refactor flow of check_expr in useless_vec

Author: ericwu17

clippy_lints/src/lib.rs

@@ -50,7 +50,7 @@ extern crate clippy_utils;
 #[macro_use]
 extern crate declare_clippy_lint;
 
-use std::collections::{BTreeMap, BTreeSet};
+use std::collections::BTreeMap;
 
 use rustc_data_structures::fx::FxHashSet;
 use rustc_lint::{Lint, LintId};
@@ -725,7 +725,6 @@ pub fn register_lints(store: &mut rustc_lint::LintStore, conf: &'static Conf) {
             too_large_for_stack,
             msrv: msrv(),
             span_to_lint_map: BTreeMap::new(),
-            lintable_exprs: BTreeSet::new(),
         })
     });
     store.register_late_pass(|_| Box::new(panic_unimplemented::PanicUnimplemented));

clippy_lints/src/vec.rs

@@ -1,4 +1,4 @@
-use std::collections::{BTreeMap, BTreeSet};
+use std::collections::BTreeMap;
 use std::ops::ControlFlow;
 
 use clippy_config::msrvs::{self, Msrv};
@@ -14,15 +14,14 @@ use rustc_lint::{LateContext, LateLintPass};
 use rustc_middle::ty::layout::LayoutOf;
 use rustc_middle::ty::{self, Ty};
 use rustc_session::impl_lint_pass;
-use rustc_span::{sym, Span};
+use rustc_span::{sym, DesugaringKind, Span};
 
 #[expect(clippy::module_name_repetitions)]
 #[derive(Clone)]
 pub struct UselessVec {
     pub too_large_for_stack: u64,
     pub msrv: Msrv,
     pub span_to_lint_map: BTreeMap<Span, Option<(HirId, SuggestedType, String, Applicability)>>,
-    pub lintable_exprs: BTreeSet<HirId>,
 }
 
 declare_clippy_lint! {
@@ -72,61 +71,70 @@ pub fn is_allowed_vec_method(cx: &LateContext<'_>, e: &Expr<'_>) -> bool {
 
