src/tools/clippy/clippy_lints/src/default.rs - third_party/rust - Git at Google

 use clippy_utils::diagnostics::{span_lint_and_note, span_lint_and_sugg};
 use clippy_utils::source::snippet_with_context;
 use clippy_utils::ty::{has_drop, is_copy};
 use clippy_utils::{any_parent_is_automatically_derived, contains_name, get_parent_expr, is_from_proc_macro};
 use rustc_data_structures::fx::FxHashSet;
 use rustc_errors::Applicability;
 use rustc_hir::def::Res;
 use rustc_hir::{Block, Expr, ExprKind, PatKind, QPath, Stmt, StmtKind};
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_middle::ty;
 use rustc_middle::ty::print::with_forced_trimmed_paths;
 use rustc_session::impl_lint_pass;
 use rustc_span::symbol::{Ident, Symbol};
 use rustc_span::{sym, Span};

 declare_clippy_lint! {
     /// ### What it does
     /// Checks for literal calls to `Default::default()`.
     ///
     /// ### Why is this bad?
     /// It's easier for the reader if the name of the type is used, rather than the
     /// generic `Default`.
     ///
     /// ### Example
     /// ```no_run
     /// let s: String = Default::default();
     /// ```
     ///
     /// Use instead:
     /// ```no_run
     /// let s = String::default();
     /// ```
     #[clippy::version = "pre 1.29.0"]
     pub DEFAULT_TRAIT_ACCESS,
     pedantic,
     "checks for literal calls to `Default::default()`"
 }

 declare_clippy_lint! {
     /// ### What it does
     /// Checks for immediate reassignment of fields initialized
     /// with Default::default().
     ///
     /// ### Why is this bad?
     ///It's more idiomatic to use the [functional update syntax](https://doc.rust-lang.org/reference/expressions/struct-expr.html#functional-update-syntax).
     ///
     /// ### Known problems
     /// Assignments to patterns that are of tuple type are not linted.
     ///
     /// ### Example
     /// ```no_run
     /// # #[derive(Default)]
     /// # struct A { i: i32 }
     /// let mut a: A = Default::default();
     /// a.i = 42;
     /// ```
     ///
     /// Use instead:
     /// ```no_run
     /// # #[derive(Default)]
     /// # struct A { i: i32 }
     /// let a = A {
     ///     i: 42,
     ///     .. Default::default()
     /// };
     /// ```
     #[clippy::version = "1.49.0"]
     pub FIELD_REASSIGN_WITH_DEFAULT,
     style,
     "binding initialized with Default should have its fields set in the initializer"
 }

 #[derive(Default)]
 pub struct Default {
     // Spans linted by `field_reassign_with_default`.
     reassigned_linted: FxHashSet<Span>,
 }

 impl_lint_pass!(Default => [DEFAULT_TRAIT_ACCESS, FIELD_REASSIGN_WITH_DEFAULT]);

 impl<'tcx> LateLintPass<'tcx> for Default {
     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
         if !expr.span.from_expansion()
             // Avoid cases already linted by `field_reassign_with_default`
             && !self.reassigned_linted.contains(&expr.span)
             && let ExprKind::Call(path, ..) = expr.kind
             && !any_parent_is_automatically_derived(cx.tcx, expr.hir_id)
             && let ExprKind::Path(ref qpath) = path.kind
             && let Some(def_id) = cx.qpath_res(qpath, path.hir_id).opt_def_id()
             && cx.tcx.is_diagnostic_item(sym::default_fn, def_id)
             && !is_update_syntax_base(cx, expr)
             // Detect and ignore <Foo as Default>::default() because these calls do explicitly name the type.
             && let QPath::Resolved(None, _path) = qpath
             && let expr_ty = cx.typeck_results().expr_ty(expr)
             && let ty::Adt(def, ..) = expr_ty.kind()
             && !is_from_proc_macro(cx, expr)
         {
             let replacement = with_forced_trimmed_paths!(format!("{}::default()", cx.tcx.def_path_str(def.did())));
             span_lint_and_sugg(
                 cx,
                 DEFAULT_TRAIT_ACCESS,
                 expr.span,
                 &format!("calling `{replacement}` is more clear than this expression"),
                 "try",
                 replacement,
                 Applicability::Unspecified, // First resolve the TODO above
             );
         }
     }

