needless_collect: Lint cases with type annotations

clippy_lints/src/loops/needless_collect.rs

@@ -7,9 +7,10 @@ use clippy_utils::{is_trait_method, path_to_local_id, paths};
 use if_chain::if_chain;
 use rustc_errors::Applicability;
 use rustc_hir::intravisit::{walk_block, walk_expr, NestedVisitorMap, Visitor};
-use rustc_hir::{Block, Expr, ExprKind, GenericArg, HirId, Local, Pat, PatKind, QPath, StmtKind};
+use rustc_hir::{Block, Expr, ExprKind, GenericArg, GenericArgs, HirId, Local, Pat, PatKind, QPath, StmtKind, Ty};
 use rustc_lint::LateContext;
 use rustc_middle::hir::map::Map;
+
 use rustc_span::symbol::{sym, Ident};
 use rustc_span::{MultiSpan, Span};
 
@@ -58,18 +59,30 @@ fn check_needless_collect_direct_usage<'tcx>(expr: &'tcx Expr<'_>, cx: &LateCont
 }
 
 fn check_needless_collect_indirect_usage<'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) {
+    fn get_hir_id<'tcx>(ty: Option<&Ty<'tcx>>, method_args: Option<&GenericArgs<'tcx>>) -> Option<HirId> {
+        if let Some(ty) = ty {
+            return Some(ty.hir_id);
+        }
+
+        if let Some(generic_args) = method_args {
+            if let Some(GenericArg::Type(ref ty)) = generic_args.args.get(0) {
+                return Some(ty.hir_id);
+            }
+        }
+
+        None
+    }
     if let ExprKind::Block(block, _) = expr.kind {
         for stmt in block.stmts {
             if_chain! {
                 if let StmtKind::Local(
                     Local { pat: Pat { hir_id: pat_id, kind: PatKind::Binding(_, _, ident, .. ), .. },
-                    init: Some(init_expr), .. }
+                    init: Some(init_expr), ty, .. }
                 ) = stmt.kind;
                 if let ExprKind::MethodCall(method_name, collect_span, &[ref iter_source], ..) = init_expr.kind;
                 if method_name.ident.name == sym!(collect) && is_trait_method(cx, init_expr, sym::Iterator);
-                if let Some(generic_args) = method_name.args;
-                if let Some(GenericArg::Type(ref ty)) = generic_args.args.get(0);
-                if let ty = cx.typeck_results().node_type(ty.hir_id);
+                if let Some(hir_id) = get_hir_id(*ty, method_name.args);
+                if let ty = cx.typeck_results().node_type(hir_id);
                 if is_type_diagnostic_item(cx, ty, sym::vec_type) ||
                     is_type_diagnostic_item(cx, ty, sym::vecdeque_type) ||
                     match_type(cx, ty, &paths::LINKED_LIST);

tests/ui/needless_collect_indirect.rs

@@ -1,4 +1,4 @@
-use std::collections::{HashMap, VecDeque};
+use std::collections::{HashMap, LinkedList, VecDeque};
 
 fn main() {
     let sample = [1; 5];
@@ -43,3 +43,30 @@ fn main() {
             .collect::<Vec<_>>();
     }
 }
+
+mod issue7110 {
+    // #7110 - lint for type annotation cases
+    use super::*;
+
+    fn lint_vec(string: &str) -> usize {
+        let buffer: Vec<&str> = string.split('/').collect();
+        buffer.len()
+    }
+    fn lint_vec_deque() -> usize {
+        let sample = [1; 5];
+        let indirect_len: VecDeque<_> = sample.iter().collect();
+        indirect_len.len()
+    }
+    fn lint_linked_list() -> usize {
+        let sample = [1; 5];
+        let indirect_len: LinkedList<_> = sample.iter().collect();
+        indirect_len.len()
+    }
+    fn dont_lint(string: &str) -> usize {
+        let buffer: Vec<&str> = string.split('/').collect();
+        for buff in &buffer {
+            println!("{}", buff);
+        }
+        buffer.len()
+    }
+}

tests/ui/needless_collect_indirect.stderr

@@ -69,5 +69,47 @@ LL |
 LL |     sample.into_iter().any(|x| x == a);
    |
 
-error: aborting due to 5 previous errors
+error: avoid using `collect()` when not needed
+  --> $DIR/needless_collect_indirect.rs:52:51
+   |
+LL |         let buffer: Vec<&str> = string.split('/').collect();
+   |                                                   ^^^^^^^
+LL |         buffer.len()
+   |         ------------ the iterator could be used here instead
+   |
+help: take the original Iterator's count instead of collecting it and finding the length
+   |
+LL |         
+LL |         string.split('/').count()
+   |
+
+error: avoid using `collect()` when not needed
+  --> $DIR/needless_collect_indirect.rs:57:55
+   |
+LL |         let indirect_len: VecDeque<_> = sample.iter().collect();
+   |                                                       ^^^^^^^
+LL |         indirect_len.len()
+   |         ------------------ the iterator could be used here instead
+   |
+help: take the original Iterator's count instead of collecting it and finding the length
+   |
+LL |         
+LL |         sample.iter().count()
+   |
+
+error: avoid using `collect()` when not needed
+  --> $DIR/needless_collect_indirect.rs:62:57
+   |
+LL |         let indirect_len: LinkedList<_> = sample.iter().collect();
+   |                                                         ^^^^^^^
+LL |         indirect_len.len()
+   |         ------------------ the iterator could be used here instead
+   |
+help: take the original Iterator's count instead of collecting it and finding the length
+   |
+LL |         
+LL |         sample.iter().count()
+   |
+
+error: aborting due to 8 previous errors