gleam-lang/gleam · error

failed regex to match any non-lowercase and…

Error message

failed regex to match any non-lowercase and non-alphanumeric characters

What it means

In suggest_valid_name (InvalidProjectNameReason::Format branch), the regex [^a-z0-9] used to replace invalid characters with underscores is compiled with an .expect panic. Like the other new.rs regexes, the constant pattern is always valid, so this panic signals a regex-engine internal failure rather than bad input.

Solutions

1. Rebuild/update gleam — this is a build/dependency problem, not a naming problem
2. Update the regex crate in Cargo.lock if a regression exists
3. Report to Gleam maintainers with platform details if reproducible

fn suggestion_charset_ok(s: &str) -> bool {
    s.chars().all(|c| c.is_ascii_lowercase() || c.is_ascii_digit() || c == '_')
}

When it happens

Trigger: `gleam new` with a name that has invalid format, triggering the suggestion path, in a build where the regex crate cannot compile the fixed pattern — normally unreachable.

Common situations: Broken dependency builds, unusual targets, or binary corruption. Users with invalid names should otherwise receive a suggestion or a normal InvalidProjectName error.

Related errors

• failed regex to match consecutive underscores
• failed regex to match valid but non-lowercase name format
• failed regex to match valid name format
• Index out of bounds
• is_gleam_path() RE regex

AI-assisted analysis of gleam-lang/gleam@15b07c7830 (2026-09-14). Data as JSON: /api/errors/7caf33c743282701. Report an issue: GitHub.

Appendix: source

Thrown at compiler-cli/src/new.rs:411

            }
            _ => None,
        },
        InvalidProjectNameReason::ErlangReservedWord => Some(format!("{invalid_name}_app")),
        InvalidProjectNameReason::ErlangStandardLibraryModule => {
            Some(format!("{invalid_name}_app"))
        }
        InvalidProjectNameReason::GleamReservedWord => Some(format!("{invalid_name}_app")),
        InvalidProjectNameReason::GleamReservedModule => {
            if invalid_name == "gleam" {
                Some("app_gleam".into())
            } else {
                Some(format!("{invalid_name}_app"))
            }
        }
        InvalidProjectNameReason::FormatNotLowercase => Some(invalid_name.to_lowercase()),
        InvalidProjectNameReason::Format => {
            let suggestion = regex::Regex::new(r"[^a-z0-9]")
                .expect("failed regex to match any non-lowercase and non-alphanumeric characters")
                .replace_all(&invalid_name.to_lowercase(), "_")
                .to_string();

            let suggestion = regex::Regex::new(r"_+")
                .expect("failed regex to match consecutive underscores")
                .replace_all(&suggestion, "_")
                .to_string();

            match validate_name(&suggestion) {
                Ok(_) => Some(suggestion),
                Err(_) => None,
            }
        }
    }
}

fn get_valid_project_name(
    provided_name: Option<&str>,

View on GitHub (pinned to 15b07c7830)