Fix build failure when frontend_path is set without prerendering

[masenf]

Type of change

• Bug fix (non-breaking change which fixes an issue)

Description

Fixes a FileNotFoundError that occurs when running reflex run --env prod or reflex export with frontend_path configured and route prerendering disabled (REFLEX_SSR=false).

Root cause: When prerendering is disabled, the static output directory structure is not created with the frontend_path prefix. The build process attempted to move files into a non-existent prefix directory, causing the failure.

Solution: Explicitly create the prefix directory before attempting to relocate static files into it. This ensures the directory exists regardless of whether prerendering created it.

Changes

1. reflex/utils/build.py: Modified the build() function to create the prefix directory before moving files, and simplified the file movement logic to use the pre-computed prefix_dir variable.

2. tests/units/utils/test_build.py:

   • Extracted common test setup into _patch_build() helper to reduce duplication
   • Extracted static file creation into _write_static_output() helper
   • Added test_build_relocates_static_output_without_prerendered_prefix_dir() to verify files are correctly relocated when prerendering is off
   • Added test_build_merges_static_output_into_prerendered_prefix_dir() to verify prerendered output is preserved when merging with non-prerendered assets

3. news/+frontend-path-noprerender-build.bugfix.md: Added changelog entry documenting the fix.

Test Plan

Added comprehensive unit tests covering both scenarios:

• Static output relocation when the prefix directory doesn't exist (prerendering off)
• Merging of static output into an existing prerendered prefix directory

All existing tests continue to pass.

https://claude.ai/code/session_01UwbNDEaQNGWeHWS8nxsURd

[codspeed-hq]

Merging this PR will not alter performance

✅ 32 untouched benchmarks
⏩ 8 skipped benchmarks¹

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_{Comparing claude/happy-brown-ajf67r (04b3cef) with main (fb04aa1)}

Footnotes

1. 8 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[greptile-apps]

Greptile Summary

This PR creates the configured frontend prefix before relocating production build artifacts and adds regression coverage for builds with and without prerendered prefix output. The latest changes also reject parent-directory segments in frontend_path and document that configuration behavior.

• Creates the relocation destination before moving static output.
• Preserves existing prerendered files while merging other build assets.
• Rejects bare .. path segments during configuration normalization.
• Adds root-package and reflex-base changelog fragments.

Confidence Score: 4/5

The PR does not yet appear safe to merge because the existing output-containment issue remains unresolved.

The previous finding is only partially fixed: rejecting .. segments prevents the reported traversal form, but _normalize_paths ensures configured frontend paths begin with /, and converting that value to an absolute PosixPath means static_dir / frontend_path discards static_dir. Consequently, ordinary values such as /app can still create and populate an output directory outside .web/build/client.

Files Needing Attention: reflex/utils/build.py, packages/reflex-base/src/reflex_base/config.py

Important Files Changed

Filename	Overview
reflex/utils/build.py	Creates the frontend prefix directory before relocation, but the earlier path-containment finding remains only partially addressed.
packages/reflex-base/src/reflex_base/config.py	Rejects parent-directory segments during normal configuration construction, while leaving absolute-path containment to the build logic.
tests/units/utils/test_build.py	Adds coverage for absent and prerendered prefix directories, though the expected destination conflicts with absolute PosixPath joining semantics.
tests/units/test_config.py	Covers rejection of bare parent segments and acceptance of non-traversal dotted names.

_{Reviews (2): Last reviewed commit: "Reject ".." segments in frontend_path" | Re-trigger Greptile}

[cubic-dev-ai]

All reported issues were addressed across 3 files

<sub>Reply with feedback, questions, or to request a fix.

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