Stop repeat exports corrupting files which contain a table

[Mike-Crowley]

Fixes #1725

Why it looked like a heisenbug

The corruption never happens on a fresh file — which is why the repro in #1725 didn't reproduce. It happens when the same export runs into an existing file, the classic regenerated-report pattern:

# run this twice (no -ClearSheet, no -Append) and the file is corrupt:
$data | Export-Excel $xlsx_path -WorksheetName "Geteilte Postfächer" -AutoSize -AutoFilter -TableStyle Light2

Two distinct illegal states get written, both confirmed by inspecting the raw sheet XML and by real Excel refusing to open the files via COM automation:

1. Two overlapping tables. With -TableStyle but no -TableName, Add-ExcelTable always called Tables.Add(), so the second run stacked Table2 on top of Table1 over the same cells.
2. A table plus a worksheet autofilter on the same cells. A leftover sheet autofilter from an earlier -AutoFilter export clashed with a table added later — and vice versa, -AutoFilter happily added a filter over an existing table.

Excel repairs both by stripping the table parts — which is exactly the reported "style not applied", and explains @jamesrudolph's observation that opening and saving the file once made future overwrites work (the repair removes the leftover state).

Changes

• Add-ExcelTable: when the target range overlaps an existing table, that table is now updated instead of a new one being stacked over it (matching what the named-table path already intended). The update:
  • goes through EPPlus's Address property so its cached address stays in step with the XML — later property changes such as turning the totals row on compute from that cache;
  • keeps the extra row of a table that shows a totals row, and points the table's internal filter at the header + data rows only;
  • rebuilds the tableColumns definitions when the column count changed (Excel requires them to match the header cells exactly — a mismatch is itself a repair condition);
  • renames via the Name property when a -TableName differs from the overlapped table's name, so EPPlus's name lookup keeps working in -PassThru/-ExcelPackage sessions.
  • Tables.Delete is deliberately not used — in the bundled EPPlus 4.5.3.2 it leaves the deleted table part in the saved package (verified).
• Export-Excel: removes a leftover worksheet autofilter that overlaps a newly created table, and the -AutoFilter branch warns and skips when an existing table already covers the data range (non-overlapping autofilters and disjoint tables are left alone).
• New private helper Test-ExcelRangeOverlap (EPPlus's Collide is not public in 4.5).

This also repairs two related pre-existing corruptions that reproduce on master even with -TableName: re-exporting with a changed column count (ref width no longer matched the stored column definitions), and re-exporting over a table that shows a totals row (totalsRowCount was kept while the range shrank onto the data).

Verification

• Matrix of 15 overwrite scenarios (rerun ×2/×3, alternating autofilter/table, row growth/shrink, column growth/shrink, named↔unnamed transitions, totals-row tables, in-session -PassThru chains, disjoint side-by-side tables) — every resulting file inspected at the XML level and opened in real Excel via COM; all open cleanly with exactly one correctly-styled table. Before the fix, seven of those scenarios produced files Excel refused to open.
• 11 new Pester tests (__tests__/TableOverwrite.tests.ps1), EPPlus-only so they run on the Linux/macOS CI.
• Full local suite: no new failures vs master (289 passed; the 5 failures present are the pre-existing Set-ItResult -Pending ones addressed by Make the CI pipeline work with Pester 5 and later #1743).
• Fresh single-export files are unchanged in shape; two disjoint tables on one sheet still work; the -Append-to-table path still stretches the table correctly.

Known remaining gaps, unchanged from master and out of scope here: repeat exports of System.Data.DataTable input (the table is created inside EPPlus's LoadFromDataTable, which throws on collision rather than corrupting), and calling Export-Excel with table parameters but no data onto a sheet holding several disjoint tables.

🤖 Generated with Claude Code

[Copilot]

Pull request overview

Fixes file corruption when repeatedly exporting into an existing worksheet where tables and worksheet-level autofilters can end up overlapping (Excel repairs by stripping table parts/styles, or refuses to open the file).

Changes:

• Rework Add-ExcelTable to detect overlap with an existing table and update/rename that table in-place instead of stacking a new one over the same cells.
• Update Export-Excel to (a) remove a leftover worksheet autofilter when creating a table over the same range, and (b) warn/skip adding a worksheet autofilter when an overlapping table already provides filtering.
• Add Test-ExcelRangeOverlap helper plus a new Pester test suite covering repeat-export scenarios (growth/shrink, column width changes, totals-row tables, named↔unnamed transitions, and in-session -PassThru chains).

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
Public/Export-Excel.ps1	Avoids writing an invalid worksheet-autofilter/table overlap during repeated exports by removing or skipping conflicting autofilters.
Public/Add-ExcelTable.ps1	Prevents overlapping tables by reusing/updating (and optionally renaming) an existing table when the target range collides.
Private/Test-ExcelRangeOverlap.ps1	Adds a small overlap predicate for EPPlus address/range objects to support collision detection (EPPlus 4.5 lacks a public collide API).
tests/TableOverwrite.tests.ps1	Adds regression tests to verify repeated exports don’t produce overlapping tables or conflicting autofilters and that table metadata stays consistent.

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