clippy_lints/src/if_then_some_else_none.rs

   1 use clippy_utils::diagnostics::span_lint_and_help;
   2 use clippy_utils::source::snippet_with_macro_callsite;
   3 use clippy_utils::{match_qpath, meets_msrv, parent_node_is_if_expr};
   4 use if_chain::if_chain;
   5 use rustc_hir::{Expr, ExprKind};
   6 use rustc_lint::{LateContext, LateLintPass, LintContext};
   7 use rustc_middle::lint::in_external_macro;
   8 use rustc_semver::RustcVersion;
   9 use rustc_session::{declare_tool_lint, impl_lint_pass};
  10
  11 const IF_THEN_SOME_ELSE_NONE_MSRV: RustcVersion = RustcVersion::new(1, 50, 0);
  12
  13 declare_clippy_lint! {
  14     /// **What it does:** Checks for if-else that could be written to `bool::then`.
  15     ///
  16     /// **Why is this bad?** Looks a little redundant. Using `bool::then` helps it have less lines of code.
  17     ///
  18     /// **Known problems:** None.
  19     ///
  20     /// **Example:**
  21     ///
  22     /// ```rust
  23     /// # let v = vec![0];
  24     /// let a = if v.is_empty() {
  25     ///     println!("true!");
  26     ///     Some(42)
  27     /// } else {
  28     ///     None
  29     /// };
  30     /// ```
  31     ///
  32     /// Could be written:
  33     ///
  34     /// ```rust
  35     /// # let v = vec![0];
  36     /// let a = v.is_empty().then(|| {
  37     ///     println!("true!");
  38     ///     42
  39     /// });
  40     /// ```
  41     pub IF_THEN_SOME_ELSE_NONE,
  42     restriction,
  43     "Finds if-else that could be written using `bool::then`"
  44 }
  45
  46 pub struct IfThenSomeElseNone {
  47     msrv: Option<RustcVersion>,
  48 }
  49
  50 impl IfThenSomeElseNone {
  51     #[must_use]
  52     pub fn new(msrv: Option<RustcVersion>) -> Self {
  53         Self { msrv }
  54     }
  55 }
  56
  57 impl_lint_pass!(IfThenSomeElseNone => [IF_THEN_SOME_ELSE_NONE]);
  58
  59 impl LateLintPass<'_> for IfThenSomeElseNone {
  60     fn check_expr(&mut self, cx: &LateContext<'_>, expr: &'tcx Expr<'_>) {
  61         if !meets_msrv(self.msrv.as_ref(), &IF_THEN_SOME_ELSE_NONE_MSRV) {
  62             return;
  63         }
  64
  65         if in_external_macro(cx.sess(), expr.span) {
  66             return;
  67         }
  68
  69         // We only care about the top-most `if` in the chain
  70         if parent_node_is_if_expr(expr, cx) {
  71             return;
  72         }
  73
  74         if_chain! {
  75             if let ExprKind::If(ref cond, ref then, Some(ref els)) = expr.kind;
  76             if let ExprKind::Block(ref then_block, _) = then.kind;
  77             if let Some(ref then_expr) = then_block.expr;
  78             if let ExprKind::Call(ref then_call, [then_arg]) = then_expr.kind;
  79             if let ExprKind::Path(ref then_call_qpath) = then_call.kind;
  80             if match_qpath(then_call_qpath, &clippy_utils::paths::OPTION_SOME);
  81             if let ExprKind::Block(ref els_block, _) = els.kind;
  82             if els_block.stmts.is_empty();
  83             if let Some(ref els_expr) = els_block.expr;
  84             if let ExprKind::Path(ref els_call_qpath) = els_expr.kind;
  85             if match_qpath(els_call_qpath, &clippy_utils::paths::OPTION_NONE);
  86             then {
  87                 let cond_snip = snippet_with_macro_callsite(cx, cond.span, "[condition]");
  88                 let cond_snip = if matches!(cond.kind, ExprKind::Unary(_, _) | ExprKind::Binary(_, _, _)) {
  89                     format!("({})", cond_snip)
  90                 } else {
  91                     cond_snip.into_owned()
  92                 };
  93                 let arg_snip = snippet_with_macro_callsite(cx, then_arg.span, "");
  94                 let closure_body = if then_block.stmts.is_empty() {
  95                     arg_snip.into_owned()
  96                 } else {
  97                     format!("{{ /* snippet */ {} }}", arg_snip)
  98                 };
  99                 let help = format!(
 100                     "consider using `bool::then` like: `{}.then(|| {})`",
 101                     cond_snip,
 102                     closure_body,
 103                 );
 104                 span_lint_and_help(
 105                     cx,
 106                     IF_THEN_SOME_ELSE_NONE,
 107                     expr.span,
 108                     "this could be simplified with `bool::then`",
 109                     None,
 110                     &help,
 111                 );
 112             }
 113         }
 114     }
 115
 116     extract_msrv_attr!(LateContext);
 117 }