Result '{}' did not match expected format. Please return 'fi

Error message

Result '{}' did not match expected format. Please return 'file_path:line_number:column_number'

What it means

resolve_field_definition runs the user-provided locate command and expects its stdout to be exactly 'file_path:line_number:column_number'. After trimming and splitting on ':' it requires exactly 3 parts; anything else (2 parts, 4 parts due to Windows drive letters or paths containing colons) produces this formatted error string.

Source

Thrown at compiler/crates/relay-bin/src/main.rs:629

        project_name: String,
        parent_type: String,
        field_info: Option<FieldSchemaInfo>,
    ) -> Result<Option<FieldDefinitionSourceInfo>, String> {
        let entity_name = match field_info {
            Some(field_info) => format!("{}.{}", parent_type, field_info.name),
            None => parent_type,
        };
        let result = Command::new(&self.locate_command)
            .arg(project_name)
            .arg(entity_name)
            .output()
            .map_err(|e| format!("Failed to run locate command: {}", e))?;

        let result = String::from_utf8(result.stdout).expect("Failed to parse output");

        // Parse file_path:line_number:column_number
        let result_trimmed = result.trim();
        let result = result_trimmed.split(':').collect::<Vec<_>>();
        if result.len() != 3 {
            return Err(format!(
                "Result '{}' did not match expected format. Please return 'file_path:line_number:column_number'",
                result_trimmed
            ));
        }
        let file_path = result[0];
        let line_number = result[1].parse::<u64>().unwrap() - 1;
        let column_number = result[2].parse::<u64>().unwrap_or(1_u64) - 1;

        Ok(Some(FieldDefinitionSourceInfo {
            file_path: file_path.to_string(),
            line_number,
            column_number,
            is_local: true,
        }))
    }
}

View on GitHub (pinned to 668b1b85e0)

Solutions

Fix the locate command to print exactly file_path:line_number:column_number and nothing else
Quote or normalize paths so they contain no ':' characters (or use relative paths)
Test the locate command standalone: it should output a single line like 'src/x.ts:12:5'
Update the locate script to strip extra output (stderr is ignored, so move diagnostics to stderr)

Example fix

// before (locate script)
echo "Located at src/Foo.ts:10:3"
// after
echo "src/Foo.ts:10:3"

Defensive patterns

Strategy: validation

Validate before calling

const out = execFileSync(locateCmd, [project, entity], { encoding: 'utf8' }).trim();
if (!/^.+:\d+:\d+$/.test(out)) {
  throw new Error(`Locate output malformed: "${out}"; expected file:line:column`);
}

Try / catch

try {
  resolveFieldDefinition(project, entity);
} catch (e) {
  if (/did not match expected format/.test(e.message)) {
    console.error('Fix locate command to print only file_path:line_number:column_number.');
  } else throw e;
}

Prevention

Keep locate scripts single-purpose: one line of stdout only
Send diagnostics to stderr, never stdout
Avoid ':' inside file paths; test on Windows-style paths
Unit-test the locate command's output format

When it happens

Trigger: A custom locate command (e.g. configured for IDE jumping) prints output that doesn't split into exactly 3 colon-separated segments.

Common situations: Locate script printing extra text or a trailing message; absolute Windows paths (C:\...) adding an extra colon segment; tool output lacking line/column numbers; scripts appending newline-separated warnings.

Related errors

AI-assisted analysis of facebook/relay@668b1b85e0 (2026-09-02). Data as JSON: /api/errors/a465af206821fa4b. Report an issue: GitHub.