Auto merge of #12116 - J-ZhengLi:issue12101, r=Alexendoo

fix suggestion error in [`useless_vec`]

fixes: #12101

---

changelog: fix suggestion error in [`useless_vec`]

r+ `@matthiaskrgr` since they opened the issue?

4 files changed, 120 insertions, 107 deletions

diff --git a/clippy_lints/src/vec.rs b/clippy_lints/src/vec.rs
index b3489142558..7cfcf3fe946 100644
--- a/clippy_lints/src/vec.rs
+++ b/clippy_lints/src/vec.rs
@@ -4,12 +4,12 @@ use std::ops::ControlFlow;
 use clippy_config::msrvs::{self, Msrv};
 use clippy_utils::consts::{constant, Constant};
 use clippy_utils::diagnostics::span_lint_hir_and_then;
-use clippy_utils::source::snippet_with_applicability;
+use clippy_utils::source::snippet_opt;
 use clippy_utils::ty::is_copy;
 use clippy_utils::visitors::for_each_local_use_after_expr;
 use clippy_utils::{get_parent_expr, higher, is_trait_method};
 use rustc_errors::Applicability;
-use rustc_hir::{BorrowKind, Expr, ExprKind, HirId, Mutability, Node, PatKind};
+use rustc_hir::{BorrowKind, Expr, ExprKind, HirId, Local, Mutability, Node, Pat, PatKind};
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_middle::ty;
 use rustc_middle::ty::layout::LayoutOf;
@@ -52,35 +52,27 @@ declare_clippy_lint! {
 
 impl_lint_pass!(UselessVec => [USELESS_VEC]);
 
-fn adjusts_to_slice(cx: &LateContext<'_>, e: &Expr<'_>) -> bool {
-    matches!(cx.typeck_results().expr_ty_adjusted(e).kind(), ty::Ref(_, ty, _) if ty.is_slice())
-}
-
-/// Checks if the given expression is a method call to a `Vec` method
-/// that also exists on slices. If this returns true, it means that
-/// this expression does not actually require a `Vec` and could just work with an array.
-pub fn is_allowed_vec_method(cx: &LateContext<'_>, e: &Expr<'_>) -> bool {
-    const ALLOWED_METHOD_NAMES: &[&str] = &["len", "as_ptr", "is_empty"];
-
-    if let ExprKind::MethodCall(path, ..) = e.kind {
-        ALLOWED_METHOD_NAMES.contains(&path.ident.name.as_str())
-    } else {
-        is_trait_method(cx, e, sym::IntoIterator)
-    }
-}
-
 impl<'tcx> LateLintPass<'tcx> for UselessVec {
     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
-        if let Some(vec_args) = higher::VecArgs::hir(cx, expr.peel_borrows()) {
+        let Some(vec_args) = higher::VecArgs::hir(cx, expr.peel_borrows()) else {
+            return;
+        };
+        // the parent callsite of this `vec!` expression, or span to the borrowed one such as `&vec!`
+        let callsite = expr.span.parent_callsite().unwrap_or(expr.span);
+
+        match cx.tcx.parent_hir_node(expr.hir_id) {
             // 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.parent_hir_node(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
-            {
-                let only_slice_uses = for_each_local_use_after_expr(cx, id, expr.hir_id, |expr| {
+            Node::Local(Local {
+                ty: None,
+                pat:
+                    Pat {
+                        kind: PatKind::Binding(_, id, ..),
+                        ..
+                    },
+                ..
+            }) => {
+                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)
@@ -94,60 +86,40 @@ impl<'tcx> LateLintPass<'tcx> for UselessVec {
                 })
                 .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);
+                    self.check_vec_macro(cx, &vec_args, callsite, expr.hir_id, SuggestedType::Array);
                 } else {
-                    self.span_to_lint_map.insert(span, None);
+                    self.span_to_lint_map.insert(callsite, None);
                 }
-            }
+            },
             // 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.parent_hir_node(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);
-            }
+            Node::Local(Local { ty: Some(_), .. }) if higher::VecArgs::hir(cx, expr).is_some() => {
+                self.span_to_lint_map.insert(callsite, 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)
+            Node::Expr(Expr { span, .. })
+                if 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.check_vec_macro(cx, &vec_args, span, expr.hir_id, SuggestedType::Array);
-            }
+                let suggest_slice = suggest_type(expr);
+                self.check_vec_macro(cx, &vec_args, callsite, expr.hir_id, suggest_slice);
+            },
             // 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)
-                };
+            _ => {
+                let suggest_slice = suggest_type(expr);
 
