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};
   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 const IF_THEN_SOME_ELSE_NONE_MSRV: RustcVersion = RustcVersion::new(1, 50, 0);
  13
  14 declare_clippy_lint! {
  15     /// **What it does:** Checks for if-else that could be written to `bool::then`.
  16     ///
  17     /// **Why is this bad?** Looks a little redundant. Using `bool::then` helps it have less lines of code.
  18     ///
  19     /// **Known problems:** None.
  20     ///
  21     /// **Example:**
  22     ///
  23     /// ```rust
  24     /// # let v = vec![0];
  25     /// let a = if v.is_empty() {
  26     ///     println!("true!");
  27     ///     Some(42)
  28     /// } else {
  29     ///     None
  30     /// };
  31     /// ```
  32     ///
  33     /// Could be written:
  34     ///
  35     /// ```rust
  36     /// # let v = vec![0];
  37     /// let a = v.is_empty().then(|| {
  38     ///     println!("true!");
  39     ///     42
  40     /// });
  41     /// ```
  42     pub IF_THEN_SOME_ELSE_NONE,
  43     restriction,
  44     "Finds if-else that could be written using `bool::then`"
  45 }
  46
  47 pub struct IfThenSomeElseNone {
  48     msrv: Option<RustcVersion>,
  49 }
  50
  51 impl IfThenSomeElseNone {
  52     #[must_use]
  53     pub fn new(msrv: Option<RustcVersion>) -> Self {
  54         Self { msrv }
  55     }
  56 }
  57
  58 impl_lint_pass!(IfThenSomeElseNone => [IF_THEN_SOME_ELSE_NONE]);
  59
  60 impl LateLintPass<'_> for IfThenSomeElseNone {
  61     fn check_expr(&mut self, cx: &LateContext<'_>, expr: &'tcx Expr<'_>) {
  62         if !meets_msrv(self.msrv.as_ref(), &IF_THEN_SOME_ELSE_NONE_MSRV) {
  63             return;
  64         }
  65
  66         if in_external_macro(cx.sess(), expr.span) {
  67             return;
  68         }
  69
  70         // We only care about the top-most `if` in the chain
  71         if is_else_clause(cx.tcx, expr) {
  72             return;
  73         }
  74
  75         if_chain! {
  76             if let ExprKind::If(cond, then, Some(els)) = expr.kind;
  77             if let ExprKind::Block(then_block, _) = then.kind;
  78             if let Some(then_expr) = then_block.expr;
  79             if let ExprKind::Call(then_call, [then_arg]) = then_expr.kind;
  80             if let ExprKind::Path(ref then_call_qpath) = then_call.kind;
  81             if is_lang_ctor(cx, then_call_qpath, OptionSome);
  82             if let ExprKind::Block(els_block, _) = els.kind;
  83             if els_block.stmts.is_empty();
  84             if let Some(els_expr) = els_block.expr;
  85             if let ExprKind::Path(ref qpath) = els_expr.kind;
  86             if is_lang_ctor(cx, qpath, OptionNone);
  87             then {
  88                 let cond_snip = snippet_with_macro_callsite(cx, cond.span, "[condition]");
  89                 let cond_snip = if matches!(cond.kind, ExprKind::Unary(_, _) | ExprKind::Binary(_, _, _)) {
  90                     format!("({})", cond_snip)
  91                 } else {
  92                     cond_snip.into_owned()
  93                 };
  94                 let arg_snip = snippet_with_macro_callsite(cx, then_arg.span, "");
  95                 let closure_body = if then_block.stmts.is_empty() {
  96                     arg_snip.into_owned()
  97                 } else {
  98                     format!("{{ /* snippet */ {} }}", arg_snip)
  99                 };
 100                 let help = format!(
 101                     "consider using `bool::then` like: `{}.then(|| {})`",
 102                     cond_snip,
 103                     closure_body,
 104                 );
 105                 span_lint_and_help(
 106                     cx,
 107                     IF_THEN_SOME_ELSE_NONE,
 108                     expr.span,
 109                     "this could be simplified with `bool::then`",
 110                     None,
 111                     &help,
 112                 );
 113             }
 114         }
 115     }
 116
 117     extract_msrv_attr!(LateContext);
 118 }