     #[expect(clippy::too_many_lines)]
     fn check_block(&mut self, cx: &LateContext<'tcx>, block: &Block<'tcx>) {
         // start from the `let mut _ = _::default();` and look at all the following
         // statements, see if they re-assign the fields of the binding
         let stmts_head = match block.stmts {
             // Skip the last statement since there cannot possibly be any following statements that re-assign fields.
             [head @ .., _] if !head.is_empty() => head,
             _ => return,
         };
         for (stmt_idx, stmt) in stmts_head.iter().enumerate() {
             // find all binding statements like `let mut _ = T::default()` where `T::default()` is the
             // `default` method of the `Default` trait, and store statement index in current block being
             // checked and the name of the bound variable
             let (local, variant, binding_name, binding_type, span) = if let StmtKind::Let(local) = stmt.kind
                 // only take `let ...` statements
                 && let Some(expr) = local.init
                 && !any_parent_is_automatically_derived(cx.tcx, expr.hir_id)
                 && !expr.span.from_expansion()
                 // only take bindings to identifiers
                 && let PatKind::Binding(_, binding_id, ident, _) = local.pat.kind
                 // only when assigning `... = Default::default()`
                 && is_expr_default(expr, cx)
                 && let binding_type = cx.typeck_results().node_type(binding_id)
                 && let ty::Adt(adt, args) = *binding_type.kind()
                 && adt.is_struct()
                 && let variant = adt.non_enum_variant()
                 && (adt.did().is_local() || !variant.is_field_list_non_exhaustive())
                 && let module_did = cx.tcx.parent_module(stmt.hir_id)
                 && variant
                     .fields
                     .iter()
                     .all(|field| field.vis.is_accessible_from(module_did, cx.tcx))
                 && let all_fields_are_copy = variant
                     .fields
                     .iter()
                     .all(|field| {
                         is_copy(cx, cx.tcx.type_of(field.did).instantiate(cx.tcx, args))
                     })
                 && (!has_drop(cx, binding_type) || all_fields_are_copy)
             {
                 (local, variant, ident.name, binding_type, expr.span)
             } else {
                 continue;
             };

             let init_ctxt = local.span.ctxt();

             // find all "later statement"'s where the fields of the binding set as
             // Default::default() get reassigned, unless the reassignment refers to the original binding
             let mut first_assign = None;
             let mut assigned_fields = Vec::new();
             let mut cancel_lint = false;
             for consecutive_statement in &block.stmts[stmt_idx + 1..] {
                 // find out if and which field was set by this `consecutive_statement`
                 if let Some((field_ident, assign_rhs)) = field_reassigned_by_stmt(consecutive_statement, binding_name) {
                     // interrupt and cancel lint if assign_rhs references the original binding
                     if contains_name(binding_name, assign_rhs, cx) || init_ctxt != consecutive_statement.span.ctxt() {
                         cancel_lint = true;
                         break;
                     }

                     // if the field was previously assigned, replace the assignment, otherwise insert the assignment
                     if let Some(prev) = assigned_fields
                         .iter_mut()
                         .find(|(field_name, _)| field_name == &field_ident.name)
                     {
                         *prev = (field_ident.name, assign_rhs);
                     } else {
                         assigned_fields.push((field_ident.name, assign_rhs));
                     }

                     // also set first instance of error for help message
                     if first_assign.is_none() {
                         first_assign = Some(consecutive_statement);
                     }
                 }
                 // interrupt if no field was assigned, since we only want to look at consecutive statements
                 else {
                     break;
                 }
             }