 impl<'tcx> LateLintPass<'tcx> for UselessVec {
     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
-        // search for `let foo = vec![_]` expressions where all uses of `foo`
-        // adjust to slices or call a method that exist on slices (e.g. len)
-        if let Some(vec_args) = higher::VecArgs::hir(cx, expr)
-            && let Node::Local(local) = cx.tcx.hir().get_parent(expr.hir_id)
-            // for now ignore locals with type annotations.
-            // this is to avoid compile errors when doing the suggestion here: let _: Vec<_> = vec![..];
-            && local.ty.is_none()
-            && let PatKind::Binding(_, id, ..) = local.pat.kind
-            && is_copy(cx, vec_type(cx.typeck_results().expr_ty_adjusted(expr)))
-        {
-            let only_slice_uses = for_each_local_use_after_expr(cx, id, expr.hir_id, |expr| {
-                // allow indexing into a vec and some set of allowed method calls that exist on slices, too
-                if let Some(parent) = get_parent_expr(cx, expr)
-                    && (adjusts_to_slice(cx, expr)
-                        || matches!(parent.kind, ExprKind::Index(..))
-                        || is_allowed_vec_method(cx, parent))
-                {
-                    ControlFlow::Continue(())
+        if let Some(vec_args) = higher::VecArgs::hir(cx, expr.peel_borrows()) {
+            // search for `let foo = vec![_]` expressions where all uses of `foo`
+            // adjust to slices or call a method that exist on slices (e.g. len)
+            if let Node::Local(local) = cx.tcx.hir().get_parent(expr.hir_id)
+                // for now ignore locals with type annotations.
+                // this is to avoid compile errors when doing the suggestion here: let _: Vec<_> = vec![..];
+                && local.ty.is_none()
+                && let PatKind::Binding(_, id, ..) = local.pat.kind
+                && is_copy(cx, vec_type(cx.typeck_results().expr_ty_adjusted(expr.peel_borrows())))
+            {
+                let only_slice_uses = for_each_local_use_after_expr(cx, id, expr.hir_id, |expr| {
+                    // allow indexing into a vec and some set of allowed method calls that exist on slices, too
+                    if let Some(parent) = get_parent_expr(cx, expr)
+                        && (adjusts_to_slice(cx, expr)
+                            || matches!(parent.kind, ExprKind::Index(..))
+                            || is_allowed_vec_method(cx, parent))
+                    {
+                        ControlFlow::Continue(())
+                    } else {
+                        ControlFlow::Break(())
+                    }
+                })
+                .is_continue();
+
+                let span = expr.span.ctxt().outer_expn_data().call_site;
+                if only_slice_uses {
+                    self.check_vec_macro(cx, &vec_args, span, expr.hir_id, SuggestedType::Array);
                 } else {
-                    ControlFlow::Break(())
+                    self.span_to_lint_map.insert(span, None);
                 }
-            })
-            .is_continue();
-
-            if only_slice_uses {
+            }
+            // if the local pattern has a specified type, do not lint.
+            else if let Some(_) = higher::VecArgs::hir(cx, expr)
+                && let Node::Local(local) = cx.tcx.hir().get_parent(expr.hir_id)
+                && local.ty.is_some()
+            {
+                let span = expr.span.ctxt().outer_expn_data().call_site;
+                self.span_to_lint_map.insert(span, None);
+            }
+            // search for `for _ in vec![...]`
+            else if let Some(parent) = get_parent_expr(cx, expr)
+                && parent.span.is_desugaring(DesugaringKind::ForLoop)
+                && self.msrv.meets(msrvs::ARRAY_INTO_ITERATOR)
+            {
+                // report the error around the `vec!` not inside `<std macros>:`
                 let span = expr.span.ctxt().outer_expn_data().call_site;
-                self.lintable_exprs.insert(expr.hir_id);
                 self.check_vec_macro(cx, &vec_args, span, expr.hir_id, SuggestedType::Array);
             }
-        }
-        // search for `for _ in vec![…]`
-        else if let Some(higher::ForLoop { arg, .. }) = higher::ForLoop::hir(expr)
-            && let Some(vec_args) = higher::VecArgs::hir(cx, arg)
-            && self.msrv.meets(msrvs::ARRAY_INTO_ITERATOR)
-        {
-            // report the error around the `vec!` not inside `<std macros>:`
-            let span = arg.span.ctxt().outer_expn_data().call_site;
-            self.lintable_exprs.insert(arg.hir_id);
-            self.check_vec_macro(cx, &vec_args, span, arg.hir_id, SuggestedType::Array);
-        }
-        // search for `&vec![_]` or `vec![_]` expressions where the adjusted type is `&[_]`
-        else if let Some(vec_args) = higher::VecArgs::hir(cx, expr.peel_borrows()) {
-            let (suggest_slice, span) = if let ExprKind::AddrOf(BorrowKind::Ref, mutability, _) = expr.kind {
-                // `expr` is `&vec![_]`, so suggest `&[_]` (or `&mut[_]` resp.)
-                (SuggestedType::SliceRef(mutability), expr.span)
-            } else {
-                // `expr` is the `vec![_]` expansion, so suggest `[_]`
-                // and also use the span of the actual `vec![_]` expression
-                (SuggestedType::Array, expr.span.ctxt().outer_expn_data().call_site)
-            };
-
-            if adjusts_to_slice(cx, expr) {
-                self.check_vec_macro(cx, &vec_args, span, expr.hir_id, suggest_slice);
-            } else if !self.lintable_exprs.contains(&expr.hir_id) {
-                self.span_to_lint_map.insert(span, None);
+            // search for `&vec![_]` or `vec![_]` expressions where the adjusted type is `&[_]`
+            else {
+                let (suggest_slice, span) = if let ExprKind::AddrOf(BorrowKind::Ref, mutability, _) = expr.kind {
+                    // `expr` is `&vec![_]`, so suggest `&[_]` (or `&mut[_]` resp.)
+                    (SuggestedType::SliceRef(mutability), expr.span)
+                } else {
+                    // `expr` is the `vec![_]` expansion, so suggest `[_]`
+                    // and also use the span of the actual `vec![_]` expression
+                    (SuggestedType::Array, expr.span.ctxt().outer_expn_data().call_site)
+                };
+
+                if adjusts_to_slice(cx, expr) {
+                    self.check_vec_macro(cx, &vec_args, span, expr.hir_id, suggest_slice);
+                } else {
+                    self.span_to_lint_map.insert(span, None);
+                }
             }
         }
     }