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Auto merge of rust-lang#8188 - jamesmcm:recursive_display_impl, r=cam…
…steffen new lint: `recursive_format_impl` The to_string_in_display lint is renamed to recursive_format_impl A check is added for the use of self formatted with Display or Debug inside any format string in the same impl The to_string_in_display check is kept as is - like in the format_in_format_args lint This is my first contribution so please check it for better / more idiomatic checks + error messages. Note the format macro paths are shared with the `format_in_format_args` lint - maybe those could be moved to clippy utils too. This relates to issues rust-lang#2691 and rust-lang#7830 ------ changelog: Renamed `to_string_in_display` lint to [`recursive_format_impl`] with new check for any use of self as Display or Debug inside the same format trait impl.
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,190 @@ | ||
| use clippy_utils::diagnostics::span_lint; | ||
| use clippy_utils::macros::{is_format_macro, root_macro_call_first_node, FormatArgsArg, FormatArgsExpn}; | ||
| use clippy_utils::{is_diag_trait_item, path_to_local, peel_ref_operators}; | ||
| use if_chain::if_chain; | ||
| use rustc_hir::{Expr, ExprKind, Impl, Item, ItemKind, QPath}; | ||
| use rustc_lint::{LateContext, LateLintPass}; | ||
| use rustc_session::{declare_tool_lint, impl_lint_pass}; | ||
| use rustc_span::{sym, symbol::kw, Symbol}; | ||
|
|
||
| #[derive(Clone, Copy)] | ||
| enum FormatTrait { | ||
| Debug, | ||
| Display, | ||
| } | ||
|
|
||
| impl FormatTrait { | ||
| fn name(self) -> Symbol { | ||
| match self { | ||
| FormatTrait::Debug => sym::Debug, | ||
| FormatTrait::Display => sym::Display, | ||
| } | ||
| } | ||
| } | ||
|
|
||
| declare_clippy_lint! { | ||
| /// ### What it does | ||
| /// Checks for format trait implementations (e.g. `Display`) with a recursive call to itself | ||
| /// which uses `self` as a parameter. | ||
| /// This is typically done indirectly with the `write!` macro or with `to_string()`. | ||
| /// | ||
| /// ### Why is this bad? | ||
| /// This will lead to infinite recursion and a stack overflow. | ||
| /// | ||
| /// ### Example | ||
| /// | ||
| /// ```rust | ||
| /// use std::fmt; | ||
| /// | ||
| /// struct Structure(i32); | ||
| /// impl fmt::Display for Structure { | ||
| /// fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { | ||
| /// write!(f, "{}", self.to_string()) | ||
| /// } | ||
| /// } | ||
| /// | ||
| /// ``` | ||
| /// Use instead: | ||
| /// ```rust | ||
| /// use std::fmt; | ||
| /// | ||
| /// struct Structure(i32); | ||
| /// impl fmt::Display for Structure { | ||
| /// fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { | ||
| /// write!(f, "{}", self.0) | ||
| /// } | ||
| /// } | ||
| /// ``` | ||
| #[clippy::version = "1.48.0"] | ||
| pub RECURSIVE_FORMAT_IMPL, | ||
| correctness, | ||
| "Format trait method called while implementing the same Format trait" | ||
| } | ||
|
|
||
| #[derive(Default)] | ||
| pub struct RecursiveFormatImpl { | ||
| // Whether we are inside Display or Debug trait impl - None for neither | ||
| format_trait_impl: Option<FormatTrait>, | ||
| } | ||
|
|
||
| impl RecursiveFormatImpl { | ||
| pub fn new() -> Self { | ||
| Self { | ||
| format_trait_impl: None, | ||
| } | ||
| } | ||
| } | ||
|
|
||
| impl_lint_pass!(RecursiveFormatImpl => [RECURSIVE_FORMAT_IMPL]); | ||
|
|
||
| impl<'tcx> LateLintPass<'tcx> for RecursiveFormatImpl { | ||
| fn check_item(&mut self, cx: &LateContext<'_>, item: &Item<'_>) { | ||
| if let Some(format_trait_impl) = is_format_trait_impl(cx, item) { | ||
| self.format_trait_impl = Some(format_trait_impl); | ||
| } | ||
| } | ||
|
|
||
| fn check_item_post(&mut self, cx: &LateContext<'_>, item: &Item<'_>) { | ||
| // Assume no nested Impl of Debug and Display within eachother | ||
