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