Fix various problems with reflow

- No longer reflow lines where the full unwrapped line contains the cursor
- Add guards to prevent y and ybase becoming invalid values

Part of Microsoft/vscode#67364
Fixes #1910

src/Buffer.ts

@@ -3,13 +3,13 @@
  * @license MIT
  */
 
-import { CircularList, IInsertEvent, IDeleteEvent } from './common/CircularList';
-import { CharData, ITerminal, IBuffer, IBufferLine, BufferIndex, IBufferStringIterator, IBufferStringIteratorResult } from './Types';
-import { EventEmitter } from './common/EventEmitter';
 import { IMarker } from 'xterm';
 import { BufferLine } from './BufferLine';
+import { reflowLargerApplyNewLayout, reflowLargerCreateNewLayout, reflowLargerGetLinesToRemove, reflowSmallerGetNewLineLengths } from './BufferReflow';
+import { CircularList, IDeleteEvent, IInsertEvent } from './common/CircularList';
+import { EventEmitter } from './common/EventEmitter';
 import { DEFAULT_COLOR } from './renderer/atlas/Types';
-import { reflowSmallerGetNewLineLengths, reflowLargerGetLinesToRemove, reflowLargerCreateNewLayout, reflowLargerApplyNewLayout } from './BufferReflow';
+import { BufferIndex, CharData, IBuffer, IBufferLine, IBufferStringIterator, IBufferStringIteratorResult, ITerminal } from './Types';
 
 export const DEFAULT_ATTR = (0 << 18) | (DEFAULT_COLOR << 9) | (256 << 0);
 export const CHAR_DATA_ATTR_INDEX = 0;
@@ -212,7 +212,7 @@ export class Buffer implements IBuffer {
     this.scrollBottom = newRows - 1;
 
     if (this._hasScrollback) {
-      this._reflow(newCols);
+      this._reflow(newCols, newRows);
 
       // Trim the end of the line off if cols shrunk
       if (this._cols > newCols) {
@@ -226,7 +226,7 @@ export class Buffer implements IBuffer {
     this._rows = newRows;
   }
 
-  private _reflow(newCols: number): void {
+  private _reflow(newCols: number, newRows: number): void {
     if (this._cols === newCols) {
       return;
     }
@@ -235,12 +235,12 @@ export class Buffer implements IBuffer {
     if (newCols > this._cols) {
       this._reflowLarger(newCols);
     } else {
-      this._reflowSmaller(newCols);
+      this._reflowSmaller(newCols, newRows);
     }
   }
 
   private _reflowLarger(newCols: number): void {
-    const toRemove: number[] = reflowLargerGetLinesToRemove(this.lines, newCols);
+    const toRemove: number[] = reflowLargerGetLinesToRemove(this.lines, newCols, this.ybase + this.y);
     if (toRemove.length > 0) {
       const newLayoutResult = reflowLargerCreateNewLayout(this.lines, toRemove);
       reflowLargerApplyNewLayout(this.lines, newLayoutResult.layout);
@@ -253,9 +253,13 @@ export class Buffer implements IBuffer {
     let viewportAdjustments = countRemoved;
     while (viewportAdjustments-- > 0) {
       if (this.ybase === 0) {
-        this.y--;
-        // Add an extra row at the bottom of the viewport
-        this.lines.push(new BufferLine(newCols, FILL_CHAR_DATA));
+        if (this.y > 0) {
+          this.y--;
+        }
+        if (this.lines.length < this._rows) {
+          // Add an extra row at the bottom of the viewport
+          this.lines.push(new BufferLine(newCols, FILL_CHAR_DATA));
+        }
       } else {
         if (this.ydisp === this.ybase) {
           this.ydisp--;
@@ -265,7 +269,7 @@ export class Buffer implements IBuffer {
     }
   }
 
-  private _reflowSmaller(newCols: number): void {
+  private _reflowSmaller(newCols: number, newRows: number): void {
     // Gather all BufferLines that need to be inserted into the Buffer here so that they can be
     // batched up and only committed once
     const toInsert = [];
@@ -285,6 +289,13 @@ export class Buffer implements IBuffer {
         wrappedLines.unshift(nextLine);
       }
 
