New lint: struct_fields_rest_default

CHANGELOG.md

@@ -6139,6 +6139,7 @@ Released 2018-09-13
 [`strlen_on_c_strings`]: https://rust-lang.github.io/rust-clippy/master/index.html#strlen_on_c_strings
 [`struct_excessive_bools`]: https://rust-lang.github.io/rust-clippy/master/index.html#struct_excessive_bools
 [`struct_field_names`]: https://rust-lang.github.io/rust-clippy/master/index.html#struct_field_names
+[`struct_fields_rest_default`]: https://rust-lang.github.io/rust-clippy/master/index.html#struct_fields_rest_default
 [`stutter`]: https://rust-lang.github.io/rust-clippy/master/index.html#stutter
 [`suboptimal_flops`]: https://rust-lang.github.io/rust-clippy/master/index.html#suboptimal_flops
 [`suspicious_arithmetic_impl`]: https://rust-lang.github.io/rust-clippy/master/index.html#suspicious_arithmetic_impl

clippy_lints/src/declared_lints.rs

@@ -710,6 +710,7 @@ pub static LINTS: &[&crate::LintInfo] = &[
     crate::strings::STR_TO_STRING_INFO,
     crate::strings::TRIM_SPLIT_WHITESPACE_INFO,
     crate::strlen_on_c_strings::STRLEN_ON_C_STRINGS_INFO,
+    crate::struct_fields_rest_default::STRUCT_FIELDS_REST_DEFAULT_INFO,
     crate::suspicious_operation_groupings::SUSPICIOUS_OPERATION_GROUPINGS_INFO,
     crate::suspicious_trait_impl::SUSPICIOUS_ARITHMETIC_IMPL_INFO,
     crate::suspicious_trait_impl::SUSPICIOUS_OP_ASSIGN_IMPL_INFO,

clippy_lints/src/lib.rs

@@ -349,6 +349,7 @@ mod std_instead_of_core;
 mod string_patterns;
 mod strings;
 mod strlen_on_c_strings;
+mod struct_fields_rest_default;
 mod suspicious_operation_groupings;
 mod suspicious_trait_impl;
 mod suspicious_xor_used_as_pow;
@@ -984,5 +985,6 @@ pub fn register_lints(store: &mut rustc_lint::LintStore, conf: &'static Conf) {
     store.register_late_pass(move |_| Box::new(non_std_lazy_statics::NonStdLazyStatic::new(conf)));
     store.register_late_pass(|_| Box::new(manual_option_as_slice::ManualOptionAsSlice::new(conf)));
     store.register_late_pass(|_| Box::new(single_option_map::SingleOptionMap));
+    store.register_late_pass(|_| Box::new(struct_fields_rest_default::StructFieldsDefault));
     // add lints here, do not remove this comment, it's used in `new_lint`
 }

clippy_lints/src/struct_fields_rest_default.rs

@@ -0,0 +1,90 @@
+use clippy_utils::diagnostics::span_lint_and_help;
+use clippy_utils::is_trait_item;
+use clippy_utils::source::snippet;
+use rustc_hir::{ExprKind, StructTailExpr};
+use rustc_lint::{LateLintPass, LintContext};
+use rustc_session::declare_lint_pass;
+use rustc_span::sym;
+
+declare_clippy_lint! {
+    /// ### What it does
+    /// Check struct initialization uses `..*::default()` pattern to skip rest of struct field initialization.
+    ///
+    /// ### Why restrict this?
+    /// Using `..*::default()` can hide field initialization when new fields are added to structs,
+    /// potentially leading to bugs where developers forget to explicitly set values for new fields.
+    ///
+    /// ### Example
+    /// ```no_run
+    /// #[derive(Default)]
+    /// struct Foo {
+    ///     a: i32,
+    ///     b: i32,
+    ///     // when add new filed `c`
+    ///     c: i32,
+    /// }
+    ///
+    /// let _ = Foo {
+    ///     a: Default::default(),
+    ///     ..Default::default()
+    ///     // developer may forget to explicitly set field `c` and cause bug
+    /// };
+    /// ```
+    /// Use instead:
+    /// ```no_run
+    /// #[derive(Default)]
+    /// struct Foo {
+    ///     a: i32,
+    ///     b: i32,
+    ///     // when add new filed `c`
+    ///     c: i32,
+    /// }
+    ///
+    /// // make the compiler check for new fields to avoid bug.
+    /// let _ = Foo {
+    ///     a: Default::default(),
+    ///     b: Default::default(),
+    ///     c: Default::default(),
+    /// };
+    ///
+    /// impl Foo {
+    ///     fn get_foo() -> Self {
+    ///         Foo{ a: 0, b: 0, c: 0}
+    ///     }
+    /// }
+    ///
+    /// // or avoid using `..*::default()`
+    /// let _ = Foo {
+    ///     a: Default::default(),
+    ///     ..Foo::get_foo()
+    /// };
+    /// ```
+    #[clippy::version = "1.87.0"]
+    pub STRUCT_FIELDS_REST_DEFAULT,
+    restriction,
+    "should not use `..*::default()` pattern to omit rest of struct field initialization"
+}
+
+declare_lint_pass!(StructFieldsDefault => [STRUCT_FIELDS_REST_DEFAULT]);
+
+impl<'tcx> LateLintPass<'tcx> for StructFieldsDefault {
+    fn check_expr(&mut self, cx: &rustc_lint::LateContext<'tcx>, expr: &'tcx rustc_hir::Expr<'tcx>) {
+        if !expr.span.in_external_macro(cx.sess().source_map())
+            && let ExprKind::Struct(_, _, StructTailExpr::Base(base)) = &expr.kind
+            && let ExprKind::Call(func, _) = base.kind
+            && is_trait_item(cx, func, sym::Default)
+        {
+            span_lint_and_help(
+                cx,
+                STRUCT_FIELDS_REST_DEFAULT,
+                base.span,
+                format!(
+                    "should not use `..{}` to omit rest of struct field initialization",
+                    snippet(cx, base.span, "")
+                ),
+                Some(expr.span),
+                "explicitly specify all fields or use other base value instead of `..*::default()`",
+            );
+        }
+    }
+}