                 if adjusts_to_slice(cx, expr) {
-                    self.check_vec_macro(cx, &vec_args, span, expr.hir_id, suggest_slice);
+                    self.check_vec_macro(cx, &vec_args, callsite, expr.hir_id, suggest_slice);
                 } else {
-                    self.span_to_lint_map.insert(span, None);
+                    self.span_to_lint_map.insert(callsite, None);
                 }
-            }
+            },
         }
     }
 
     fn check_crate_post(&mut self, cx: &LateContext<'tcx>) {
         for (span, lint_opt) in &self.span_to_lint_map {
             if let Some((hir_id, suggest_slice, snippet, applicability)) = lint_opt {
-                let help_msg = format!(
-                    "you can use {} directly",
-                    match suggest_slice {
-                        SuggestedType::SliceRef(_) => "a slice",
-                        SuggestedType::Array => "an array",
-                    }
-                );
+                let help_msg = format!("you can use {} directly", suggest_slice.desc(),);
                 span_lint_hir_and_then(cx, USELESS_VEC, *hir_id, *span, "useless use of `vec!`", |diag| {
                     diag.span_suggestion(*span, help_msg, snippet, *applicability);
                 });
@@ -158,14 +130,6 @@ impl<'tcx> LateLintPass<'tcx> for UselessVec {
     extract_msrv_attr!(LateContext);
 }
 
-#[derive(Copy, Clone)]
-pub(crate) enum SuggestedType {
-    /// Suggest using a slice `&[..]` / `&mut [..]`
-    SliceRef(Mutability),
-    /// Suggest using an array: `[..]`
-    Array,
-}
-
 impl UselessVec {
     fn check_vec_macro<'tcx>(
         &mut self,
@@ -179,8 +143,6 @@ impl UselessVec {
             return;
         }
 
-        let mut applicability = Applicability::MachineApplicable;
-
         let snippet = match *vec_args {
             higher::VecArgs::Repeat(elem, len) => {
                 if let Some(Constant::Int(len_constant)) = constant(cx, cx.typeck_results(), len) {
@@ -194,50 +156,60 @@ impl UselessVec {
                         return;
                     }
 
-                    let elem = snippet_with_applicability(cx, elem.span, "elem", &mut applicability);
-                    let len = snippet_with_applicability(cx, len.span, "len", &mut applicability);
-
-                    match suggest_slice {
-                        SuggestedType::SliceRef(Mutability::Mut) => format!("&mut [{elem}; {len}]"),
-                        SuggestedType::SliceRef(Mutability::Not) => format!("&[{elem}; {len}]"),
-                        SuggestedType::Array => format!("[{elem}; {len}]"),
-                    }
+                    suggest_slice.snippet(cx, Some(elem.span), Some(len.span))
                 } else {
                     return;
                 }
             },
             higher::VecArgs::Vec(args) => {
-                if let Some(last) = args.iter().last() {
+                let args_span = if let Some(last) = args.iter().last() {
                     if args.len() as u64 * size_of(cx, last) > self.too_large_for_stack {
                         return;
                     }
-                    let span = args[0].span.source_callsite().to(last.span.source_callsite());
-                    let args = snippet_with_applicability(cx, span, "..", &mut applicability);
-
-                    match suggest_slice {
-                        SuggestedType::SliceRef(Mutability::Mut) => {
-                            format!("&mut [{args}]")
-                        },
-                        SuggestedType::SliceRef(Mutability::Not) => {
-                            format!("&[{args}]")
-                        },
-                        SuggestedType::Array => {
-                            format!("[{args}]")
-                        },
-                    }
+                    Some(args[0].span.source_callsite().to(last.span.source_callsite()))
                 } else {
-                    match suggest_slice {
-                        SuggestedType::SliceRef(Mutability::Mut) => "&mut []".to_owned(),
-                        SuggestedType::SliceRef(Mutability::Not) => "&[]".to_owned(),
-                        SuggestedType::Array => "[]".to_owned(),
-                    }
-                }
+                    None
+                };
+                suggest_slice.snippet(cx, args_span, None)
             },
         };
 
