143 lines
4.5 KiB
Rust
143 lines
4.5 KiB
Rust
use if_chain::if_chain;
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use rustc_ast::ast;
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use rustc_ast::visit::FnKind;
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use rustc_errors::Applicability;
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use rustc_lint::{EarlyContext, EarlyLintPass, LintContext};
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use rustc_session::{declare_lint_pass, declare_tool_lint};
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use rustc_span::source_map::Span;
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use rustc_span::BytePos;
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use crate::utils::{position_before_rarrow, span_lint_and_sugg};
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declare_clippy_lint! {
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/// **What it does:** Checks for unit (`()`) expressions that can be removed.
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///
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/// **Why is this bad?** Such expressions add no value, but can make the code
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/// less readable. Depending on formatting they can make a `break` or `return`
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/// statement look like a function call.
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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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/// fn return_unit() -> () {
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/// ()
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/// }
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/// ```
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pub UNUSED_UNIT,
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style,
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"needless unit expression"
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}
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declare_lint_pass!(UnusedUnit => [UNUSED_UNIT]);
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impl EarlyLintPass for UnusedUnit {
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fn check_fn(&mut self, cx: &EarlyContext<'_>, kind: FnKind<'_>, span: Span, _: ast::NodeId) {
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if_chain! {
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if let ast::FnRetTy::Ty(ref ty) = kind.decl().output;
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if let ast::TyKind::Tup(ref vals) = ty.kind;
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if vals.is_empty() && !ty.span.from_expansion() && get_def(span) == get_def(ty.span);
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then {
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lint_unneeded_unit_return(cx, ty, span);
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}
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}
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}
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fn check_block(&mut self, cx: &EarlyContext<'_>, block: &ast::Block) {
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if_chain! {
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if let Some(ref stmt) = block.stmts.last();
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if let ast::StmtKind::Expr(ref expr) = stmt.kind;
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if is_unit_expr(expr) && !stmt.span.from_expansion();
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then {
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let sp = expr.span;
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span_lint_and_sugg(
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cx,
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UNUSED_UNIT,
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sp,
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"unneeded unit expression",
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"remove the final `()`",
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String::new(),
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Applicability::MachineApplicable,
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);
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}
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}
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}
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fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &ast::Expr) {
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match e.kind {
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ast::ExprKind::Ret(Some(ref expr)) | ast::ExprKind::Break(_, Some(ref expr)) => {
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if is_unit_expr(expr) && !expr.span.from_expansion() {
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span_lint_and_sugg(
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cx,
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UNUSED_UNIT,
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expr.span,
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"unneeded `()`",
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"remove the `()`",
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String::new(),
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Applicability::MachineApplicable,
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);
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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_poly_trait_ref(&mut self, cx: &EarlyContext<'_>, poly: &ast::PolyTraitRef, _: &ast::TraitBoundModifier) {
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let segments = &poly.trait_ref.path.segments;
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if_chain! {
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if segments.len() == 1;
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if ["Fn", "FnMut", "FnOnce"].contains(&&*segments[0].ident.name.as_str());
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if let Some(args) = &segments[0].args;
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if let ast::GenericArgs::Parenthesized(generic_args) = &**args;
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if let ast::FnRetTy::Ty(ty) = &generic_args.output;
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if ty.kind.is_unit();
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then {
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lint_unneeded_unit_return(cx, ty, generic_args.span);
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}
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}
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}
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}
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// get the def site
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#[must_use]
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fn get_def(span: Span) -> Option<Span> {
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if span.from_expansion() {
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Some(span.ctxt().outer_expn_data().def_site)
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} else {
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None
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}
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}
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// is this expr a `()` unit?
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fn is_unit_expr(expr: &ast::Expr) -> bool {
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if let ast::ExprKind::Tup(ref vals) = expr.kind {
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vals.is_empty()
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} else {
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false
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}
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}
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fn lint_unneeded_unit_return(cx: &EarlyContext<'_>, ty: &ast::Ty, span: Span) {
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let (ret_span, appl) = if let Ok(fn_source) = cx.sess().source_map().span_to_snippet(span.with_hi(ty.span.hi())) {
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position_before_rarrow(fn_source).map_or((ty.span, Applicability::MaybeIncorrect), |rpos| {
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(
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#[allow(clippy::cast_possible_truncation)]
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ty.span.with_lo(BytePos(span.lo().0 + rpos as u32)),
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Applicability::MachineApplicable,
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)
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})
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} else {
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(ty.span, Applicability::MaybeIncorrect)
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};
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span_lint_and_sugg(
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cx,
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UNUSED_UNIT,
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ret_span,
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"unneeded unit return type",
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"remove the `-> ()`",
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String::new(),
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appl,
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);
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}
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