mirror of
https://github.com/rust-lang/rust-clippy
synced 2024-12-30 15:03:36 +00:00
305 lines
13 KiB
Rust
305 lines
13 KiB
Rust
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use crate::utils::{any_parent_is_automatically_derived, contains_name, match_def_path, paths, qpath_res, snippet};
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use crate::utils::{span_lint_and_note, span_lint_and_sugg};
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use if_chain::if_chain;
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use rustc_data_structures::fx::FxHashSet;
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use rustc_errors::Applicability;
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use rustc_hir::def::Res;
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use rustc_hir::{Block, Expr, ExprKind, PatKind, QPath, Stmt, StmtKind};
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use rustc_lint::{LateContext, LateLintPass};
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use rustc_middle::ty::{self, Adt, Ty};
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use rustc_session::{declare_tool_lint, impl_lint_pass};
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use rustc_span::symbol::{Ident, Symbol};
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use rustc_span::Span;
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declare_clippy_lint! {
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/// **What it does:** Checks for literal calls to `Default::default()`.
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///
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/// **Why is this bad?** It's more clear to the reader to use the name of the type whose default is
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/// being gotten than the generic `Default`.
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///
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/// **Known problems:** None.
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///
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/// **Example:**
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/// ```rust
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/// // Bad
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/// let s: String = Default::default();
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///
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/// // Good
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/// let s = String::default();
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/// ```
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pub DEFAULT_TRAIT_ACCESS,
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pedantic,
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"checks for literal calls to `Default::default()`"
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}
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declare_clippy_lint! {
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/// **What it does:** Checks for immediate reassignment of fields initialized
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/// with Default::default().
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///
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/// **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).
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///
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/// **Known problems:** Assignments to patterns that are of tuple type are not linted.
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///
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/// **Example:**
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/// Bad:
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/// ```
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/// # #[derive(Default)]
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/// # struct A { i: i32 }
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/// let mut a: A = Default::default();
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/// a.i = 42;
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/// ```
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/// Use instead:
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/// ```
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/// # #[derive(Default)]
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/// # struct A { i: i32 }
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/// let a = A {
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/// i: 42,
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/// .. Default::default()
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/// };
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/// ```
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pub FIELD_REASSIGN_WITH_DEFAULT,
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style,
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"binding initialized with Default should have its fields set in the initializer"
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}
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#[derive(Default)]
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pub struct Default {
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// Spans linted by `field_reassign_with_default`.
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reassigned_linted: FxHashSet<Span>,
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}
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impl_lint_pass!(Default => [DEFAULT_TRAIT_ACCESS, FIELD_REASSIGN_WITH_DEFAULT]);
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impl LateLintPass<'_> for Default {
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fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
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if_chain! {
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// Avoid cases already linted by `field_reassign_with_default`
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if !self.reassigned_linted.contains(&expr.span);
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if let ExprKind::Call(ref path, ..) = expr.kind;
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if !any_parent_is_automatically_derived(cx.tcx, expr.hir_id);
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if let ExprKind::Path(ref qpath) = path.kind;
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if let Some(def_id) = cx.qpath_res(qpath, path.hir_id).opt_def_id();
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if match_def_path(cx, def_id, &paths::DEFAULT_TRAIT_METHOD);
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// Detect and ignore <Foo as Default>::default() because these calls do explicitly name the type.
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if let QPath::Resolved(None, _path) = qpath;
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then {
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let expr_ty = cx.typeck_results().expr_ty(expr);
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if let ty::Adt(def, ..) = expr_ty.kind() {
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// TODO: Work out a way to put "whatever the imported way of referencing
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// this type in this file" rather than a fully-qualified type.
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let replacement = format!("{}::default()", cx.tcx.def_path_str(def.did));
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span_lint_and_sugg(
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cx,
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DEFAULT_TRAIT_ACCESS,
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expr.span,
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&format!("calling `{}` is more clear than this expression", replacement),
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"try",
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replacement,
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Applicability::Unspecified, // First resolve the TODO above
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);
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}
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}
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}
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}
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fn check_block<'tcx>(&mut self, cx: &LateContext<'tcx>, block: &Block<'tcx>) {
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// find all binding statements like `let mut _ = T::default()` where `T::default()` is the
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// `default` method of the `Default` trait, and store statement index in current block being
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// checked and the name of the bound variable
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let binding_statements_using_default = enumerate_bindings_using_default(cx, block);
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// start from the `let mut _ = _::default();` and look at all the following
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// statements, see if they re-assign the fields of the binding
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for (stmt_idx, binding_name, binding_type, span) in binding_statements_using_default {
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// the last statement of a block cannot trigger the lint
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if stmt_idx == block.stmts.len() - 1 {
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break;
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}
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// find all "later statement"'s where the fields of the binding set as
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// Default::default() get reassigned, unless the reassignment refers to the original binding
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let mut first_assign = None;
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let mut assigned_fields = Vec::new();
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let mut cancel_lint = false;
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for consecutive_statement in &block.stmts[stmt_idx + 1..] {
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// interrupt if the statement is a let binding (`Local`) that shadows the original
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// binding
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if stmt_shadows_binding(consecutive_statement, binding_name) {
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break;
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}
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// find out if and which field was set by this `consecutive_statement`
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else if let Some((field_ident, assign_rhs)) =
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field_reassigned_by_stmt(consecutive_statement, binding_name)
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{
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// interrupt and cancel lint if assign_rhs references the original binding
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if contains_name(binding_name, assign_rhs) {
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cancel_lint = true;
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break;
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}
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// if the field was previously assigned, replace the assignment, otherwise insert the assignment
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if let Some(prev) = assigned_fields
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.iter_mut()
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.find(|(field_name, _)| field_name == &field_ident.name)
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{
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*prev = (field_ident.name, assign_rhs);
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} else {
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assigned_fields.push((field_ident.name, assign_rhs));
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}
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// also set first instance of error for help message
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if first_assign.is_none() {
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first_assign = Some(consecutive_statement);
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}
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}
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// interrupt also if no field was assigned, since we only want to look at consecutive statements
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else {
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break;
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}
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}
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// if there are incorrectly assigned fields, do a span_lint_and_note to suggest
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// construction using `Ty { fields, ..Default::default() }`
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if !assigned_fields.is_empty() && !cancel_lint {
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// take the original assignment as span
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let stmt = &block.stmts[stmt_idx];
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if let StmtKind::Local(preceding_local) = &stmt.kind {
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// filter out fields like `= Default::default()`, because the FRU already covers them
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let assigned_fields = assigned_fields
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.into_iter()
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.filter(|(_, rhs)| !is_expr_default(rhs, cx))
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.collect::<Vec<(Symbol, &Expr<'_>)>>();
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// if all fields of the struct are not assigned, add `.. Default::default()` to the suggestion.