-        self.span_to_lint_map
-            .entry(span)
-            .or_insert(Some((hir_id, suggest_slice, snippet, applicability)));
+        self.span_to_lint_map.entry(span).or_insert(Some((
+            hir_id,
+            suggest_slice,
+            snippet,
+            Applicability::MachineApplicable,
+        )));
+    }
+}
+
+#[derive(Copy, Clone)]
+pub(crate) enum SuggestedType {
+    /// Suggest using a slice `&[..]` / `&mut [..]`
+    SliceRef(Mutability),
+    /// Suggest using an array: `[..]`
+    Array,
+}
+
+impl SuggestedType {
+    fn desc(self) -> &'static str {
+        match self {
+            Self::SliceRef(_) => "a slice",
+            Self::Array => "an array",
+        }
+    }
+
+    fn snippet(self, cx: &LateContext<'_>, args_span: Option<Span>, len_span: Option<Span>) -> String {
+        let maybe_args = args_span.and_then(|sp| snippet_opt(cx, sp)).unwrap_or_default();
+        let maybe_len = len_span
+            .and_then(|sp| snippet_opt(cx, sp).map(|s| format!("; {s}")))
+            .unwrap_or_default();
+
+        match self {
+            Self::SliceRef(Mutability::Mut) => format!("&mut [{maybe_args}{maybe_len}]"),
+            Self::SliceRef(Mutability::Not) => format!("&[{maybe_args}{maybe_len}]"),
+            Self::Array => format!("[{maybe_args}{maybe_len}]"),
+        }
     }
 }
 
@@ -245,3 +217,30 @@ fn size_of(cx: &LateContext<'_>, expr: &Expr<'_>) -> u64 {
     let ty = cx.typeck_results().expr_ty_adjusted(expr);
     cx.layout_of(ty).map_or(0, |l| l.size.bytes())
 }
+
+fn adjusts_to_slice(cx: &LateContext<'_>, e: &Expr<'_>) -> bool {
+    matches!(cx.typeck_results().expr_ty_adjusted(e).kind(), ty::Ref(_, ty, _) if ty.is_slice())
+}
+
+/// Checks if the given expression is a method call to a `Vec` method
+/// that also exists on slices. If this returns true, it means that
+/// this expression does not actually require a `Vec` and could just work with an array.
+pub fn is_allowed_vec_method(cx: &LateContext<'_>, e: &Expr<'_>) -> bool {
+    const ALLOWED_METHOD_NAMES: &[&str] = &["len", "as_ptr", "is_empty"];
+
+    if let ExprKind::MethodCall(path, ..) = e.kind {
+        ALLOWED_METHOD_NAMES.contains(&path.ident.name.as_str())
+    } else {
+        is_trait_method(cx, e, sym::IntoIterator)
+    }
+}
+
+fn suggest_type(expr: &Expr<'_>) -> SuggestedType {
+    if let ExprKind::AddrOf(BorrowKind::Ref, mutability, _) = expr.kind {
+        // `expr` is `&vec![_]`, so suggest `&[_]` (or `&mut[_]` resp.)
+        SuggestedType::SliceRef(mutability)
+    } else {
+        // `expr` is the `vec![_]` expansion, so suggest `[_]`
+        SuggestedType::Array
+    }
+}
diff --git a/tests/ui/vec.fixed b/tests/ui/vec.fixed
index b318fd42f7c..9e755a82af4 100644
--- a/tests/ui/vec.fixed
+++ b/tests/ui/vec.fixed
@@ -217,3 +217,7 @@ fn issue_11958() {
     // should not lint, `String` is not `Copy`
     f(&vec!["test".to_owned(); 2]);
 }
+
+fn issue_12101() {
+    for a in &[1, 2] {}
+}
diff --git a/tests/ui/vec.rs b/tests/ui/vec.rs
index 08ad6efa37f..c483271438b 100644
--- a/tests/ui/vec.rs
+++ b/tests/ui/vec.rs
@@ -217,3 +217,7 @@ fn issue_11958() {
     // should not lint, `String` is not `Copy`
     f(&vec!["test".to_owned(); 2]);
 }
+
+fn issue_12101() {
+    for a in &(vec![1, 2]) {}
+}
diff --git a/tests/ui/vec.stderr b/tests/ui/vec.stderr
index 6fd4748fff3..3faea8033fe 100644
--- a/tests/ui/vec.stderr
+++ b/tests/ui/vec.stderr
@@ -121,5 +121,11 @@ error: useless use of `vec!`
 LL |     this_macro_doesnt_need_vec!(vec![1]);
    |                                 ^^^^^^^ help: you can use an array directly: `[1]`
 
-error: aborting due to 20 previous errors
+error: useless use of `vec!`
+  --> tests/ui/vec.rs:222:14
+   |
+LL |     for a in &(vec![1, 2]) {}
+   |              ^^^^^^^^^^^^^ help: you can use a slice directly: `&[1, 2]`
+
+error: aborting due to 21 previous errors