Used by addMarkedSpan
   }
   pushOperation(cm.curOp)
 }

src/line/spans.js

@@ -18,6 +18,7 @@ export function getMarkedSpanFor(spans, marker) {
     if (span.marker == marker) return span
   }
 }
+
 // Remove a span from an array, returning undefined if no spans are
 // left (we don't store arrays for lines without spans).
 export function removeMarkedSpan(spans, span) {
@@ -26,9 +27,16 @@ export function removeMarkedSpan(spans, span) {
     if (spans[i] != span) (r || (r = [])).push(spans[i])
   return r
 }
+
 // Add a span to a line.
-export function addMarkedSpan(line, span) {
-  line.markedSpans = line.markedSpans ? line.markedSpans.concat([span]) : [span]
+export function addMarkedSpan(line, span, op) {
+  let inThisOp = op && window.WeakSet && (op.markedSpans || (op.markedSpans = new WeakSet))
+  if (inThisOp && inThisOp.has(line.markedSpans)) {
+    line.markedSpans.push(span)
+  } else {
+    line.markedSpans = line.markedSpans ? line.markedSpans.concat([span]) : [span]
+    if (inThisOp) inThisOp.add(line.markedSpans)
+  }
   span.marker.attachLine(line)
 }
 

src/model/mark_text.js

@@ -187,7 +187,7 @@ export function markText(doc, from, to, options, type) {
     if (marker.collapsed && curLine != from.line) updateLineHeight(line, 0)
     addMarkedSpan(line, new MarkedSpan(marker,
                                        curLine == from.line ? from.ch : null,
-                                       curLine == to.line ? to.ch : null))
+                                       curLine == to.line ? to.ch : null), doc.cm && doc.cm.curOp)
     ++curLine
   })
   // lineIsHidden depends on the presence of the spans, so needs a second pass

test/lint.js

@@ -3,7 +3,7 @@ var blint = require("blint");
 ["mode", "lib", "addon", "keymap"].forEach(function(dir) {
   blint.checkDir(dir, {
     browser: true,
-    allowedGlobals: ["CodeMirror", "define", "test", "requirejs", "globalThis"],
+    allowedGlobals: ["CodeMirror", "define", "test", "requirejs", "globalThis", "WeakSet"],
     ecmaVersion: 5,
     tabs: dir == "lib"
   });
@@ -12,6 +12,7 @@ var blint = require("blint");
 ["src"].forEach(function(dir) {
   blint.checkDir(dir, {
     browser: true,
+    allowedGlobals: ["WeakSet"],
     ecmaVersion: 6,
     semicolons: false
   });