--- /dev/null
+use crate::utils::{get_trait_def_id, implements_trait, paths, span_lint_and_sugg, sugg};
+use if_chain::if_chain;
+use rustc_errors::Applicability;
+use rustc_hir as hir;
+use rustc_lint::{LateContext, LintContext};
+use rustc_middle::ty::Ty;
+
+use super::FROM_ITER_INSTEAD_OF_COLLECT;
+
+pub(super) fn check(cx: &LateContext<'_>, expr: &hir::Expr<'_>, args: &[hir::Expr<'_>]) {
+ let ty = cx.typeck_results().expr_ty(expr);
+ let arg_ty = cx.typeck_results().expr_ty(&args[0]);
+
+ if_chain! {
+ if let Some(from_iter_id) = get_trait_def_id(cx, &paths::FROM_ITERATOR);
+ if let Some(iter_id) = get_trait_def_id(cx, &paths::ITERATOR);
+
+ if implements_trait(cx, ty, from_iter_id, &[]) && implements_trait(cx, arg_ty, iter_id, &[]);
+ then {
+ // `expr` implements `FromIterator` trait
+ let iter_expr = sugg::Sugg::hir(cx, &args[0], "..").maybe_par();
+ let turbofish = extract_turbofish(cx, expr, ty);
+ let sugg = format!("{}.collect::<{}>()", iter_expr, turbofish);
+ span_lint_and_sugg(
+ cx,
+ FROM_ITER_INSTEAD_OF_COLLECT,
+ expr.span,
+ "usage of `FromIterator::from_iter`",
+ "use `.collect()` instead of `::from_iter()`",
+ sugg,
+ Applicability::MaybeIncorrect,
+ );
+ }
+ }
+}
+
+fn extract_turbofish(cx: &LateContext<'_>, expr: &hir::Expr<'_>, ty: Ty<'tcx>) -> String {
+ if_chain! {
+ let call_site = expr.span.source_callsite();
+ if let Ok(snippet) = cx.sess().source_map().span_to_snippet(call_site);
+ let snippet_split = snippet.split("::").collect::<Vec<_>>();
+ if let Some((_, elements)) = snippet_split.split_last();
+
+ then {
+ // is there a type specifier? (i.e.: like `<u32>` in `collections::BTreeSet::<u32>::`)
+ if let Some(type_specifier) = snippet_split.iter().find(|e| e.starts_with('<') && e.ends_with('>')) {
+ // remove the type specifier from the path elements
+ let without_ts = elements.iter().filter_map(|e| {
+ if e == type_specifier { None } else { Some((*e).to_string()) }
+ }).collect::<Vec<_>>();
+ // join and add the type specifier at the end (i.e.: `collections::BTreeSet<u32>`)
+ format!("{}{}", without_ts.join("::"), type_specifier)
+ } else {
+ // type is not explicitly specified so wildcards are needed
+ // i.e.: 2 wildcards in `std::collections::BTreeMap<&i32, &char>`
+ let ty_str = ty.to_string();
+ let start = ty_str.find('<').unwrap_or(0);
+ let end = ty_str.find('>').unwrap_or_else(|| ty_str.len());
+ let nb_wildcard = ty_str[start..end].split(',').count();
+ let wildcards = format!("_{}", ", _".repeat(nb_wildcard - 1));
+ format!("{}<{}>", elements.join("::"), wildcards)
+ }
+ } else {
+ ty.to_string()
+ }
+ }
+}