diff options
Diffstat (limited to 'compiler/rustc_lint/src/map_unit_fn.rs')
-rw-r--r-- | compiler/rustc_lint/src/map_unit_fn.rs | 120 |
1 files changed, 120 insertions, 0 deletions
diff --git a/compiler/rustc_lint/src/map_unit_fn.rs b/compiler/rustc_lint/src/map_unit_fn.rs new file mode 100644 index 000000000..62e8b4fe9 --- /dev/null +++ b/compiler/rustc_lint/src/map_unit_fn.rs @@ -0,0 +1,120 @@ +use crate::lints::MappingToUnit; +use crate::{LateContext, LateLintPass, LintContext}; + +use rustc_hir::{Expr, ExprKind, HirId, Stmt, StmtKind}; +use rustc_middle::{ + query::Key, + ty::{self, Ty}, +}; + +declare_lint! { + /// The `map_unit_fn` lint checks for `Iterator::map` receive + /// a callable that returns `()`. + /// + /// ### Example + /// + /// ```rust + /// fn foo(items: &mut Vec<u8>) { + /// items.sort(); + /// } + /// + /// fn main() { + /// let mut x: Vec<Vec<u8>> = vec![ + /// vec![0, 2, 1], + /// vec![5, 4, 3], + /// ]; + /// x.iter_mut().map(foo); + /// } + /// ``` + /// + /// {{produces}} + /// + /// ### Explanation + /// + /// Mapping to `()` is almost always a mistake. + pub MAP_UNIT_FN, + Warn, + "`Iterator::map` call that discard the iterator's values" +} + +declare_lint_pass!(MapUnitFn => [MAP_UNIT_FN]); + +impl<'tcx> LateLintPass<'tcx> for MapUnitFn { + fn check_stmt(&mut self, cx: &LateContext<'tcx>, stmt: &Stmt<'_>) { + if stmt.span.from_expansion() { + return; + } + + if let StmtKind::Semi(expr) = stmt.kind { + if let ExprKind::MethodCall(path, receiver, args, span) = expr.kind { + if path.ident.name.as_str() == "map" { + if receiver.span.from_expansion() + || args.iter().any(|e| e.span.from_expansion()) + || !is_impl_slice(cx, receiver) + || !is_diagnostic_name(cx, expr.hir_id, "IteratorMap") + { + return; + } + let arg_ty = cx.typeck_results().expr_ty(&args[0]); + if let ty::FnDef(id, _) = arg_ty.kind() { + let fn_ty = cx.tcx.fn_sig(id).skip_binder(); + let ret_ty = fn_ty.output().skip_binder(); + if is_unit_type(ret_ty) { + cx.emit_spanned_lint( + MAP_UNIT_FN, + span, + MappingToUnit { + function_label: cx.tcx.span_of_impl(*id).unwrap(), + argument_label: args[0].span, + map_label: arg_ty.default_span(cx.tcx), + suggestion: path.ident.span, + replace: "for_each".to_string(), + }, + ) + } + } else if let ty::Closure(id, subs) = arg_ty.kind() { + let cl_ty = subs.as_closure().sig(); + let ret_ty = cl_ty.output().skip_binder(); + if is_unit_type(ret_ty) { + cx.emit_spanned_lint( + MAP_UNIT_FN, + span, + MappingToUnit { + function_label: cx.tcx.span_of_impl(*id).unwrap(), + argument_label: args[0].span, + map_label: arg_ty.default_span(cx.tcx), + suggestion: path.ident.span, + replace: "for_each".to_string(), + }, + ) + } + } + } + } + } + } +} + +fn is_impl_slice(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool { + if let Some(method_id) = cx.typeck_results().type_dependent_def_id(expr.hir_id) { + if let Some(impl_id) = cx.tcx.impl_of_method(method_id) { + return cx.tcx.type_of(impl_id).skip_binder().is_slice(); + } + } + false +} + +fn is_unit_type(ty: Ty<'_>) -> bool { + ty.is_unit() || ty.is_never() +} + +fn is_diagnostic_name(cx: &LateContext<'_>, id: HirId, name: &str) -> bool { + if let Some(def_id) = cx.typeck_results().type_dependent_def_id(id) { + if let Some(item) = cx.tcx.get_diagnostic_name(def_id) { + if item.as_str() == name { + return true; + } + } + } + false +} |