el/engrams/el-lint/src/rules.rs

//! Style and correctness rules for el-lint (beyond el-arch architectural rules).

use el_parser::{Program, Stmt};

use crate::report::{LintDiagnostic, LintSeverity};

/// Run all style rules against the program and return diagnostics.
pub fn check_style(program: &Program) -> Vec<LintDiagnostic> {
    let mut diags = Vec::new();

    for stmt in &program.stmts {
        check_stmt(stmt, &mut diags);
    }

    diags
}

fn check_stmt(stmt: &Stmt, diags: &mut Vec<LintDiagnostic>) {
    match stmt {
        Stmt::FnDef { name, body, .. } => {
            // S001: Function body too long (>50 statements)
            if body.len() > 50 {
                diags.push(LintDiagnostic {
                    severity: LintSeverity::Warning,
                    code: "S001".into(),
                    message: format!(
                        "function `{name}` has {} statements — consider splitting",
                        body.len()
                    ),
                    location: format!("function {name}"),
                    suggestion: Some(
                        "extract sub-functions for each logical concern".into(),
                    ),
                });
            }

            // S002: Function name not snake_case
            if name.chars().any(|c| c.is_uppercase()) {
                diags.push(LintDiagnostic {
                    severity: LintSeverity::Warning,
                    code: "S002".into(),
                    message: format!("function `{name}` should be snake_case"),
                    location: format!("function {name}"),
                    suggestion: Some(format!("rename to `{}`", to_snake_case(name))),
                });
            }

            // S003: Empty function body
            if body.is_empty() {
                diags.push(LintDiagnostic {
                    severity: LintSeverity::Info,
                    code: "S003".into(),
                    message: format!("function `{name}` has an empty body"),
                    location: format!("function {name}"),
                    suggestion: Some("add implementation or remove if unused".into()),
                });
            }

            // Recurse into nested function defs
            for s in body {
                check_stmt(s, diags);
            }
        }

        Stmt::TypeDef { name, .. } => {
            // S004: Type name not PascalCase
            if !is_pascal_case(name) {
                diags.push(LintDiagnostic {
                    severity: LintSeverity::Warning,
                    code: "S004".into(),
                    message: format!("type `{name}` should be PascalCase"),
                    location: format!("type {name}"),
                    suggestion: None,
                });
            }
        }

        Stmt::EnumDef { name, .. } => {
            // S004 also applies to enums
            if !is_pascal_case(name) {
                diags.push(LintDiagnostic {
                    severity: LintSeverity::Warning,
                    code: "S004".into(),
                    message: format!("enum `{name}` should be PascalCase"),
                    location: format!("enum {name}"),
                    suggestion: None,
                });
            }
        }

        Stmt::ImplDef { methods, .. } => {
            for m in methods {
                check_stmt(m, diags);
            }
        }

        _ => {}
    }
}

/// Convert CamelCase/mixed to snake_case.
fn to_snake_case(s: &str) -> String {
    let mut result = String::new();
    for (i, c) in s.chars().enumerate() {
        if c.is_uppercase() && i > 0 {
            result.push('_');
        }
        result.push(c.to_lowercase().next().unwrap());
    }
    result
}

/// Returns true if the first character is uppercase (PascalCase convention).
fn is_pascal_case(s: &str) -> bool {
    s.chars().next().map(|c| c.is_uppercase()).unwrap_or(false)
}