clippy_lints/src/loops/manual_flatten.rs

   1 use super::utils::make_iterator_snippet;
   2 use super::MANUAL_FLATTEN;
   3 use clippy_utils::diagnostics::span_lint_and_then;
   4 use clippy_utils::visitors::is_local_used;
   5 use clippy_utils::{is_lang_ctor, path_to_local_id};
   6 use if_chain::if_chain;
   7 use rustc_errors::Applicability;
   8 use rustc_hir::LangItem::{OptionSome, ResultOk};
   9 use rustc_hir::{Expr, ExprKind, MatchSource, Pat, PatKind, StmtKind};
  10 use rustc_lint::LateContext;
  11 use rustc_middle::ty;
  12 use rustc_span::source_map::Span;
  13
  14 /// Check for unnecessary `if let` usage in a for loop where only the `Some` or `Ok` variant of the
  15 /// iterator element is used.
  16 pub(super) fn check<'tcx>(
  17     cx: &LateContext<'tcx>,
  18     pat: &'tcx Pat<'_>,
  19     arg: &'tcx Expr<'_>,
  20     body: &'tcx Expr<'_>,
  21     span: Span,
  22 ) {
  23     if let ExprKind::Block(block, _) = body.kind {
  24         // Ensure the `if let` statement is the only expression or statement in the for-loop
  25         let inner_expr = if block.stmts.len() == 1 && block.expr.is_none() {
  26             let match_stmt = &block.stmts[0];
  27             if let StmtKind::Semi(inner_expr) = match_stmt.kind {
  28                 Some(inner_expr)
  29             } else {
  30                 None
  31             }
  32         } else if block.stmts.is_empty() {
  33             block.expr
  34         } else {
  35             None
  36         };
  37
  38         if_chain! {
  39             if let Some(inner_expr) = inner_expr;
  40             if let ExprKind::Match(
  41                 match_expr, [true_arm, _else_arm], MatchSource::IfLetDesugar{ contains_else_clause: false }
  42             ) = inner_expr.kind;
  43             // Ensure match_expr in `if let` statement is the same as the pat from the for-loop
  44             if let PatKind::Binding(_, pat_hir_id, _, _) = pat.kind;
  45             if path_to_local_id(match_expr, pat_hir_id);
  46             // Ensure the `if let` statement is for the `Some` variant of `Option` or the `Ok` variant of `Result`
  47             if let PatKind::TupleStruct(ref qpath, _, _) = true_arm.pat.kind;
  48             let some_ctor = is_lang_ctor(cx, qpath, OptionSome);
  49             let ok_ctor = is_lang_ctor(cx, qpath, ResultOk);
  50             if some_ctor || ok_ctor;
  51             // Ensure epxr in `if let` is not used afterwards
  52             if !is_local_used(cx, true_arm, pat_hir_id);
  53             then {
  54                 let if_let_type = if some_ctor { "Some" } else { "Ok" };
  55                 // Prepare the error message
  56                 let msg = format!("unnecessary `if let` since only the `{}` variant of the iterator element is used", if_let_type);
  57
  58                 // Prepare the help message
  59                 let mut applicability = Applicability::MaybeIncorrect;
  60                 let arg_snippet = make_iterator_snippet(cx, arg, &mut applicability);
  61                 let copied = match cx.typeck_results().expr_ty(match_expr).kind() {
  62                     ty::Ref(_, inner, _) => match inner.kind() {
  63                         ty::Ref(..) => ".copied()",
  64                         _ => ""
  65                     }
  66                     _ => ""
  67                 };
  68
  69                 span_lint_and_then(
  70                     cx,
  71                     MANUAL_FLATTEN,
  72                     span,
  73                     &msg,
  74                     |diag| {
  75                         let sugg = format!("{}{}.flatten()", arg_snippet, copied);
  76                         diag.span_suggestion(
  77                             arg.span,
  78                             "try",
  79                             sugg,
  80                             Applicability::MaybeIncorrect,
  81                         );
  82                         diag.span_help(
  83                             inner_expr.span,
  84                             "...and remove the `if let` statement in the for loop",
  85                         );
  86                     }
  87                 );
  88             }
  89         }
  90     }
  91 }