clippy_lints/src/option_env_unwrap.rs

use clippy_utils::diagnostics::span_lint_and_help;
use clippy_utils::is_direct_expn_of;
use rustc_ast::ast::{Expr, ExprKind, MethodCall};
use rustc_lint::{EarlyContext, EarlyLintPass};
use rustc_session::declare_lint_pass;
use rustc_span::sym;

declare_clippy_lint! {
    /// ### What it does
    /// Checks for usage of `option_env!(...).unwrap()` and
    /// suggests usage of the `env!` macro.
    ///
    /// ### Why is this bad?
    /// Unwrapping the result of `option_env!` will panic
    /// at run-time if the environment variable doesn't exist, whereas `env!`
    /// catches it at compile-time.
    ///
    /// ### Example
    /// ```rust,no_run
    /// let _ = option_env!("HOME").unwrap();
    /// ```
    ///
    /// Is better expressed as:
    ///
    /// ```rust,no_run
    /// let _ = env!("HOME");
    /// ```
    #[clippy::version = "1.43.0"]
    pub OPTION_ENV_UNWRAP,
    correctness,
    "using `option_env!(...).unwrap()` to get environment variable"
}

declare_lint_pass!(OptionEnvUnwrap => [OPTION_ENV_UNWRAP]);

impl EarlyLintPass for OptionEnvUnwrap {
    fn check_expr(&mut self, cx: &EarlyContext<'_>, expr: &Expr) {
        if let ExprKind::MethodCall(box MethodCall { seg, receiver, .. }) = &expr.kind
            && matches!(seg.ident.name, sym::expect | sym::unwrap)
            && is_direct_expn_of(receiver.span, sym::option_env).is_some()
        {
            span_lint_and_help(
                cx,
                OPTION_ENV_UNWRAP,
                expr.span,
                "this will panic at run-time if the environment variable doesn't exist at compile-time",
                None,
                "consider using the `env!` macro instead",
            );
        }
    }
}