diff options
Diffstat (limited to 'src/tools/clippy/clippy_lints/src/new_without_default.rs')
| -rw-r--r-- | src/tools/clippy/clippy_lints/src/new_without_default.rs | 169 |
1 files changed, 169 insertions, 0 deletions
diff --git a/src/tools/clippy/clippy_lints/src/new_without_default.rs b/src/tools/clippy/clippy_lints/src/new_without_default.rs new file mode 100644 index 000000000..5c45ee6d9 --- /dev/null +++ b/src/tools/clippy/clippy_lints/src/new_without_default.rs @@ -0,0 +1,169 @@ +use clippy_utils::diagnostics::span_lint_hir_and_then; +use clippy_utils::return_ty; +use clippy_utils::source::snippet; +use clippy_utils::sugg::DiagnosticExt; +use if_chain::if_chain; +use rustc_errors::Applicability; +use rustc_hir as hir; +use rustc_hir::HirIdSet; +use rustc_lint::{LateContext, LateLintPass, LintContext}; +use rustc_middle::lint::in_external_macro; +use rustc_session::{declare_tool_lint, impl_lint_pass}; +use rustc_span::sym; + +declare_clippy_lint! { + /// ### What it does + /// Checks for public types with a `pub fn new() -> Self` method and no + /// implementation of + /// [`Default`](https://doc.rust-lang.org/std/default/trait.Default.html). + /// + /// ### Why is this bad? + /// The user might expect to be able to use + /// [`Default`](https://doc.rust-lang.org/std/default/trait.Default.html) as the + /// type can be constructed without arguments. + /// + /// ### Example + /// ```ignore + /// pub struct Foo(Bar); + /// + /// impl Foo { + /// pub fn new() -> Self { + /// Foo(Bar::new()) + /// } + /// } + /// ``` + /// + /// To fix the lint, add a `Default` implementation that delegates to `new`: + /// + /// ```ignore + /// pub struct Foo(Bar); + /// + /// impl Default for Foo { + /// fn default() -> Self { + /// Foo::new() + /// } + /// } + /// ``` + #[clippy::version = "pre 1.29.0"] + pub NEW_WITHOUT_DEFAULT, + style, + "`pub fn new() -> Self` method without `Default` implementation" +} + +#[derive(Clone, Default)] +pub struct NewWithoutDefault { + impling_types: Option<HirIdSet>, +} + +impl_lint_pass!(NewWithoutDefault => [NEW_WITHOUT_DEFAULT]); + +impl<'tcx> LateLintPass<'tcx> for NewWithoutDefault { + fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'_>) { + if let hir::ItemKind::Impl(hir::Impl { + of_trait: None, + generics, + self_ty: impl_self_ty, + items, + .. + }) = item.kind + { + for assoc_item in *items { + if assoc_item.kind == (hir::AssocItemKind::Fn { has_self: false }) { + let impl_item = cx.tcx.hir().impl_item(assoc_item.id); + if in_external_macro(cx.sess(), impl_item.span) { + return; + } + if let hir::ImplItemKind::Fn(ref sig, _) = impl_item.kind { + let name = impl_item.ident.name; + let id = impl_item.hir_id(); + if sig.header.constness == hir::Constness::Const { + // can't be implemented by default + return; + } + if sig.header.unsafety == hir::Unsafety::Unsafe { + // can't be implemented for unsafe new + return; + } + if cx.tcx.is_doc_hidden(impl_item.def_id) { + // shouldn't be implemented when it is hidden in docs + return; + } + if !impl_item.generics.params.is_empty() { + // when the result of `new()` depends on a parameter we should not require + // an impl of `Default` + return; + } + if_chain! { + if sig.decl.inputs.is_empty(); + if name == sym::new; + if cx.access_levels.is_reachable(impl_item.def_id); + let self_def_id = cx.tcx.hir().get_parent_item(id); + let self_ty = cx.tcx.type_of(self_def_id); + if self_ty == return_ty(cx, id); + if let Some(default_trait_id) = cx.tcx.get_diagnostic_item(sym::Default); + then { + if self.impling_types.is_none() { + let mut impls = HirIdSet::default(); + cx.tcx.for_each_impl(default_trait_id, |d| { + if let Some(ty_def) = cx.tcx.type_of(d).ty_adt_def() { + if let Some(local_def_id) = ty_def.did().as_local() { + impls.insert(cx.tcx.hir().local_def_id_to_hir_id(local_def_id)); + } + } + }); + self.impling_types = Some(impls); + } + + // Check if a Default implementation exists for the Self type, regardless of + // generics + if_chain! { + if let Some(ref impling_types) = self.impling_types; + if let Some(self_def) = cx.tcx.type_of(self_def_id).ty_adt_def(); + if let Some(self_local_did) = self_def.did().as_local(); + let self_id = cx.tcx.hir().local_def_id_to_hir_id(self_local_did); + if impling_types.contains(&self_id); + then { + return; + } + } + + let generics_sugg = snippet(cx, generics.span, ""); + let self_ty_fmt = self_ty.to_string(); + let self_type_snip = snippet(cx, impl_self_ty.span, &self_ty_fmt); + span_lint_hir_and_then( + cx, + NEW_WITHOUT_DEFAULT, + id, + impl_item.span, + &format!( + "you should consider adding a `Default` implementation for `{}`", + self_type_snip + ), + |diag| { + diag.suggest_prepend_item( + cx, + item.span, + "try adding this", + &create_new_without_default_suggest_msg(&self_type_snip, &generics_sugg), + Applicability::MaybeIncorrect, + ); + }, + ); + } + } + } + } + } + } + } +} + +fn create_new_without_default_suggest_msg(self_type_snip: &str, generics_sugg: &str) -> String { + #[rustfmt::skip] + format!( +"impl{} Default for {} {{ + fn default() -> Self {{ + Self::new() + }} +}}", generics_sugg, self_type_snip) +} |