This PR is to fix issue #30437

RenderTable._computeColumnWidths() had a logic error that caused flex columns to be collapsed to their minimum widths in certain situations dependent on the layout width constraint and the number of flex columns.

The problem was in a loop at the end of RenderTable._computeColumnWidths. After the flex columns are grown to fill the width constraint and if the table size is now greater than the constraint, this loop is supposed to evenly remove a portion of the deficit from each flex column to bring the table width into the constraint. Instead it removes all of flex space in each column and in the example code reduces every column to zero width.

The error is in the last if/else statement:

              if (availableDelta <= delta) {
                // shrank to minimum
                deficit -= widths[x] - minWidths[x];
                widths[x] = minWidths[x];
              } else {
                deficit -= availableDelta;
                widths[x] -= availableDelta;
                newAvailableColumns += 1;
              }

The delta variable was calculated to be the even portion of the deficit that is to be subtracted from each column:

final double delta = deficit / availableColumns;

The if/else statement is supposed to remove the availableDelta from a column width if availableDelta is less than delta, otherwise it should be subtracting delta from the columnWidth.

Instead, if availableDelta is greater than delta, it's removing all of availableDelta from the column width, which collapses it to its minimum width. The else statements should have been subtracting delta, not availableDelta.

Tests

A test was added to verify that a table with a constrained width evenly distributes its width between its columns. Prior to the fix, this test would fail and would result in zero width columns.

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