Preserve index prefix lengths and order in SHOW CREATE TABLE primary keys

[samuelmbabhazi]

Summary

SHOW CREATE TABLE reconstructs the PRIMARY KEY clause from the information schema, but unlike the branch that handles all other indexes, it emitted only the quoted column names. Index prefix lengths (SUB_PART) and descending order (COLLATION = 'D') were dropped, so a table created with PRIMARY KEY (session_id(100)) on a MEDIUMTEXT column came back as PRIMARY KEY (session_id).

The practical impact: exports built on top of SHOW CREATE TABLE (for example wp sqlite export, which WordPress Studio uses for its push feature) produce a dump that MySQL rejects with ERROR 1170 (42000): BLOB/TEXT column used in key specification without a key length. The prefix is recorded correctly in _wp_sqlite_mysql_information_schema_statistics (SUB_PART = 100); the bug was emission only. Discovered through Automattic/studio#4739.

Fixes #501

Fix

The column formatting closure that already handled SUB_PART and DESC for regular keys is hoisted and shared by the PRIMARY KEY branch, so both paths emit identical column definitions.

Testing

• New regression test: a PRIMARY KEY (session_id(100)) on MEDIUMTEXT round-trips through SHOW CREATE TABLE with its prefix, a composite key PRIMARY KEY (a, b(50)) keeps the prefix only where defined, and PRIMARY KEY (a DESC, b) keeps its descending key part. The test fails on the previous code.
• Verified against a real MySQL 8 server: its SHOW CREATE TABLE emits PRIMARY KEY (session_id(100)) and PRIMARY KEY (a DESC,b) for the same tables, matching the fixed output; the previous output fails to import there with ERROR 1170, the fixed output imports cleanly.
• Full mysql-on-sqlite unit suite: 875 tests, 1428750 assertions, no failures (the same 17 skipped and 2 incomplete as on trunk, PHP 8.5).
• composer run check-cs is clean on both changed files.

Summary by CodeRabbit

• Bug Fixes
  • Corrected SHOW CREATE TABLE output to preserve primary-key index prefix lengths for single-column and composite keys.
  • Ensured descending key parts and column definitions are represented accurately in generated table-creation statements.
  • Improved consistency between primary-key and secondary-index formatting.

[coderabbitai]

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📥 Commits

Reviewing files that changed from the base of the PR and between abf0dac and 9e45b6e.

📒 Files selected for processing (2)

• packages/mysql-on-sqlite/src/sqlite/class-wp-mysql-on-sqlite.php
• packages/mysql-on-sqlite/tests/WP_MySQL_On_SQLite_Metadata_Tests.php

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📝 Walkthrough

Walkthrough

The table-definition generator now uses shared formatting for primary and secondary index columns. The formatter preserves column names, prefix lengths, and descending order. Metadata tests cover single-column and composite primary keys.

Changes

MySQL-on-SQLite metadata

Layer / File(s)	Summary
Index formatting and validation packages/mysql-on-sqlite/src/sqlite/class-wp-mysql-on-sqlite.php, packages/mysql-on-sqlite/tests/WP_MySQL_On_SQLite_Metadata_Tests.php	A shared formatter handles primary and secondary index columns. Tests verify primary-key prefix lengths and descending order in SHOW CREATE TABLE output.

Estimated code review effort: 2 (Simple) | ~10 minutes

Merge Risk: ⚪ Minimal · up to 9e45b

This localized change preserves primary-key prefix lengths and descending order in generated table definitions, preventing invalid exports while leaving other index formatting unchanged. No actionable merge-blocking risk remains after normal checks and review.

Suggested reviewers: janjakes

🚥 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
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.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: preserving index prefix lengths and order when reconstructing primary keys in SHOW CREATE TABLE.

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