+      // If these lines contain the cursor don't touch them, the program will handle fixing up
+      // wrapped lines with the cursor
+      const absoluteY = this.ybase + this.y;
+      if (absoluteY >= y && absoluteY < y + wrappedLines.length) {
+        continue;
+      }
+
       const lastLineLength = wrappedLines[wrappedLines.length - 1].getTrimmedLength();
       const destLineLengths = reflowSmallerGetNewLineLengths(wrappedLines, this._cols, newCols);
       const linesToAdd = destLineLengths.length - wrappedLines.length;
@@ -357,10 +368,13 @@ export class Buffer implements IBuffer {
             this.ydisp++;
           }
         } else {
-          if (this.ybase === this.ydisp) {
-            this.ydisp++;
+          // Ensure ybase does not exceed its maximum value
+          if (this.ybase < Math.min(this.lines.maxLength, this.lines.length + countToInsert) - newRows) {
+            if (this.ybase === this.ydisp) {
+              this.ydisp++;
+            }
+            this.ybase++;
           }
-          this.ybase++;
         }
       }
     }

src/BufferReflow.ts

@@ -3,10 +3,10 @@
  * @license MIT
  */
 
+import { FILL_CHAR_DATA } from './Buffer';
 import { BufferLine } from './BufferLine';
 import { CircularList, IDeleteEvent } from './common/CircularList';
 import { IBufferLine } from './Types';
-import { FILL_CHAR_DATA } from './Buffer';
 
 export interface INewLayoutResult {
   layout: number[];
@@ -19,7 +19,7 @@ export interface INewLayoutResult {
  * @param lines The buffer lines.
  * @param newCols The columns after resize.
  */
-export function reflowLargerGetLinesToRemove(lines: CircularList<IBufferLine>, newCols: number): number[] {
+export function reflowLargerGetLinesToRemove(lines: CircularList<IBufferLine>, newCols: number, bufferAbsoluteY: number): number[] {
   // Gather all BufferLines that need to be removed from the Buffer here so that they can be
   // batched up and only committed once
   const toRemove: number[] = [];
@@ -39,6 +39,13 @@ export function reflowLargerGetLinesToRemove(lines: CircularList<IBufferLine>, n
       nextLine = lines.get(++i) as BufferLine;
     }
 
+    // If these lines contain the cursor don't touch them, the program will handle fixing up wrapped
+    // lines with the cursor
+    if (bufferAbsoluteY >= y && bufferAbsoluteY < i) {
+      y += wrappedLines.length - 1;
+      continue;
+    }
+
     // Copy buffer data to new locations
     let destLineIndex = 0;
     let destCol = wrappedLines[destLineIndex].getTrimmedLength();
@@ -64,7 +71,7 @@ export function reflowLargerGetLinesToRemove(lines: CircularList<IBufferLine>, n
       }
 
       // Make sure the last cell isn't wide, if it is copy it to the current dest
-      if (destCol === 0) {
+      if (destCol === 0 && destLineIndex !== 0) {
         if (wrappedLines[destLineIndex - 1].getWidth(newCols - 1) === 2) {
           wrappedLines[destLineIndex].copyCellsFrom(wrappedLines[destLineIndex - 1], newCols - 1, destCol++, 1, false);
           // Null out the end of the last row
@@ -166,7 +173,6 @@ export function reflowLargerApplyNewLayout(lines: CircularList<IBufferLine>, new
  */
 export function reflowSmallerGetNewLineLengths(wrappedLines: BufferLine[], oldCols: number, newCols: number): number[] {
   const newLineLengths: number[] = [];
-
   const cellsNeeded = wrappedLines.map(l => l.getTrimmedLength()).reduce((p, c) => p + c);
 
   // Use srcCol and srcLine to find the new wrapping point, use that to get the cellsAvailable and