wip

CHANGELOG.md

@@ -5692,7 +5692,6 @@ Released 2018-09-13
 [`redundant_field_names`]: https://rust-lang.github.io/rust-clippy/master/index.html#redundant_field_names
 [`redundant_guards`]: https://rust-lang.github.io/rust-clippy/master/index.html#redundant_guards
 [`redundant_locals`]: https://rust-lang.github.io/rust-clippy/master/index.html#redundant_locals
-[`redundant_owned_struct_recreation`]: https://rust-lang.github.io/rust-clippy/master/index.html#redundant_owned_struct_recreation
 [`redundant_pattern`]: https://rust-lang.github.io/rust-clippy/master/index.html#redundant_pattern
 [`redundant_pattern_matching`]: https://rust-lang.github.io/rust-clippy/master/index.html#redundant_pattern_matching
 [`redundant_pub_crate`]: https://rust-lang.github.io/rust-clippy/master/index.html#redundant_pub_crate

clippy_lints/src/declared_lints.rs

@@ -619,7 +619,6 @@ pub(crate) static LINTS: &[&crate::LintInfo] = &[
     crate::redundant_else::REDUNDANT_ELSE_INFO,
     crate::redundant_field_names::REDUNDANT_FIELD_NAMES_INFO,
     crate::redundant_locals::REDUNDANT_LOCALS_INFO,
-    crate::redundant_owned_struct_recreation::REDUNDANT_OWNED_STRUCT_RECREATION_INFO,
     crate::redundant_pub_crate::REDUNDANT_PUB_CRATE_INFO,
     crate::redundant_slicing::DEREF_BY_SLICING_INFO,
     crate::redundant_slicing::REDUNDANT_SLICING_INFO,

clippy_lints/src/lib.rs

@@ -297,7 +297,6 @@ mod redundant_closure_call;
 mod redundant_else;
 mod redundant_field_names;
 mod redundant_locals;
-mod redundant_owned_struct_recreation;
 mod redundant_pub_crate;
 mod redundant_slicing;
 mod redundant_static_lifetimes;
@@ -705,7 +704,6 @@ pub fn register_lints(store: &mut rustc_lint::LintStore, conf: &'static Conf) {
     store.register_late_pass(|_| Box::new(default_numeric_fallback::DefaultNumericFallback));
     store.register_late_pass(|_| Box::new(inconsistent_struct_constructor::InconsistentStructConstructor));
     store.register_late_pass(|_| Box::new(non_octal_unix_permissions::NonOctalUnixPermissions));
-    store.register_late_pass(|_| Box::new(redundant_owned_struct_recreation::RedundantOwnedStructRecreation));
     store.register_early_pass(|| Box::new(unnecessary_self_imports::UnnecessarySelfImports));
     store.register_late_pass(move |_| Box::new(approx_const::ApproxConstant::new(msrv())));
     let format_args = format_args_storage.clone();

clippy_lints/src/unnecessary_struct_initialization.rs

@@ -2,14 +2,15 @@ use clippy_utils::diagnostics::span_lint_and_sugg;
 use clippy_utils::source::snippet;
 use clippy_utils::ty::is_copy;
 use clippy_utils::{get_parent_expr, path_to_local};
-use rustc_hir::{BindingMode, Expr, ExprKind, Node, PatKind, UnOp};
+use rustc_hir::{BindingMode, Expr, ExprField, ExprKind, Node, PatKind, Path, QPath, UnOp};
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_session::declare_lint_pass;
 
 declare_clippy_lint! {
     /// ### What it does
-    /// Checks for initialization of a `struct` by copying a base without setting
-    /// any field.
+    /// Checks for initialization of an identical `struct` from another instance
+    /// of the type, either by copying a base without setting any field or by
+    /// moving all fields individually.
     ///
     /// ### Why is this bad?
     /// Readability suffers from unnecessary struct building.
@@ -29,9 +30,14 @@ declare_clippy_lint! {
     /// let b = a;
     /// ```
     ///
+    /// The struct literal ``S { ..a }`` in the assignment to ``b`` could be replaced
+    /// with just ``a``.
+    ///
     /// ### Known Problems
     /// Has false positives when the base is a place expression that cannot be
     /// moved out of, see [#10547](https://github.com/rust-lang/rust-clippy/issues/10547).
+    ///
+    /// Empty structs are ignored by the lint.
     #[clippy::version = "1.70.0"]
     pub UNNECESSARY_STRUCT_INITIALIZATION,
     nursery,
@@ -41,42 +47,112 @@ declare_lint_pass!(UnnecessaryStruct => [UNNECESSARY_STRUCT_INITIALIZATION]);
 
 impl LateLintPass<'_> for UnnecessaryStruct {
     fn check_expr(&mut self, cx: &LateContext<'_>, expr: &Expr<'_>) {
-        if let ExprKind::Struct(_, &[], Some(base)) = expr.kind {
-            if let Some(parent) = get_parent_expr(cx, expr)
-                && let parent_ty = cx.typeck_results().expr_ty_adjusted(parent)
-                && parent_ty.is_any_ptr()
-            {
-                if is_copy(cx, cx.typeck_results().expr_ty(expr)) && path_to_local(base).is_some() {
-                    // When the type implements `Copy`, a reference to the new struct works on the
-                    // copy. Using the original would borrow it.
-                    return;
-                }
-
-                if parent_ty.is_mutable_ptr() && !is_mutable(cx, base) {
-                    // The original can be used in a mutable reference context only if it is mutable.
-                    return;
-                }
-            }
+        let ExprKind::Struct(_, fields, base) = expr.kind else {
+            return;
+        };
 
