pemistahl/grex · error

The specified file could not be found

Error message

The specified file could not be found

What it means

RegExpBuilder::from_file reads the file at file_path with std::fs::read_to_string; on an io::Error of kind NotFound it panics with 'The specified file could not be found'. The builder treats a missing file path as unrecoverable for its purpose and aborts instead of constructing an empty builder.

Solutions

  1. Verify the path exists (std::path::Path::exists) before calling from_file
  2. Fix typos in the path and prefer absolute paths or paths anchored to an env-provided base directory
  3. Read the file yourself with std::fs::read_to_string and handle the NotFound error, then pass the lines to RegExpBuilder::from

Example fix

// before
let builder = RegExpBuilder::from_file("data/examples.txt");
// after
let path = Path::new("data/examples.txt");
assert!(path.exists(), "examples file not found: {}", path.display());
let builder = RegExpBuilder::from_file(path);
Defensive patterns

Strategy: validation

Validate before calling

let path = Path::new(file_path);
if !path.exists() { return Err(anyhow!("examples file not found: {}", path.display())); }

Try / catch

std::panic::catch_unwind(|| RegExpBuilder::from_file(&path))
    .map_err(|_| format!("could not read examples file: {}", path.display()))

Prevention

When it happens

Trigger: Calling RegExpBuilder::from_file("missing.txt") (or any PathBuf that does not exist on disk) — including typos in the path, wrong working directory, or a file deleted before the call.

Common situations: Running the binary from a different cwd than expected so a relative path no longer resolves; passing a path from config/CLI that was never validated; the file lives in a packaged container without being copied in.

Understand the failure class

Background: "File not found" and ENOENT errors: why libraries can't find a file that should exist — this error's family across 50 libraries.

Related errors

AI-assisted analysis of pemistahl/grex@99cc347707 (2026-09-13). Data as JSON: /api/errors/51f5dbb517a9fd34. Report an issue: GitHub.

Appendix: source

Thrown at src/builder.rs:76

    /// The test cases need not be sorted because `RegExpBuilder` sorts them internally.
    ///
    /// Each test case needs to be on a separate line.
    /// Lines may be ended with either a newline (`\n`) or
    /// a carriage return with a line feed (`\r\n`).
    /// The final line ending is optional.
    ///
    /// ⚠ Panics if:
    /// - the file cannot be found
    /// - the file's encoding is not valid UTF-8 data
    /// - the file cannot be opened because of conflicting permissions
    pub fn from_file<T: Into<PathBuf>>(file_path: T) -> Self {
        match std::fs::read_to_string(file_path.into()) {
            Ok(file_content) => Self {
                test_cases: file_content.lines().map(|it| it.to_string()).collect_vec(),
                config: RegExpConfig::new(),
            },
            Err(error) => match error.kind() {
                ErrorKind::NotFound => panic!("The specified file could not be found"),
                ErrorKind::InvalidData => {
                    panic!("The specified file's encoding is not valid UTF-8")
                }
                ErrorKind::PermissionDenied => {
                    panic!("Permission denied: The specified file could not be opened")
                }
                _ => panic!("{}", error),
            },
        }
    }

    /// Converts any Unicode decimal digit to character class `\d`.
    ///
    /// This method takes precedence over
    /// [`with_conversion_of_words`](Self::with_conversion_of_words) if both are set.
    /// Decimal digits are converted to `\d`, the remaining word characters to `\w`.
    ///
    /// This method takes precedence over

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