Avoid quadratic copying in Table::getDisplayLines()

[swissspidy]

Table::getDisplayLines() merged each rendered row into the output with $out = array_merge( $out, $row ). That copies the entire output array for every row, so rendering takes quadratic time in the number of rows.

This shows up in WP-CLI's --format=table for large result sets. On a test site with ~96,600 posts, wp post list --format=table --fields=ID,post_title took 46 s, compared to ~7 s for --format=csv with the same data. With this change it takes 7.4 s, and the output is byte-identical.

The fix appends each rendered line to $out instead.

Measurements

Rendering a two-column table with getDisplayLines(), PHP 8.3:

Rows	Before	After
10,000	0.25 s	0.07 s
20,000	0.85 s	0.14 s
40,000	4.08 s	0.26 s

Testing

Added test_display_lines_keep_row_order_with_many_rows. It renders 5,000 rows, every 100th of which spans two lines, and checks the line count, the order of the rows and the placement of the wrapped lines. The full PHPUnit suite passes. PHPCS reports no new violations in the touched files.

Found while profiling WP-CLI for large lists (wp-cli/ideas#81, wp-cli/ideas#91).

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https://claude.ai/code/session_01D26yjkN2BiqCXT6p6o1WqS

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Generated by Claude Code

Summary by CodeRabbit

• Performance
  • Large tables now render rows with less intermediate processing, which may improve rendering efficiency. The displayed content and row order remain unchanged.
• Tests
  • Added coverage for large tables, including multiline values, row ordering, and table borders.

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• lib/cli/Table.php
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📝 Walkthrough

Walkthrough

getDisplayLines() now appends each rendered row line directly to the output array. A regression test checks ASCII output for 5,000 rows, including multiline values.

Changes

Table rendering

Layer / File(s)	Summary
Append rendered lines and verify table output lib/cli/Table.php, tests/Test_Table.php	getDisplayLines() appends rendered row lines directly to the output array. A regression test checks line count, row order, multiline values, and borders for 5,000 rows.

Priority: ➖ Normal

Estimated code review effort: 2 (Simple) | ~8 minutes

Change: Bug fix

Suggested reviewers: mrsdizzie, schlessera

Merge Risk: ⚪ Minimal · up to ea83d

The supplied evidence identifies no unresolved behavior or merge-blocking risk in this localized rendering optimization.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 25.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 4 functions across 2 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: avoiding quadratic copying in Table::getDisplayLines().
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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