Limit diff output to 55,000 characters

[chrisbuetti]

Limit the diff output to 55,000 characters and add a message indicating truncation.

[sentry]

Bug: The code slices a string at a fixed byte offset MAX_DIFF_CHARS. This will panic if the offset falls in the middle of a multi-byte UTF-8 character, crashing the program.
_{Severity: CRITICAL}

Suggested Fix

Instead of slicing by a raw byte index, find a valid character boundary at or before MAX_DIFF_CHARS. You can achieve this by iterating through the string's characters and stopping once the byte length exceeds the limit, or by using is_char_boundary to find the last valid boundary before the limit. For example: let mut end = MAX_DIFF_CHARS; while !output.is_char_boundary(end) { end -= 1; } and then use end as the slicing index.

Prompt for AI Agent

Review the code at the location below. A potential bug has been identified by an AI
agent.
Verify if this is a real issue. If it is, propose a fix; if not, explain why it's not
valid.

Location: src/main.rs#L117

Potential issue: The code at `src/main.rs:117` truncates diff output by slicing the
string `output` at a fixed byte offset, `MAX_DIFF_CHARS`. However, `output` is a UTF-8
string, and slicing a `&str` at a byte index that does not align with a character
boundary will cause a panic. Since `git diff` output can contain multi-byte Unicode
characters (e.g., emoji, non-Latin scripts), there is a significant risk that the
`MAX_DIFF_CHARS` boundary will fall within a multi-byte character. This will trigger a
panic and crash the application when a user generates a large diff containing such
characters. The subsequent `rfind` call does not prevent this, as the problematic slice
occurs first.

_{Did we get this right? 👍 / 👎 to inform future reviews.}