From 66fcdb2583edf3e23ee7f5a9d3069b72c3917c5f Mon Sep 17 00:00:00 2001
From: Daniel Imms <2193314+Tyriar@users.noreply.github.com>
Date: Fri, 1 May 2026 14:11:14 -0700
Subject: [PATCH] Fix test/startCol handling

---
 src/common/buffer/BufferLine.test.ts | 32 ++++++++++------------------
 src/common/buffer/BufferLine.ts      |  6 +++---
 2 files changed, 14 insertions(+), 24 deletions(-)

diff --git a/src/common/buffer/BufferLine.test.ts b/src/common/buffer/BufferLine.test.ts
index 10781745d..f7d434532 100644
--- a/src/common/buffer/BufferLine.test.ts
+++ b/src/common/buffer/BufferLine.test.ts
@@ -808,40 +808,30 @@ describe('BufferLine', function(): void {
       assert.equal(extendedAttributes(line, 4), extendedAttributes(initial, 4));
     });
 
-    it('should cache canonical trimmed string translations', () => {
+    it('should cache canonical non-trimmed string translations', () => {
       const line = new TestBufferLine(3);
       line.setCell(0, createCellData(1, 'a', 1));
       line.setCell(1, createCellData(1, 'b', 1));
       line.setCell(2, createCellData(1, 'c', 1));
 
-      const originalGetTrimmedLength = line.getTrimmedLength.bind(line);
-      let trimmedLengthCalls = 0;
-      line.getTrimmedLength = (): number => {
-        trimmedLengthCalls++;
-        return originalGetTrimmedLength();
-      };
-
+      const translated = line.translateToString(false, undefined, undefined, undefined);
+      assert.equal(translated, 'abc');
+      assert.equal((line as any)._cachedTrimmedString, 'abc');
+      (line as any)._cachedTrimmedString = 'cached';
+      assert.equal(line.translateToString(false, undefined, undefined, undefined), 'cached');
+      // Any optional translation argument should bypass cache.
+      assert.equal(line.translateToString(false, 0, 2, undefined), 'ab');
       assert.equal(line.translateToString(true, undefined, undefined, undefined), 'abc');
-      assert.equal(line.translateToString(true, undefined, undefined, undefined), 'abc');
-      assert.equal(trimmedLengthCalls, 1);
     });
 
     it('should invalidate cached trimmed strings on line mutations', () => {
       const assertCacheInvalidated = (mutate: (line: TestBufferLine) => void): void => {
         const line = new TestBufferLine(5);
         line.fill(createCellData(1, 'a', 1));
-        const originalGetTrimmedLength = line.getTrimmedLength.bind(line);
-        let trimmedLengthCalls = 0;
-        line.getTrimmedLength = (): number => {
-          trimmedLengthCalls++;
-          return originalGetTrimmedLength();
-        };
-        assert.equal(line.translateToString(true, undefined, undefined, undefined), 'aaaaa');
-        assert.equal(line.translateToString(true, undefined, undefined, undefined), 'aaaaa');
-        assert.equal(trimmedLengthCalls, 1);
+        line.translateToString(false, undefined, undefined, undefined);
+        assert.equal((line as any)._cachedTrimmedString, 'aaaaa');
         mutate(line);
-        line.translateToString(true, undefined, undefined, undefined);
-        assert.equal(trimmedLengthCalls, 2);
+        assert.equal((line as any)._cachedTrimmedString, undefined);
       };
 
       assertCacheInvalidated(line => line.set(0, [0, 'b', 1, 'b'.charCodeAt(0)]));
diff --git a/src/common/buffer/BufferLine.ts b/src/common/buffer/BufferLine.ts
index d8e911906..40c963190 100644
--- a/src/common/buffer/BufferLine.ts
+++ b/src/common/buffer/BufferLine.ts
@@ -520,8 +520,8 @@ export class BufferLine implements IBufferLine {
   }
 
   /**
-   * Translates the buffer line to a string. Using any of the optional arguments will disable the
-   * cache.
+   * Translates the buffer line to a string. Caching only applies to canonical non-trimmed
+   * translation requests. Using `trimRight` or any optional range/mapping arguments disables cache.
    *
    * @param trimRight Whether to trim any empty cells on the right.
    * @param startCol The column to start the string (0-based inclusive).
@@ -534,7 +534,7 @@ export class BufferLine implements IBufferLine {
    * returned string, the corresponding entries in `outColumns` will have the same column number.
    */
   public translateToString(trimRight?: boolean, startCol?: number, endCol?: number, outColumns?: number[]): string {
-    const isCanonicalTrimmedRequest = !trimRight && !startCol && endCol === undefined && outColumns === undefined;
+    const isCanonicalTrimmedRequest = !trimRight && (startCol === undefined || startCol === 0) && endCol === undefined && outColumns === undefined;
     if (isCanonicalTrimmedRequest && this._cachedTrimmedString !== undefined) {
       return this._cachedTrimmedString;
     }