             // if there are incorrectly assigned fields, do a span_lint_and_note to suggest
             // construction using `Ty { fields, ..Default::default() }`
             if !assigned_fields.is_empty() && !cancel_lint {
                 // if all fields of the struct are not assigned, add `.. Default::default()` to the suggestion.
                 let ext_with_default = !variant
                     .fields
                     .iter()
                     .all(|field| assigned_fields.iter().any(|(a, _)| a == &field.name));

                 let mut app = Applicability::Unspecified;
                 let field_list = assigned_fields
                     .into_iter()
                     .map(|(field, rhs)| {
                         // extract and store the assigned value for help message
                         let value_snippet = snippet_with_context(cx, rhs.span, init_ctxt, "..", &mut app).0;
                         format!("{field}: {value_snippet}")
                     })
                     .collect::<Vec<String>>()
                     .join(", ");

                 // give correct suggestion if generics are involved (see #6944)
                 let binding_type = if let ty::Adt(adt_def, args) = binding_type.kind()
                     && !args.is_empty()
                 {
                     let adt_def_ty_name = cx.tcx.item_name(adt_def.did());
                     let generic_args = args.iter().collect::<Vec<_>>();
                     let tys_str = generic_args
                         .iter()
                         .map(ToString::to_string)
                         .collect::<Vec<_>>()
                         .join(", ");
                     format!("{adt_def_ty_name}::<{}>", &tys_str)
                 } else {
                     binding_type.to_string()
                 };

                 let sugg = if ext_with_default {
                     if field_list.is_empty() {
                         format!("{binding_type}::default()")
                     } else {
                         format!("{binding_type} {{ {field_list}, ..Default::default() }}")
                     }
                 } else {
                     format!("{binding_type} {{ {field_list} }}")
                 };

                 // span lint once per statement that binds default
                 span_lint_and_note(
                     cx,
                     FIELD_REASSIGN_WITH_DEFAULT,
                     first_assign.unwrap().span,
                     "field assignment outside of initializer for an instance created with Default::default()",
                     Some(local.span),
                     &format!("consider initializing the variable with `{sugg}` and removing relevant reassignments"),
                 );
                 self.reassigned_linted.insert(span);
             }
         }
     }
 }

 /// Checks if the given expression is the `default` method belonging to the `Default` trait.
 fn is_expr_default<'tcx>(expr: &'tcx Expr<'tcx>, cx: &LateContext<'tcx>) -> bool {
     if let ExprKind::Call(fn_expr, _) = &expr.kind
         && let ExprKind::Path(qpath) = &fn_expr.kind
         && let Res::Def(_, def_id) = cx.qpath_res(qpath, fn_expr.hir_id)
     {
         // right hand side of assignment is `Default::default`
         cx.tcx.is_diagnostic_item(sym::default_fn, def_id)
     } else {
         false
     }
 }

 /// Returns the reassigned field and the assigning expression (right-hand side of assign).
 fn field_reassigned_by_stmt<'tcx>(this: &Stmt<'tcx>, binding_name: Symbol) -> Option<(Ident, &'tcx Expr<'tcx>)> {
     if let StmtKind::Semi(later_expr) = this.kind
         // only take assignments
         && let ExprKind::Assign(assign_lhs, assign_rhs, _) = later_expr.kind
         // only take assignments to fields where the left-hand side field is a field of
         // the same binding as the previous statement
         && let ExprKind::Field(binding, field_ident) = assign_lhs.kind
         && let ExprKind::Path(QPath::Resolved(_, path)) = binding.kind
         && let Some(second_binding_name) = path.segments.last()
         && second_binding_name.ident.name == binding_name
     {
         Some((field_ident, assign_rhs))
     } else {
         None
     }
 }

