What causes "No diff blocks found in section {}" in zed-industries/zed?

Check the raw response for a missing or malformed ``` fence after the section marker

No diff blocks found in section {}

Error message

No diff blocks found in section {}

What it means

Bailed by extract_diff_block when the named section (e.g. EDIT_HISTORY: or EXPECTED_PATCH:) exists in the response but no fenced code block with diff content could be extracted from its body. This differs from a missing section: the heading was found, yet the scanner located no ``` fenced block, so the hunks list stayed empty.

Source

Thrown at crates/edit_prediction_cli/src/synthesize.rs:658

            .find('\n')
            .map(|i| abs_diff_start + i + 1)
            .unwrap_or(abs_diff_start);

        if let Some(block_end_rel) = section_content[block_content_start..].find("```") {
            let block_end = block_content_start + block_end_rel;
            let diff_content = section_content[block_content_start..block_end].trim();

            // Split this block into hunks (in case multiple hunks in one block)
            hunks.extend(split_into_hunks(diff_content));

            search_start = block_end + 3;
        } else {
            break;
        }
    }

    if hunks.is_empty() {
        anyhow::bail!("No diff blocks found in section {}", section_marker);
    }

    Ok(hunks)
}

/// Split a diff block into individual hunks, preserving file headers
fn split_into_hunks(diff: &str) -> Vec<String> {
    let mut hunks = Vec::new();
    let mut current_file_header: Option<String> = None;
    let mut current_hunk: Vec<String> = Vec::new();
    let mut in_hunk = false;

    for line in diff.lines() {
        if line.starts_with("--- a/") || line.starts_with("--- /") {
            // Start of file header - flush previous hunk
            if in_hunk && !current_hunk.is_empty() {
                let mut hunk_text = String::new();
                if let Some(ref header) = current_file_header {

View on GitHub (pinned to f4178619ac)

Solutions

Check the raw response for a missing or malformed ``` fence after the section marker
Retry with a stricter prompt showing the exact fence format expected
As a code-level option, extend extract_diff_block to also accept hunks starting with `diff --git`/`--- ` outside fences

Defensive patterns

Strategy: retry

Validate before calling

fn has_fenced_block_after(text: &str, marker: &str) -> bool {
    text.find(marker)
        .map(|i| text[i + marker.len()..].contains("```"))
        .unwrap_or(false)
}

Type guard

fn has_fenced_block_after(text: &str, marker: &str) -> bool {
    text.find(marker)
        .map(|i| text[i + marker.len()..].contains("```"))
        .unwrap_or(false)
}

Try / catch

Distinguish 'section missing' from 'section present but unfenced' in the caught error; retry the latter with an explicit instruction to wrap the diff in triple-backtick fences.

Prevention

Show the exact fenced format in the prompt example
Pre-scan model output for ``` fences under each section marker before full parsing
If a model consistently omits fences, switch models or accept unfenced hunks via a parser extension

When it happens

Trigger: The model writes prose or bare diff text under the heading without a fenced code block, or uses malformed fences (four backticks, indented fences) so the block scanner cannot find a ``` pair after the marker.

Common situations: Models describing the edit in natural language instead of a diff; fence style variation across models; markdown escaping in intermediate processing.

Related errors

AI-assisted analysis of zed-industries/zed@f4178619ac (2026-08-20). Data as JSON: /api/errors/05af470ae63d6363. Report an issue: GitHub.