-            // TODO: do not propose to replace *XX if XX is not Copy
-            if let ExprKind::Unary(UnOp::Deref, target) = base.kind
-                && matches!(target.kind, ExprKind::Path(..))
-                && !is_copy(cx, cx.typeck_results().expr_ty(expr))
-            {
-                // `*base` cannot be used instead of the struct in the general case if it is not Copy.
-                return;
-            }
+        if expr.span.from_expansion() {
+            // Prevent lint from hitting inside macro code
+            return;
+        }
+
+        let field_path = same_path_in_all_fields(cx, expr, fields);
+
+        let sugg = match (field_path, base) {
+            (Some(&path), None) => {
+                // all fields match, no base given
+                path.span
+            },
+            (Some(path), Some(base)) if base_is_suitable(cx, expr, base) && path_matches_base(path, base) => {
+                // all fields match, has base: ensure that the path of the base matches
+                base.span
+            },
+            (None, Some(base)) if fields.is_empty() && base_is_suitable(cx, expr, base) => {
+                // just the base, no explicit fields
+
+                base.span
+            },
+            _ => return,
+        };
+
+        span_lint_and_sugg(
+            cx,
+            UNNECESSARY_STRUCT_INITIALIZATION,
+            expr.span,
+            "unnecessary struct building",
+            "replace with",
+            snippet(cx, sugg, "..").into_owned(),
+            rustc_errors::Applicability::MachineApplicable,
+        );
+    }
+}
+
+fn base_is_suitable(cx: &LateContext<'_>, expr: &Expr<'_>, base: &Expr<'_>) -> bool {
+    if !check_references(cx, expr, base) {
+        return false;
+    }
+
+    // TODO: do not propose to replace *XX if XX is not Copy
+    if let ExprKind::Unary(UnOp::Deref, target) = base.kind
+        && matches!(target.kind, ExprKind::Path(..))
+        && !is_copy(cx, cx.typeck_results().expr_ty(expr))
+    {
+        // `*base` cannot be used instead of the struct in the general case if it is not Copy.
+        return false;
+    }
+    true
+}
+
+/// Check whether all fields of a struct assignment match.
+/// Returns a [Path] item that one can obtain a span from for the lint suggestion.
+///
+/// Conditions that must be satisfied to trigger this variant of the lint:
+///
+/// - source struct of the assignment must be of same type as the destination
+/// - names of destination struct fields must match the field names of the source
+///
+/// We don’t check here if all struct fields are assigned as the remainder may
+/// be filled in from a base struct.
+fn same_path_in_all_fields<'tcx>(
+    cx: &LateContext<'_>,
+    expr: &Expr<'_>,
+    fields: &[ExprField<'tcx>],
+) -> Option<&'tcx Path<'tcx>> {
+    let ty = cx.typeck_results().expr_ty(expr);
 
-            span_lint_and_sugg(
-                cx,
-                UNNECESSARY_STRUCT_INITIALIZATION,
-                expr.span,
-                "unnecessary struct building",
-                "replace with",
-                snippet(cx, base.span, "..").into_owned(),
-                rustc_errors::Applicability::MachineApplicable,
-            );
+    let mut found = None;
+
+    for f in fields.iter().filter(|f| !f.is_shorthand) {
+        // fields are assigned from expression
+        if let ExprKind::Field(src_expr, ident) = f.expr.kind
+            // expression type matches
+            && ty == cx.typeck_results().expr_ty(src_expr)
+            // field name matches
+            && f.ident == ident
+            // assigned from a path expression
+            && let ExprKind::Path(QPath::Resolved(None, src_path)) = src_expr.kind
+        {
+            let Some((_, p)) = found else {
+                // this is the first field assignment in the list
+                found = Some((src_expr, src_path));
+                continue;
+            };
+
+            if p.res == src_path.res {
+                // subsequent field assignment with same origin struct as before
+                continue;
+            }
         }
+        // source of field assignment doesn’t qualify
+        return None;
+    }
+
+    if let Some((src_expr, src_path)) = found
+        && check_references(cx, expr, src_expr)
+    {
+        Some(src_path)
+    } else {
+        None
     }
 }
 
@@ -89,3 +165,43 @@ fn is_mutable(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
         true
     }
 }
+
+fn check_references(cx: &LateContext<'_>, expr_a: &Expr<'_>, expr_b: &Expr<'_>) -> bool {
+    if let Some(parent) = get_parent_expr(cx, expr_a)
+        && let parent_ty = cx.typeck_results().expr_ty_adjusted(parent)
+        && parent_ty.is_any_ptr()
+    {
+        if is_copy(cx, cx.typeck_results().expr_ty(expr_a)) && path_to_local(expr_b).is_some() {
+            // When the type implements `Copy`, a reference to the new struct works on the
+            // copy. Using the original would borrow it.
+            return false;
+        }
+
+        if parent_ty.is_mutable_ptr() && !is_mutable(cx, expr_b) {
+            // The original can be used in a mutable reference context only if it is mutable.
+            return false;
+        }
+    }
+
+    true
+}
+
+/// When some fields are assigned from a base struct and others individually
+/// the lint applies only if the source of the field is the same as the base.
+/// This is enforced here by comparing the path of the base expression;
+/// needless to say the link only applies if it (or whatever expression it is
+/// a reference of) actually has a path.
+fn path_matches_base(path: &Path<'_>, base: &Expr<'_>) -> bool {
+    let base_path = match base.kind {
+        ExprKind::Unary(UnOp::Deref, base_expr) => {
+            if let ExprKind::Path(QPath::Resolved(_, base_path)) = base_expr.kind {
+                base_path
+            } else {
+                return false;
+            }
+        },
+        ExprKind::Path(QPath::Resolved(_, base_path)) => base_path,
+        _ => return false,
+    };
+    path.res == base_path.res
+}