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