 /// Returns whether `expr` is the update syntax base: `Foo { a: 1, .. base }`
 fn is_update_syntax_base<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> bool {
     if let Some(parent) = get_parent_expr(cx, expr)
         && let ExprKind::Struct(_, _, Some(base)) = parent.kind
     {
         base.hir_id == expr.hir_id
     } else {
         false
     }
 }
	use clippy_utils::diagnostics::{span_lint_and_note, span_lint_and_sugg};
	use clippy_utils::source::snippet_with_context;
	use clippy_utils::ty::{has_drop, is_copy};
	use clippy_utils::{any_parent_is_automatically_derived, contains_name, get_parent_expr, is_from_proc_macro};
	use rustc_data_structures::fx::FxHashSet;
	use rustc_errors::Applicability;
	use rustc_hir::def::Res;
	use rustc_hir::{Block, Expr, ExprKind, PatKind, QPath, Stmt, StmtKind};
	use rustc_lint::{LateContext, LateLintPass};
	use rustc_middle::ty;
	use rustc_middle::ty::print::with_forced_trimmed_paths;
	use rustc_session::impl_lint_pass;
	use rustc_span::symbol::{Ident, Symbol};
	use rustc_span::{sym, Span};

	declare_clippy_lint! {
	/// ### What it does
	/// Checks for literal calls to `Default::default()`.
	///
	/// ### Why is this bad?
	/// It's easier for the reader if the name of the type is used, rather than the
	/// generic `Default`.
	///
	/// ### Example
	/// ```no_run
	/// let s: String = Default::default();
	/// ```
	///
	/// Use instead:
	/// ```no_run
	/// let s = String::default();
	/// ```
	#[clippy::version = "pre 1.29.0"]
	pub DEFAULT_TRAIT_ACCESS,
	pedantic,
	"checks for literal calls to `Default::default()`"
	}

	declare_clippy_lint! {
	/// ### What it does
	/// Checks for immediate reassignment of fields initialized
	/// with Default::default().
	///
	/// ### Why is this bad?
	///It's more idiomatic to use the [functional update syntax](https://doc.rust-lang.org/reference/expressions/struct-expr.html#functional-update-syntax).
	///
	/// ### Known problems
	/// Assignments to patterns that are of tuple type are not linted.
	///
	/// ### Example
	/// ```no_run
	/// # #[derive(Default)]
	/// # struct A { i: i32 }
	/// let mut a: A = Default::default();
	/// a.i = 42;
	/// ```
	///
	/// Use instead:
	/// ```no_run
	/// # #[derive(Default)]
	/// # struct A { i: i32 }
	/// let a = A {
	/// i: 42,
	/// .. Default::default()
	/// };
	/// ```
	#[clippy::version = "1.49.0"]
	pub FIELD_REASSIGN_WITH_DEFAULT,
	style,
	"binding initialized with Default should have its fields set in the initializer"
	}

	#[derive(Default)]
	pub struct Default {
	// Spans linted by `field_reassign_with_default`.
	reassigned_linted: FxHashSet<Span>,
	}

	impl_lint_pass!(Default => [DEFAULT_TRAIT_ACCESS, FIELD_REASSIGN_WITH_DEFAULT]);

	impl<'tcx> LateLintPass<'tcx> for Default {
	fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
	if !expr.span.from_expansion()
	// Avoid cases already linted by `field_reassign_with_default`
	&& !self.reassigned_linted.contains(&expr.span)
	&& let ExprKind::Call(path, ..) = expr.kind
	&& !any_parent_is_automatically_derived(cx.tcx, expr.hir_id)
	&& let ExprKind::Path(ref qpath) = path.kind
	&& let Some(def_id) = cx.qpath_res(qpath, path.hir_id).opt_def_id()
	&& cx.tcx.is_diagnostic_item(sym::default_fn, def_id)
	&& !is_update_syntax_base(cx, expr)
	// Detect and ignore <Foo as Default>::default() because these calls do explicitly name the type.
	&& let QPath::Resolved(None, _path) = qpath
	&& let expr_ty = cx.typeck_results().expr_ty(expr)
	&& let ty::Adt(def, ..) = expr_ty.kind()
	&& !is_from_proc_macro(cx, expr)
	{
	let replacement = with_forced_trimmed_paths!(format!("{}::default()", cx.tcx.def_path_str(def.did())));
	span_lint_and_sugg(
	cx,
	DEFAULT_TRAIT_ACCESS,
	expr.span,
	&format!("calling `{replacement}` is more clear than this expression"),
	"try",
	replacement,
	Applicability::Unspecified, // First resolve the TODO above
	);
	}
	}

