rust-clippy/clippy_lints/src/fallible_impl_from.rs

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use clippy_utils::diagnostics::span_lint_and_then;
use clippy_utils::macros::{is_panic, root_macro_call_first_node};
use clippy_utils::method_chain_args;
use clippy_utils::ty::is_type_diagnostic_item;
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use if_chain::if_chain;
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use rustc_hir as hir;
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use rustc_lint::{LateContext, LateLintPass};
use rustc_middle::hir::map::Map;
use rustc_middle::ty;
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use rustc_session::{declare_lint_pass, declare_tool_lint};
use rustc_span::{sym, Span};
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declare_clippy_lint! {
/// ### What it does
/// Checks for impls of `From<..>` that contain `panic!()` or `unwrap()`
///
/// ### Why is this bad?
/// `TryFrom` should be used if there's a possibility of failure.
///
/// ### Example
/// ```rust
/// struct Foo(i32);
///
/// // Bad
/// impl From<String> for Foo {
/// fn from(s: String) -> Self {
/// Foo(s.parse().unwrap())
/// }
/// }
/// ```
///
/// ```rust
/// // Good
/// struct Foo(i32);
///
/// use std::convert::TryFrom;
/// impl TryFrom<String> for Foo {
/// type Error = ();
/// fn try_from(s: String) -> Result<Self, Self::Error> {
/// if let Ok(parsed) = s.parse() {
/// Ok(Foo(parsed))
/// } else {
/// Err(())
/// }
/// }
/// }
/// ```
#[clippy::version = "pre 1.29.0"]
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pub FALLIBLE_IMPL_FROM,
nursery,
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"Warn on impls of `From<..>` that contain `panic!()` or `unwrap()`"
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}
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declare_lint_pass!(FallibleImplFrom => [FALLIBLE_IMPL_FROM]);
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impl<'tcx> LateLintPass<'tcx> for FallibleImplFrom {
fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'_>) {
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// check for `impl From<???> for ..`
if_chain! {
if let hir::ItemKind::Impl(impl_) = &item.kind;
if let Some(impl_trait_ref) = cx.tcx.impl_trait_ref(item.def_id);
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if cx.tcx.is_diagnostic_item(sym::From, impl_trait_ref.def_id);
then {
lint_impl_body(cx, item.span, impl_.items);
}
}
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}
}
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fn lint_impl_body<'tcx>(cx: &LateContext<'tcx>, impl_span: Span, impl_items: &[hir::ImplItemRef]) {
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use rustc_hir::intravisit::{self, NestedVisitorMap, Visitor};
use rustc_hir::{Expr, ImplItemKind};
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struct FindPanicUnwrap<'a, 'tcx> {
lcx: &'a LateContext<'tcx>,
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typeck_results: &'tcx ty::TypeckResults<'tcx>,
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result: Vec<Span>,
}
impl<'a, 'tcx> Visitor<'tcx> for FindPanicUnwrap<'a, 'tcx> {
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type Map = Map<'tcx>;
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fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
if let Some(macro_call) = root_macro_call_first_node(self.lcx, expr) {
if is_panic(self.lcx, macro_call.def_id) {
self.result.push(expr.span);
}
}
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// check for `unwrap`
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if let Some(arglists) = method_chain_args(expr, &["unwrap"]) {
let reciever_ty = self.typeck_results.expr_ty(&arglists[0][0]).peel_refs();
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if is_type_diagnostic_item(self.lcx, reciever_ty, sym::Option)
|| is_type_diagnostic_item(self.lcx, reciever_ty, sym::Result)
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{
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self.result.push(expr.span);
}
}
// and check sub-expressions
intravisit::walk_expr(self, expr);
}
fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
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NestedVisitorMap::None
}
}
for impl_item in impl_items {
if_chain! {
if impl_item.ident.name == sym::from;
if let ImplItemKind::Fn(_, body_id) =
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cx.tcx.hir().impl_item(impl_item.id).kind;
then {
// check the body for `begin_panic` or `unwrap`
let body = cx.tcx.hir().body(body_id);
let mut fpu = FindPanicUnwrap {
lcx: cx,
typeck_results: cx.tcx.typeck(impl_item.id.def_id),
result: Vec::new(),
};
fpu.visit_expr(&body.value);
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// if we've found one, lint
if !fpu.result.is_empty() {
span_lint_and_then(
cx,
FALLIBLE_IMPL_FROM,
impl_span,
"consider implementing `TryFrom` instead",
move |diag| {
diag.help(
"`From` is intended for infallible conversions only. \
Use `TryFrom` if there's a possibility for the conversion to fail");
diag.span_note(fpu.result, "potential failure(s)");
});
}
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}
}
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}
}