Themes: Optimize WP_Theme::get_post_templates() for efficiency

[MarcinDudekDev]

Summary

• Replace dual file_get_contents() calls with a single get_file_data() call, which reads only the first 8KB of each file instead of the entire contents
• Move get_block_templates() query inside the cache block so the DB query only fires on a cache miss
• Add unit tests covering caching behavior, get_file_data() integration, and cache invalidation on theme switch

Details

WP_Theme::get_post_templates() previously called file_get_contents() twice per PHP file — once for Template Name and once for Template Post Type — reading the entire file each time. This replaces both calls with a single get_file_data() call that reads only the first 8KB (consistent with how WordPress parses plugin and theme headers elsewhere in core).

Additionally, get_block_templates() was called outside the cache block, executing a WP_Query with posts_per_page=-1 on every invocation regardless of cache state. Moving it inside the cache block eliminates redundant database queries on cache hits.

Trac ticket: https://core.trac.wordpress.org/ticket/42513
Related: https://core.trac.wordpress.org/ticket/42517

Test plan

• Existing Tests_Admin_IncludesTheme tests pass (8/8, 55 assertions)
• PHPCS clean on both modified files
• Single-line template headers (<?php // Template Name: ... ?>) parsed correctly
• Multi-line docblock headers parsed correctly
• Template Post Type with multiple types parsed correctly
• Child theme template inheritance works correctly
• Verify performance improvement on a theme with many PHP files

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AI assistance: Yes
Tool(s): Claude Code (Anthropic)
Model(s): Claude Opus 4.6
Used for: Analysis of the performance bottleneck, implementation of the optimization, and writing unit tests. All code was reviewed and tested.

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This Pull Request is for code review only. Please keep all other discussion in the Trac ticket. Do not merge this Pull Request. See GitHub Pull Requests for Code Review in the Core Handbook for more details.

🤖 Generated with Claude Code

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[github-actions]

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