	#[expect(clippy::too_many_lines)]
	fn check_block(&mut self, cx: &LateContext<'tcx>, block: &Block<'tcx>) {
	// start from the `let mut _ = _::default();` and look at all the following
	// statements, see if they re-assign the fields of the binding
	let stmts_head = match block.stmts {
	// Skip the last statement since there cannot possibly be any following statements that re-assign fields.
	[head @ .., _] if !head.is_empty() => head,
	_ => return,
	};
	for (stmt_idx, stmt) in stmts_head.iter().enumerate() {
	// find all binding statements like `let mut _ = T::default()` where `T::default()` is the
	// `default` method of the `Default` trait, and store statement index in current block being
	// checked and the name of the bound variable
	let (local, variant, binding_name, binding_type, span) = if let StmtKind::Let(local) = stmt.kind
	// only take `let ...` statements
	&& let Some(expr) = local.init
	&& !any_parent_is_automatically_derived(cx.tcx, expr.hir_id)
	&& !expr.span.from_expansion()
	// only take bindings to identifiers
	&& let PatKind::Binding(_, binding_id, ident, _) = local.pat.kind
	// only when assigning `... = Default::default()`
	&& is_expr_default(expr, cx)
	&& let binding_type = cx.typeck_results().node_type(binding_id)
	&& let ty::Adt(adt, args) = *binding_type.kind()
	&& adt.is_struct()
	&& let variant = adt.non_enum_variant()
	&& (adt.did().is_local() \|\| !variant.is_field_list_non_exhaustive())
	&& let module_did = cx.tcx.parent_module(stmt.hir_id)
	&& variant
	.fields
	.iter()
	.all(\|field\| field.vis.is_accessible_from(module_did, cx.tcx))
	&& let all_fields_are_copy = variant
	.fields
	.iter()
	.all(\|field\| {
	is_copy(cx, cx.tcx.type_of(field.did).instantiate(cx.tcx, args))
	})
	&& (!has_drop(cx, binding_type) \|\| all_fields_are_copy)
	{
	(local, variant, ident.name, binding_type, expr.span)
	} else {
	continue;
	};

	let init_ctxt = local.span.ctxt();

	// find all "later statement"'s where the fields of the binding set as
	// Default::default() get reassigned, unless the reassignment refers to the original binding
	let mut first_assign = None;
	let mut assigned_fields = Vec::new();
	let mut cancel_lint = false;
	for consecutive_statement in &block.stmts[stmt_idx + 1..] {
	// find out if and which field was set by this `consecutive_statement`
	if let Some((field_ident, assign_rhs)) = field_reassigned_by_stmt(consecutive_statement, binding_name) {
	// interrupt and cancel lint if assign_rhs references the original binding
	if contains_name(binding_name, assign_rhs, cx) \|\| init_ctxt != consecutive_statement.span.ctxt() {
	cancel_lint = true;
	break;
	}

	// if the field was previously assigned, replace the assignment, otherwise insert the assignment
	if let Some(prev) = assigned_fields
	.iter_mut()
	.find(\|(field_name, _)\| field_name == &field_ident.name)
	{
	*prev = (field_ident.name, assign_rhs);
	} else {
	assigned_fields.push((field_ident.name, assign_rhs));
	}

	// also set first instance of error for help message
	if first_assign.is_none() {
	first_assign = Some(consecutive_statement);
	}
	}
	// interrupt if no field was assigned, since we only want to look at consecutive statements
	else {
	break;
	}
	}