tests/ui/struct_fields_rest_default.rs

@@ -0,0 +1,60 @@
+//@aux-build:proc_macros.rs
+#![warn(clippy::struct_fields_rest_default)]
+extern crate proc_macros;
+
+#[derive(Default)]
+struct Foo {
+    a: i32,
+    b: i32,
+    c: i32,
+}
+
+impl Foo {
+    fn get_foo() -> Self {
+        Foo { a: 0, b: 0, c: 0 }
+    }
+}
+
+fn main() {
+    #[rustfmt::skip]
+    let _ = Foo {
+        a: 10,
+        ..Default::default()
+        //~^ struct_fields_rest_default
+    };
+
+    #[rustfmt::skip]
+    let _ = Foo {
+        a: 10,
+        ..Foo::default()
+        //~^ struct_fields_rest_default
+    };
+
+    // should not lint
+    #[rustfmt::skip]
+    let _ = Foo {
+        a: 10,
+        ..Foo::get_foo()
+    };
+
+    // should not lint in external macro
+    proc_macros::external! {
+        #[derive(Default)]
+        struct ExternalDefault {
+            a: i32,
+            b: i32,
+        }
+
+        let _ = ExternalDefault {
+            a: 10,
+            ..Default::default()
+        };
+    }
+
+    // should not lint
+    let _ = Foo {
+        a: Default::default(),
+        b: Default::default(),
+        c: Default::default(),
+    };
+}

tests/ui/struct_fields_rest_default.stderr

@@ -0,0 +1,38 @@
+error: should not use `..Default::default()` to omit rest of struct field initialization
+  --> tests/ui/struct_fields_rest_default.rs:22:11
+   |
+LL |         ..Default::default()
+   |           ^^^^^^^^^^^^^^^^^^
+   |
+help: explicitly specify all fields or use other base value instead of `..*::default()`
+  --> tests/ui/struct_fields_rest_default.rs:20:13
+   |
+LL |       let _ = Foo {
+   |  _____________^
+LL | |         a: 10,
+LL | |         ..Default::default()
+LL | |
+LL | |     };
+   | |_____^
+   = note: `-D clippy::struct-fields-rest-default` implied by `-D warnings`
+   = help: to override `-D warnings` add `#[allow(clippy::struct_fields_rest_default)]`
+
+error: should not use `..Foo::default()` to omit rest of struct field initialization
+  --> tests/ui/struct_fields_rest_default.rs:29:11
+   |
+LL |         ..Foo::default()
+   |           ^^^^^^^^^^^^^^
+   |
+help: explicitly specify all fields or use other base value instead of `..*::default()`
+  --> tests/ui/struct_fields_rest_default.rs:27:13
+   |
+LL |       let _ = Foo {
+   |  _____________^
+LL | |         a: 10,
+LL | |         ..Foo::default()
+LL | |
+LL | |     };
+   | |_____^
+
+error: aborting due to 2 previous errors
+