diff --git a/clippy_lints/src/collection_is_never_read.rs b/clippy_lints/src/collection_is_never_read.rs index 10f2bef268a..15a5b7dd274 100644 --- a/clippy_lints/src/collection_is_never_read.rs +++ b/clippy_lints/src/collection_is_never_read.rs @@ -1,9 +1,9 @@ use clippy_utils::diagnostics::span_lint; -use clippy_utils::ty::is_type_diagnostic_item; +use clippy_utils::ty::{is_type_diagnostic_item, is_type_lang_item}; use clippy_utils::visitors::for_each_expr_with_closures; use clippy_utils::{get_enclosing_block, get_parent_node, path_to_local_id}; use core::ops::ControlFlow; -use rustc_hir::{Block, ExprKind, HirId, Local, Node, PatKind}; +use rustc_hir::{Block, ExprKind, HirId, LangItem, Local, Node, PatKind}; use rustc_lint::{LateContext, LateLintPass}; use rustc_session::{declare_lint_pass, declare_tool_lint}; use rustc_span::symbol::sym; @@ -44,7 +44,8 @@ declare_clippy_lint! { } declare_lint_pass!(CollectionIsNeverRead => [COLLECTION_IS_NEVER_READ]); -static COLLECTIONS: [Symbol; 10] = [ +// Add `String` here when it is added to diagnostic items +static COLLECTIONS: [Symbol; 9] = [ sym::BTreeMap, sym::BTreeSet, sym::BinaryHeap, @@ -52,7 +53,6 @@ static COLLECTIONS: [Symbol; 10] = [ sym::HashSet, sym::LinkedList, sym::Option, - sym::String, sym::Vec, sym::VecDeque, ]; @@ -60,8 +60,7 @@ static COLLECTIONS: [Symbol; 10] = [ impl<'tcx> LateLintPass<'tcx> for CollectionIsNeverRead { fn check_local(&mut self, cx: &LateContext<'tcx>, local: &'tcx Local<'tcx>) { // Look for local variables whose type is a container. Search surrounding bock for read access. - let ty = cx.typeck_results().pat_ty(local.pat); - if COLLECTIONS.iter().any(|&sym| is_type_diagnostic_item(cx, ty, sym)) + if match_acceptable_type(cx, local, &COLLECTIONS) && let PatKind::Binding(_, local_id, _, _) = local.pat.kind && let Some(enclosing_block) = get_enclosing_block(cx, local.hir_id) && has_no_read_access(cx, local_id, enclosing_block) @@ -71,6 +70,13 @@ impl<'tcx> LateLintPass<'tcx> for CollectionIsNeverRead { } } +fn match_acceptable_type(cx: &LateContext<'_>, local: &Local<'_>, collections: &[rustc_span::Symbol]) -> bool { + let ty = cx.typeck_results().pat_ty(local.pat); + collections.iter().any(|&sym| is_type_diagnostic_item(cx, ty, sym)) + // String type is a lang item but not a diagnostic item for now so we need a separate check + || is_type_lang_item(cx, ty, LangItem::String) +} + fn has_no_read_access<'tcx>(cx: &LateContext<'tcx>, id: HirId, block: &'tcx Block<'tcx>) -> bool { let mut has_access = false; let mut has_read_access = false; diff --git a/tests/ui/collection_is_never_read.rs b/tests/ui/collection_is_never_read.rs index 068a49486cf..ca20031bfbe 100644 --- a/tests/ui/collection_is_never_read.rs +++ b/tests/ui/collection_is_never_read.rs @@ -163,3 +163,23 @@ fn function_argument() { let x = vec![1, 2, 3]; // Ok foo(&x); } + +fn string() { + // Do lint (write without read) + let mut s = String::new(); + s.push_str("Hello, World!"); + + // Do not lint (read without write) + let mut s = String::from("Hello, World!"); + let _ = s.len(); + + // Do not lint (write and read) + let mut s = String::from("Hello, World!"); + s.push_str("foo, bar"); + let _ = s.len(); + + // Do lint the first line, but not the second + let mut s = String::from("Hello, World!"); + let t = String::from("foo, bar"); + s = t; +} diff --git a/tests/ui/collection_is_never_read.stderr b/tests/ui/collection_is_never_read.stderr index 7654b74be3d..f5dea96116f 100644 --- a/tests/ui/collection_is_never_read.stderr +++ b/tests/ui/collection_is_never_read.stderr @@ -48,5 +48,17 @@ error: collection is never read LL | let x = vec![1, 2, 3]; // WARNING | ^^^^^^^^^^^^^^^^^^^^^^ -error: aborting due to 8 previous errors +error: collection is never read + --> $DIR/collection_is_never_read.rs:169:5 + | +LL | let mut s = String::new(); + | ^^^^^^^^^^^^^^^^^^^^^^^^^^ + +error: collection is never read + --> $DIR/collection_is_never_read.rs:182:5 + | +LL | let mut s = String::from("Hello, World!"); + | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +error: aborting due to 10 previous errors