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let ext_with_default = !fields_of_type(binding_type)
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.iter()
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.all(|field| assigned_fields.iter().any(|(a, _)| a == &field.name));
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let field_list = assigned_fields
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.into_iter()
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.map(|(field, rhs)| {
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// extract and store the assigned value for help message
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let value_snippet = snippet(cx, rhs.span, "..");
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format!("{}: {}", field, value_snippet)
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})
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.collect::<Vec<String>>()
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.join(", ");
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let sugg = if ext_with_default {
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if field_list.is_empty() {
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format!("{}::default()", binding_type)
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} else {
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format!("{} {{ {}, ..Default::default() }}", binding_type, field_list)
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}
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} else {
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format!("{} {{ {} }}", binding_type, field_list)
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};
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// span lint once per statement that binds default
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span_lint_and_note(
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cx,
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FIELD_REASSIGN_WITH_DEFAULT,
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first_assign.unwrap().span,
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"field assignment outside of initializer for an instance created with Default::default()",
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Some(preceding_local.span),
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&format!(
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"consider initializing the variable with `{}` and removing relevant reassignments",
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sugg
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),
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);
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self.reassigned_linted.insert(span);
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}
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}
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}
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}
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}
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/// Checks if the given expression is the `default` method belonging to the `Default` trait.
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fn is_expr_default<'tcx>(expr: &'tcx Expr<'tcx>, cx: &LateContext<'tcx>) -> bool {
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if_chain! {
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if let ExprKind::Call(ref fn_expr, _) = &expr.kind;
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if let ExprKind::Path(qpath) = &fn_expr.kind;
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if let Res::Def(_, def_id) = qpath_res(cx, qpath, fn_expr.hir_id);
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then {
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// right hand side of assignment is `Default::default`
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match_def_path(cx, def_id, &paths::DEFAULT_TRAIT_METHOD)
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} else {
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false
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}
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}
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}
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/// Returns the block indices, identifiers and types of bindings set as `Default::default()`, except
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/// for when the pattern type is a tuple.
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fn enumerate_bindings_using_default<'tcx>(
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cx: &LateContext<'tcx>,
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block: &Block<'tcx>,
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) -> Vec<(usize, Symbol, Ty<'tcx>, Span)> {
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block
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.stmts
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.iter()
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.enumerate()
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.filter_map(|(idx, stmt)| {
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if_chain! {
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// only take `let ...` statements
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if let StmtKind::Local(ref local) = stmt.kind;
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// only take bindings to identifiers
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if let PatKind::Binding(_, _, ident, _) = local.pat.kind;
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// that are not tuples
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let ty = cx.typeck_results().pat_ty(local.pat);
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if !matches!(ty.kind(), ty::Tuple(_));
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// only when assigning `... = Default::default()`
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if let Some(ref expr) = local.init;
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if is_expr_default(expr, cx);
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then {
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Some((idx, ident.name, ty, expr.span))
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} else {
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None
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}
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}
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})
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.collect()
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}
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fn stmt_shadows_binding(this: &Stmt<'_>, shadowed: Symbol) -> bool {
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if let StmtKind::Local(local) = &this.kind {
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if let PatKind::Binding(_, _, ident, _) = local.pat.kind {
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return ident.name == shadowed;
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}
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}
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false
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}
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/// Returns the reassigned field and the assigning expression (right-hand side of assign).
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fn field_reassigned_by_stmt<'tcx>(this: &Stmt<'tcx>, binding_name: Symbol) -> Option<(Ident, &'tcx Expr<'tcx>)> {
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if_chain! {
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// only take assignments
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if let StmtKind::Semi(ref later_expr) = this.kind;
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if let ExprKind::Assign(ref assign_lhs, ref assign_rhs, _) = later_expr.kind;
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// only take assignments to fields where the left-hand side field is a field of
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// the same binding as the previous statement
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if let ExprKind::Field(ref binding, field_ident) = assign_lhs.kind;
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if let ExprKind::Path(ref qpath) = binding.kind;
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if let QPath::Resolved(_, path) = qpath;
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if let Some(second_binding_name) = path.segments.last();
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if second_binding_name.ident.name == binding_name;
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then {
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Some((field_ident, assign_rhs))
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} else {
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None
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}
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}
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}
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/// Returns the vec of fields for a struct and an empty vec for non-struct ADTs.
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fn fields_of_type(ty: Ty<'_>) -> Vec<Ident> {
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if let Adt(adt, _) = ty.kind() {
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if adt.is_struct() {
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let variant = &adt.non_enum_variant();
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return variant.fields.iter().map(|f| f.ident).collect();
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}
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}
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vec![]
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}
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