	// if there are incorrectly assigned fields, do a span_lint_and_note to suggest
	// construction using `Ty { fields, ..Default::default() }`
	if !assigned_fields.is_empty() && !cancel_lint {
	// if all fields of the struct are not assigned, add `.. Default::default()` to the suggestion.
	let ext_with_default = !variant
	.fields
	.iter()
	.all(\|field\| assigned_fields.iter().any(\|(a, _)\| a == &field.name));

	let mut app = Applicability::Unspecified;
	let field_list = assigned_fields
	.into_iter()
	.map(\|(field, rhs)\| {
	// extract and store the assigned value for help message
	let value_snippet = snippet_with_context(cx, rhs.span, init_ctxt, "..", &mut app).0;
	format!("{field}: {value_snippet}")
	})
	.collect::<Vec<String>>()
	.join(", ");

	// give correct suggestion if generics are involved (see #6944)
	let binding_type = if let ty::Adt(adt_def, args) = binding_type.kind()
	&& !args.is_empty()
	{
	let adt_def_ty_name = cx.tcx.item_name(adt_def.did());
	let generic_args = args.iter().collect::<Vec<_>>();
	let tys_str = generic_args
	.iter()
	.map(ToString::to_string)
	.collect::<Vec<_>>()
	.join(", ");
	format!("{adt_def_ty_name}::<{}>", &tys_str)
	} else {
	binding_type.to_string()
	};

	let sugg = if ext_with_default {
	if field_list.is_empty() {
	format!("{binding_type}::default()")
	} else {
	format!("{binding_type} {{ {field_list}, ..Default::default() }}")
	}
	} else {
	format!("{binding_type} {{ {field_list} }}")
	};

	// span lint once per statement that binds default
	span_lint_and_note(
	cx,
	FIELD_REASSIGN_WITH_DEFAULT,
	first_assign.unwrap().span,
	"field assignment outside of initializer for an instance created with Default::default()",
	Some(local.span),
	&format!("consider initializing the variable with `{sugg}` and removing relevant reassignments"),
	);
	self.reassigned_linted.insert(span);
	}
	}
	}
	}

	/// Checks if the given expression is the `default` method belonging to the `Default` trait.
	fn is_expr_default<'tcx>(expr: &'tcx Expr<'tcx>, cx: &LateContext<'tcx>) -> bool {
	if let ExprKind::Call(fn_expr, _) = &expr.kind
	&& let ExprKind::Path(qpath) = &fn_expr.kind
	&& let Res::Def(_, def_id) = cx.qpath_res(qpath, fn_expr.hir_id)
	{
	// right hand side of assignment is `Default::default`
	cx.tcx.is_diagnostic_item(sym::default_fn, def_id)
	} else {
	false
	}
	}

	/// Returns the reassigned field and the assigning expression (right-hand side of assign).
	fn field_reassigned_by_stmt<'tcx>(this: &Stmt<'tcx>, binding_name: Symbol) -> Option<(Ident, &'tcx Expr<'tcx>)> {
	if let StmtKind::Semi(later_expr) = this.kind
	// only take assignments
	&& let ExprKind::Assign(assign_lhs, assign_rhs, _) = later_expr.kind
	// only take assignments to fields where the left-hand side field is a field of
	// the same binding as the previous statement
	&& let ExprKind::Field(binding, field_ident) = assign_lhs.kind
	&& let ExprKind::Path(QPath::Resolved(_, path)) = binding.kind
	&& let Some(second_binding_name) = path.segments.last()
	&& second_binding_name.ident.name == binding_name
	{
	Some((field_ident, assign_rhs))
	} else {
	None
	}
	}

	/// Returns whether `expr` is the update syntax base: `Foo { a: 1, .. base }`
	fn is_update_syntax_base<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> bool {
	if let Some(parent) = get_parent_expr(cx, expr)
	&& let ExprKind::Struct(_, _, Some(base)) = parent.kind
	{
	base.hir_id == expr.hir_id
	} else {
	false
	}
	}