src/tools/clippy/clippy_lints/src/option_env_unwrap.rs

   1 use clippy_utils::diagnostics::span_lint_and_help;
   2 use clippy_utils::is_direct_expn_of;
   3 use if_chain::if_chain;
   4 use rustc_ast::ast::{Expr, ExprKind};
   5 use rustc_lint::{EarlyContext, EarlyLintPass};
   6 use rustc_session::{declare_lint_pass, declare_tool_lint};
   7 use rustc_span::sym;
   8
   9 declare_clippy_lint! {
  10     /// ### What it does
  11     /// Checks for usage of `option_env!(...).unwrap()` and
  12     /// suggests usage of the `env!` macro.
  13     ///
  14     /// ### Why is this bad?
  15     /// Unwrapping the result of `option_env!` will panic
  16     /// at run-time if the environment variable doesn't exist, whereas `env!`
  17     /// catches it at compile-time.
  18     ///
  19     /// ### Example
  20     /// ```rust,no_run
  21     /// let _ = option_env!("HOME").unwrap();
  22     /// ```
  23     ///
  24     /// Is better expressed as:
  25     ///
  26     /// ```rust,no_run
  27     /// let _ = env!("HOME");
  28     /// ```
  29     #[clippy::version = "1.43.0"]
  30     pub OPTION_ENV_UNWRAP,
  31     correctness,
  32     "using `option_env!(...).unwrap()` to get environment variable"
  33 }
  34
  35 declare_lint_pass!(OptionEnvUnwrap => [OPTION_ENV_UNWRAP]);
  36
  37 impl EarlyLintPass for OptionEnvUnwrap {
  38     fn check_expr(&mut self, cx: &EarlyContext<'_>, expr: &Expr) {
  39         if_chain! {
  40             if let ExprKind::MethodCall(path_segment, args, _) = &expr.kind;
  41             if matches!(path_segment.ident.name, sym::expect | sym::unwrap);
  42             if let ExprKind::Call(caller, _) = &args[0].kind;
  43             if is_direct_expn_of(caller.span, "option_env").is_some();
  44             then {
  45                 span_lint_and_help(
  46                     cx,
  47                     OPTION_ENV_UNWRAP,
  48                     expr.span,
  49                     "this will panic at run-time if the environment variable doesn't exist at compile-time",
  50                     None,
  51                     "consider using the `env!` macro instead"
  52                 );
  53             }
  54         }
  55     }
  56 }