fix: when direnv diff is empty, do not try to parse it

[yaleman]

I kept getting the following error every time mise started with direnv and mise in my .zshrc:

mise WARN  failed to update DIRENV_DIFF: EOF while parsing a value at line 1 column 0 

When the DIRENV_DIFF environment variable was empty, the parser would bail out and it was a spurious warning.

This makes mise ignore empty diff's (and adds some more debug logging to figure out where it was failing 😄)

[greptile-apps]

Greptile Summary

This PR fixes a spurious WARN failed to update DIRENV_DIFF: EOF while parsing a value that appeared whenever DIRENV_DIFF was set to an empty string. The fix short-circuits DirenvDiff::parse before any decoding/decompression when the input is empty, returning an empty diff that the existing new_path().is_empty() guard in update_direnv_diff then dismisses cleanly. Additional inspect_err calls in hook_env.rs improve debug visibility for any remaining parse failures without changing error-propagation semantics.

Confidence Score: 5/5

Safe to merge — the fix is minimal, correctly targets the reported bug, and does not alter any non-empty-input code paths.

All findings are P2 (missing test for the new empty-string branch). No logic errors, data-integrity issues, or security concerns were found. The existing new_path().is_empty() guard already handles the downstream consequence of an empty diff, so the fix integrates cleanly with the surrounding control flow.

No files require special attention.

Important Files Changed

Filename	Overview
src/direnv.rs	Adds early-return guard in DirenvDiff::parse when input is empty, returning an empty diff instead of attempting to base64-decode/decompress/JSON-parse an empty string (which caused a spurious "EOF while parsing" warning). No existing tests were updated to cover this new branch.
src/cli/hook_env.rs	Adds inspect_err debug logging around each fallible call in update_direnv_diff to surface where exactly an error originates; logic and error-propagation behaviour are otherwise unchanged.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A["DIRENV_DIFF env var present?"] -->|No| Z["Skip DIRENV_DIFF update"]
    A -->|"Yes - Some(input)"| B["update_direnv_diff(input, ...)"]
    B --> C{"input.is_empty()?"}
    C -->|"Yes - NEW"| D["Return empty DirenvDiff{}"]
    C -->|No| E["base64 decode → zlib decompress → JSON parse"]
    E -->|Error| F["inspect_err debug log → propagate Err"]
    F --> G["build_path_operations: warn!"]
    D --> H{"new_path().is_empty()?"}
    E -->|Ok| H
    H -->|Yes| I["Return Ok(None) — no DIRENV_DIFF patch"]
    H -->|No| J["remove_path_from_old_and_new"]
    J --> K["add_path_to_old_and_new"]
    K --> L["diff.dump() → EnvDiffOperation::Change"]
    L --> M["Return Ok(Some(op)) → pushed to patches"]

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_{Reviews (2): Last reviewed commit: "suggestions from gemini" | Re-trigger Greptile}

[gemini-code-assist]

Code Review

This pull request implements error logging for Direnv operations in hook_env.rs and adds a check for empty input in the DirenvDiff parser. The review feedback suggests standardizing the debug log format and including contextual path information in the error logs to assist with debugging.