re-orgnize [useless_vec]'s code

Author: J-ZhengLi

clippy_lints/src/vec.rs

@@ -9,7 +9,7 @@ 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 +52,25 @@ 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;
+        };
+
+        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)
@@ -100,26 +90,22 @@ impl<'tcx> LateLintPass<'tcx> for UselessVec {
                 } else {
                     self.span_to_lint_map.insert(span, 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()
-            {
+            Node::Local(Local { ty: Some(_), .. }) if higher::VecArgs::hir(cx, expr).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)
+            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);
-            }
+            },
             // 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)
@@ -134,20 +120,14 @@ impl<'tcx> LateLintPass<'tcx> for UselessVec {
                 } else {
                     self.span_to_lint_map.insert(span, 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 +138,6 @@ 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,
@@ -194,44 +166,21 @@ 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), &mut applicability)
                 } 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, &mut applicability)
             },
         };
 
@@ -241,7 +190,62 @@ impl UselessVec {
     }
 }
 
+#[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>,
+        app: &mut Applicability,
+    ) -> String {
+        let args = args_span
+            .map(|sp| snippet_with_applicability(cx, sp, "..", app))
+            .unwrap_or_default();
+        let maybe_len = len_span
+            .map(|sp| format!("; {}", snippet_with_applicability(cx, sp, "len", app)))
+            .unwrap_or_default();
+
+        match self {
+            Self::SliceRef(Mutability::Mut) => format!("&mut [{args}{maybe_len}]"),
+            Self::SliceRef(Mutability::Not) => format!("&[{args}{maybe_len}]"),
+            Self::Array => format!("[{args}{maybe_len}]"),
+        }
+    }
+}
+
 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)
+    }
+}