clippy_lints/src/methods/from_iter_instead_of_collect.rs

   1 use clippy_utils::diagnostics::span_lint_and_sugg;
   2 use clippy_utils::ty::implements_trait;
   3 use clippy_utils::{is_expr_path_def_path, paths, sugg};
   4 use if_chain::if_chain;
   5 use rustc_errors::Applicability;
   6 use rustc_hir as hir;
   7 use rustc_lint::{LateContext, LintContext};
   8 use rustc_middle::ty::Ty;
   9 use rustc_span::sym;
  10
  11 use super::FROM_ITER_INSTEAD_OF_COLLECT;
  12
  13 pub(super) fn check(cx: &LateContext<'_>, expr: &hir::Expr<'_>, args: &[hir::Expr<'_>], func: &hir::Expr<'_>) {
  14     if_chain! {
  15         if is_expr_path_def_path(cx, func, &paths::FROM_ITERATOR_METHOD);
  16         let ty = cx.typeck_results().expr_ty(expr);
  17         let arg_ty = cx.typeck_results().expr_ty(&args[0]);
  18         if let Some(iter_id) = cx.tcx.get_diagnostic_item(sym::Iterator);
  19
  20         if implements_trait(cx, arg_ty, iter_id, &[]);
  21         then {
  22             // `expr` implements `FromIterator` trait
  23             let iter_expr = sugg::Sugg::hir(cx, &args[0], "..").maybe_par();
  24             let turbofish = extract_turbofish(cx, expr, ty);
  25             let sugg = format!("{}.collect::<{}>()", iter_expr, turbofish);
  26             span_lint_and_sugg(
  27                 cx,
  28                 FROM_ITER_INSTEAD_OF_COLLECT,
  29                 expr.span,
  30                 "usage of `FromIterator::from_iter`",
  31                 "use `.collect()` instead of `::from_iter()`",
  32                 sugg,
  33                 Applicability::MaybeIncorrect,
  34             );
  35         }
  36     }
  37 }
  38
  39 fn extract_turbofish(cx: &LateContext<'_>, expr: &hir::Expr<'_>, ty: Ty<'tcx>) -> String {
  40     fn strip_angle_brackets(s: &str) -> Option<&str> {
  41         s.strip_prefix('<')?.strip_suffix('>')
  42     }
  43
  44     let call_site = expr.span.source_callsite();
  45     if_chain! {
  46         if let Ok(snippet) = cx.sess().source_map().span_to_snippet(call_site);
  47         let snippet_split = snippet.split("::").collect::<Vec<_>>();
  48         if let Some((_, elements)) = snippet_split.split_last();
  49
  50         then {
  51             if_chain! {
  52                 if let [type_specifier, _] = snippet_split.as_slice();
  53                 if let Some(type_specifier) = strip_angle_brackets(type_specifier);
  54                 if let Some((type_specifier, ..)) = type_specifier.split_once(" as ");
  55                 then {
  56                     type_specifier.to_string()
  57                 } else {
  58                     // is there a type specifier? (i.e.: like `<u32>` in `collections::BTreeSet::<u32>::`)
  59                     if let Some(type_specifier) = snippet_split.iter().find(|e| strip_angle_brackets(e).is_some()) {
  60                         // remove the type specifier from the path elements
  61                         let without_ts = elements.iter().filter_map(|e| {
  62                             if e == type_specifier { None } else { Some((*e).to_string()) }
  63                         }).collect::<Vec<_>>();
  64                         // join and add the type specifier at the end (i.e.: `collections::BTreeSet<u32>`)
  65                         format!("{}{}", without_ts.join("::"), type_specifier)
  66                     } else {
  67                         // type is not explicitly specified so wildcards are needed
  68                         // i.e.: 2 wildcards in `std::collections::BTreeMap<&i32, &char>`
  69                         let ty_str = ty.to_string();
  70                         let start = ty_str.find('<').unwrap_or(0);
  71                         let end = ty_str.find('>').unwrap_or_else(|| ty_str.len());
  72                         let nb_wildcard = ty_str[start..end].split(',').count();
  73                         let wildcards = format!("_{}", ", _".repeat(nb_wildcard - 1));
  74                         format!("{}<{}>", elements.join("::"), wildcards)
  75                     }
  76                 }
  77             }
  78         } else {
  79             ty.to_string()
  80         }
  81     }
  82 }