| if is_format_trait_impl(cx, item).is_some() { | ||
| self.format_trait_impl = None; | ||
| } | ||
| } | ||
|
|
||
| fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) { | ||
| match self.format_trait_impl { | ||
| Some(FormatTrait::Display) => { | ||
| check_to_string_in_display(cx, expr); | ||
| check_self_in_format_args(cx, expr, FormatTrait::Display); | ||
| }, | ||
| Some(FormatTrait::Debug) => { | ||
| check_self_in_format_args(cx, expr, FormatTrait::Debug); | ||
| }, | ||
| None => {}, | ||
| } | ||
| } | ||
| } | ||
|
|
||
| fn check_to_string_in_display(cx: &LateContext<'_>, expr: &Expr<'_>) { | ||
| if_chain! { | ||
| // Get the hir_id of the object we are calling the method on | ||
| if let ExprKind::MethodCall(path, [ref self_arg, ..], _) = expr.kind; | ||
| // Is the method to_string() ? | ||
| if path.ident.name == sym!(to_string); | ||
| // Is the method a part of the ToString trait? (i.e. not to_string() implemented | ||
| // separately) | ||
| if let Some(expr_def_id) = cx.typeck_results().type_dependent_def_id(expr.hir_id); | ||
| if is_diag_trait_item(cx, expr_def_id, sym::ToString); | ||
| // Is the method is called on self | ||
| if let ExprKind::Path(QPath::Resolved(_, path)) = self_arg.kind; | ||
| if let [segment] = path.segments; | ||
| if segment.ident.name == kw::SelfLower; | ||
| then { | ||
| span_lint( | ||
| cx, | ||
| RECURSIVE_FORMAT_IMPL, | ||
| expr.span, | ||
| "using `self.to_string` in `fmt::Display` implementation will cause infinite recursion", | ||
| ); | ||
| } | ||
| } | ||
| } | ||
|
|
||
| fn check_self_in_format_args<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, impl_trait: FormatTrait) { | ||
| // Check each arg in format calls - do we ever use Display on self (directly or via deref)? | ||
| if_chain! { | ||
| if let Some(outer_macro) = root_macro_call_first_node(cx, expr); | ||
| if let macro_def_id = outer_macro.def_id; | ||
| if let Some(format_args) = FormatArgsExpn::find_nested(cx, expr, outer_macro.expn); | ||
| if is_format_macro(cx, macro_def_id); | ||
| if let Some(args) = format_args.args(); | ||
| then { | ||
| for arg in args { | ||
| if arg.format_trait != impl_trait.name() { | ||
| continue; | ||
| } | ||
| check_format_arg_self(cx, expr, &arg, impl_trait); | ||
| } | ||
| } | ||
| } | ||
| } | ||
|
|
||
| fn check_format_arg_self(cx: &LateContext<'_>, expr: &Expr<'_>, arg: &FormatArgsArg<'_>, impl_trait: FormatTrait) { | ||
| // Handle multiple dereferencing of references e.g. &&self | ||
| // Handle dereference of &self -> self that is equivalent (i.e. via *self in fmt() impl) | ||
| // Since the argument to fmt is itself a reference: &self | ||
| let reference = peel_ref_operators(cx, arg.value); | ||
| let map = cx.tcx.hir(); | ||
| // Is the reference self? | ||
| let symbol_ident = impl_trait.name().to_ident_string(); | ||
| if path_to_local(reference).map(|x| map.name(x)) == Some(kw::SelfLower) { | ||
| span_lint( | ||
| cx, | ||
| RECURSIVE_FORMAT_IMPL, | ||
| expr.span, | ||
| &format!( | ||
| "using `self` as `{}` in `impl {}` will cause infinite recursion", | ||
| &symbol_ident, &symbol_ident | ||
| ), | ||
| ); | ||
| } | ||
| } | ||
|
|
||
| fn is_format_trait_impl(cx: &LateContext<'_>, item: &Item<'_>) -> Option<FormatTrait> { | ||
| if_chain! { | ||
| // Are we at an Impl? | ||
| if let ItemKind::Impl(Impl { of_trait: Some(trait_ref), .. }) = &item.kind; | ||
| if let Some(did) = trait_ref.trait_def_id(); | ||
| if let Some(name) = cx.tcx.get_diagnostic_name(did); | ||
| then { | ||
| // Is Impl for Debug or Display? | ||
| match name { | ||
| sym::Debug => Some(FormatTrait::Debug), | ||
| sym::Display => Some(FormatTrait::Display), | ||
| _ => None, | ||
| } | ||
| } else { | ||
| None | ||
| } | ||
| } | ||
| } |
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