[features-] fix cursor index in hide-uniform-cols

[midichef]

Closes #2577.

Repro case:
echo "a,a\n1,1\n1,1" |vd -f csv then move the cursor to the right column, then hide-uniform-cols:

File "/home/midichef/.venv/lib/python3.12/site-packages/visidata/sheets.py", line 780, in allAggregators
    col = self.availCols[vcolidx]
          ~~~~~~~~~~~~~~^^^^^^^^^
IndexError: list index out of range

In this PR, I do the cursor move in hide_uniform_cols(), not inside Column.hide(). That's because I think of hide() as a low level width adjuster that does not conceptually involve the cursor, and we don't want to be calling calcColLayout() in it unnecessarily. Or does that leave the door open for a repeat of this error with other callers of Column.hide()?

[saulpw]

Does it work to just call checkCursor() after the columns are hidden? That would be my preferred method, whether in the execstr or hide_uniform_cols or in .hide() itself.

[midichef]

It almost works, but the problem is in one of the checkCursor() calls. The full stack trace shows the problem is in the new allAggregators function from 551b06c.

  File "/home/midichef/.venv/lib/python3.12/site-packages/visidata/mainloop.py", line 252, in mainloop
    vd.callNoExceptions(sheet.checkCursor)
...
  File "/home/midichef/.venv/lib/python3.12/site-packages/visidata/sheets.py", line 643, in checkCursor
    elif self.bottomRowIndex < self.cursorRowIndex:
...                                            ^^^^^^^^^^^^^^^^
  File "/home/midichef/.venv/lib/python3.12/site-packages/visidata/sheets.py", line 427, in nFooterRows
    return len(self.allAggregators) + 1
               ^^^^^^^^^^^^^^^^^^^
...
  File "/home/midichef/.venv/lib/python3.12/site-packages/visidata/sheets.py", line 780, in allAggregators
    col = self.availCols[vcolidx]
          ~~~~~~~~~~~~~~^^^^^^^^^
IndexError: list index out of range

It seems like availCols is using a cached value that is wrong due to the col.hide() calls. The IndexError goes away if I clear the cache with Sheet.visibleCols.fget.cache_clear() in hide_uniform_cols(), right after col.hide(). But the error still happens if I instead clear the cache on availCols with Sheet.availCols.fget.cache_clear().

What's the right solution here?

[saulpw]

Hmmm...does Sheet.clear_all_caches() work? That's the recommended way to clear these caches; instead of trying to find the exact right one to clear, just clear them all. (Cache invalidation being one of the hardest problems in computer science.)

[midichef]

The allAggregators IndexError error is being triggered in other situations:

    col = self.availCols[vcolidx]
          ~~~~~~~~~~~~~~^^^^^^^^^
IndexError: list index out of range

For example, it can be triggered on a standard TsvSheet by pressing i, then U. So there is more work to do relating to allAggregators. I'll open a separate Issue for that.

[saulpw]

Thanks for fixing this!